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Factors Controlling Zooplankton Dynamics in a Subtropical Lake during Cyanobacterial Bloom Events

Permanent Link: http://ufdc.ufl.edu/UFE0042219/00001

Material Information

Title: Factors Controlling Zooplankton Dynamics in a Subtropical Lake during Cyanobacterial Bloom Events
Physical Description: 1 online resource (76 p.)
Language: english
Creator: Srifa, Akeapot
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: bloom, controlling, cyanobacerial, dynamics, factors, florida, functional, george, groups, interaction, lake, phytoplankton, relationship, subtropical, succession, toxins, zooplankton
Forest Resources and Conservation -- Dissertations, Academic -- UF
Genre: Fisheries and Aquatic Sciences thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Intensive field observations were performed to elucidate the effect of cyanobacterial blooms and other environmental factors to zooplankton community structure and abundance in Lake George, Florida. Samples were obtained weekly during night time and bi-weekly during day time in two different locations in the lake. Water samples were collected with an integrated pole that collected water from the surface to the bottom of the water column. Zooplankton were identified, enumerated, and measured for biovolume estimates using an inverted microscope. Other parameters included water temperature, conductivity, dissolved oxygen, turbidity, color, pH, cyanobacterial toxins, chlorophyll a level, silica, and nitrogen and phosphorus contents. The study period (March 25, 2009 ? June 17, 2009) was characterized by three major trends; 1) Phytoplankton bloom in April with an equal mix of nitrogen-fixing cyanobacteria and diatoms, 2) A second larger phytoplankton bloom (up to 92 ?g/L of chlorophyll a) dominated by cyanobacteria, and 3) A major rainfall event that resulted in a large influx of water from the watershed, associated with an increase in nutrient concentrations but a decrease in phytoplankton biomass. Cyanobacterial toxin levels (cylindrospermopsin, microcystins, and saxitoxin) were coincident with chlorophyll a levels and phytoplankton community composition. Fifty-one zooplankton taxa were observed and subdivided into three major groups: rotifers, cladocerans, and copepods. The three major groups were further subdivided into eleven functional groups based on zooplankton major feeding habit and body size. Rotifers were the major zooplankton during the first phytoplankton bloom, and were succeeded with cladocerans during the bloom intersession, before copepods became more abundant during the second bloom. Correlation analyses were performed between zooplankton composites ? all abundance indices and the full suite of other parameters determined in the study. A numbers of significant relationships were revealed which provided insights into the potential driving factors for the succession pattern of zooplankton observed over the study period. The primary correlated factors included chlorophyll a levels, nitrogen concentration, cyanobacterial toxin levels, and temperature, suggesting that both phytoplankton biomass and composition play important roles in zooplankton dynamics. The correlation varied between functional groups indicating that differences in feeding preferences and sensitivities to toxins also play an important role in succession.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Akeapot Srifa.
Thesis: Thesis (M.S.)--University of Florida, 2010.
Local: Adviser: Phlips, Edward J.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2011-02-28

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0042219:00001

Permanent Link: http://ufdc.ufl.edu/UFE0042219/00001

Material Information

Title: Factors Controlling Zooplankton Dynamics in a Subtropical Lake during Cyanobacterial Bloom Events
Physical Description: 1 online resource (76 p.)
Language: english
Creator: Srifa, Akeapot
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: bloom, controlling, cyanobacerial, dynamics, factors, florida, functional, george, groups, interaction, lake, phytoplankton, relationship, subtropical, succession, toxins, zooplankton
Forest Resources and Conservation -- Dissertations, Academic -- UF
Genre: Fisheries and Aquatic Sciences thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Intensive field observations were performed to elucidate the effect of cyanobacterial blooms and other environmental factors to zooplankton community structure and abundance in Lake George, Florida. Samples were obtained weekly during night time and bi-weekly during day time in two different locations in the lake. Water samples were collected with an integrated pole that collected water from the surface to the bottom of the water column. Zooplankton were identified, enumerated, and measured for biovolume estimates using an inverted microscope. Other parameters included water temperature, conductivity, dissolved oxygen, turbidity, color, pH, cyanobacterial toxins, chlorophyll a level, silica, and nitrogen and phosphorus contents. The study period (March 25, 2009 ? June 17, 2009) was characterized by three major trends; 1) Phytoplankton bloom in April with an equal mix of nitrogen-fixing cyanobacteria and diatoms, 2) A second larger phytoplankton bloom (up to 92 ?g/L of chlorophyll a) dominated by cyanobacteria, and 3) A major rainfall event that resulted in a large influx of water from the watershed, associated with an increase in nutrient concentrations but a decrease in phytoplankton biomass. Cyanobacterial toxin levels (cylindrospermopsin, microcystins, and saxitoxin) were coincident with chlorophyll a levels and phytoplankton community composition. Fifty-one zooplankton taxa were observed and subdivided into three major groups: rotifers, cladocerans, and copepods. The three major groups were further subdivided into eleven functional groups based on zooplankton major feeding habit and body size. Rotifers were the major zooplankton during the first phytoplankton bloom, and were succeeded with cladocerans during the bloom intersession, before copepods became more abundant during the second bloom. Correlation analyses were performed between zooplankton composites ? all abundance indices and the full suite of other parameters determined in the study. A numbers of significant relationships were revealed which provided insights into the potential driving factors for the succession pattern of zooplankton observed over the study period. The primary correlated factors included chlorophyll a levels, nitrogen concentration, cyanobacterial toxin levels, and temperature, suggesting that both phytoplankton biomass and composition play important roles in zooplankton dynamics. The correlation varied between functional groups indicating that differences in feeding preferences and sensitivities to toxins also play an important role in succession.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Akeapot Srifa.
Thesis: Thesis (M.S.)--University of Florida, 2010.
Local: Adviser: Phlips, Edward J.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2011-02-28

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0042219:00001


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FACTORS CONTROLLING ZOOPLANKTON DYNAMICS IN A SUBTROPICAL LAKE
DURING CYANOBACTERIAL BLOOM EVENTS

















By

AKEAPOT SRIFA


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2010






























2010 Akeapot Srifa



























To my parents, my role models in diligence and positive thinking









ACKNOWLEDGMENTS

First of all, I would like to express my most sincere gratitude to my supervisor,

Professor Edward J. Phlips, for his ceaseless academic dedication during my graduate

study in the University of Florida. He has willingly supported me from the beginning in

academia and provided excellent research experiences during the past two years.

I would like to express my most sincere to other supervisory committee members,

Professor Karl E. Havens and Professor Mark Brenner, for sharing me their professional

research excellence, and for giving me invaluable and constructive suggestions and

comments to the research I made during my study.

I would like to gratefully acknowledge Professor Charles E. Cichra and Mary

Cichra for their generosity and dedications in the academic supports and guidance.

Without the supports from them, this research would not have been completed.

My special thanks also extend to Dr. Mete Yilmaz for his invaluable help and

suggestions in professional laboratory skills, Dr. Lance Riley for his captaincy on the

research vessel, Don O'steen and Linghan Dong for their helps in sampling sessions,

Dorota Roth and Joey Chait for their help in sample analyses, Amanda Croteau and

Brittany Baugher for their help in the identification of microscopic zooplankton, my

colleagues Nikki Dix, Loren Mathews, and Paula Viveros for their kind help throughout

my laboratory works as well as academic skills.

Last but not least, I would like to express my heartiest gratitude to my parents and

my brother in Thailand for their tireless encouragements and continuous support

throughout my study.









TABLE OF CONTENTS

page

ACKNOW LEDGMENTS............ .................................................. .......

LIST O F TA BLES .................................. .......................... ...... ..............7

LIST O F FIG U R ES .................................. .......................... ..... ..............8

LIST O F A BBR EV IA T IO N S ..................................................................................... ............ 10

A B S T R A C T .................................11.......... .................

CHAPTER

1 IN T R O D U C T IO N ............................................................................................. ........ 13

2 RESEARCH DESIGN AND METHODOLOGY....................... ................16

Study Site .................................. ............................... ......... 16
S am pling Locations ............................................ ................. ........................ 16
Field Observation and Water Sampling .................................... 17
Cyanobacterial Toxin Analysis ..................................... ................ ................ 19
Microscopic Analysis of Zooplankton .................. ..................... 19
Precipitation and River Flow Rate .................. ........................... 20

3 R E S U LT S ................................................................................. .. .................. 22

Chlorophyll a Concentration ................................................................................. 22
Cyanobacterial Toxin Levels ....................................... ............ ......... .............. 22
W ater Chem istry and Physical Variables ................ ............................ .......... 23
Overview Survey of Zooplankton ......................................26
Dynamics of Three Major Zooplankton Groups .................................................... 26
Cladocerans ............. ......... .............. ........ 26
Copepods ............... ......... ........................ 26
Rotifers .................. ........... ... ..................... 27
Zooplankton Dynamics in Different Functional Groups ................... ........... 28
Cladocerans ............. ......... .............. ........ 28
Copepods ............... ......... ........................ 29
Rotifers .................. ... ............. ............................ 29
Relationship between Zooplankton and Physical-Chemical Variables ................ 30
Major Group Level ......................... ................ 30
Functional Group Level ................. .. ........... ...... ... ... ............ 31









4 D IS C U S S IO N ............. ................................................................................... 53

Cladoceran Dynam ics ............... .. ............................. ......... ............. 57
Copepod Dynamics .............................................. ........... ....... 61
Rotifer Dynam ics ............... ............................. ....................... 64

5 CONCLUSION .......................................... .................... 69

ZOOPLANKTON FUNCTIONAL GROUPS...................................... 70

L IS T O F R E F E R E N C E S ................................................................................................. 7 1

BIOGRAPHICAL SKETCH ....................................... ..........................................76







































6









LIST OF TABLES


Table page

3-1 Zooplankton species list found during this study period. ................................. 49

3-2 Correlation between water physical-chemical parameters and zooplankton
absolute biovolumes in different levels of functional groups and taxa in the
sta tio n of L E O ................. ......... ...... ......... ...... .................................................... 5 1

3-3 Correlation between water physical-chemical parameters and zooplankton
absolute biovolumes in different levels of functional groups and taxa in the
sta tio n of LA G ................. ......... ...... ......... ......................................................... 52

4-1 Significant differences in zooplankton abundance indices between the two
sampling stations and the two sampling times among 51 zooplankton genera
and 11 functional groups..................................... .......... .. ... .................. 68









LIST OF FIGURES


Figure page

2-1 Location of Lake George in Florida regional outline map and locations of the
two selected sampling sites, LEO and LAG, in Lake George ............................21

2-2 Total daily precipitation at the LEO station during the study period ............... 21

3-1 Dynamics of chlorophyll a levels during the study period................ ................ 33

3-2 Dynamics of three cyanobacterial toxins: Saxitoxin, Cylindrospermopsin ,
a n d M ic ro c y stin s ................ .......................................................... 3 4

3-3 D epths at the sam pling sites ............................................................ ................ 35

3-4 Tem perature at the w ater surface. .................................... ................... ............... 35

3-5 S ecchi depths in the lake. .................................................... .................. .... 36

3-6 Turbidity in NTU during the study period ......................................... ............... 36

3-7 W ater color (CDOM) during the study period ................................. .............. .. 37

3-8 Dissolved oxygen levels in water surface and 20 cm above the lake bottom......38

3-9 Specific conductivity during the study period.................... ................ 39

3-10 pH at the water surface during the study period ............................................ 39

3-11 Phosphorus content in water samples were Total Phosphorus and Soluble
Reactive Phosphorus. ...... .... ... .............. ... .. ........... .... ........ .. 40

3-12 The examination of nitrogen contents in water samples included Total
Nitrogen, Am m onium Nitrate, and Nitrite.................................. ...... ............ .... 41

3-13 Silica levels during the study period................................. ............... 42

3-14 Cladoceran abundance indices included their absolute biovolume, relative
biovolume, absolute abundance, and relative abundance. ................................43

3-15 Copepod abundance indices included their biovolume, relative biovolume,
abundance, and relative abundance. ........... ..................... .................... 44

3-16 Rotifer abundance indices included their biovolume, relative biovolume,
abundance, and relative abundance. ..................................... ...... .............. 45

3-17 Biovolume in three cladoceran functional groups Bosminidae, Sididae, and
D aphniidae. ............. ...................... ........... ... ..........46









3-18 Biovolume in four copepod functional groups copepod nauplii, herbivorous
copepod, carnivorous copepod, and omnivorous copepod.............................. 47

3-19 Biovolume in four rotifer functional groups microrotifers, mesorotifers,
megarotifers, and raptorial rotifers ....... ..................... ................ 48









LIST OF ABBREVIATIONS


AAB Abundance

ABV Biovolume

CYL Cylindrospermopsin

DO Dissolved oxygen

MBV Mean biovolume

MCY Microcystins

RAB Relative abundance to total zooplankton abundance

RBV Relative biovolume to total zooplankton biovolume

SAX Saxitoxin

SRP Soluble reactive phosphorus

TN Total nitrogen

TP Total phosphorus









Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

FACTORS CONTROLLING ZOOPLANKTON DYNAMICS IN A SUBTROPICAL LAKE
DURING CYANOBACTERIAL BLOOM EVENTS

By

Akeapot Srifa

August 2010

Chair: Edward J. Phlips
Major: Fisheries and Aquatic Sciences

Intensive field observations were performed to elucidate the effect of

cyanobacterial blooms and other environmental factors to zooplankton community

structure and abundance in Lake George, Florida. Samples were obtained weekly

during night time and bi-weekly during day time in two different locations in the lake.

Water samples were collected with an integrated pole that collected water from the

surface to the bottom of the water column. Zooplankton were identified, enumerated,

and measured for biovolume estimates using an inverted microscope. Other parameters

included water temperature, conductivity, dissolved oxygen, turbidity, color, pH,

cyanobacterial toxins, chlorophyll a level, silica, and nitrogen and phosphorus contents.

The study period (March 25, 2009 June 17, 2009) was characterized by three

major trends; 1) Phytoplankton bloom in April with an equal mix of nitrogen-fixing

cyanobacteria and diatoms, 2) A second larger phytoplankton bloom (up to 92 pg/L of

chlorophyll a) dominated by cyanobacteria, and 3) A major rainfall event that resulted in

a large influx of water from the watershed, associated with an increase in nutrient

concentrations but a decrease in phytoplankton biomass. Cyanobacterial toxin levels









(cylindrospermopsin, microcystins, and saxitoxin) were coincident with chlorophyll a

levels and phytoplankton community composition.

Fifty-one zooplankton taxa were observed and subdivided into three major

groups: rotifers, cladocerans, and copepods. The three major groups were further

subdivided into eleven functional groups based on zooplankton major feeding habit and

body size. Rotifers were the major zooplankton during the first phytoplankton bloom,

and were succeeded with cladocerans during the bloom intersession, before copepods

became more abundant during the second bloom.

Correlation analyses were performed between zooplankton composites all

abundance indices and the full suite of other parameters determined in the study. A

numbers of significant relationships were revealed which provided insights into the

potential driving factors for the succession pattern of zooplankton observed over the

study period. The primary correlated factors included chlorophyll a levels, nitrogen

concentration, cyanobacterial toxin levels, and temperature, suggesting that both

phytoplankton biomass and composition play important roles in zooplankton dynamics.

The correlation varied between functional groups indicating that differences in feeding

preferences and sensitivities to toxins also play an important role in succession.









CHAPTER 1
INTRODUCTION

Eutrophication of surface waters and the associated blooms of phytoplankton

and plants are important issues of concern in many regions around the world (Nixon,

1995; Smith, 1998; Smith et al., 1999; Paerl et al., 2001; Phlips et al., 2002). In

eutrophic and hypereutrophic lakes, intense phytoplankton blooms can be associated

with harmful effects, including hypoxia, strong light attenuation, loss of species diversity,

and alterations of food web interrelationships (Kotak et al., 1993; McComb & Davis,

1993; Chorus & Bartram, 1999; Haider et al., 2003). In the case of blooms involving

cyanobacteria, the poor palatability and potential toxicity of certain species can

represent unique challenges to the health and stability of ecosystems (Lawton & Codd,

1991; Martin & Cooke, 1994; Kaebernick & Neilan, 2001).

The ecological implications of toxic cyanobacteria have been an important area

of research for decades (Chorus & Bartram, 1999). A number of major strains in these

cyanobacteria may produce toxins, which can be harmful to aquatic organisms including

zooplankton (Haider et al., 2003; Kaebernick & Neilan, 2001).

Interactions between phytoplankton and zooplankton in freshwater ecosystems

have become an important focus of research for decades (Porter, 1977; Mitra & Flynn,

2005; Carpenter & Kitchell, 1988; Havens et al, 1996). Zooplankton play a pivotal role

in freshwater ecosystems as a critical link between phytoplankton producers and

planktivores in the food web. Alterations in zooplankton community structure,

abundance, and size can lead to changes in fish and invertebrate communities, thereby

affecting the structure and function of the entire ecosystems (Carpenter & Kitchell,

1988; Havens et al., 1996). It has been shown that phytoplankton and zooplankton can









have mutually supportive interactions with respect to grazing or nutrient regeneration

(Havens et al., 1996; Carney & Elser, 1990). Large colonial or filamentous

phytoplankton and toxic species, however, are less efficiently grazed by most

zooplankton, enhancing the potential for blooms (Dong, 2010).

The focus of this study was the dynamics of zooplankton in relation to

cyanobacterial blooms. The central objective of the study was to follow changes in the

zooplankton community during the course of cyanobacterial blooms in Lake George, a

large subtropical eutrophic lake in Florida, with a long history of intense cyanobacterial

blooms. Lake George is part of the St. Johns River ecosystem, which is recognized as

one of the most important river basins in the United States (SJRWMD, 2010; SJRWMD,

2008). Phytoplankton blooms in Lake George have included cyanobacteria species that

are potentially toxic, such as Cylindrospermopsis sp., Anabaena sp., Anabaenopsis sp.,

and Aphanizomenon sp. (Dong, 2010).

Temporally intensive field observations were carried out in Lake George to

describe changes in chlorophyll concentration, major cyanobacterial toxins, zooplankton

composition and abundance, and related physical and chemical variables. A

complimentary study of phytoplankton dynamics provided information for comparative

analyses (Dong, 2010). Zooplankton abundance and environmental factors were

examined statistically to help define relationships between phytoplankton, zooplankton,

and water column conditions. It was hypothesized that spring/early summer

phytoplankton blooms in Lake George are dominated by a succession of cyanobacteria

species that are correlated with temporal changes in zooplankton structure and









abundance, reflecting the relative adaptability of different functional groups to trends in

phytoplankton composition and abundance.









CHAPTER 2
RESEARCH DESIGN AND METHODOLOGY

Study Site

Lake George is the second largest lake in Florida, and located in the subtropical

zone in the northeast region of the state. Lake George is a freshwater, and the largest

lake on the St Johns River basin with approximately 175 km2 in its surface area (Piehler

et al., 2009). The drainage basin of Lake George encompasses 2,025 km2 in East

Central Florida (Bass, 1983). The lake has been designated by a state agency, the St

Johns River Water Management District, as a major water source that has high potential

to supply Central Florida municipal area.

Major inflows to the lake include St. Johns River at the southern end, Salt Spring

Creek, Silver Glen Springs Run, and Juniper creek. The major outflow is the St. Johns

River in the northern end near the city of Georgetown. Lake George is categorized as a

river lake, which literally means that the lake is relatively dynamic and circulation within

the lake is dominated by the river.

Sampling Locations

Two sampling locations in the lake were selected for this study: LEO (29 18' 29.9"

N, 81 36' 22.95" W) and LAG (29 15' 17.82" N, 81 35' 28.2" W) (Figure 2-1). Both

sampling sites were located in the main navigation channel in the lake. LAG was

located at channel marker 9 in the south part of the lake, near the inflow of the upper St.

Johns River. LEO is located in the north-central region of the lake near channel marker

4. LEO has no aquatic macrophyte coverage, whereas LAG is closer to the shoreline

and thus may be influenced by littoral vegetation (Cichra, 2009). These two sites are









monitored regularly for physical and chemical variables by SJRWMD and The United

States Geological Survey (USGS).

Field Observation and Water Sampling

Field observations and water sampling were carried out at LEO and LAG in 2009

from March 25, 2009 to June 23, 2009. Sampling consisted of water collection and field

measurements of meteorological and water column physical variables. Day time

sampling was done biweekly every Monday and Thursday between 0930 and 1130 hrs.

Night time sampling was done weekly every Thursday between 0300 and 0500 hrs.

Sampling was suspended from May 18-21, 2009 due to inclement weather.

Water depth, temperature, specific conductivity, dissolved oxygen, and pH were

measured with a calibrated multiprobe Hydrolab Quanta Environmental Multiprobe.

These variables were measured at the water surface and every 50 cm below the

surface. Water transparency was determined with a 20-cm Secchi disk during daytime

sampling.

Water samples were composite from at least five integrated PVC tubes that

collected water from the surface to near the bottom of the water column, thereby

reducing the effect of vertical stratification of plankton. Subsamples of water were

withdrawn from these combine samples for measurements of chlorophyll a

concentration (250 ml), zooplankton enumeration (3,000 ml), cyanobacterial toxin

analysis (15 ml), and water chemistry analyses (125 ml).

Phytoplankton was filtered onto 0.7 pm glass fiber filters. Filters were kept on ice

in the dark and returned to the laboratory for analyses. Chlorophyll a was extracted on

the same day as sampling according to (Sartory & Grobbelaar, 1984). Filter paper was

placed in 90% ethanol at 78C for five minutes then incubated in the dark at room









temperature for at least 24 hr. Samples were centrifuged at 20,000 rpm and MDfor 20

min. to eliminate filter debris. Spectrophotometric analysis for chlorophyll a and

phaeophytin was determined spectrophotometrically according to the method 10200 H.2

(APHA, 2005).

Water subsamples (125 ml) for nutrient analysis were kept in acid-washed plastic

bottles and kept frozen. Turbidity was determined using a Lamotte 2020 turbidimeter

and expressed in Nephelometric Turbidity Units (NTU). Colored dissolved organic

matter (CDOM) was determined spectrophotometrically using samples filtered through

glass fiber filters (0.7 pm pore size) according to standard methods (APHA, 2005) and

expressed as platinum cobalt units (PCU).

Total Phosphorus (TP) and Soluble Reactive Phosphorus (SRP) were determined

spetrophotometrically, using the molybdenum-ascorbate method 4500-P (APHA, 2005).

Persulfate digestion and autoclaving were for TP determination.

Total Nitrogen (TN), Ammonium (NH4+) Nitrite (NO2-), and Nitrite/Nitrate (NOx)

were determined using a continuous flow autoanalyzer. For TN analysis, persulfate-

digested samples were injected through a cadmium column. NH4+, NOx and NO2 were

determined on samples filtered through 0.7 pm glass fiber filters. NOx and N02- were

determined with and without a coupling cadmium column respectively. Nitrate

concentrations were obtained by subtracting nitrite value from NOx concentration.

Silica levels in water samples were determined spectrophotometrically using

ammonium molybdate reagent in the molybdosilicate method 4500-Si02 C (APHA,

2005).









Cyanobacterial Toxin Analysis

Aliquots of water subsamples (5 ml) were kept frozen in glass tubes until analysis

for toxins including cylindrospermopsin (CYL), microcystins (MCY), and saxitoxin (SAX).

They were determined using enzyme-linked immunosorbent assay method (ELISA).

ELISA test kits for the three toxins were obtained from Abraxis LLC (Microtiter plate

ELISA kit PN 522011 for CYL and PN 52255B for SAX, and tube ELISA kit PN 520012

for MCY).

Preparation for CYL and SAX involved triple freeze-thaw cycles for toxin

extraction. Extraction for MCY involved 1-minute incubation in 100C distilled water and

cooled down to room temperature. Extracted samples were centrifuged at 20,000 rpm

and 20C for 20 minutes. Supernatant was loaded into multiwell plates before analysis.

Microscopic Analysis of Zooplankton

Subsamples for zooplankton analysis were preserved in the field using Lugol's

solution (APHA, 2005). Each preserved sample was filtered onto a 41 pm nylon mesh

and brought to a final volume of 20 ml. Zooplankton were identified and counted

according to the Utermohl method (Utermohl, 1958) in a glass settling chamber using

an inverted compound microscope at 100x magnification. Samples were identified to the

lowest practical taxonomic level. Sample enumeration was continued until at least 100

individuals of a dominant taxon were counted in the sample, and at least 3 ml of

adjusted volume was enumerated. Zooplankton species and/or genera were

categorized into major phyla and eleven functional groups based on their common

feeding habit and body size (see Appendix A).

For biovolume determinations, zoopankton were measured with a micrometer-

equipped ocular. At least 30 individuals from each taxonomic unit were measured.









Absolute and relative biovolume of zooplankton were estimated by assigning the closest

geometric shape to each taxon (Halliday, 2001; Sarkar & Jana, 1985).

Precipitation and River Flow Rate

Daily total precipitation data were obtained from the United States Geological

Survey (USGS) archive website at LEO station (USGS Station number 291-830-081-

362-200, Lake George at Mile Marker 5 near Salt Spring, FL)

(http://waterdata.usgs.gov/fl/nwis/current/?type=precip, Accession date: May 21, 2010).

Figure 2-2 illustrates the data over time. Precipitations were generally observed at

approximately 2 cm except in the period of mid-April to mid-May, when there was nearly

no precipitation. The highest precipitation recorded during the study period was in mid-

May (May 18, 2009) when there was 7.85 cm of rainfall. This rainfall peak was followed

by several peaks soon afterwards.










St Johns River Outlet


Crescent Lake

I Lake George



St Johns River Inlet


- 11


Figure 2-1. Location of Lake George in Florida regional outline map and locations of the
two selected sampling sites, LEO and LAG, in Lake George.


Figure 2-2. Total daily precipitation at the LEO station during the study period. Data
were available only for the LEO site, and were obtained from the United
States Geological Survey archive website
(http://waterdata.usgs.gov/fl/nwis/current/?type=precip). Accession date was
May 21, 2010)


Total Daily Precipitation in LEO


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Ln rl 1 cc 6n N 0) rWD 0 r- M' 0 rh-
r-1 N N r N "I "
-- 4 ~ '. .--. lo
rfl Q O QO O









CHAPTER 3
RESULTS

Chlorophyll a Concentration

Chlorophyll a concentrations revealed two peak periods of phytoplankton

biomass, one in mid-April and one in late May to early June (Figure 3-1) Mean group

analysis showed three distinct temporal stages of chlorophyll a dynamics: 1)

development of the first bloom, 2) development of the second bloom, and 3) the decline

of the second bloom. Two-way Analysis of Variance (ANOVA) revealed there was no

significant different in overall chlorophyll a levels either between the two sampling sites

(LEO and LAG) or between the sampling times (day and night) (F = 1.89, p = 0.1450).

There was one noteworthy difference in chlorophyll a concentrations at LAG and

LEO. Chlorophyll a concentration during the second bloom event at LAG decline sharply

from approximately 70 pg/L to 20 pg/L between May 21 and June 3, but concentrations

at LEO continued to increase to 90 pg/L until a sharp decline to 45 pg/L from June 6 to

June 10.

Cyanobacterial Toxin Levels

Three cyanobacterial toxins were detected at both stations in Lake George,

cylindrospermopsin, microcystins, and saxitoxin. Saxitoxin levels (Figure 3-2A) ranged

between 0.01 and 0.43 pg/L. The peak value of 0.43 pg/L were observed during mid-

April and decreased slightly after the peak. This trend was similar to that of the first

planktonic chlorophyll bloom. Cylindrospermopsin concentrations ranged from 0.02 to

0.77 pg/L (Figure 3-2B). The concentrations generally followed the trend in chlorophyll a

concentration during the second bloom period at the two stations (LEO and LAG).

Microcystin levels (Figure 3-2C) generally increased during the study period, and









ranged between 0.05 and 1.06 pg/L. The overall means of these three cyanobacterial

toxin levels were not significantly different between the two sampling sites (LEO and

LAG) or between the two sampling times (day and night).

Water Chemistry and Physical Variables

Fifteen water column variables were included in the study: depth, temperature,

Secchi depth, turbidity, CDOM, dissolved oxygen, conductivity, pH, TP, SRP, TN, NO3,

NO2-, NH4 and Si.

Water depth (Figure 3-3) remained near 3 m from the beginning of the study

through mid-May. Thereafter, water depth increased to approximately 4 m until the end

of the study. This general trend was observed at both LEO and LAG. Water depths at

both sampling sites were not significantly different (F = 1.55, p = 0.2132)

Surface water temperatures (Figure 3-4) were not significantly different either

between LEO and LAG or between day and night (F = 0.15, p = 0.9319). However,

daytime temperature levels were generally higher than nighttime temperature.

Temperature gradually increased from 22C in late March to approximately 32C in late

June.

Secchi depth (Figure 3-5) ranged from 0.6 m to 1.0 m during the study. Mean

values were not significantly different between LEO and LAG (F = 1.23, p = 0.2542).

There were two periods when Secchi depth at LAG was lower than that at LEO on April

22 and Jun 3, 2009.

In general, turbidity had the same overall trend with chlorophyll a level (Figure 3-

6). No significant differences, either between LEO and LAG or between day and night,

were observed for turbidity (F = 0.60, P = 0.6178). There were two peaks values, which

ranged from 4-10 NTU. The first and second peaks were observed during mid-April and









late May, respectively. The first peak was higher in LAG than in LEO while turbidity in

LEO during the second peak was generally higher than that in LAG.

True water color, measured as colored dissolved organic matter, ranged between

about 40 to 200 PCU (Figure 3-7). Color levels in both LEO and LAG were not

significantly different (F = 1.40, p = 0.2540). However, the levels in both sampling sites

were similar in their trends in that they generally decreased from the beginning of the

study through May 27, when the color was approximately 40 PCU in LEO. After that, the

levels sharply increased from late May to the end of the study, and were usually higher

in LAG than in LEO.

Dissolved oxygen (Figure 3-8) was observed at both the water surface and near

the lake bottom. Measurements at both depths were not significantly different, either

between sampling sites or between day and night (Surface: F = 2.37, p = 0.0832;

Bottom: F = 0.40, p = 0.7559). However, the overall patterns in dissolved oxygen

dynamics at the water surface and at the lake bottom were not similar. Dissolved

oxygen at the water surface ranged approximately between 4 and 12 mg/L, and was

usually lower in night samples. The two lowest values were observed on May 6 and

June 3. Near the lake bottom, dissolved oxygen remained more stable than at the

surface, with DO ranging from approximately 8 to 10 mg/L before decreasing to 2 mg/L

in mid-June.

Specific conductivity (Figure 3-9) was not statistically different either between

LEO and LAG or between day and night (F = 0.35, p = 0.7926). Values at the two sites

displayed similar trend, ranging between 1.0 to 0.8 mS/cm. They gradually increased

during late March to mid May before dropping, and remained at approximately 0.8









mS/cm until the end of the study. The levels at LAG in the declining period

weregenerally lower than those at LEO.

No statistical difference was found in pH between LEO and LAG or between day

and night samples (F = 0.99, p = 0.4070). pH generally ranged between 8.00 and 9.25

during this study (Figure 3-10). However, a significant, sharp drop in pH was observed

from April 29 to May 6, when the pH dropped to approximately 7.25.

TP and SRP (Figure 3-11) showed similar overall temporal patterns although

they were not significantly different either between LEO and LAG or between day and

night samples (TP: F = 1.22, p = 0.3130; SRP: F = 1.01, p = 0.3952). TP and SRP

ranged from 0.02 to 0.14 and 0.01 to 0.11 mg/L (as P), respectively. They were

relatively stable from late March to the end of May. After that, the levels increased

sharply, and were significantly higher in LAG than in LEO.

Total nitrogen concentrations (Figure 3-12), ranged from 0.75 to 1.71 mg/L as N,

which was present, in part, as ammonium (0.04 0.23 mg/L as N), nitrate (0 0.04

mg/L as N), and nitrite (0 0.01 mg/L as N). TN and ammonium generally displayed

similar trends. They gradually increased during the study with peaks on April 22 and Jun

7. TN was significantly higher in LEO than in LAG (F = 2.66, p = 0.0594) while no

significant difference was found between the sites for NO3-, NO2-, and NH4 (NO3-: F =

0.64, p = 0.5940, NO2-: F = 0.84, p = 0.4778, and NH4+: F = 0.41, p = 0.7443). Nitrate

and nitrite followed similar trends in that they remained stable from late March to late

May. After that, sharp increases were observed in both variables at both sampling sites.

Nitrate and nitrite were distinctly higher in LAG than in LEO during this period of

increase.









Overview Survey of Zooplankton

Fifty-one identifiable zooplankton genera and/or species were observed in the

water samples collected at LEO and LAG over the study period. The genera observed

fell within two major phyla: Arthropoda and Rotifera. The observed taxa are shown in

Table 3-1.

Dynamics of Three Major Zooplankton Groups

Cladocerans

Cladoceran biovolume remained below 206x106 pm3/L until a sharp increase in

early May (Figure 3-14), peaking in mid-May. Cladoceran biovolume decreased again in

early June before reaching the second peak in mid-June. Cladoceran biovolume

showed similar trends at both sites and in day and night samples.

Biovolume of cladocerans relative to total zooplankton biovolume ranged from

2.4 to 81.5 % during the study period. Relative biovolume of cladocerans exceeded

80% during periods of peak abundance in mid-May and mid-June, with similar trend at

both sites and in both day and night samples.

Cladoceran abundances ranged from 2 to 1,171 individuals/L, with peaks in mid-

May and mid-June at both sites and in both day and night samples (Figure 3-14).

Cladoceran abundance relative to total zooplankton abundance ranged from 0.2% to

37.3% (Figure 3-14). The trends for abundance and relative abundance were similar to

that observed for biovolume and relative biovolume.

Copepods

Copepod biovolume generally increased during the study period (Figure 3-15).

The value ranged from 9.7x106 to 734.7x106 Pm3/L with two peaks in mid-May and mid-

June, which showed much higher copepod biovolume in LEO than in LAG. It started









increasing in late April. During this increasing period, copepods in LEO were generally

more abundant in the night than in the day until the end of May. This trend was also

observed in LAG, but it was observed in late June.

Relative biovolume of copepod to total zooplankton followed the trend in copepod

absolute biovolume (Figure 3-15). The relative value generally ranged from 3.6% to

75.5% during the study period. The highest peak of copepod relative biovolume was

observed in early June. LEO and LAG were similar in their copepod relative biovolume,

but LAG had higher copepod relative biovolume from early May to the end of the study.

Copepods were generally more abundant in night time than in day time before the

beginning of the increase in relative biovolume.

Copepod abundance ranged from 32 630 individuals/L (Figure 3-15), which

accounted for 1.5% to 53.8% of the total zooplankton abundance. The trend observed

was similar to that of biovolume and relative biovolume.

Rotifers

Rotifer biovolume ranged from 18.6x106 to 1,267x106 pm3/L with two distinct

peaks in late April and in mid-June (Figure 3-16). The second peak was relatively

smaller than the first peak. Rotifer biovolume in LEO was generally higher than that in

LAG from late March to the top of the first peak. The first peak decreased sharply and

remained low during May to early June. The second peak was observed in mid-June,

which showed the higher rotifer biovolume in LEO than in LAG.

Rotifer relative biovolume ranged from 1.7% 90.6% during the study period

(Figure 3-16). The overall trend followed its biovolume dynamics in that there were two

peaks, in late April and in mid- June. The highest peak in rotifer relative biovolume was

approximately at 90%, which decreased sharply in early May to about 10-20% before









increasing slightly in June. Rotifers were generally more abundant during day time than

during night time.

Rotifer abundance ranged from 174 8,390 individuals/L (Figure 3-16), which

accounts for 28.4% 97.7% in term of its relative abundance (Figure 3-16). The

observed trend was similar to that of its biovolume and relative biovolume.

Zooplankton Dynamics in Different Functional Groups

Zooplankton species were assigned to different ecological functional groups

according to their similar ecological guilds in feeding habit, body size, and taxonomic

categories (Appendix A). Eleven fuctional groups of zooplankton include: Bosminidae;

Sididae; Daphniidae; Copepod nauplii; Herbivorous copepods; Carnivorous copepods;

Omnivorous copepods; Microrotifers; Mesorotifers; Megarotifers; and Raptorial rotifers.

Two-way ANOVA revealed none of the zooplankton among eleven functional groups

was statistically different either in their biovolume or abundance between the two

sampling sites.

Cladocerans

The cladocerans belonged to three functional groups; Bosminidae, Daphniidae,

and Sididae. The general trend of these three groups mostly follows the dynamic trend

of cladocerans. Bosminidae was the most abundant among the group of cladocerans,

and was found throughout the study period in all samples (Figure 3-17) while the group

of Sididae (Diaphanosoma spp.) was found from early May to late June (Figure 3-17).

Daphniidae (Daphnia and Ceriodaphnia) was the group with least biovolume of these

three functional groups, and was limited from late May to late June (Figure 3-17).









Copepods

Copepods were categorized by feeding habits to four different functional groups:

Copepod nauplii, Herbivorous, Carnivorous, and Omnivorous Copepods. Copepod

nauplii were the most abundant in term of biovolume among the copepods. Its dynamic

trend was gradually increased in biovolume over time, and generally followed the trend

of the copepod group as a whole (Figure 3-18). Herbivorous copepods were present

from late April and were at their most abundant during mid-June, when the second

planktonic algal bloom occurred (Figure 3-18). Carnivorous copepods were found

mainly during day time in both sampling sites, and displayed peak biovolume during

mid-May to late-May, before dramatically decreasing in June (Figure 3-18). Omnivorous

copepods were the groups with the lowest peak biovolume among the copepods, and

generally had two peaks in early May and early June (Figure 3-18).

Rotifers

Four different functional groups of rotifers (Microrotifers, Mesorotifers,

Megarotifers, and Raptorial Rotifers) were differentiated based on body size and

feeding habits. The overall trend of microrotifers, mesorotifers, and megarotifers mostly

followed the dynamics of the rotifer group as a whole, with two observed peaks in their

absolute biovolume in early May and in mid-June. Mesorotifers were the most abundant

group in terms of biovolume (Figure 3-19), while microrotifers and megarotifers were

approximately the same. Microrotifers were almost absent after the first peak in early

May (Figure 3-19) while Megarotifers dominated the second peak in biovolume (Figure

3-19). Raptorial rotifers were also abundant in the first peak during early may at the

LAG site, and one-week later for the LEO site (Figure 3-19).









Relationship between Zooplankton and Physical-Chemical Variables

Major Group Level

In general, zooplankton biovolumes were associated with more physical and

chemical variables as well as cyanobacterial toxins at the LEO site than at LAG.

Cladoceran biovolumes at LEO (Table 3-2 column xii) were mainly positively

correlated with variables including temperature, depth, color, TN, NO2, NH4, TP, SRP

and Si while they were not significantly correlated in LAG station (Table 3-3 column xii)

except temperature and TN. Conductivity and dissolved oxygen at the lake bottom in

LEO were negatively correlated to cladoceran biovolume. Cylindrospermopsin and

microcystins were positively correlated with cladoceran biovolume while saxitoxin

showed negative correlation with cladoceran biovolume at LEO. No significant

correlation was found between cyanobacterial toxins and cladoceran biovolume at LAG.

For copepod taxa, correlations in LEO (Table 3-2 column xiii) were generally

similar to those in LAG (Table 3-3 column xiii). The biovolumes of copepods were

positively correlated with temperature, color, silica, NOx, NO2, TP and SRP in both

station while there were significant positive correlations only in LEO for NH4 and only in

LAG for NO3. Correlation with cyanobacterial toxins yielded in the same trend in both

sites in that copepod biovolume was positively correlated to cylindrospermopsin and

microcystins, and negatively correlated to saxitoxin.

Rotifer biovolume was mostly negatively correlated with various physical and

chemical variables including water depth, chlorophyll levels and TN in both stations.

Additionally, at LEO (Table 3-2 column xiv), they were negatively correlated with

turbidity and pH, while temperature, silica, NH4, TP and SRP were found to be

negatively correlated with rotifer biovolume at LAG (Table 3-3 column xiv). Saxitoxin









level was positively correlated to rotifer at both stations, but cylindrospermopsin was

found to be negatively related to rotifer biovolume at LAG.

Functional Group Level

Biovolumes of three functional groups of cladocerans (Bosminidae, Sididae, and

Daphniidae) were analyzed for their correlation with physical and chemical variables.

Bosminidae (Table 3-2 and Table 3-3 column i) was more strongly correlated with

physical and chemical variables at LEO than at LAG, while Daphniidae (Table 3-2 and

Table 3-3 column iii) were more highly correlated with those variables at LAG than at

LEO. Color, silica, NOx, NO2, NH4, TP, SRP as well as the three cyanobacterial toxins

were positively correlated to the functional group Bosminidae, while the group was

negatively correlated with conductivity and dissolved oxygen at LEO. No significant

correlation between Daphniidae and physical-chemical variables was observed at LEO,

but many variables, including temperature, color, dissolved inorganic nitrogen forms and

SRP were positively correlated with Daphniidae absolute biovolume. In terms of

cyanobacterial toxins, Bosminidae showed positive correlation with the three toxins at

LEO, and no other significant relationship was found either at LAG or in other

cladoceran functional groups.

Four copepod functional groups including nauplii, herbivorous, carnivorous, and

omnivorous types were categorized according to their different feeding habits (Table 3-2

and Table 3-3 column iv-vii). Carnivorous and omnivorous copepods were generally not

associated with physical and chemical variables. Secchi depth and carnivorous

copepod biovolume, however, displayed a significant relation at both stations.

Omnivorous copepod biovolume was positively and negatively correlated to

temperature and dissolved oxygen at water surface, respectively at LEO station, but not









at LAG. Copepod nauplii were positively correlated with many chemical variables in

LEO, but herbivorous copepods were not associated with chemical variables at both

sites. Conductivity and dissolved oxygen were negatively correlated to both nauplii and

herbivorous copepod biovolume, while temperature was positively correlated. Copepod

nauplii and herbivorous copepods were positively correlated to cyanobacterial toxins,

copepod nauplii and herbivorous copepod were positively correlated to

cylindrospermopsin and microcystins, and negatively correlated with saxitoxin at LEO.

At LAG, there was no significant correlation between cylindrospermopsin and the two

functional groups. Carnivorous and omnivorous copepods had no significant

relationship with the three toxins.

Four rotifer functional groups were classified based on their body size and

feeding habit. They were micro-, meso-, megarotifers, and raptorial rotifers. No

significant correlation was found between raptorial rotifer biovolume and any physical or

chemical variables at both sites (Table 3-2 and 3-3 column xi). Generally, micro-, meso-

, and megarotifers were associated with more variables in LEO than in LAG (Table 3-2

and 3-3 column viii-x). Most of the significant correlation found with these three rotifer

functional groups and water chemistry variables were negative. Temperature,

conductivity, and dissolved oxygen at the lake bottom were positively correlated with

mesorotifer biovolume in LAG. Cylindrospermopsin and saxitoxin were correlated

negatively and positively with microrotifers and mesorotifers, respectively. Microcystins

had a positive correlation with megarotifer biovolume at LAG.













Chlorophyll a concentration in LEO and LAG
100

90

_5 80
S70
60

50 LEO Day

S40 r -LAG Day
30 LEO Night
20 --N-LAG Night
U
10

0
0 0 0 0 0l 0 0 0 0 0 0 0 0

r- 00 r-4 0) 0 r,
Figure 3-1. Dynamics of chlorophyll a levels during the study period.



Figure 3-1. Dynamics of chlorophyll a levels during the study period.














Saxitoxin Level


---LEO Day
---LAG Day
- LEO Night
---LAG Night


1.100
1.000
0.900
0.800
0.700
0.600
0.500
0.400
0.300
0.200
0.100
0.000


--LEO Day
---LAG Day
- LEO Night
- LAG Night


a ^ Lt a N s ri a N
cN s B


Microcystins Level


o M 0 0 M M M M M 0 0 0
9 9 9 a 9 a 9
a af a. a. a. C E IC C a = a
- CO ft N at it a N' ,- 0
N N oI N N


-LEO Day
---LAG Day
- LEO Night
-#-LAG Night






C


Figure 3-2. Dynamics of three cyanobacterial toxins: A) Saxitoxin, B)

Cylindrospermopsin, and C) Microcystins.


a 0 a 0 0 0 0 0 0 0 0 0 0

C a. a a a ^ a a a -

Cylindrospermopsin Level

Cyindrospermopsin Level



































Figure 3-3. Depths at the sampling sites.


Figure 3-4. Temperature at the water surface.


Total Depth (m)






0.0 LEO Day
1.0 LAG Day
2.0 LEO Night
o -r




S0 LAG Night
54,0 ---


5.0

6.0


Temperature (oC)


36.00
34.00
32.00
30.00
28.00
26.00
24.00
22.00
20.00
18.00


1-LEO Day
-- LAG Day


---LAG Night


2- D

220 F'FiI


0-1 00 0 0 0 0 0 0 0 0
a a i ^. ^. ^ a H
L 00 Llrl aN rr C
SN r N N




































Figure 3-5. Secchi depths in the lake.


Figure 3-6. Turbidity in NTU during the study period.


Secchi Depth (m)

I > A, ,




0.00 -- LEO Day

0.20 ---LAG Day
E
U0.40 LEO Night
0-0 ----------------------- LE O Day

C020 -LLAGDay

" 0.60 ----LAG Night

1r
u 0.80
1.00

1.20


Turbidity (NTU) in LEO and LAG

12




5 8
1-


S6 -4-LEO Day
-nI
--W-LAG Day
LEO Night
2 --4-LAG Night

0
0 00 0_ 0 0 0 0 0 0

Ns rq N N













Water true color (PCU) in LEO and LAG

240


200


- 160
u

S120 --LEO Day
a
S -u-LAGDay
80 LE' lidit

0 LAG Night
40


0
0 o 0 0 0) 0 0 0 0 0 0 0 0

00 lN r) r,


Figure 3-7. Water color (CDOM) during the study period.













Dissolved Oxygen (mg/L) TOP

14.00
12.00
10.00

SI -4-LEO Day
6 6.00
o .00 --LAG Day
a 4.00
2.00 LEO Night
0.00 LAG Night
9 9 9 9 9 9 9 9 9 9 9 9 9

rN W Ln N 0 rMCD 0N





Dissolved Oxygen (mg/L) BOTTOM

14.00
12.00
.. lo.oo -----------
E
E 8.00
S600 4 E-LEO Day
6.00
m -U-- LAG Day
4.00
2.00 LEO Night

0.00 gLAG Night

S0 0 0 0 0 00
5 00 a N 0 a S' rl 0 N
Ci ONi N B
N N N N' N' N N ^


Figure 3-8. Dissolved oxygen levels in A) water surface and B) 20 cm above the lake
bottom.


































Figure 3-9. Specific conductivity during the study period.


Figure 3-10. pH at the water surface during the study period.


Specific Conductivity (mS/cm)

1.300
U 1.200



. -- LEO Day
0.900
- LAG Day
0.800
0.0 0LEO Night
. 0.700
" -0.600 LA G Night

L L L L ~ .
a) m C (m m C C C a a =


4 r I rj r. -


pH

10.00
9.50
9.00
8.50
S8.00 --4-LEO Day
7.50 -LAG Day
0 LEO Night
6.50
6.00 ---LAG Night



NN N -, I,












TP Concentration in LEO and LAG


0.16
0.14
- 0.12
S0.10


0.06
I 0.04
0.02
0.00


C? CT? CT? C? C? C7? Ci C7 C? C? CI: C?
o o 0 0 0 0 0 0 0 0 0 0 0
Mo a a a aL a Cc m c 0 M M
S :< < :< N N ^ ^ o -^
N 00 i nl r ri A N N r.
S^ "I r rl


-LEO Day

--LAG Day

LEO Night

-- LAG Night


SRP concentration in LEO and LAG


/IV


0 0 0 0 0 0 0 0 0 0 0 0 0
r L 'L L -~ ~

-0 LN N- C) rf 0 r.
Ni r N rN


--LEO Day
---LAG Day

ALEO Night
- --LAG Night




B


Figure 3-11. Phosphorus content in water samples were A) Total Phosphorus and B)
Soluble Reactive Phosphorus.


0.12
0.10

a 0.08
S0.06
0.04

0.02
0.00


-----M------ M















TN Concentration in LEO and LAG





0.8 --*--LEO Day
01.6


0 6 0 --LAGDay
04 LEO Night
0. --LAG Night

1-~~ ~ --------------------

A



NH4 Concentration in LEO and LAG

0.25

0.20

0.15
Eb LEO Day
0.10
0.10 LAG Day
z0.05 LEO Night

-N-LAG Night
0,00 ------------------------------


<% <, <, <, | | | | "? -N N



N03 concentration in LEO and LAG
0.045
0.040
S0.035
S0.030
0.025 "--$--LEO Day

S0.015 -I--LAG Day
20.010 LEONight
0.010

0.08 -N-LAG Night



C


N02 concentration in LAG and LEO


-LEO Day
---LAG Day
LEO Night
--LAG Night


= 0 0 0 0 0 0 0 0 0 0 0
f A N N0% NONS N -
^~~~~~ 9


Figure 3-12. The examination of nitrogen contents in water samples included A) Total

Nitrogen, B) Ammonium, C) Nitrate, and D) Nitrite.













Si Concentration in LEO and LAG

6.000


5.000


o 4.000
to
E

I 3.000 --LEO Day
-LAG Day
= 2.000 LEO Night

--* LAG Night
1.000


0.000 -)-C) -)


o 0 0 0
N ^ N NT !^ N S N ^


Figure 3-13. Silica levels during the study period.















Cladoceran Biovolume


2500
E
2000

S1500

1000

0 500

0 -
u t < :<


a a a c


-6-LEODay
--MLAG Day
-- LEO Night
- LAG Night





A


Cladoceran Relative Biovolume

100
t 90
80
S70
60
S50 -- -LEO Day
40 --I- LAG Day

20 -ALEO Night
S10
S0 L- LAG Night

a a a. a. a a a a a 3 a a




Cladoceran Abundance
1400
1200
S1000
800
--LEO Day
600
c ---LAG Day

200
-[AG Night
0









80 0
Cladoceran Relative Abundance



I 80
S70
S60
S50 --LEO Day
40 --LAG Day
30
20 LEO Night
10 -- LAG Night
0 .


Figure 3-14. Cladoceran abundance indices included their A) absolute biovolume, B)

relative biovolume, C) absolute abundance, and D) relative abundance.















Copepod Biovolume









U Ve






N NN4 atN -


-a-LEO Day
--LAG Day
-- LEO Night
-LAG Night


Copepod Relative Biovolume
100
S90
S80
E
70

. 50 --LEO Day
, 40t
30 ---LAG Day
S 20 -LEO Night
L 10
S 0 -+-LAG Night

K




Copepod Abundance
700
600
500
400j -*--LEODay

300 +--WLAGDay
a 200
200 LEONight
a 100
S 00 -4-LAG Night


0




Copepod Relative Abundance


a. a a at a
-Q ia l N N~ at 0^ N t


LEO Day
--LAG Day
SLEO Night
-LAG Night



D


Figure 3-15. Copepod abundance indices included their A) biovolume, B) relative

biovolume, C) abundance, and D) relative abundance.















Rotifer Biovolume


0c? 9 0
o o o o o o o 6
&.na ~ ~ &.s .s.g -s-s


-*-LEO Day
-U-LAG Day
-LEO Night
-- LAG Night




A


Rotifer Relative Biovolume

100
i 90
i 80
S70
g 60
S50 LEO Day
40
> 30 ---LAG Day
20 ----LEO Night
S10
0 -- -,LAG Night
S0 99. 0 0 0 9n 9 9 0 S 00 0










3000 ---- / / 4 lAGDay
Rotifer Abundance
9000
8000
S7000
6000
5000 so LEO Day
4000
3000 --LAG Day
20 -r-LEONight
1000 -LAG Night








0 0 -----------
0-


Rotifer Relative Abundance
100


70
S60
Sso -LEO Day
L 40
--WLAG Day
20 -LEO Night
0 10 LAG Night
0


D


Figure 3-16. Rotifer abundance indices included their A) biovolume, B) relative

biovolume, C) abundance, and D) relative abundance.













Bosminidae Absolute Biovolume


oo0 0 0 0 0
g s s s g s
S> ? .> =
a r o "
N I M N -


--LEO Day ABV
--LAG Day ABV
- LEO Night ABV
#-LAGNightABV



A


Sididae Absolute Biovolume


ra a 3 a a a a ^
NN N N N
2 1 4 1 4


-4LEO Day ABV
--LAG Day ABV
- LEO NightABV
--LAG NightABV



B


Daphniidae Absolute Biovolume


a a a a a, a, a, a a a am


.^ -f oo L~ ^ m 8 Ji 6 rj m
3 N4 N N
I a aab ,r (r

N1 CO S N 0l 0 N
N ~N N 0N CN N


--LEO Day ABV
--LAG Day ABV
SLEO NightABV
-LAG NightABV



C


Figure 3-17. Biovolume in three cladoceran functional groups A) Bosminidae, B)
Sididae, and C) Daphniidae.


0 0 0 0
cc co
N- C'
<.<. ^-1 Xi LT r


I














Copepod Nauplii Absolute Biovolume
450
5 400
E 350
S 300
_2 250
S200 --LEO Day ABV
S 150 -- LAG Day ABV
S 100 --LEO NightABV
50
0 g- --LAG NightABV






Herbivorous Copepods Absolute Biovolume
350
E 3 00
S250
E 200
--$-LEO DayABV
150
00 -- AG DayABV
100
50 -LEONightABV
0 -LAG NightABV

a a. a a .




Carnivorous Copepod Absolute Biovolume
140
8 120
ELEO
100
I 80
~- --LEO Day ABV
> 60
4 0 \ ---LAG Day ABV
0 -LEO NightABV
0 --- LAGNightABV

2 .. .

C

Omnivorous Copepods Absolute Biovolume
90
80


40 LEODayABV
4 60


30 --0-LAG Day ABV
20 --LEO Night ABV
10
SLAG NightABV

o. o o o
b sa -^aa^ l


Figure 3-18. Biovolume in four copepod functional groups A) copepod nauplii, B)

herbivorous copepod, C) carnivorous copepod, and D) omnivorous copepod.














Microrotifers Absolute Biovolume
160
S140
E
120
i 100
S 80 +LEODayABV
60 ---LAGDayABV
a, 40
S 40 --A-LEONightABV
0 20
0 -- -LAG NightABV

.c C. .




Mesorotifers Absolute Biovolume
1200
_ 1000
800
I 600 LEO DayABV
a 400 --- LAG DayABV
S 200 -LEO NightABV
0 -+(-LAGNightABV

5 ^. C .. = = = C C C


B

Megarotifers Absolute Biovolume
180
160
E 140
120
o 100
10 -LEO DayABV
S 60 --LAG DayABV
S40 1 f -LEO Night ABV
-0 LAG Night ABV






Raptorial Rotifers Absolute Biovolume


9 9 N
Vi S Vi 1


F F F F F


-LEO Day ABV
--LAG Day ABV
--LEO NightABV
- LAG Night ABV


D


Figure 3-19. Biovolume in four rotifer functional groups A) microrotifers, B) mesorotifers,

C) megarotifers, and D) raptorial rotifers.


"^ / ^\L ^









Table 3-1. Zooplankton species list found during this study period. "x" mark represents
the presence of particular genera and species in samples collected at LEO
and LAG during the day and night.
LEO LAG
Species list
Species list Day Night Day Night
Phylum Arthropoda
Subphylum Crustacea
Class Branchiopoda
Bosmina spp. x x x x
Ceriodaphnia spp. x x x x
Daphnia ambigua x x
Daphnia spp. x
Diaphanosoma birgei x x x x
Diaphanosoma brachyurum x x
Eubosmina spp. x x x x
Class Copepoda
Copepod nauplii x x x x
Juvenile calanoid copepods x x x x
Juvenile cyclopoid copepods x x x x
Adult Calanoid copepod spp. x x x x
Mesocyclops edax (female) x x x x
Mesocyclops edax (male) x x x x
Tropocyclops spp. (female) x x x
Tropocyclops spp. (male) x
Phylum Rotifera
Aneuropsis spp. x x x x
Asplanchna spp. x x x x
Asplanchna-like rotifer x x x x
Brachinus angularis x x x x
Brachionus caudatus x
Brachionus havanensis x x x x
Brachionus quadridentatus x
Brachionus spp. x
Cephalodella spp. x x x x
Collotheca mutabilis x x x x
Collotheca pelagica x x x x
Conochiloides spp. x x x x
Conochilus unicornis x x x x
Filinia longiseta x x x x
Filinia terminalis x
Harringia spp. x x
Hexarthra spp. x x x x
Keratella chochlearis longtaill form) x x x x
Keratella chochlearis shorttaill form) x x x x









Table 3-1. Continued
LEO LAG
Species list
Species list Day Night Day Night
Phylum Rotifera (continued)
Keratella chochlearis (knobtail form) x
Keratella tecta x x x x
Keratella tropica x x x
Keratella valga x x x x
Lecane spp. x x x
Lepadella spp. x x x
Monostyla spp. x x
Notholca spp. x x x
Notommata spp. x x x x
Polyarthra spp. x x x x
Synchaeta spp. x
Synchaeta sp4. (round form) x x x x
Trichocerca multicranis x x x x
Trichocerca similis x x x x
Trichocerca sp.3 (non-descript form) x x x x
Unidentified rotifer (round form) x x
Unidentified rotifer (top-shaped form) x x x










Table 3-2. Correlation between water physical-chemical parameters and zooplankton absolute biovolumes in different
levels of functional groups and taxa in the station of LEO. Positive (+) and negative (-) significant correlation at
the confidence level of 95% are represented in the table. Blank cells represent the insignificant correlation
between the parameters.
Functional group level Taxa level
Cladocerans Copepods Rotifers
Bosm Sidi Daph Naup Herb Cam Omni Micr Meso Mega Raptp
(i) (ii) (iii) (iv) (v) (vi) (vii) (viii) (ix) (x) (xi) (xii) (xiii) (xiv) (xv)
Temperature + + + + + + + +
Conductivity
DO Top-
DO Bottom
Depth + +
Secchi depth
Turbidity
Color + + + + + + +
pH
Chlorophyll
Silica + + + + + + +
TN + -+
NOx + + + + +
NO2 + + + + + + +
NO3 + +
NH4 + + + + +
TP + + + + + +
SRP + + + + + + +
CYL + + + + +
MCY + + + + + +
SAX + + + +










Table 3-3. Correlation between water physical-chemical parameters and zooplankton absolute biovolumes in different
levels of functional groups and taxa in the station of LAG. Positive (+) and negative (-) significant correlation at
the confidence level of 95% are represented in the table. Blank cells represent the insignificant correlation
between the parameters.
Functional group level Taxa level
Cladocerans Copepods Roifers
Bosm Sidi Daph Naup Herb Cam Omni Micr Meso Mega Raptp
(i) (ii) (iii) (iv) (v) (vi) (vii) (viii) (ix) (x) (xi) (xii) (xiii) (xiv) (xv)
Temperature + + + + + + + + +
Conductivity __+ +
DO Top
DO Bottom__ +
Depth_ +
Secchi depth
Turbidity
Color + + + +
pH
Chlorophyll +
Silica + + +
TN + + +
NOx + + +
NO2 + + +
NO3 + + +
NH4 + +
TP + -+ -
SRP + + + -+ -
CYL + -
MCY + + + +
SAX + + +









CHAPTER 4
DISCUSSION

The study period was characterized by shifts in the dominance structure of the

zooplankton community in Lake George. The shifts began with a rotifer peak in late

April, followed by a peak in cladoceran biovolume in May, accompanied by a decline in

rotifer biovolume, then an increase in the relative importance of copepods in late May to

early June.

It is useful to view the dynamics of the three major groups, along with functional

guilds within the three groups, in relation to temporal trends in phytoplankton dynamics

and changes in key water column characteristics including phytoplankton biomass,

phytoplankton composition, cyanobacterial toxins, temperature, turbidity, and dissolved

oxygen concentrations.

With respect to phytoplankton biomass, the study period was not dramatically

different from many previous years of the historical record (SJRWMD, 2010). Two

peaks in chlorophyll a levels were observed, one in April and a larger peak in May

reaching 91.8 pg/L. Lake George is a eutrophic lake with annual average chlorophyll a

concentrations in excess of 40 pg/L. The lake is also subject to frequent algal blooms

with chlorophyll a levels near or exceeding 100 pg/L during spring, summer, and

autumn.

Phytoplankton composition over the study period exhibited trends common to

eutrophic lakes in Florida, with a dominant of cyanobacteria (Dong, 2010), particularly

during the second bloom when chlorophyll a concentrations reached 92 pg/L.

Dominance of cyanobacteria during periods of high chlorophyll a is a prominent feature

of Florida's eutrophic lakes (Canfield et al., 1989). Due to high phosphorus loads to









Lake George, nitrogen limitation of phytoplankton growth is an important feature of the

lake that leads to a major role for nitrogen-fixing cyanobacteria (Dong, 2010; Piehler et

al,. 2009).

Some of the important cyanobacterial species observed in this study have been

implicated in the production of toxins in other ecosystems around the world (Chorus &

Bartram, 1999). Anabaena spp., Aphanizomenon spp., Anabaenopsis spp.

Cylindrospermopsis sp., Lyngbya sp., and Planktothrix sp. have been identified as

potential saxitoxin producers ((Clark et al., 1999; Landsberg, 2002)). In this study,

Anabaena sp., Anabaenopsis sp., and Aphanizomenon sp. were abundant during the

first bloom period, coincident with the appearance of saxitoxin.

The second bloom period was associated with increases in the abundance and

biovolume of Cylindrospermopsis sp., Oscillatoria spp. and Aphanizomenon spp.

((Dong, 2010)). Levels of the hepatotoxin cylindrospermopsin increased together with

chlorophyll levels during the second bloom period. Cylinderspermopsis has been found

worldwide and certain strains of C. raciborskii have been observed to produce

cylindrospermopsin in Australia and Europe, but not in the United States (Li et al., 2001;

Yilmaz et al., 2008; Briand et al., 2004). The toxin has, however, been detected in

Florida lakes (Aubel et al., 2006). It is possible that the cylindrospermopsin observed in

Lake George may be produced by another cyanobacterium observed during the second

bloom, such as Aphanizomenon spp. (Yilmaz et al., 2008), or a heretofore undescribed

strain of Cylindrospermopsis.

Levels of another common hepatotoxin, microcystin, gradually increased over the

last month of the study period, when the second bloom reached its peak. Some









cyanobacteria species, including certain strains of Anabaena flos-aquae, Microcystis

aeruginosa, and Oscillatoria agardhii var. isothrix, have been reported to produce

microcystins (Namikoshi & Rinehart, 1996)). Microcystis sp. was observed in Lake

George in June (Dong, 2010). The World Health Organization has published a

provisional guideline for microcystins in recreational and drinking water of less than 20

pg/L and 1.0 pg/L, respectively (WHO, 2006). The microcystin levels observed in this

study were mostly below 1.0 pg/L.

From a spatial perspective, no significant differences were observed in mean

chlorophyll a concentrations between the sampling sites. There were, however,

noteworthy differences in bloom dynamics at LEO and LAG. During the second bloom

period, phytoplankton biovolume declined precipitously in late May at LAG, but

continued to rise at LEO until a sharp decline in early June. This might be related to

hydrologic patterns in Lake George. The upper St Johns River flows into the lake at the

southern end. LAG is the site located nearest to the river inlet, whereas LEO is located

in the north-central region of the lake. The location of these two sampling sites causes

LAG to be influenced by major freshwater inflows earlier and more profoundly than

LEO. This results in the accumulation of planktonic organisms at the LEO site, where

the flow has more retention time and greater water age. The chlorophyll concentration

pattern supports this as there were no distinct differences between the two sampling

station observed when river inputs to the lake were small. However, from mid-May

through June, high rainfall levels caused in substantially elevated river discharge into

the southern end of the lake. Turbidity during the high precipitation period also

increased.









Meteorological factors, such as precipitation and wind velocity, can influence the

spatial and temporal distribution of phytoplankton (Phlips et al., 2007). There can be

dilution as a consequence of an increase in incoming freshwater from the upper river,

i.e. the more water input, the greater dilution factor. If the rate of dilution is greater than

accumulation rate, the phytoplanktonic chlorophyll a decreases as observed in late May

at LAG and early June at LEO.

Factors other than phytoplankton can affect zooplankton abundance distribution

and dynamics. Temperature is one of the factors that can enhance or inhibit growth

rate of certain types of zooplankton (Gliwicz, 1990). For example, Daphnia sp. and

Diaphanosoma sp. were less abundant during late spring and summer (Cichra, 2009).

The surface temperature during the study period gradually increased from 2C to 32C,

which might have been due to the seasonal transition over the 3-month period.

However, this was not consistent with the trend in the historical records from the St.

Johns River.

Turbidity is a variable that affects the susceptibility of zooplankton to visual-

feeding predators, such as fish and invertebrate larvae ((Wellington et al., 2010; Vinyard

& Obrien, 1976)). Elevated turbidity values (~2.5x) were found during the first and the

second bloom. This could enhance survivorship of zooplankton during bloom periods,

as their natural predators might not be able to feed efficiently.

Low dissolved oxygen is a factor that can negatively impact zooplankton (Rivkin

& Legendre, 2001). Dissolved oxygen can shift significantly during phytoplankton bloom

events. In healthy blooms, photosynthesis increases daytime oxygen levels, whereas

nighttime respiration depletes oxygen levels. In senescing blooms, bacterial respiration









associated with organic matter decomposition can cause hypoxic conditions. Oxygen

concentrations during the study period showed depletion in early May and late June,

after the two major peaks of phytoplankton blooms. The lowest dissolved oxygen level,

however, was approximately 4 mg/L, which should not be limiting to zooplankton

survival.

Fifty-one zooplankton taxa were identified in this study, including three major

groups; crustaceans, copepods, and rotifers. All of the taxa have been observed in Lake

George over the past fifteen years (SJRWMD, 2010; Cichra, 2009). It is useful to

examine the major trends in abundance and composition of each of these three groups,

within the context of the variables discussed above.

Cladoceran Dynamics

Cladocerans were a major component of the zooplankton community in terms of

biovolume through most of the last half of the sampling period, i.e. during the second

cyanobacterial bloom. By contrast, cladoceran abundances were low during the first

phytoplankton bloom period. From a spatial perspective, the two sites sampled in this

study exhibited no major differences in overall cladoceran composition or abundance

during the study period. However, differences over more restricted time frames resulted

in spatial disparities in the correlations between cladoceran abundance and physical-

chemical conditions in the water column.

Cladoceran biovolume was significantly correlated to fourteen physical-chemical

variables at LEO, but only two variables at LAG. At LEO, positive correlations were

observed with temperature, depth, color, silica, TN, nitrite, ammonium, TP, SRP,

cylindrospermopsin, and microcystins, while conductivity, dissolved oxygen at the

bottom of the lake, and saxitoxins were negatively correlated to cladoceran biovolume.









By contrast to the numerous significant correlations at LEO, only temperature and TN

were positively correlated with cladoceran biovolume at LAG. The lack of additional

correlations may be related to the strong influence of river inputs to the southern end of

Lake George causing greater temporal variability in a wide range of variables.

The importance of these correlations can be view from three different

perspectives: 1) factors that directly impact cladoceran abundance such as

temperature, 2) factors that indirectly impact abundance through their influence on other

trophic levels, such as phytoplankton (bottom-up control) or fish biomass (top-down

control), and 3) factors that are auto-correlated with variations in real driving factors, but

are not considered functionally important.

The differences between sites extended to the three cladoceran functional

groups, which responded differently in correlation analyses. Bosminidae (Bosmina spp.

and Eubosmina spp.) were correlated with more factors at LEO than LAG. Conversely,

Daphniidae (Daphnia spp. and Ceriodaphnia spp.) showed greater numbers of

correlations at LAG than LEO. These differences between the sites might be related to

the differences in physical, chemical, and biological variables between the two

locations. TN was the only variable that was higher at LEO than at LAG, while other

variables, such as color, silica, nitrite, TP and SRP, were slightly higher in LAG than in

LEO during the second bloom period. It is possible that differences in physical and

chemical variables between the two sites influenced the dominance of different

cladoceran functional group. The effect of top-down control by fish and invertebrate

larvae predation, however, was not determined during this study. It therefore remains a

potentially important consideration for future investigation.









The correlation trends for total cladocerans resembled to those for the functional

group of Bosminidae at both sites, while Sididae and Daphniidae did not follow the trend

of total cladocerans. Bosmina spp. and Eubosmina spp. were identified in all samples

during this study, and they were high in relative biomass compared to other

cladocerans. This supports the observations of Blancher (1984), Elmore et al. (1984),

and Crisman & Beaver (1990) that small cladoceran species (body siz5 700 pm), such

as the Bosminidae functional group, are common in Florida. High numbers of

correlations in this functional group may imply that they are controlled by various

physical and chemical variables, and that changes in these environmental factors could

lead to changes in Bosminidae populations.

Few individuals of Sididae (Diaphanosoma spp.) and Daphniidae (Daphnia spp.

and Ceriodaphnia spp.) were observed in this study. This was in accordance with many

studies that have observed seasonal disappearances of large cladocerans in

subtropical lakes (Gillooly & Dodson 2000; K. A. Work & Havens 2003; K. Work, et al.

2005; Havens, et al. 2009). Summer water temperature may be a limiting factor in the

abundance of certain cladoceran species (Gillooly & Dodson 2000), although the results

of this study and other historical data (SJRWMD 2010) suggest that many indigenous

cladocerans are adapted to summer temperatures. Although it cannot be confirmed in

this study, Havens et al. (2009) suggests that increases in the number of opportunistic

filter-feeding planktivores are, in part, responsible for the low cladoceran abundance in

subtropical lakes.

Availability of nutrients is necessary for phytoplankton growth. Most forms of

nitrogen, phosphorus, and silica were positively correlated with cladoceran biovolume,









perhaps reflecting the positive effect of nutrient availability on phytoplankton

productivity. Chlorophyll a concentrations, however, were not significantly correlated

with cladoceran biovolume. This suggests that some major phytoplankton taxa are

inefficiently grazed and drive increases in chlorophyll a level. Some cyanobacteria are

less efficiently grazed by cladocerans for a number of reasons, such as large size or

toxin content. In addition, filamentous and colonial cyanobacteria are considered to be

poor food for zooplankton due to their low nutrition content (Gliwicz, 1990). Alternatively,

bacteria have been shown to be an efficient food source for cladocerans and played

important role in the microbial loop by helping the transfer of energy and carbon to

higher trophic level in the food web (Tranvik, 1992; Havens & East, 1997). It might be

possible that cladocerans graze on bacteria in this study.

It may be hypothesized that saxitoxin-producing cyanobacteria in Lake George

in April restricted the abundance of cladocerans. It has been documented that

cyanobacterial toxins and toxic algal strains have negative effects on cladocerans.

Cladoceran feeding is also disrupted by filamentous cyanobacteria (Epp, 1996). Toxic

Microcystis aeruginosa (strain PCC7820) and purified microcystins have negative

effects on survival and feeding of two cladocerans, Moina micrura and Ceriodaphnia

cornuta (Liu et al., 2006). Feeding and growth of Daphnia magna was found to be

suppressed with increased proportions of Cylindrospermopsis raciborskii in their diet

(Soares, et al. 2009). Filtering rate of Daphnia sp. was reduced when C. raciborskii was

presented. Larger species of Daphnia were found to be more susceptible to the

presence of C. raciborskii than smaller species (Hawkins & Lampert 1989).









In terms of the effect of cyanobacterial hepatotoxins, both cylindrospermopsin

and microcystins were positively correlated with cladoceran biovolume in Lake George.

This was also observed in the functional group of Bosminidae, which was also positively

correlated with saxitoxin, unlike most cladocerans, with which it was negatively

correlated. The differences between functional groups in terms of correlations with toxin

levels may be related to differences in food preferences or varying sensitivities to toxins

among species. It is also possible that the impacts of toxins at the levels observed in

this study were not strong enough to significantly influence cladoceran abundance, and

the correlations to toxins observed were auto-correlated to other more important

environmental factors.

In terms of diurnal variability, Diaphanosoma brachyurum was the only

cladoceran that was found only in daytime samples in both stations. This might be due

to the behavior of this species, which is more active during the day. D. brachyurum has

been shown to be less susceptible to fish predation based on its diurnal vertical

distribution patterns (Thys & Hoffmann, 2005)) by being more abundant at water surface

during the day. This supports the observation in this study that the species was found

only in day time samples.

Copepod Dynamics

As in the case of cladocerans, biovolume of copepods in LEO was positively

correlated with temperature, color, silica, dissolved inorganic nitrogen, nitrite,

ammonium, TP, SRP, cylindrospermopsin, and microcystins. In contrast, conductivity,

saxitoxin, and dissolved oxygen were negatively correlated to copepod biovolume at

both sites. Additional positive correlations were found for dissolved oxygen at the lake

bottom and nitrate at LAG, while turbidity was negatively correlated. Many of these









variables are related to phytoplankton biomass, suggesting that copepod abundance is

correlated with phytoplankton dynamics, particularly during the second bloom period. By

contrast, copepod abundances were low during the first bloom period. There are a

number of possible reasons for this pattern. One hypothesis is the preference of

copepods for high temperature. Copepod abundance has been linked to seasonal shifts

in temperature (Shireman & Martin, 1978). The abundance of copepods in this study

increased along with temperature. Low temperature may reduce growth rates of

copepods while warmer conditions, which increased in the second half of the study,

generally increase the grazing rate of zooplankton (Williamson et al., 2010).

Nevertheless, copepod abundance was low during the biomass peak of diatom.

According to a study of gut analysis, macrozooplankton copepodss and cladocerans)

prefer diatoms, although they can graze filamentous and colonial cyanobacteria (Work

& Havens, 2003)). This suggests that temperature may control copepod abundance,

apart from factors related to food availability. However, this hypothesis is not supported

by historical observations of copepods in Lake George which indicate major peaks in

abundance in spring as well as summer ((SJRWMD, 2010)).

Copepods were positively correlated with nutrient sources including nitrogen and

phosphorus, which are necessary for optimal growth of copepod food sources. This

suggests that there might be more food availability for copepods during periods of

enhanced nutrient availability supported by the major bloom of nitrogen-fixing

cyanobacteria during the second bloom period.

Another possible contributor to the low copepod abundances observed in April is

the presence of the cyanobacteria species Anabaena spp. and Aphanizomenon spp.,









both of which are potential saxitoxin producers, and may explain the higher significant

levels of saxitoxin observed in April. Like cladocerans, cyanobacterial toxins have been

documented to have adverse effects on many groups of copepods. For example,

feeding experiments revealed the ability of the copepod Diaptomus birgei to reject food

source that may contain defensive chemicals i.e. toxins, and indicated its susceptibility

to microcystin (Demott & Moxter, 1991; Demott et al., 1991)).

Copepods have diverse food preferences, including bacteria, protozoa, and small

phytoplankton for nauplii and herbivorous copepods, and zooplankton such as rotifers

for carnivorous taxa (Work, et al. 2005). Therefore, separating copepods into different

functional guilds is important for evaluating trends.

Correlation trends with physical and chemical variables among the four copepod

functional groups were similar at both sampling sites. Nauplii and herbivorous copepods

were correlated with many physical and chemical variables, while few significant

correlations were found for carnivorous and omnivorous copepods, which are less

directly linked to phytoplankton. Although they have wide feeding habits, nauplii and

herbivorous copepods feed mainly on bacteria and phytoplankton (Tranvik, 1992;

Havens & East, 1997). Therefore, factors linked to phytoplankton biomass, such as

nutrient concentrations, should be correlated with their biovolume.

In terms of diel pattern of distribution, copepods shared a dominant role in

zooplankton abundance through the last month and a half of the study period at both

sites. Whereas cladocerans had two peaks in abundance, copepod biovolume gradually

increased from late April through mid-June. Despite the increase in both copepod and

cladoceran biovoluume during May and June, they did not appear to limit the second









phytoplankton bloom from reaching substantial biomass levels at both sites. This

observation is in keeping with the results of other research on eutrophic lakes in Florida,

which indicate that top-down pressure is not typically strong enough to suppress bloom

formation (Havens et al., 1996). This finding may be connected to the dominant role

played by filamentous cyanobacteria in eutrophic Florida lakes, which may be a less

than optimal source of food for zooplankton (Canfield et al., 1989; Gliwicz, 1990).

One copepod taxon, male Tropocyclops spp., showed a distinct diurnal pattern.

This cyclopoid copepod was observed only in daytime samples at LEO. This finding was

in accordance with a diurnal study in Lake Wales, Florida by Shireman & Martin (1978),

who found that the number of cyclopoid copepods differed between day and night.

Many other copepod taxa showed crepuscularity and different diurnal distribution

patterns. Calanoid spp., Mesocyclops spp., and carnivorous copepods were more

abundant during nighttime than daytime. This result supports previous observations that

copepods are more active during the night than the day to avoid visual feeders, such as

fish (Shireman & Martin, 1978).

Rotifer Dynamics

Rotifers were often the dominant zooplankton group, a pattern seen in many

other eutrophic lakes in Florida (Havens et al., 2009). Due to their comparatively small

body size, however, rotifers were relatively less important than copepods and

cladocerans in terms of biovolume, except during the first month of the project, when

they reached peak biovolume. The small size of most rotifer taxa places them in unique

functional groups focused on herbivory, particularly small size classes of phytoplankton.

It is noteworthy that rotifers peaked during the first bloom event when diatoms and

cyanobacteria were both major component of the phytoplankton community (Dong,









2010). Presence of significant amounts of centric diatoms may have provided rotifers

with an acceptable food source. After the decline of diatom biomass, replacement by a

cyanobacterial bloom may have limited the ability of rotifers to recover from their decline

at the end of April. Alternatively, rotifers may graze on bacterial and protozoan

community during this period. Nevertheless, these data were not included in this

research study.

Correlations between rotifers and various physical and chemical variables were

different from those of cladocerans and copepods. Five variables were negatively

correlated to rotifer biovolume at LEO, including depth, turbidity, pH, chlorophyll, and

TN. Saxitoxin was the only variable with which rotifer were positively correlated. In the

case of cladocerans and copepods, many of these variables displayed opposite

correrlations. At LAG, temperature, depth, chlorophyll, silica, TN, ammonium, TP, SRP,

and cylindrospermopsin were negatively correlated with rotifer biovolume whereas

conductivity and saxitoxin were the variables yielding positive correlations.

Negative correlations between rotifer biovolume and many variables associated

with phytoplankton abundance are related to the timing of the peak in rotifer abundance

in between the two bloom peaks. It might be argued that rotifers played a role in grazing

down major elements of the first blooms, especially diatoms. Alternatively, the large

amount of cyanobacteria in the first bloom, and dominance of cyanobacteria in the

second bloom, may have precluded a major buildup of rotifer biomass in the latter

period. High concentrations of saxitoxin in the first bloom and the hepatotoxin

cylindrospermopsin in the second bloom may have played a role in this relationship.

The significant biomass of the cyanobacteria Anabaena spp. and Aphanizomenon spp.,









both potential neurotoxin saxitoxin producers, in the first bloom period, did not suppress

the buildup of rotifer biomass late in the bloom, perhaps due to the presence of

significant quantities of alternative food items, such as diatoms. By contrast, the second

bloom period was dominated by cyanobacteria, and was also marked by the presence

of significant amounts of the hepatotoxin cylinderspermopsin and microcystin, perhaps

restricting the buildup of rotifer biomass. These relationships are further supported by

the correlation analyses involving different functional groups.

Microrotifers and mesorotifers were positively correlated with saxitoxin levels, but

the toxin was not correlated with larger rotifers. Gilbert (1996) experimentally

demonstrated susceptibilities of two large rotifers, Brachionus calycifloris and

Asplanchna girodi, to toxins produced by Anabaena flos-aquae. Bigger rotifers are

usually more tolerant of chemical stresses such as cyanobacterial toxins, possibly due

to their feeding preferences, which can include non-algal foods.

Different physical and chemical variables were correlated with rotifer functional

groups at the two sampling sites. Megarotifers were correlated with a number of

variables at LEO, whereas mesorotifers were correlated with more variables at LAG.

Raptorial rotifers were not correlated with any physical or chemical variables. These

findings might be due to the effect of size-selective feeding in zooplankton.

Microzooplankton and mesozooplankton usually graze on smaller phytoplankton, while

megarotifers can handle bigger phytoplankton or even other small zooplankton. The

high proportion of larger filamentous cyanobacteria at LEO than in LAG may contribute

to spatial differences in the distribution of rotifer functional groups.









In a diurnal perspective, Monostyla spp. were found only in daytime samples.

Brachionus caudatus were observed only in daytime samples at LEO while Brachionus

quadridentatus and Brachionus spp. were found only in daytime samples at LAG. These

rotifer species have not been previously documented to be diurnal migrators. Findings

in this study might be coincidental because few individuals of these species were found

in the samples.

Asplanchna spp. and raptorial rotifers were more abundant in the water column

during nighttime than daytime (Table 4-1). Similarly, Asplanchna sp. showed up at the

water surface at night and decreased during daytime in a study of Lake Balsamand in

India (Jakher, 1984). In addition A. priodonta was found to remain in the deeper layers

of the water column (5-35 m) during mid-day in a Patagonian lake (Obertegger et al.,

2008)). The finding in this study supports the crepuscular behavior of Asplanchna sp.

This might be related to the avoidance of visual fish predators.

For a spatial perspective, Harringia spp. and Asplanchna spp. were more

abundant at LAG than at LEO, while Filinia spp. was more abundant at LEO than at

LAG (Table 4-1). Like Asplanchna, this could be related to avoidance of visual feeders

on rotifers. Harringia sp. is relatively big compared to Asplanchna and other rotifers.

There was a difference between LAG and LEO with respect to water color (CDOM), with

the former site having higher color values during the second phytoplankton bloom

period. This distinction may affect the response of zooplankton to visual fish predators.









Table 4-1. Significant differences in zooplankton abundance indices (AAB: Absolute
abundance, RAB: Relative abundance, ABV: Absolute biovolume, RBV:
Relative biovolume, MBV: Mean biovolume) between the two sampling
stations and the two sampling times among 51 zooplankton genera and 11
functional groups.
Indices F-value Pr > F Post hoc analysis
Genera levels
Calanoid spp. MBV 3.65 0.0311 Night > Day
Mesocyclops spp. ABV 2.87 0.0556 Night > Day
(Female) RBV 4.84 0.0083 Night > Day
MBV 8.65 0.0004 Night > Day
Asplanchna spp. AAB 5.27 0.0325 LAG > LEO, Night > Day
Filinia spp. RBV 3.64 0.0256 LEO > LAG
Harringia spp. AAB 35.52 0.0270 LAG > LEO
ABV 2596.83 0.0125 LAG > LEO
MBV 224.10 0.0425 LAG > LEO
RBV 6256.33 0.0080 LAG > LEO
Functional group levels
Carnivorous ABV 4.54 000105 Night > Day
copepods RBV 6.75 0.0015 Night > Day
Raptorial rotifers AAB 3.45 0.0340 Night > Day









CHAPTER 5
CONCLUSION

This intensive study included the study of phytoplankton biomass, cyanobacterial

toxins, and water chemistry variables that could be potential factors controlling

zooplankton dynamics during cyanobacterial bloom events in Lake George. Changes in

total zooplankton abundance and biomass during this study period were hypothesized

to be correlated to the character of phytoplankton blooms and associated water physical

and chemical variables. Major findings and conclusions include:

1. Two peaks of phytoplankton chlorophyll a level with different community
composition were identified during the study period. The first bloom was observed
in April with an equal mix of nitrogen-fixing cyanobacteria and diatoms, whereas
the second bloom in early June was dominated by cyanobacteria.

2. Three cyanobacterial toxins (cylindrospermopsin, microcystins and saxitoxin) were
identified. Levels of the three toxins peaked at different times. Saxitoxin
concentrations had a peak in mid-April while cylindrospermopsin and microcystin
concentrations peaked in early June.

3. Fifty-one zooplankton taxa were observed and subdivided into three major groups:
rotifers, cladocerans, and copepods. Rotifers were the major zooplankton during
the first phytoplankton bloom period, and were succeeded with cladocerans during
the period between blooms, before copepods became more abundant during the
second bloom.

4. Zooplankton were categorized into difference in functional groups based on
zooplankton major feeding habit and body size to elucidate the difference in
relationships with physical and chemical variables. A numbers of significant
relationships were revealed which provided insights into the potential driving
factors for the succession pattern of zooplankton.

5. The primary correlated factors included chlorophyll a levels, nitrogen
concentration, cyanobacterial toxin levels, and temperature, suggesting that both
phytoplankton biomass and composition play important roles in zooplankton
dynamics. The correlation varied between functional groups indicating that
differences in feeding preferences and sensitivities to toxins may play important
roles in succession.










APPENDIX
ZOOPLANKTON FUNCTIONAL GROUPS


1. Bosminidae
a. Bosmina sp.
b. Eubosmina sp.
2. Sididae
a. Diaphanosoma birgei
b. Diaphanosoma brachyurum
3. Daphniidae
a. Ceriodaphnia
b. Daphnia spp.
4. Copepod Nauplii
a. Copepod Nauplii
5. Herbivorous Copepods
a. Juvenile Calanoid
b. Adult Calanoid Copepod
c. Tropocyclops sp.
6. Carnivorous Copepods
a. Mesocyclops edax (female)
b. Mesocyclops edax (male)
7. Omnivorous Copepods
a. Juvenile Cyclopoid
8. Microrotifers
a. Aneuropsis sp.
b. Cephalodella sp.
c. Collotheca spp.
d. Felinia spp.
e. Lecane sp.
f. Lepadella sp.


8. Mesorotifers
a. Conochiloides sp.
b. Conochilus unicornis
c. Harringia sp.
d. Hexarthrasp.
e. Keratella chochlearis longtaill)
f. Keratella chochlearis shorttaill)
g. Polyarthra sp.
h. Synchaeta sp.3
i. Top Rotifer
9. Megarotifers
a. Brachionus havanensis
b. Brachionus angularis
c. Brachionus sp.
d. Brachionus caudatus
e. Keratella tecta
f. Keratella knobtail
g. Keratella tropica
h. Keratella vulga
i. Notholca
j. Trichocerca multicranis
10. Raptorial Rotifers
a. Asplanchna sp.
b. Asplanchna-like (Unknown sp.4)


g. Monostyla spp.
h. Notommata sp.
i. Trichocerca sp.1 (non-descript)
j. Trichocerca similis
k. Trichocerca sp.

Classification to Functional Groups in Rotifers


Classification

Microrotifers

Mesorotifers

Megarotifers


Smallest
dimension
< 40 pm

40-70 pm

> 70 pm


Approximate figure

Spindle-shaped

Round and chuncky

Big round with spines


Grazed
Vulnerability
High

Medium

Low









LIST OF REFERENCES


APHA (American Public Health Association), American Water Works Association &
Water Environment Federation. (2005) Standard methods for the examination of water
and wastewater. APHA, Washington, D.C, USA.

Aubel M., D'Aiuto P., Chapman A.D., Casamatta D., Reich A., Ketchen S. & Williams C.
(2006)
Blue-green algae in St. Johns River, FL. Lake Line, 26, 40-50.

Bass D.G. (1983) Rivers of Florida and Their Fishes.

Blancher E.C. (1984) Zooplankton-Trophic State Relationships in some North and
Central Florida Lakes. Hydrobiologia, 109, 251-263.

Briand J.F., Leboulanger C., Humbert J.F., Bernard C. & Dufour P. (2004)
Cylindrospermopsis raciborskii (Cyanobacteria) invasion at mid-latitudes: Selection,
wide physiological tolerance, or global warming? Journal of Phycology, 40, 231-238.

Canfield D.E., Phlips E. & Duarte C.M. (1989) Factors Influencing the Abundance of
Blue-Green-Algae in Florida Lakes. Canadian Journal of Fisheries and Aquatic
Sciences, 46, 1232-1237.

Carney H.J. & Elser J.J. Strength of zooplankton-phytoplankton coupling in relation to
lake trophic state. In: Large Lakes: Ecological Structures and Functions (Eds M.M.
Tizler & C. Serruya), pp. 615-631. Springer-Verlag, New York.

Carpenter S.R. & Kitchell J.F. (1988) Consumer Control of Lake Productivity.
Bioscience, 38, 764-769.

Chorus I. & Bartram J. (1999) Toxic cyanobacteria in water: A guide to their public
health consequences, monitoring, management. E & FN Spon London, London,
England.

Cichra M. (2009) Lake George Characteristics. Personal communication.

Clark R.F., Williams S.R., Nordt S.P. & Manoguerra A.S. (1999) A review of selected
seafood poisonings. Undersea & Hyperbaric Medicine, 26, 175-184.

Crisman T.L. & Beaver J.R. (1990) Applicability of planktonic biomanipulation for
managing eutrophication in the subtropics. Hydrobiologia, 200, 185.

Demott W.R. & Moxter F. (1991) Foraging on Cyanobacteria by Copepods Responses
to Chemical Defenses and Resource Abundance. Ecology, 72, 1820-1834.









Demott W.R., Zhang Q.X. & Carmichael W.W. (1991) Effects of Toxic Cyanobacteria
and Purified Toxins on the Survival and Feeding of a Copepod and 3 Species of
Daphnia. Limnology and Oceanography, 36, 1346-1357.

Dong L. (2010) Factors Controlling Phytoplankton Community and Dynamics During
Cyanobacterial Bloom. Master's Thesis. University of Florida.

Elmore J.L., Cowell B.C. & Vodopich D.S. (1984) Biological Communities of 3 Sub-
Tropical Florida Lakes of Different Trophic Character. Archiv Fur Hydrobiologie, 100,
455-478.

Epp G.T. (1996) Grazing on filamentous cyanobacteria by Daphnia pulicaria. Limnology
and Oceanography, 41, 560-567.

Gilbert J.J. (1996) Effect of temperature on the response of planktonic rotifers to a toxic
cyanobacterium. Ecology, 77, 1174-1180.

Gillooly J.F. & Dodson S.I. (2000) Latitudinal patterns in the size distribution and
seasonal dynamics of new world, freshwater cladocerans. Limnology and
Oceanography, 45, 22-30.

Gliwicz Z.M. (1990) Daphnia Growth at Different Concentrations of Blue-Green
Filaments. Archiv Fur Hydrobiologie, 120, 51-65.

Haider S., Naithani V., Viswanathan P.N. & Kakkar P. (2003) Cyanobacterial toxins: a
growing environmental concern. Chemosphere, 52, 1-21.

Halliday N.C. (2001) A comparison of morphometric and geometric methods for the
estimation of individual zooplankton volumes. Sarsia, 86, 101-105.

Havens K.E. & East T.L. (1997) Carbon dynamics in the 'grazing food chain' of a
subtropical lake. Journal of Plankton Research, 19, 1687-1711.

Havens K.E., East T.L. & Beaver J.R. (1996) Experimental studies of zooplankton-
phytoplankton-nutrient interactions in a large subtropical lake (Lake Okeechobee,
Florida, USA). Freshwater Biology, 36, 579-597.

Havens K.E., Elia A.C., Taticchi M.I. & Fulton R.S. (2009) Zooplankton-phytoplankton
relationships in shallow subtropical versus temperate lakes Apopka (Florida, USA) and
Trasimeno (Umbria, Italy). Hydrobiologia, 628, 165-175.

Hawkins P. & Lampert W. (1989) The Effect of Daphnia Body Size on Filtering Rate
Inhibition in the Presence of a Filamentous Cyanobacterium. Limnology and
Oceanography, 34, 1084-1088.









Jakher G.R. (1984) Diurnal Rhythm of Zooplankton and Certain Abiotic Factors in Lake
Balsamand Jodhpur India. Oikoassay, 1, 32-36.

Kaebernick M. & Neilan B.A. (2001) Ecological and molecular investigations of
cyanotoxin production. FEMS microbiology ecology, 35, 1-9.

Kotak B.G., Kenefick S.L., Fritz D.L., Rousseaux C.G., Prepas E.E. & Hrudey S.E.
(1993) Occurrence and toxicological evaluation of cyanobacterial toxins in Alberta lakes
and farm dugouts. Water Research, 27, 495-506.

Landsberg J.H. (2002) The effects of harmful algal blooms on aquatic organisms.
Reviews in Fisheries Science, 10, 113-390.

Lawton L.A. & Codd G.A. (1991) Cyanobacterial (Blue-Green-Algal) Toxins and their
Significance in UK and European Waters. Journal of the Institution of Water and
Environmental Management, 5, 460-465.

Li R., Carmichael W.W., Brittain S., Eaglesham G.K., Shaw G.R., Mahakhant A.,
Noparatnaraporn N., Yongmanitchai W., Kaya K. & Watanabe M.M. (2001) Isolation and
identification of the cyanotoxin cylindrospermopsin and deoxy-cylindrospermopsin from
a Thailand strain of Cylindrospermopsis raciborskii (Cyanobacteria). Toxicon, 39, 973-
980.

Liu Y., Xie P. & Wu X.P. (2006) Effects of toxic and nontoxic Microcystis aeruginosa on
survival, population-increase, and feeding of two small cladocerans. Bulletin of
environmental contamination and toxicology, 77, 566-573.

Martin A. & Cooke G.D. (1994) Health risks in eutrophic water supplies. Lake Line, 14,
24-26.

McComb A.J. & Davis J.A. (1993) Eutrophic waters of southwestern Australia. Fertilizer
Research, 36, 104-114.

Mitra A. & Flynn K.J. (2005) Predator-prey interactions: is 'ecological stoichiometry'
sufficient when good food goes bad? Journal of Plankton Research, 27, 393-399.

Namikoshi M. & Rinehart K.L. (1996) Bioactive compounds produced by cyanobacteria.
Journal of industrial microbiology & biotechnology, 17, 373-384.

Nixon S.W. (1995) Coastal marine eutrophication: a definition, causes, and future
concerns. Ophelia, 41, 119-219.

Obertegger U., Flaim G. & Sommaruga R. (2008) Multifactorial nature of rotifer water
layer preferences in an oligotrophic lake. Journal of Plankton Research, 30, 633-643.









Paerl H.W., Fulton R.S.,III, Moisander P.H. & Dyble J. (2001) Harmful freshwater algal
blooms, with an emphasis on cyanobacteria. TheScientificWorld, 1, 76-113.

Phlips E.J. (2002) Algae and eutrophication. In: Encyclopedia of Environmental
Microbiology (Ed G. Bitton). Wiley.

Phlips E.J., Hendrickson J., Quinlan E.L. & Cichra M. (2007) Meteorological influences
on algal bloom potential in a nutrient-rich blackwater river. Freshwater Biology, 52,
2141-2155.

Piehler M.F., Dyble J., Moisander P.H., Chapman A.D., Hendrickson J. & Paerl H.W.
(2009) Interactions between nitrogen dynamics and the phytoplankton community in
Lake George, Florida, USA. Lake and Reservoir Management, 25, 1-14.

Porter K.G. (1977) Plant-Animal Interface in Freshwater Ecosystems. American
Scientist, 65, 159-170.

Rivkin R.B. & Legendre L. (2001) Biogenic carbon cycling in the upper ocean: Effects of
microbial respiration. Science, 291, 2398-2400.

Sarkar S. & Jana B.B. (1985) Biomass Determination in some Species using a
Geometric Equivalent Technique of Plankton Organisms. Acta Hydrochimica et
Hydrobiologica, 13, 217-221.

Sartory D.P. & Grobbelaar J.U. (1984) Extraction of Chlorophyll-a from Fresh-Water
Phytoplankton for Spectrophotometric Analysis. Hydrobiologia, 114, 177-187.

Shireman J.V. & Martin R.G. (1978) Seasonal and Diurnal Zoo Plankton Investigations
of a South Central Florida Usa Lake. Florida Scientist, 41, 193-201.

SJRWMD (2010) Historical records in zooplankton in Lake George. Personal
communication

SJRWMD (2008) A Story of the St. Johns River. Personal communication

Smith V.H. (1998) Cultural eutrophication of inland, estuarine, and costal waters. In:
Successes, limitations, and frontiers in ecosystem science (Eds M.L. Pace & P.M.
Groffman). Springer-Verlag, New York City, New York, U.S.A.

Smith V.H., Tilman G.D. & Nekola J.C. (1999) Eutrophication: impacts of excess
nutrient inputs on freshwater, marine, and terrestrial ecosystems. Environmental
Pollution, 100, 179-196.

Soares M.C.S., Lurling M., Panosso R. & Huszar V. (2009) Effects of the
cyanobacterium Cylindrospermopsis raciborskii on feeding and life-history









characteristics of the grazer Daphnia magna. Ecotoxicology and environmental safety,
72, 1183-1189.

Thys I. & Hoffmann L. (2005) Diverse responses of planktonic crustaceans to fish
predation by shifts in depth selection and size at maturity. Hydrobiologia, 551, 87-98.

Tranvik L.J. (1992) Allochthonous Dissolved Organic-Matter as an Energy-Source for
Pelagic Bacteria and the Concept of the Microbial Loop. Hydrobiologia, 229, 107-114.

Utermohl H. (1958) Zur Vervollkommnung der quantitiven Phytoplankton-methodik.
Mitteilungen-lnternationale Vereinigung fur Theoretische und Angewandte Limnologie,
9, 1-38.

Vinyard G.L. & Obrien W.J. (1976) Effects of Light and Turbidity on Reactive Distance
of Bluegill (Lepomis-Macrochirus). Journal of the Fisheries Research Board of Canada,
33, 2845-2849.

Wellington C.G., Mayer C.M., Bossenbroek J.M. & Stroh N.A. (2010) Effects of turbidity
and prey density on the foraging success of age 0 year yellow perch Perca flavescens.
Journal of fish biology, 76, 1729-1741.

Williamson C.E., Salm C., Cooke S.L. & Saros J.E. (2010) How do UV radiation,
temperature, and zooplankton influence the dynamics of alpine phytoplankton
communities? Hydrobiologia, 648, 73-81.

Work K., Havens K., Sharfstein B. & East T. (2005) How important is bacterial carbon to
planktonic grazers in a turbid, subtropical lake? Journal of Plankton Research, 27, 357-
372.

Work K.A. & Havens K.E. (2003) Zooplankton grazing on bacteria and cyanobacteria in
a eutrophic lake. Journal of Plankton Research, 25, 1301-1306.

World Health Organization. (2006) Guidelines for drinking-water quality [electronic
resource]: incorporating first addendum. Vol. 1, Recommendations.

Yilmaz M., Phlips E.J., Szabo N.J. & Badylak S. (2008) A comparative study of Florida
strains of Cylindrospermopsis and Aphanizomenon for cylindrospermopsin production.
Toxicon, 51, 130-139.









BIOGRAPHICAL SKETCH

Akeapot Srifa was born in Surat Thani, Thailand in November, 1984. He was

graduated from Mahidol Wittayanusorn School in Nakhon Pathom, Thailand, before

started his undergraduate study, majoring in Biology, at Mahidol University, Bangkok,

Thailand in 2003. He has a wide range of interests in aquatic, marine and environmental

sciences.

He got a scholarship from the university's distinction program to experience

international research career and fulfill his undergraduate thesis at the Center for

Environmental Research (UFZ) in Leipzig, Germany in 2007. His undergraduate thesis

was on the topic of the effectiveness of constructed wetlands in arsenic removal from

contaminated water.

Upon his graduation, he got a scholarship from the Royal Thai Government to

pursue further graduate studies. He came to University of Florida in 2008 and started

his Masters research under the supervision of Professor Edward J. Phlips. His research

has been focusing with the interrelationship between phytoplankton-zooplankton and

water quality.





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1 FACTORS CONTROLLING ZOOPLANKTON DYNAMICS IN A SUBTROPICAL LAKE DURING CYANOBACTERIAL BLOOM EVENTS By AKEAPOT SRIFA A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUI REMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2010

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2 2010 Akeapot Srifa

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3 To my parents, my role models in diligence and positive thinking

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4 ACKNOWLEDGMENTS First of all, I would like to express my most sincere gratitude to my supervisor, Professor Edward J. Phlips, for his ceaseless academic dedication during my graduate study in the University of Florida. He has willingly supported me from the beginning in academia and provided excellent research experienc es during the past two years. I would like to express my most sincere to other supervisory committee members, Professor Karl E. Havens and Professor Mark Brenner, for sharing me their professional research excellence, and for giving me invaluable and constructive suggestions and comments to the research I made during my study. I would like to gratefully acknowledge Professor Charles E. Cichra and Mary Cichra for their generosity and dedications in the academic supports and guidance. Without the supports from them, this research would not have been completed. My special thanks also extend to Dr. Mete Yilmaz for his invaluable help and suggestions in professional laboratory skills, Dr. Lance Riley for his captaincy on the research vessel, Don Osteen and Li nghan Dong for their helps in sampling sessions, Dorota Roth and Joey Chait for their help in sample analyses, Amanda Croteau and Brittany Baugher for their help in the identification of microscopic zooplankton, my colleagues Nikki Dix, Loren Mathews, and Paula Viveros for their kind help throughout my laboratory works as well as academic skills. Last but not least, I would like to express my heartiest gratitude to my parents and my brother in Thailand for their tireless encouragements and continuous support throughout my study.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ...................................................................................................... 4 LIST OF TABLES ................................................................................................................ 7 LIST OF FIGURES .............................................................................................................. 8 LIST OF ABBREVIATIONS .............................................................................................. 10 ABSTRACT ........................................................................................................................ 11 CHAPTER 1 INTRODUCTION ........................................................................................................ 13 2 RESEARCH DESIGN AND METHODOLOGY .......................................................... 16 Study Site .................................................................................................................... 16 Sampl ing Locations .................................................................................................... 16 Field Observation and Water Sampling ..................................................................... 17 Cyanobacterial Toxin Analysis ................................................................................... 19 Microscopic Analysis of Zooplankton ......................................................................... 19 Precipitation and River Flow Rate .............................................................................. 20 3 RESULTS .................................................................................................................... 22 Chlorophyll a Concentration ....................................................................................... 22 Cyanobacterial Toxin Levels ...................................................................................... 22 Water Chemistry and Physical Variables ................................................................... 23 Overview Survey of Zooplankton ............................................................................... 26 Dynamics of Three Major Zooplankton Groups ......................................................... 26 Cladocerans ......................................................................................................... 26 Copepods ............................................................................................................. 26 Rotifers ................................................................................................................. 27 Zooplankton Dynamics in Different Functional Groups ............................................. 28 Cladocerans ......................................................................................................... 28 Copepods ............................................................................................................. 29 Rotifers ................................................................................................................. 29 Relationship between Zooplankton and Physical -Chemical Variables ..................... 30 Major Group Level ................................................................................................ 30 Functional Group Level ........................................................................................ 31

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6 4 DISCUSSION .............................................................................................................. 53 Cladoceran Dynamics ................................................................................................ 57 Copepod Dynamics .................................................................................................... 61 Rotifer Dynamics ........................................................................................................ 64 5 CONCLUSION ............................................................................................................ 69 ZOOPLANKTON FUNCTIONAL GROUPS ...................................................................... 70 LIST OF REFERENCES ................................................................................................... 71 BIOGR APHICAL SKETCH ................................................................................................ 76

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7 LIST OF TABLES Table page 3 -1 Zooplankton species list found during this study period. ...................................... 49 3 -2 Correlation between water physical -chemical parameters and zooplankton absolute biovolumes in different levels of functional groups and taxa in the station of LEO ......................................................................................................... 51 3 -3 Correlation between water physical -chemical parameters and zooplankton absolute biovolumes in different levels of functional groups and taxa in the station of LAG ......................................................................................................... 52 4 -1 Significant diff erences in zooplankton abundance indices between the two sampling stations and the two sampling times among 51 zooplankton genera and 11 functional groups. ....................................................................................... 68

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8 LIST OF FIGURES Figure page 2 -1 Location of Lake George in Florida regional outline map and locations of the two selected sampling sites, LEO and LAG, in Lake George. .............................. 21 2 -2 Total daily precipitation at the LEO station during the study period ..................... 21 3 -1 Dynamics of chlorophyll a levels during the study period. .................................... 33 3 -2 Dynamics of three cyanobacterial toxins: Saxitoxin, Cylindrospermopsin and Microcystins. ................................................................................................... 34 3 -3 Depths at the sampling sites. ................................................................................. 35 3 -4 Temperature at the water surface. ........................................................................ 35 3 -5 Secchi depths in the lake. ...................................................................................... 36 3 -6 Turbidity in NTU during the study period. .............................................................. 36 3 -7 Water color (CDOM) during the study period. ....................................................... 37 3 -8 Dissolved oxygen levels in water surface and 20 cm above the lak e bottom. ..... 38 3 -9 Specific conductivity during the study period. ....................................................... 39 3 -10 pH at the water surface during the study period. .................................................. 39 3 -11 Phosphorus content in water samples were Total Phosphorus and Soluble Reactive Phosphorus. ............................................................................................ 40 3 -12 The examination of nitrogen contents in water samples included Total Nitrogen, Ammonium, Nitrate, and Nitrite. ............................................................. 41 3 -13 Silica levels during the study period. ..................................................................... 42 3 -14 Cladoceran abundance indices included their absolute biovolume, relative biovolume, absolute abundance, and relative abundance. .................................. 43 3 -15 Copepod abundance indices included their biovolume, relative biovolume, abundance, and relative abundance. .................................................................... 44 3 -16 Rotifer abundance indices included their biovolume, relative biovolume, abundance, and relative abundance. .................................................................... 45 3 -17 Biovolume in three cladoceran functional groups Bosminidae, Sididae, and Daphniidae. ............................................................................................................ 46

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9 3 -18 Biovolume in four copepod functional groups copepod nauplii, herbivorous copepod, carnivorous copepod, and omnivorous copepod. ............................... 47 3 -19 Biovolume in four rotifer functional groups microrotifers, mesorotifers, megarotifers, and r aptorial rotifers. ....................................................................... 48

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10 LIST OF ABBREVIATION S AAB Abundance ABV Biovolume CYL Cylindrospermopsin DO Dissolved oxygen MBV Mean biovolume MCY Microcystin s RAB Relative abundance to total zooplankton abundance RBV Relative bio volume to total zooplankton biovolume SAX Saxitoxin SRP Soluble reactive phosphorus TN Total nitrogen TP Total phosphorus

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11 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Re quirements for the Degree of Master of Science FACTORS CONTROLLING ZOOPLANKTON DYNAMICS IN A SUBTROPICAL LAKE DURING CYANOBACTERIAL BLOOM EVENTS By Akeapot Srifa August 2010 Chair: Edward J. Phlips Major: Fisheries and Aquatic Sciences Intensive field observations were performed to elucidate the effect of cyanobacterial blooms and other environmental factors to zooplankton community structure and abundance in Lake George, Florida. Samples were obtained weekly during night time and bi weekly during day t ime in two different locations in the lake. Water samples were collected with an integrated pole that collected water from the surface to the bottom of the water column. Zooplankton were identified, enumerated, and measured for biovolume estimates using an inverted microscope. Other parameters included water temperature, conductivity, dissolved oxygen, turbidity, color, pH, cyanobacterial toxins, chlorophyll a level, silica, and nitrogen and phosphorus contents. The study period (March 25, 2009 June 17, 2009) was characterized by three major trends; 1) Phytoplankton bloom in April with an equal mix of nitrogen-fixing chlorophyll a ) dominated by cyanobacteria, and 3) A majo r rainfall event that resulted in a large influx of water from the watershed, associated with an increase in nutrient concentrations but a decrease in phytoplankton biomass. Cyanobacterial toxin levels

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12 (cylindrospermopsin, microcystins, and saxitoxin) were coincident with chlorophyll a levels and phytoplankton community composition. Fifty one zooplankton taxa were observed and subdivided into three major groups: rotifers, cladocerans, and copepods. The three major groups were further subdivided into eleven functional groups based on zooplankton major feeding habit and body size. Rotifers were the major zooplankton during the first phytoplankton bloom, and were succeeded with cladocerans during the bloom intersession, before copepods became more abundant duri ng the second bloom. Correlation analyses were performed between zooplankton composites all abundance indices and the full suite of other parameters determined in the study. A numbers of significant relationships were revealed which provided insights into the potential driving factors for the succession pattern of zooplankton observed over the study period. The primary correlated factors included chlorophyll a levels, nitrogen concentration, cyanobacterial toxin levels, and temperature, suggesting that b oth phytoplankton biomass and composition play important roles in zooplankton dynamics. The correlation varied between functional groups indicating that differences in feeding preferences and sensitivities to toxins also play an important role in succession.

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13 CHAPTER 1 INTRODUCTION Eutrophication of surface waters and the associated blooms of phytoplankton and plants are important issues of concern in many regions around the world (Nixon, 1995; Smith, 1998; Smith et al. 1999; Paerl et al., 2001; Phlips et al., 2002) In eutrophic and hypereutrophic lakes, intense phytoplankton blooms can be associated wit h harmful effects, including hypoxia, strong light attenuation, loss of species diversity, and alterations of food web interrelationships (Kotak et al., 19 93; McComb & Davis, 1993; Chorus & Bartram, 1999; Haider et al., 2003) In the case of blooms involving cyanobacteria, the poor palatability and potential toxicity of certain species can represent unique challenges to the health and stability of ecosystem s (Lawton & Codd, 1991; Martin & Cooke, 1994; Kaebernick & Neilan, 2001) The ecological implications of toxic cyanobacteria have been an important area of research for d ecades (Chorus & Bartram, 1999) A number of major strains in these cyanobacteria may produce toxins, which can be harmful to aquatic organisms including zooplankton (Haider et al., 2003; Kaebernick & Neilan, 2001) Interactions between phytoplankton and zooplankton in freshwater ecosystems have become an important focus of research for decades (Porter, 1977; Mitra & Flynn, 2005; Carpenter & Kitchell, 1988; Havens et al 1996) Zooplankton play a pivotal role in freshwater ecosystems as a critical link between phytoplankton producers and planktivores in the food web. Alterations in zooplankton community structure, abundance, and size can lead to changes in fish and invertebrate communities, thereby affecting the structure and function of the entire ecosystems (Carpenter & Kitchell, 1988; Havens et al., 1996) It has been shown that phytoplankton and zooplankton can

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14 have mutually supportive interactions with respect to grazing or nutrient regeneration (Havens et al., 1996; Car ney & Elser, 1990) Large colonial or filamentous phytoplankton and toxic species, however, are less efficiently grazed by most zooplankton, enhancing the potential for blooms (Dong, 2010) The focus of this study was the dynamics of zooplankton in relation to cyanobacterial blooms. T he central objective of the study was to follow changes in the zooplankton community during the course of cyanobacterial blooms in Lake George, a large subtropical eutrophic lake in Florid a, with a long history of intense cyanobacterial blooms. Lake George is part of the St. Johns River ecosystem, which is recognized as one of the most important river basins in the United States (SJRWMD, 20 10; SJRWMD, 2008) Phytoplankton blooms in Lake George have included cyanobacteria species that are potentially toxic, such as Cylindrospermopsis sp., Anabaena sp., Anabaenopsis sp., and Aphanizomenon sp. (Dong, 2010) Temporally intensive field observations were carried out in Lake George to describe changes in chlorophyll concentration, major cyanobacterial toxins, zooplankton composition and abundance, and related physical and chemical variables. A complimentary study of phytoplankt on dynamics provided information for comparative analyses (Dong, 2010) Zooplankton abundance and environmental factors were examined statistically to help define relationships between phytoplankton, zooplankton, and water column conditions. It was hypothesized that spring/early summer phytoplankton blooms in Lake George are dominated by a succession of cyanobacteria species that are correlated with temporal changes in zooplankton structure and

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15 abundance, reflecting the relative adaptability of different functional groups to trends in phytoplankton composition and abundance.

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16 CHAPTER 2 RESEARCH DESIGN AND METHODOLOGY Study Site Lake George is the second largest lake in Florida, and located in the subtropical zone in th e northeast region of the state. Lake George is a freshwater, and the largest lake on the St Johns River basin with approximately 175 km2 in its surface area (Piehler et al., 2009) The drainage basin of Lake George encompasses 2,025 km2 in East Central Florida (Bass, 1983) The lake has been designated by a state agency, the St Johns River Water Management District, as a major water source that has high potential to supply Cent ral Florida municipal area. Major inflows to the lake include St. Johns River at the southern end, Salt Spring Creek, Silver Glen Springs Run, and Juniper creek. The major outflow is the St. Johns River in the northern end near the city of Georgetown. Lake George is categorized as a river lake, which literally means that the lake is relatively dynamic and circulation within the lake is dominated by the river. Sampling Locations Two sampling locations in the lake were selected for this study: LEO (29 N, 81 1). Both sampling sites were located in the main navigation channel in the lake. LAG was located at channel marker 9 in the south part of the lake, near the inflow o f the upper St. Johns River. LEO is located in the north-central region of the lake near channel marker 4. LEO has no aquatic macrophyte coverage, whereas LAG is closer to the shoreline and thus may be influenced by littoral vegetation (Cichra, 2009) These two sites are

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17 monitored regularly for physical and chemical variables by SJRWMD and The United States Geological Survey (USGS). Field Observation and Water Sampling Field observations and water sampling were car ried out at LEO and LAG in 2009 from March 25, 2009 to June 23, 2009. Sampling consisted of water collection and field measurements of meteorological and water column physical variables. Day time sampling was done biweekly every Monday and Thursday between 0930 and 1130 hrs. Night time sampling was done weekly every Thursday between 0300 and 0500 hrs. Sampling was suspended from May 1821, 2009 due to inclement weather. Water depth, temperature, specific conductivity, dissolved oxygen, and pH were measured with a calibrated multiprobe Hydrolab Quanta Environmental Multiprobe. These variables were measured at the water surface and every 50 cm below the surface. Water transparency was determined with a 20-cm Secchi disk during daytime sampling. Water samples were composited from at least five integrated PVC tubes that collected water from the surface to near the bottom of the water column, thereby reducing the effect of vertical stratification of plankton. Subsamples of water were withdrawn from these combine samples for measurements of chlorophyll a concentration (250 ml), zooplankton enumeration (3,000 ml), cyanobacterial toxin analysis (15 ml), and water chemistry analyses (125 ml). Phytoplankton was filtered onto 0.7 m glass fiber filters. Filters were kept on ice in the dark and returned to the laboratory for analyses. Chlorophyll a was extracted on the same day as sampling according to (Sartory & Grobbelaar, 1984) Filter paper was placed in 90% ethanol at 78

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18 temperature for at least 24 hr. Samples were centrifuged at 20,000 rpm and 20 min. to eliminate filter debris. Spectrophotometric analysis for chlorophyll a and phaeophytin was determined spectrophotometrically according to the method 10200 H.2 (APHA, 2005). Water subsamples (125 ml) for nutrient analysis were kept in acidwashed plastic bottles and kept frozen. Turbidity was determined using a Lamotte 2020 tur bidimeter and expressed in Nephelometric Turbidity Units (NTU). Colored dissolved organic matter (CDOM) was determined spectrophotometrically using samples filtered through glass fiber filters (0.7 m pore size) according to standard methods (APHA, 2005) and expressed as platinum cobalt units (PCU). Total Phosphorus (TP) and Soluble Reactive Phosphorus (SRP) were determined spetrophotometrically, using the molybdenum ascorbate method 4500 -P (APHA, 2005). Persulfate digestion and autoclaving were for TP dete rmination. Total Nitrogen (TN), Ammonium (NH4 +) Nitrite (NO2 -), and Nitrite/Nitrate (NOx) were determined using a continuous flow autoanalyzer. For TN analysis, persulfatedigested samples were injected through a cadmium column. NH4 +, NOx and NO2 were det ermined on samples filtered through 0.7 m glass fiber filters. NOx and NO2 were determined with and without a coupling cadmium column respectively. Nitrate concentrations were obtained by subtracting nitrite value from NOx concentration. Silica levels in water samples were determined spectrophotometrically using ammonium molybdate reagent in the molybdosilicate method 4500 -SiO2 C (APHA, 2005).

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19 Cyanobacterial Toxin Analysis Aliquots of water subsamples (5 ml) were kept frozen in glass tubes until analysis for toxins including cylindrospermopsin (CYL), microcystins (MCY), and saxitoxin (SAX). They were determined using enzyme -linked immunosorbent assay method (ELISA). ELISA test kits for the three toxins were obtained from Abraxis LLC (Microtiter plate ELI SA kit PN 522011 for CYL and PN 52255B for SAX, and tube ELISA kit PN 520012 for MCY). Preparation for CYL and SAX involved triple freeze thaw cycles for toxin extraction. Extraction for MCY involved 1minute incubation in 100 cooled down to room temperature. Extracted samples were centrifuged at 20,000 rpm and 20 Microscopic Analysis of Zooplankton Subsamples for zooplankton analysis were preserved in the field using Lugols solution (APHA, 2005) Each preserved sample was filtered onto a 41 m nylon mesh and brought to a final volume of 20 ml. Zooplank ton were identified and counted according to the Utermohl method (Utermohl, 1958) in a glass settling chamber using an inverted compound microscope at 100x magnification. Samples were identified to the lowest practical taxonomic level. Sample enumeration was continued until at least 100 individuals of a dominant taxon were counted in the sample, and at least 3 ml of adjusted volume was enumerated. Zooplankton species and/or genera were categorized into major phyla and eleven functional groups based on their common feeding habit and body size (see Appendix A). For biovolume determinations, zoopankton were measured with a micrometer equipped ocular. At least 30 individuals from each taxonomic unit were measured.

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20 Absolute and relative biovolume of zooplankton were estimated by assigning the closest geometric shape to each taxon (Halliday, 2001; Sarkar & Jana, 1985) Precipitation and River Flow Rate Daily total pr ecipitation data were obtained from the United States Geological Survey (USGS) archive website at LEO station (USGS Station number 291-830081362-200, Lake George at Mile Marker 5 near Salt Spring, FL) (http://waterdata.usgs.gov/fl/nwis/current/?type=prec ip, Accession date: May 21, 2010). Figure 22 illustrates the data over time. Precipitations were generally observed at approximately 2 cm except in the period of mid-April to midMay, when there was nearly no precipitation. The highest precipitation recor ded during the study period was in mid May (May 18, 2009) when there was 7.85 cm of rainfall. This rainfall peak was followed by several peaks soon afterwards.

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21 Figure 21. Location of Lake George in Florida regional outline map and locations of the two selected sampling sites, LEO and LAG, in Lake George. Figure 22. Total daily precipitation at the LEO station during the study period. Data were available only for the LEO site, and were obtained from the United States Geolog ical Survey archive website (http://waterdata.usgs.gov/fl/nwis/current/?type=precip). Accession date was May 21, 2010) Lake George St Johns River Inlet St Johns River Outlet Crescent Lak e Lake Ocklawaha LEO LAG + +

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22 CHAPTER 3 RESULTS Chlorophyll a Concentration Chlorophyll a concentrations revealed two peak periods of phytoplankton biomass, one in m id April and one in late May to early June (Figure 3 -1) Mean group analysis showed three distinct temporal stages of chlorophyll a dynamics: 1) development of the first bloom, 2) development of the second bloom, and 3) the decline of the second bloom. Twoway Analysis of Variance (ANOVA) revealed there was no significant different in overall chlorophyll a levels either between the two sampling sites (LEO and LAG) or between the sampling times (day and night) (F = 1.89, p = 0.1450). There was one noteworthy difference in chlorophyll a concentrations at LAG and LEO. Chlorophyll a concentration during the second bloom event at LAG decline sharply from approximately 70 g/L to 20 g/L between May 21 and June 3, but concentrations at LEO continued to increase to 90 g/L until a sharp decline to 45 g/L from June 6 to June 10. Cyanobacterial Toxin Levels Three cyanobacterial toxins were detected at both stations in Lake George, cylindrospermopsin, microcystins, and saxitoxin. Saxitoxin levels (Figure 32A) ranged b etween 0.01 and 0.43 g/L. The peak value of 0.43 g/L were observed during midApril and decreased slightly after the peak. This trend was similar to that of the first planktonic chlorophyll bloom. Cylindrospermopsin concentrations ranged from 0.02 to 0.7 7 g/L (Figure 32B). The concentrations generally followed the trend in chlorophyll a concentration during the second bloom period at the two stations (LEO and LAG). Microcystin levels (Figure 3-2C) generally increased during the study period, and

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23 ranged between 0.05 and 1.06 g/L. The overall means of these three cyanobacterial toxin levels were not significantly different between the two sampling sites (LEO and LAG) or between the two sampling times (day and night). Water Chemistry and Physical Variables Fifteen water column variables were included in the study: depth, temperature, Secchi depth, turbidity, CDOM, dissolved oxygen, conductivity, pH, TP, SRP, TN, NO3 -, NO2 -, NH4 + and Si. Water depth (Figure 33) remained near 3 m from the beginning of th e study through midMay. Thereafter, water depth increased to approximately 4 m until the end of the study. This general trend was observed at both LEO and LAG. Water depths at both sampling sites were not significantly different (F = 1.55, p = 0.2132) Sur face water temperatures (Figure 3-4) were not significantly different either between LEO and LAG or between day and night (F = 0.15, p = 0.9319). However, daytime temperature levels were generally higher than nighttime temperature. Temperature gradually increased from 22 June. Secchi depth (Figure 35) ranged from 0.6 m to 1.0 m during the study. Mean values were not significantly different between LEO and LAG (F = 1.23, p = 0.2542). There were two periods when Secchi depth at LAG was lower than that at LEO on April 22 and Jun 3, 2009. In general, turbidity had the same overall trend with chlorophyll a level (Figure 3 6). No significant differences, either between LEO and LAG or between day and night, were obser ved for turbidity (F = 0.60, P = 0.6178). There were two peaks values, which ranged from 4 -10 NTU. The first and second peaks were observed during mid-April and

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24 late May, respectively. The first peak was higher in LAG than in LEO while turbidity in LEO dur ing the second peak was generally higher than that in LAG. True water color, measured as colored dissolved organic matter, ranged between about 40 to 200 PCU (Figure 37). Color levels in both LEO and LAG were not significantly different (F = 1.40, p = 0.2540). However, the levels in both sampling sites were similar in their trends in that they generally decreased from the beginning of the study through May 27, when the color was approximately 40 PCU in LEO. After that, the levels sharply increased from l ate May to the end of the study, and were usually higher in LAG than in LEO. Dissolved oxygen (Figure 3-8) was observed at both the water surface and near the lake bottom. Measurements at both depths were not significantly different, either between samplin g sites or between day and night (Surface: F = 2.37, p = 0.0832; Bottom: F = 0.40, p = 0.7559). However, the overall patterns in dissolved oxygen dynamics at the water surface and at the lake bottom were not similar. Dissolved oxygen at the water surface r anged approximately between 4 and 12 mg/L, and was usually lower in night samples. The two lowest values were observed on May 6 and June 3. Near the lake bottom, dissolved oxygen remained more stable than at the surface, with DO ranging from approximately 8 to 10 mg/L before decreasing to 2 mg/L in mid -June. Specific conductivity (Figure 3-9) was not statistically different either between LEO and LAG or between day and night (F = 0.35, p = 0.7926). Values at the two sites displayed similar trend, ranging between 1.0 to 0.8 mS/cm. They gradually increased during late March to mid May before dropping, and remained at approximately 0.8

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25 mS/cm until the end of the study. The levels at LAG in the declining period weregenerally lower than those at LEO. No statisti cal difference was found in pH between LEO and LAG or between day and night samples (F = 0.99, p = 0.4070). pH generally ranged between 8.00 and 9.25 during this study (Figure 310). However, a significant, sharp drop in pH was observed from April 29 to May 6, when the pH dropped to approximately 7.25. TP and SRP (Figure 3-11) showed similar overall temporal patterns although they were not significantly different either between LEO and LAG or between day and night samples (TP: F = 1.22, p = 0.3130; SRP: F = 1.01, p = 0.3952). TP and SRP ranged from 0.02 to 0.14 and 0.01 to 0.11 mg/L (as P), respectively. They were relatively stable from late March to the end of May. After that, the levels increased sharply, and were significantly higher in LAG than in LEO. Total nitrogen concentrations (Figure 3 -12), ranged from 0.75 to 1.71 mg/L as N, which was present, in part, as ammonium (0.04 0.23 mg/L as N), nitrate (0 0.04 mg/L as N), and nitrite (0 0.01 mg/L as N). TN and ammonium generally displayed similar t rends. They gradually increased during the study with peaks on April 22 and Jun 7. TN was significantly higher in LEO than in LAG (F = 2.66, p = 0.0594) while no significant difference was found between the sites for NO3 -, NO2 -, and NH4 + (NO3 -: F = 0.64, p = 0.5940, NO2 -: F = 0.84, p = 0.4778, and NH4 +: F = 0.41, p = 0.7443). Nitrate and nitrite followed similar trends in that they remained stable from late March to late May. After that, sharp increases were observed in both variables at both sampling sites Nitrate and nitrite were distinctly higher in LAG than in LEO during this period of increase.

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26 Overview Survey of Zooplankton Fifty one identifiable zooplankton genera and/or species were observed in the water samples collected at LEO and LAG over the st udy period. The genera observed fell within two major phyla: Arthropoda and Rotifera. The observed taxa are shown in Table 3 1. Dynamics of Three Major Zooplankton Groups Cladocerans Cladoceran biovolume remained below 206106 m3/L until a sharp increase in early May (Figure 314), peaking in midMay. Cladoceran biovolume decreased again in early June before reaching the second peak in mid-June. Cladoceran biovolume showed similar trends at both sites and in day and night samples. Biovolume of cladocerans relative to total zooplankton biovolume ranged from 2.4 to 81.5 % during the study period. Relative biovolume of cladocerans exceeded 80% during periods of peak abundance in midMay and mid-June, with similar trend at both sites and in both day and night samples. Cladoceran abundances ranged from 2 to 1,171 individuals/L, with peaks in midMay and mid-June at both sites and in both day and night samples (Figure 3 14). Cladoceran abundance relative to total zooplankton abundance ranged from 0.2% to 37.3% (F igure 314). The trends for abundance and relative abundance were similar to that observed for biovolume and relative biovolume. Copepods Copepod biovolume generally increased during the study period (Figure 315). The value ranged from 9.7106 to 734.7 106 m3/L with two peaks in mid May and midJune, which showed much higher copepod biovolume in LEO than in LAG. It started

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27 increasing in late April. During this increasing period, copepods in LEO were generally more abundant in the night than in the day until the end of May. This trend was also observed in LAG, but it was observed in late June. Relative biovolume of copepod to total zooplankton followed the trend in copepod absolute biovolume (Figure 3-15). The relative value generally ranged from 3.6% t o 75.5% during the study period. The highest peak of copepod relative biovolume was observed in early June. LEO and LAG were similar in their copepod relative biovolume, but LAG had higher copepod relative biovolume from early May to the end of the study. Copepods were generally more abundant in night time than in day time before the beginning of the increase in relative biovolume. Copepod abundance ranged from 32 630 individuals/L (Figure 3 -15), which accounted for 1.5% to 53.8% of the total zooplankton abundance. The trend observed was similar to that of biovolume and relative biovolume. Rotifers Rotifer biovolume ranged from 18.6106 to 1,267106 m3/L with two distinct peaks in late April and in mid-June (Figure 316). The second peak was relatively smaller than the first peak. Rotifer biovolume in LEO was generally higher than that in LAG from late March to the top of the first peak. The first peak decreased sharply and remained low during May to early June. The second peak was observed in mid-June, w hich showed the higher rotifer biovolume in LEO than in LAG. Rotifer relative biovolume ranged from 1.7% 90.6% during the study period (Figure 316). The overall trend followed its biovolume dynamics in that there were two peaks, in late April and in midJune. The highest peak in rotifer relative biovolume was approximately at 90%, which decreased sharply in early May to about 10-20% before

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28 increasing slightly in June. Rotifers were generally more abundant during day time than during night time. Rotifer abundance ranged from 174 8,390 individuals/L (Figure 3 16) which accounts for 28.4% 97.7% in term of its relative abundance (Figure 3-16). The observed trend was similar to that of its biovolume and relative biovolume. Zooplankton Dynamics in Differe nt Functional Groups Zooplankton species were assigned to different ecological functional groups according to their similar ecological guilds in feeding habit, body size, and taxonomic categories (Appendix A). Eleven fuctional groups of zooplankton include: Bosminidae; Sididae; Daphniidae; Copepod nauplii; Herbivorous copepods; Carnivorous copepods; Omnivorous copepods; Microrotifers; Mesorotifers; Megarotifers; and Raptorial rotifers. Two way ANOVA revealed none of the zooplankton among eleven functional groups was statistically different either in their biovolume or abundance between the two sampling sites. Cladocerans The cladocerans belonged to three functional groups; Bosminidae, Daphniidae, and Sididae. The general trend of these three groups mostly f ollows the dynamic trend of cladocerans. Bosminidae was the most abundant among the group of cladocerans, and was found throughout the study period in all samples (Figure 3-17) while the group of Sididae ( Diaphanosoma spp.) was found from early May to late June (Figure 3-17). Daphniidae ( Daphnia and Ceriodaphnia ) was the group with least biovolume of these three functional groups, and was limited from late May to late June (Figure 317).

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29 Copepods Copepods were categorized by feeding habits to four different functional groups: Copepod nauplii, Herbivorous, Carnivorous, and Omnivorous Copepods. Copepod nauplii were the most abundant in term of biovolume among the copepods. Its dynamic trend was gradually increased in biovolume over time, and generally followed the trend of the copepod group as a whole (Figure 318). Herbivorous copepods were present from late April and were at their most abundant during mid-June, when the second planktonic algal bloom occurred (Figure 318). Carnivorous copepods were found main ly during day time in both sampling sites, and displayed peak biovolume during mid May to lateMay, before dramatically decreasing in June (Figure 3-18). Omnivorous copepods were the groups with the lowest peak biovolume among the copepods, and generally had two peaks in early May and early June (Figure 318). Rotifers Four different functional groups of rotifers (Microrotifers, Mesorotifers, Megarotifers, and Raptorial Rotifers) were differentiated based on body size and feeding habits. The overall trend o f microrotifers, mesorotifers, and megarotifers mostly followed the dynamics of the rotifer group as a whole, with two observed peaks in their absolute biovolume in early May and in mid-June. Mesorotifers were the most abundant group in terms of biovolume (Figure 3 19), while microrotifers and megarotifers were approximately the same. Microrotifers were almost absent after the first peak in early May (Figure 3-19) while Megarotifers dominanted the second peak in biovolume (Figure 3 -19). Raptorial rotifers w ere also abundant in the first peak during early may at the LAG site, and oneweek later for the LEO site (Figure 319).

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30 Relationship between Zooplankton and Physical-Chemical Variables Major Group Level In general, zooplankton biovolumes were associated w ith more physical and chemical variables as well as cyanobacterial toxins at the LEO site than at LAG. Cladoceran biovolumes at LEO (T able 3-2 column xii) were mainly positively correlated with variables including temperature, depth, color, TN, NO2, NH4, TP, SRP and Si while they were not significantly correlated in LAG station (T able 33 column xii) except temperature and TN. Conductivity and dissolved oxygen at the lake bottom in LEO were negatively correlated to cladoceran biovolume. Cylindrospermopsin and microcystins were positively correlated with cladoceran biovolume while saxitoxin showed negative correlation with cladoceran biovolume at LEO. No significant correlation was found between cyanobacterial toxins and cladoceran biovolume at LAG. For cop epod taxa, correlations in LEO (T able 3 -2 column xiii) were generally similar to those in LAG (T able 3-3 column xiii). The biovolumes of copepods were positively correlated with temperature, color, silica, NOx, NO2, TP and SRP in both station while there w ere significant positive correlations only in LEO for NH4 and only in LAG for NO3. Correlation with cyanobacterial toxins yielded in the same trend in both sites in that copepod biovolume was positively correlated to cylindrospermopsin and microcystins, and negatively correlated to saxitoxin. Rotifer biovolume was mostly negatively correlated with various physical and chemical variables including water depth, chlorophyll levels and TN in both stations. Additionally, at LEO (T able 3 2 column xiv), they were negatively correlated with turbidity and pH, while temperature, silica, NH4, TP and SRP were found to be negatively correlated with rotifer biovolume at LAG (T able 3 3 column xiv). Saxitoxin

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31 level was positively correlated to rotifer at both stations, but cylindrospermopsin was found to be negatively related to rotifer biovolume at LAG. Functional Group Level Biovolumes of three functional groups of cladocerans (Bosminidae, Sididae, and Daphniidae) were analyzed for their correlation with physical and chem ical variables. Bosminidae (T able 3-2 and T able 3-3 column i) was more strongly correlated with physical and chemical variables at LEO than at LAG, while Daphniidae (T able 3 2 and T able 3 3 column iii) were more highly correlated with those variables at LAG than at LEO. Color, silica, NOx, NO2, NH4, TP, SRP as well as the three cyanobacterial toxins were positively correlated to the functional group Bosminidae, while the group was negatively correlated with conductivity and dissolved oxygen at LEO. No sig nificant correlation between Daphniidae and physical -chemical variables was observed at LEO, but many variables, including temperature, color, dissolved inorganic nitrogen forms and SRP were positively correlated with Daphniidae absolute biovolume. In term s of cyanobacterial toxins, Bosminidae showed positive correlation with the three toxins at LEO, and no other significant relationship was found either at LAG or in other cladoceran functional groups. Four copepod functional groups including nauplii, herb ivorous, carnivorous, and omnivorous types were categorized according to their different feeding habits (T able 32 and Table 3 3 column iv vii). Carnivorous and omnivorous copepods were generally not associated with physical and chemical variables. Secchi depth and carnivorous copepod biovolume, however, displayed a significant relation at both stations. Omnivorous copepod biovolume was positively and negatively correlated to temperature and dissolved oxygen at water surface, respectively at LEO station, but not

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32 at LAG. Copepod nauplii were positively correlated with many chemical variables in LEO, but herbivorous copepods were not associated with chemical variables at both sites. Conductivity and dissolved oxygen were negatively correlated to both nauplii and herbivorous copepod biovolume, while temperature was positively correlated. Copepod nauplii and herbivorous copepods were positively correlated to cyanobacterial toxins, copepod nauplii and herbivorous copepod were positively correlated to cylindrosperm opsin and microcystins, and negatively correlated with saxitoxin at LEO. At LAG, there was no significant correlation between cylindrospermopsin and the two functional groups. Carnivorous and omnivorous copepods had no significant relationship with the three toxins. Four rotifer functional groups were classified based on their body size and feeding habit. They were micro-, meso -, megarotifers, and raptorial rotifers. No significant correlation was found between raptorial rotifer biovolume and any physical or chemical variables at both sites (T able 3-2 and 33 column xi). Generally, micro -, meso and megarotifers were associated with more variables in LEO than in LAG (T able 3 2 and 3 -3 column viii x). Most of the significant correlation found with these th ree rotifer functional groups and water chemistry variables were negative. Temperature, conductivity, and dissolved oxygen at the lake bottom were positively correlated with mesorotifer biovolume in LAG. Cylindrospermopsin and saxitoxin were correlated neg atively and positively with microrotifers and mesorotifers, respectively. Microcystins had a positive correlation with megarotifer biovolume at LAG.

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33 Figure 31. Dynamics of chlorophyll a levels during the study period.

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34 Figure 32. Dyn amics of three cyanobacterial toxins: A) Saxitoxin, B) Cylindrospermopsin and C) Microcystins. A B C

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35 Figure 33. Depths at the sampling sites. Figure 34. Temperature at the water surface.

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36 Figure 35. Secchi depths in the lake. Figure 36. Turbidity in NTU during the study period.

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37 Figure 37. Water color (CDOM) during the study period.

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38 Figure 38. Dissolved oxygen levels in A) water surface and B) 20 cm above the lake bottom. A B

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39 Figure 39. Specific conductivity dur ing the study period. Figure 310. pH at the water surface during the study period.

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40 Figure 311. Phosphorus content in water samples were A) Total Phosphorus and B) Soluble Reactive Phosphorus. A B

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41 Figure 312. The examination of nitrogen contents in water samples included A) Total Nitrogen, B) Ammonium, C) Nitrate, and D) Nitrite. A B C D

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42 Figure 313. Silica levels during the study period.

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43 Figure 314. Cladoceran abundance indices included their A) absolute biovolume, B) relative biovolume, C) absolute abundance, and D) relative abundance. A B C D

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44 Figure 315. Copepod abundance indices included their A) biovolume, B) relative biovolume, C) abundance, and D) relative abundance. A B C D

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45 Figure 3 16. Rotifer abundance indices included their A) biovolume, B) relative biovolume, C) abundance, and D) relative abundance. A B C D

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46 Figure 317. Biovolume in three cladoceran functional groups A) Bosminidae, B) Sididae, and C) Daphniidae. A B C

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47 Figure 318. Biovolume in four copepod functional groups A) copepod nauplii, B) herbivorous copepod, C) carnivorous copepod, and D) omnivorous copepod. A B C D

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48 Figure 319. Biovolume in four rotifer functional groups A) microrotifers, B) mesoroti fers, C) megarotifers, and D) raptorial rotifers. A B C D

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49 Table 3 1. Zooplankton species list found during this study period. x mark represents the presence of particular genera and species in samples collected at LEO and LAG during the day and night. Species list LEO LAG Day Night Day Night Phylum Arthropoda Subphylum Crustacea Class Branchiopoda Bosmina spp. x x x x Ceriodaphnia spp. x x x x Daphnia ambigua x x Daphnia spp. x Diaphanosoma birgei x x x x Di aphanosoma brachyurum x x Eubosmina spp. x x x x Class Copepoda Copepod nauplii x x x x Juvenile calanoid copepods x x x x Juvenile cyclopoid copepods x x x x Adult Calanoid copepod spp. x x x x Mesocyclops edax (female ) x x x x Mesocyclops edax (male) x x x x Tropocyclops spp. (female) x x x Tropocyclops spp. (male) x Phylum Rotifera Aneuropsis spp. x x x x Asplanchna spp. x x x x Asplanchna like rotifer x x x x Brachinus angularis x x x x Brachionus caudatus x Brachionus havanensis x x x x Brachionus quadridentatus x Brachionus spp. x Cephalodella spp. x x x x Collotheca mutabilis x x x x Collotheca pelagica x x x x Conochiloides spp. x x x x Conochilus unicornis x x x x Filinia longiseta x x x x Filinia terminalis x Harringia spp. x x Hexarthra spp. x x x x Keratella chochlearis (longtail form) x x x x Keratella chochlearis (shorttail form) x x x x

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50 Table 3 1. Continued Species l ist LEO LAG Day Night Day Night Phylum Rotifera (continued) Keratella chochlearis (knobtail form) x Keratella tecta x x x x Keratella tropica x x x Keratella valga x x x x Lecane spp. x x x Lepadella spp. x x x Monostyla s pp. x x Notholca spp. x x x Notommata spp. x x x x Polyarthra spp. x x x x Synchaeta spp. x Synchaeta sp4. (round form) x x x x Trichocerca multicranis x x x x Trichocerca similis x x x x Trichocerca sp.3 (non descript form) x x x x Unidentified rotifer (round form) x x Unidentified rotifer (top shaped form) x x x

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51 Table 3 2. Correlation between water physical -chemical parameters and zooplankton absolute biovolumes in different levels of functional groups and taxa in the station of LEO. Positive (+) and negative ( -) significant correlation at the confidence level of 95% are represented in the table. Blank cells represent the insignificant correlation between the parameters. Functional group level Taxa level Total Zoo Cladocerans Copepods Rotifers Clad Cope Rotf Bosm Sidi Daph Naup Herb Carn Omni Micr Meso Mega Rapt (i) (ii) (iii) (iv) (v) (vi) (vii) (viii) (ix) (x) (xi) (xii) (xiii) (xiv) (xv) Temperature + + + + + + + + Conductivity DO Top DO Bottom Depth + + Secchi depth Turbidity Color + + + + + + + pH Chlorophyll Silica + + + + + + + TN + + NO x + + + + + NO 2 + + + + + + + NO 3 + + NH 4 + + + + + TP + + + + + + SRP + + + + + + + CYL + + + + + MCY + + + + + + SAX + + + +

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52 T able 3 3 Correlation between water physical -chemical parameters and zooplankton absolute biovolumes in different levels of functional groups and taxa in the station of LAG. Positive (+) and negative ( -) significant correlation at the confidence level of 95% are represented in the table. Blank cells represent the insignificant correlation between the parameters. Functional group level Taxa level Total Zoo Cladocerans Copepods Roifers Clad Cope Rotf Bosm Sidi Daph Naup Herb Carn Om ni Micr Meso Mega Rapt (i) (ii) (iii) (iv) (v) (vi) (vii) (viii) (ix) (x) (xi) (xii) (xiii) (xiv) (xv) Temperature + + + + + + + + + Conductivity + + DO Top DO Bottom + Depth + Secchi depth Turbidity Color + + + + pH Chlorophyll + Silica + + + TN + + + NO x + + + NO 2 + + + NO 3 + + + NH 4 + + TP + + SRP + + + + CYL + MCY + + + + SAX + + +

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53 CHAPTER 4 DISCUSSION The study period was characterized by shifts in the dominance structure of the zooplankton community in Lake George. The shifts began with a rotifer peak in late April, followed by a peak in cladoceran biovolume in May, accompanied by a decline in rotifer biovolume, then an increase in the relative importance of copepods in late May to early June. It is useful to view the dynamics of the three major groups, along with functional guilds within the three groups, in relation to temporal trends in phytoplankton dynamics and changes in key water column characteristics including phytoplank ton biomass, phytoplankton compostition, cyanobacterial toxins, temperature, turbidity, and dissolved oxygen concentrations. With respect to phytoplankton biomass, the study period was not dramatically different from many previous years of the historical r ecord (SJRWMD, 2010) Two peaks in chlorophyll a levels were observed, one in April and a larger peak in May reaching 91.8 g/L. Lake George is a eutrophic lake with annual average chlorophyll a concentrations in excess o f 40 g/L. The lake is also subject to frequent algal blooms with chlorophyll a levels near or exceeding 100 g/L during spring, summer, and autumn. Phytoplankton composition over the study period exhibited trends common to eutrophic lakes in Florida, wit h a dominant of cyanobacteria (Dong, 2010) particularly during the second bloom when chlorophyll a concentrations reached 92 g/L. Dominance of cyanobacteria during periods of high chlorophyll a is a prominent feature of Floridas eutrophic lakes (Canfield et al. 1989) Due to high phosphorus loads to

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54 Lake George, nitrogen limitation of phytoplankton growth is an important feature of the lake that leads to a major role for nitr ogen-fixing cyanobacteria (Dong, 2010; Piehler et al,. 2009) Some of the important cyanobacterial species observed in this study have been implicated in the production of toxins in other ecosyst ems around the world (Chorus & Bartram, 1999) Anabaena spp., Aphanizomenon spp., Anabaenopsis spp. Cylindrospermopsis sp., Lyngbya sp., and Planktothrix sp. have been identified as potential saxitoxin producers ( (Clark et al., 1999; Landsberg, 2002) ). In this study, Anabaena sp., Anabaenopsis sp., and Aphanizomenon sp. were abundant during the first bloom period, coincident with the appearance of saxitoxi n. The second bloom period was associated with increases in the abundance and biovolume of Cylindrospermopsis sp., Oscillatoria spp. and Aphanizomenon spp. ((Dong, 2010) ). Levels of the hepatotoxin cylindrospermopsin increased together with chlorophyll levels during the second bloom period. Cylinderspermopsis has been found worldwide and certain strains of C. raciborskii have been observed to produce cylindrospermopsin in Australia and Europe, but not in the United St ates (Li et al., 2001; Yilmaz et al., 2008; Briand et al., 2004) The toxin has, however, been detected in Florida lakes (Aubel et al., 2006) It is possible that the cylindrospermopsin observed in Lake George may be produced by another cyanobacterium observed during the second bloom, such as Aphanizomenon spp. ( Yilmaz et al., 2008) or a heretofore undescri bed strain of Cylindrospermopsis Levels of another common hepatotoxin, microcystin, gradually increased over the last month of the study period, when the second bloom reached its peak. Some

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55 cyanobacteria species, including certain strains of Anabaena flos aquae, Microcystis aeruginosa, and Oscillatoria agardhii var. isothrix, have been reported to produce microcystins (Namikoshi & Rinehart, 1996) ). Microcystis sp. was observed in Lake George in June (Dong, 2010) The World Health Organization has published a provisional guideline for microcystins in recreational and drinking water of less than 20 g/L and 1.0 g/L, respectively ( WHO, 2006) The microcystin levels observed in this study were mostly below 1.0 g/L. From a spatial perspective, no significant differences were observed in mean chlorophyll a concentrations between the sampling sites. There were, however, noteworthy di fferences in bloom dynamics at LEO and LAG. During the second bloom period, phytoplankton biovolume declined precipitously in late May at LAG, but continued to rise at LEO until a sharp decline in early June. This might be related to hydrologic patterns in Lake George. The upper St Johns River flows into the lake at the southern end. LAG is the site located nearest to the river inlet, whereas LEO is located in the north-central region of the lake. The location of these two sampling sites causes LAG to be influenced by major freshwater inflows earlier and more profoundly than LEO. This results in the accumulation of planktonic organisms at the LEO site, where the flow has more retention time and greater water age. The chlorophyll concentration pattern support s this as there were no distinct differences between the two sampling station observed when river inputs to the lake were small. However, from midMay through June, high rainfall levels caused in substantially elevated river discharge into the southern end of the lake. Turbidity during the high precipitation period also increased.

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56 Meteorological factors, such as precipitation and wind velocity, can influence the spatial and temporal distribution of phytoplankton (Phlips et al., 2007) There can be dilution as a consequence of an increase in incoming freshwater from the upper river, i.e. the more water input, the greater dilution factor. If the rate of dilution is greater than accumulation rate, the phytoplanktonic chlo rophyll a decreases as observed in late May at LAG and early June at LEO. Factors other than phytoplankton can affect zooplankton abundance distribution and dynamics. Temperature is one of the factors that can enhance or inhibit growth rate of certain typ es of zooplankton (Gliwicz, 1990) For example, Daphnia sp. and Diaphanosoma sp. were less abundant during late spring and summer (Cichra, 2009) The surface temperature during the study period gradually increased from 20 which might have been due to the seasonal transition over the 3month period. However, this was not consistent with the trend in the historical records from the St. Johns River. Turbidity is a variable that affects the susceptibility of zooplankton to visual feeding predators, such as fish and invertebrate larvae ( (Wellington et al., 2010; Vinyard & Obrien, 1976) ). Elevated turbidity values (~2.5x) were found during the first and the second bloom. This could enhance survivorship of zooplankton during bloom periods, as their natural predators might not be able to feed efficiently. Low dissolved oxygen is a factor that can negatively imp act zooplankton (Rivkin & Legendre, 2001) Dissolved oxygen can shift significantly during phytoplankton bloom events. In healthy blooms, photosynthesis increases daytime oxygen levels, whereas nighttime respiration depletes oxygen levels. In senescing blooms, bacterial respiration

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57 associated with organic matter decomposition can cause hypoxic conditions. Oxygen concentrations during the study period showed depletion in early May and late June, after the two major peaks of phytoplankton blooms. The lowest dissolved oxygen level, however, was approximately 4 mg/L, which should not be limiting to zooplankton survival. Fifty one zooplankton taxa were identified in this study, including three major groups; crustaceans, co pepods, and rotifers. All of the taxa have been observed in Lake George over the past fifteen years (SJRWMD, 2010; Cichra, 2009) It is useful to examine the major trends in abundance and composition of each of these three groups, within the context of the variables discussed above. Cladoceran Dynamics Cladocerans were a major component of the zooplankton community in terms of biovolume through most of the last half of the sampling period, i.e. duri ng the second cyanobacterial bloom. By contrast, cladoceran abundances were low during the first phytoplankton bloom period. From a spatial perspective, the two sites sampled in this study exhibited no major differences in overall cladoceran composition or abundance during the study period. However, differences over more restricted time frames resulted in spatial disparities in the correlations between cladoceran abundance and physical chemical conditions in the water column. Cladoceran biovolume was sign ificantly correlated to fourteen physical -chemical variables at LEO, but only two variables at LAG. At LEO, positive correlations were observed with temperature, depth, color, silica, TN, nitrite, ammonium, TP, SRP, cylindrospermopsin, and microcystins, while conductivity, dissolved oxygen at the bottom of the lake, and saxitoxins were negatively correlated to cladoceran biovolume.

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58 By contrast to the numerous significant correlations at LEO, only temperature and TN were positively correlated with cladoceran biovolume at LAG. The lack of additional correlations may be related to the strong influence of river inputs to the southern end of Lake George causing greater temporal variability in a wide range of variables. The importance of these correlations can be view from three different perspectives: 1) factors that directly impact cladoceran abundance such as temperature, 2) factors that indirectly impact abundance through their influence on other trophic levels, such as phytoplankton (bottom up control) or fish biomass (top -down control), and 3) factors that are auto-correlated with variations in real driving factors, but are not considered functionally important. The differences between sites extended to the three cladoceran functional groups, which responded d ifferently in correlation analyses. Bosminidae ( Bosmina spp. and Eubosmina spp.) were correlated with more factors at LEO than LAG. Conversely, Daphniidae ( Daphnia spp. and Ceriodaphnia spp.) showed greater numbers of correlations at LAG than LEO. These di fferences between the sites might be related to the differences in physical, chemical, and biological variables between the two locations. TN was the only variable that was higher at LEO than at LAG, while other variables, such as color, silica, nitrite, TP and SRP, were slightly higher in LAG than in LEO during the second bloom period. It is possible that differences in physical and chemical variables between the two sites influenced the dominance of different cladoceran functional group. The effect of top -down control by fish and invertebrate larvae predation, however, was not determined during this study. It therefore remains a potentially important consideration for future investigation.

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59 The correlation trends for total cladocerans resembled to those fo r the functional group of Bosminidae at both sites, while Sididae and Daphniidae did not follow the trend of total cladocerans. Bosmina spp. and Eubosmina spp. were identified in all samples during this study, and they were high in relative biomass compared to other cladocerans. This supports the observations of Blancher (1984) Elmore et al. (1984) and Crisman & Beaver (1990) that sm all cladoceran species (body size as the Bosminidae functional group, are common in Florida. High numbers of correlations in this functional group may imply that they are controlled by various physical and chemical variables, and that chang es in these environmental factors could lead to changes in Bosminidae populations. Few individuals of Sididae ( Diaphanosoma spp.) and Daphniidae ( Daphnia spp. and Ceriodaphnia spp.) were observed in this study. This was in accordance with many studies that have observed seasonal disappearances of large cladocerans in subtropical lakes (Gillooly & Dodson 2000; K. A. Work & Havens 2003; K. Work et al. 2005; H avens et al. 2009) Summer water temperature may be a limiting factor in the abundance of certain cladoceran species (Gillooly & Dodson 2000) although the results of this study and other historical data (SJRWMD 2010) suggest that many indigenous cladocerans are adapted to summer temperatures. Although it cannot be confirmed in this study, Havens et al. (2009) suggests that increases in the number of opportunistic filter -feeding planktivores are, in part, responsible for the low cladoceran abundance in subtropical lakes. Availability of nutrients is necessary for phytoplankton growth. Most forms of nitrogen, phosphorus, and silica were posit ively correlated with cladoceran biovolume,

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60 perhaps reflecting the positive effect of nutrient availability on phytoplankton productivity. Chlorophyll a concentrations, however, were not significantly correlated with cladoceran biovolume. This suggests tha t some major phytoplankton taxa are inefficiently grazed and drive increases in chlorophyll a level. Some cyanobacteria are less efficiently grazed by cladocerans for a number of reasons, such as large size or toxin content. In addition, filamentous and colonial cyanobacteria are considered to be poor food for zooplankton due to their low nutrition content (Gliwicz, 1990) Alternatively, bacteria have been shown to be an efficient food source for cladocerans and play ed important role in the microbial loop by helping the transfer of energy and carbon to higher trophic level in the food web (Tranvik, 1992; Havens & East, 1997) It might be possible that cladocerans graze on bacteria in this study. It may be hypothesized that saxitoxin-producing cyanobacteria in Lake George in April restricted the abundance of cladocerans. It has been documented that cyanobacterial toxins and toxic algal strains have negative effects on cladocerans. Cladoceran feeding is also disrupted by filamentous cyanobacteria (Epp, 1996) Toxic Microcystis aeruginosa (strain PCC7820) and purified microcystins have negative effects on survival and feedi ng of two cladocerans, Moina micrura and Ceriodaphnia cornuta (Liu et al. 2006) Feeding and growth of Daphnia magna was found to be suppressed with increased proportions of Cylindrospermopsis raciborskii in their diet (Soares et al. 2009) Filtering rate of Daphnia sp. was reduced when C. raciborskii was presented. Larger species of Daphnia were found to be more susceptible to the presence of C. raciborskii than smaller species (Hawkins & Lampert 1989)

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61 In terms of the effect of cyanobacterial hepatotoxins, both cylindrospermopsin and microcystins were positively correlated with cladoceran biovolume in Lake George. This was also observed in the functional group of Bosminidae, which was also positively correlated with saxitoxin, unlike most cladocerans, with which it was negatively correlated. The differences between functional groups in terms of correlations with toxin levels may be related to differences in food preferences or varying sensitivities to toxins among species. It is also possible that the impacts of toxins at the levels observed in this study were not strong enough to significantly influence cladoceran abundance, and the correl ations to toxins observed were auto -correlated to other more important environmental factors. In terms of diurnal variability, Diaphanosoma brachyurum was the only cladoceran that was found only in daytime samples in both stations. This might be due to the behavior of this species, which is more active during the day. D. brachyurum has been shown to be less susceptible to fish predation based on its diurnal vertical distribution patterns (Thys & Hoffmann, 2005) ) by being more abundant at water surface during the day. This supports the observation in this study that the species was found only in day time samples. Copepod Dynamics As in the case of cladocerans, biovolume of copepods in LEO was positively correlated with temperature, color, silica, dissolved inorganic nitrogen, nitrite, ammonium, TP, SRP, cylindrospermopsin, and microcystins. In contrast, conductivity, saxitoxin, and dissolved oxygen were negatively correlated to copepod biovolume at both sites. Additional p ositive correlations were found for dissolved oxygen at the lake bottom and nitrate at LAG, while turbidity was negatively correlated. Many of these

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62 variables are related to phytoplankton biomass, suggesting that copepod abundance is correlated with phytoplankton dynamics, particularly during the second bloom period. By contrast, copepod abundances were low during the first bloom period. There are a number of possible reasons for this pattern. One hypothesis is the preference of copepods for high temperatur e. Copepod abundance has been linked to seasonal shifts in temperature (Shireman & Martin, 1978) The abundance of copepods in this study increased along with temperature. Low temperature may reduce growth rates of copepods while warmer conditions, which increased in the second half of the study, generally increase the grazing rate of zooplankton (Williamson et al., 2010) Nevertheless, copepod abundance was low during the biomass peak of diatom. According to a study of gut analysis, macrozooplankton (copepods and cladocerans) prefer diatoms, although they can graze filamentous and colonial cyanobacteria (Work & Havens, 2003) ). This suggests that temperature may control copepod abundance, apart from factors related to food availability. However, this hypothesis is not supported by historical observations of copepods in Lake George which indicate major peaks in abundance in spring as well as summer ( (SJRWMD, 2010) ). Copepods were positively correlated with nutrient sources including nitrogen and phosphorus, which are necessary for optimal growth of copepod food sources. This suggests that there might be more food availability for copepods during periods of enhanced nutrient availability supported by the major bloom of nitrogen-fixing cyanobacteria during the second bloom period. Another possible contributor to the low copepod abundances observed in April is the presence of the cyanobacteria species Anabaena spp. and Aphanizomenon spp.,

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63 both of which are potential saxitoxin producers, and may explain the higher significant levels of saxitoxin observed in April. Like cladocerans, cyanobacterial toxins have been documented to have adverse effects on many groups of copepods. For example, feeding experiments revealed the ability of the copepod Diaptomus birgei to reject food source that may contain defensive chemicals i.e. toxins, and indicated its susceptib ility to microcystin (Demott & Moxter, 1991; Demott et al. 1991) ). Copepods have diverse food preferences, including bacteria, protozoa, and small phytoplankton for nauplii and herbivorous copepods, and zooplankton such as rotifers for carnivorous taxa (Work et al. 2005) Therefore, separating copepods into different functional guilds is important for evaluating trends. Correlation trends with physical and ch emical variables among the four copepod functional groups were similar at both sampling sites. Nauplii and herbivorous copepods were correlated with many physical and chemical variables, while few significant correlations were found for carnivorous and omnivorous copepods, which are less directly linked to phytoplankton. Although they have wide feeding habits, nauplii and herbivorous copepods feed mainly on bacteria and phytoplankton (Tranvik, 19 92; Havens & East, 1997) Therefore, factors linked to phytoplankton biomass, such as nutrient concentrations, should be correlated with their biovolume. In terms of diel pattern of distribution, copepods shared a dominant role in zooplankton abundance through the last month and a half of the study period at both sites. Whereas cladocerans had two peaks in abundance, copepod biovolume gradually increased from late April through mid-June. Despite the increase in both copepod and cladoceran biovoluume dur ing May and June, they did not appear to limit the second

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64 phytoplankton bloom from reaching substantial biomass levels at both sites. This observation is in keeping with the results of other research on eutrophic lakes in Florida, which indicate that top-d own pressure is not typically strong enough to suppress bloom formation (Havens et al., 1996) This finding may be connected to the dominant role played by filamentous cyanobacteria in eutrophic Florida lakes, which may be a less than optimal source of food for zooplankton (Canfield et al., 1989; Gliwicz, 1990) One copepod taxon, male Tropocyclops spp., showed a distinct diurnal pattern. This cyclopoid copepod was observed only in daytime samples at LEO. This finding was in accordance with a diurnal study in Lake Wales, Florida by Shireman & Martin (1978) who found that the number of cyclopoid copepods differed between day and night. Many other copepod taxa showed crepuscularity and different diurnal distribution patterns. Calanoid spp., Mesocyclops spp., and carnivorous copepods were more abundant during nighttime than daytime. This result supports previous obse rvations that copepods are more active during the night than the day to avoid visual feeders, such as fish (Shireman & Martin, 1978) Rotifer Dynamics Rotifers were often the dominant zooplankton group, a pattern seen in many other eutrophic lakes in Florida (Havens et al., 2009) Due to their comparatively small body size, however, rotifers were relatively less important than copepods and cladocerans in terms of biovolume, except during the first month of the project, when they reached peak biovolume. The small size of most rotifer taxa places them in unique functional groups focused on herbivory, particularly small size classes of phytoplankton. It is noteworthy that rotifer s peaked during the first bloom event when diatoms and cyanobacteria were both major component of the phytoplankton community (Dong,

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65 2010) Presence of significant amounts of centric diatoms may have provided rotifers w ith an acceptable food source. After the decline of diatom biomass, replacement by a cyanobacterial bloom may have limited the ability of rotifers to recover from their decline at the end of April. Alternatively, rotifers may graze on bacterial and protozoan community during this period. Nevertheless, these data were not included in this research study. Correlations between rotifers and various physical and chemical variables were different from those of cladocerans and copepods. Five variables were negati vely correlated to rotifer biovolume at LEO, including depth, turbidity, pH, chlorophyll, and TN. Saxitoxin was the only variable with which rotifer were positively correlated. In the case of cladocerans and copepods, many of these variables displayed opposite correrlations. At LAG, temperature, depth, chlorophyll, silica, TN, ammonium, TP, SRP, and cylindrospermopsin were negatively correlated with rotifer biovolume whereas conductivity and saxitoxin were the variables yielding positive correlations. Nega tive correlations between rotifer biovolume and many variables associated with phytoplankton abundance are related to the timing of the peak in rotifer abundance in between the two bloom peaks. It might be argued that rotifers played a role in grazing down major elements of the first blooms, especially diatoms. Alternatively, the large amount of cyanobacteria in the first bloom, and dominance of cyanobacteria in the second bloom, may have precluded a major buildup of rotifer biomass in the latter period. Hi gh concentrations of saxitoxin in the first bloom and the hepatotoxin cylindrospermopsin in the second bloom may have played a role in this relationship. The significant biomass of the cyanobacteria Anabaena spp. and Aphanizomenon spp.,

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66 both potential neur otoxi n saxitoxin producers, in the first bloom period, did not suppress the buildup of rotifer biomass late in the bloom, perhaps due to the presence of significant quantities of alternative food items, such as diatoms. By contrast, the second bloom period was dominated by cyanobacteria, and was also marked by the presence of signif icant amounts of the hepatotoxin cylinderspermopsin and microcystin, perhaps restricting the buildup of rotifer biomass. These relationships are further supported by the correlat ion analyses involving different functional groups. Microrotifers and mesorotifers were positively correlated with saxitoxin levels, but the toxin was not correlated with larger rotifers. Gilbert (1996) experimentally demonstrated susceptibilities of two large rotifers, Brachionus calycifloris and Asplanchna girodi to toxins produced by Anabaena flos -aquae Bigger rotifers are usually more tolerant of chemical stresses such as cyanobacterial toxins, possibly due to their feeding preferences, which can include nonalgal foods. Different physical and chemical variables were correlated with rotifer functional groups at the two sampling sites. Megarotifers were correlated with a number of variables at LEO, whereas mesorotifers were correlated with more variables at LAG. Raptorial rotifers were not correlated with any physical or chemical variables. These findings might be due to the effect of size-selective feeding in zooplankton. Microzooplankton and mesozooplankton us ually graze on smaller phytoplankton, while megarotifers can handle bigger phytoplankton or even other small zooplankton. The high proportion of larger filamentous cyanobacteria at LEO than in LAG may contribute to spatial differences in the distribution o f rotifer functional groups.

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67 In a diurnal perspective, Monostyla spp. were found only in daytime samples. Brachionus caudatus were observed only in daytime samples at LEO while Brachionus quadridentatus and Brachionus spp. were found only in daytime samples at LAG. These rotifer species have not been previously documented to be diurnal migrators. Findings in this study might be coincidental because few individuals of these species were found in the samples. Asplanchna spp. and raptorial rotifers were more abundant in the water column during nighttime than daytime (Table 4-1). Similarly, Asplanchna sp. showed up at the water surface at night and decreased during daytime in a study of Lake Balsamand in India (Jakher, 19 84) In addition A. priodonta was found to remain in the deeper layers of the water column (5-35 m) during midday in a Patagonian lake (Obertegger et al. 2008) ). The finding in this study supports the crepuscul ar behavior of Asplanchna sp. This might be related to the avoidance of visual fish predators. For a spatial perspective, Harringia spp. and Asplanchna spp. were more abundant at LAG than at LEO, while Filinia spp. was more abundant at LEO than at LAG (T able 4 1). Like Asplanchna this could be related to avoidance of visual feeders on rotifers. Harringia sp. is relatively big compared to Asplanchna and other rotifers. There was a difference between LAG and LEO with respect to water color (CDOM), with the former site having higher color values during the second phytoplankton bloom period. This distinction may affect the response of zooplankton to visual fish predators.

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68 Table 4 1. Significant differences in zooplankton abundance indices (AAB: Absolute abundance, RAB: Relative abundance, ABV: Absolute biovolume, RBV: Relative biovolume, MBV: Mean biovolume) between the two sampling stations and the two sampling times among 51 zooplankton genera and 11 functional groups. Indices F value Pr > F Post hoc ana lysis Genera levels Calanoid spp. MBV 3.65 0.0311 Night > Day Mesocyclops spp. (Female) ABV 2.87 0.0556 Night > Day RBV 4.84 0.0083 Night > Day MBV 8.65 0.0004 Night > Day Asplanchna spp. AAB 5.27 0.0325 LAG > LEO, Night > Day Filinia spp. RBV 3.64 0.0256 LEO > LAG Harringia spp. AAB 35.52 0.0270 LAG > LEO ABV 2596.83 0.0125 LAG > LEO MBV 224.10 0.0425 LAG > LEO RBV 6256.33 0.0080 LAG > LEO Functional group levels Carnivorous copepods ABV 4.54 000105 Night > Day RBV 6.75 0.0015 N ight > Day Raptorial rotifers AAB 3.45 0.0340 Night > Day

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69 CHAPTER 5 CONCLUSION This intensive study included the study of phytoplankton biomass, cyanobacterial toxins, and water chemistry variables that could be potential factors controlling zooplankt on dynamics during cyanobacterial bloom events in Lake George. Changes in total zooplankton abundance and biomass during this study period were hypothesized to be correlated to the character of phytoplankton blooms and associated water physical and chemica l variables. Major findings and conclusions include: 1 Two peaks of phytoplankton chlorophyll a level with different community composition were identified during the study period. The first bloom was observed in April with an equal mix of nitrogen-fixing cya nobacteria and diatoms, whereas the second bloom in early June was dominated by cyanobacteria. 2 Three cyanobacterial toxins (cylindrospermopsin, microcystins and saxitoxin) were identified. Levels of the three toxins peaked at different times. Saxitoxin concentrations had a peak in mid-April while cylindrospermopsin and microcystin concentrations peaked in early June. 3 Fifty one zooplankton taxa were observed and subdivided into three major groups: rotifers, cladocerans, and copepods. Rotifers were the major zooplankton during the first phytoplankton bloom period, and were succeeded with cladocerans during the period between blooms, before copepods became more abundant during the second bloom. 4 Zooplankton were categorized into difference in functional groups b ased on zooplankton major feeding habit and body size to elucidate the difference in relationships with physical and chemical variables. A numbers of significant relationships were revealed which provided insights into the potential driving factors for the succession pattern of zooplankton. 5 The primary correlated factors included chlorophyll a levels, nitrogen concentration, cyanobacterial toxin levels, and temperature, suggesting that both phytoplankton biomass and composition play important roles in zoop lankton dynamics. The correlation varied between functional groups indicating that differences in feeding preferences and sensitivities to toxins may play important roles in succession.

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70 APPENDIX ZOOPLANKTON FUNCTIONAL GROUPS 1 Bosminidae a Bosmina sp. b Eubosmina sp. 2 Sididae a Diaphanosoma birgei b Diaphanosoma brachyurum 3 Daphniidae a Ceriodaphnia b Daphnia spp. 4 Copepod Nauplii a Copepod Nauplii 5 Herbivorous Copepods a Juvenile Calanoid b Adult Calanoid Copepod c. Tropocyclops sp. 6 Carnivorous Copepods a Mesocyclops edax (female) b Mesocyclops edax (male) 7 Omnivorous Copepods a Juvenile Cyclopoid 8 Microrotifers a Aneuropsis sp. b Cephalodella sp. c. Collotheca spp. d Felinia spp. e Lecane sp. f Lepadella sp. g Monostyla spp. h Notommata sp. i Trichocerca sp.1 (nondescript) j Trichocerca similis k. Trichocerca sp. Classification to Functional Groups in Rotifers Classification Smallest dimension Approximate figure Grazed Vulnerability Microrotifers < 40 m Spindle shaped High Mesorotifers 4070 m Round and chuncky Medium Megarotifers > 70 m Big round with spines Low 8 Mesorotifers a Conochiloides sp. b Conochilus unicornis c. Harringia sp. d Hexarthra sp. e Keratella chochlearis (longtail) f Keratella chochlearis (shorttail) g Polyarthra sp. h Synchaeta sp.3 i Top Rotifer 9 Megarotifers a Brachionus havanensis b Brachionus angularis c. Brachionus sp. d Brachionus caudatus e Keratella tecta f Keratella knobtail g Keratella tropica h Keratella vulga i Notholca j Trichocerca multi cranis 10. Raptorial Rotifers a Asplanchna sp. b Asplanchna like (Unknown sp.4)

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71 LIST OF REFERENCES APHA (American Public Health Association), American Water Works Association & Water Environment Federation. (2005) Standard methods for the examination of water and wastewater APHA, Washington, D.C, USA. Aubel M., D'Aiuto P., Chapman A.D., Casamatta D., Reich A., Ketchen S. & Williams C. (2006) Blue -green algae in St. Johns River, FL. Lake Line, 26, 40 50. Bass D.G. (1983) Rivers of Florida and Their Fishes. Blancher E.C. (1984) Zooplankton-Trophic Stat e Relationships in some North and Central Florida Lakes. Hydrobiologia, 109, 251263. Briand J.F., Leboulanger C., Humbert J.F., Bernard C. & Dufour P. (2004) Cylindrospermopsis raciborskii (Cyanobacteria) invasion at mid-latitudes: Selection, wide physio logical tolerance, or global warming? Journal of Phycology, 40, 231238. Canfield D.E., Phlips E. & Duarte C.M. (1989) Factors Influencing the Abundance of Blue -Green -Algae in Florida Lakes. Canadian Journal of Fisheries and Aquatic Sciences, 46, 1232 -123 7. Carney H.J. & Elser J.J. Strength of zooplanktonphytoplankton coupling in relation to lake trophic state. In: Large Lakes: Ecological Structures and Functions (Eds M.M. Tizler & C. Serruya), pp. 615631. Springer -Verlag, New York. Carpenter S.R. & Ki tchell J.F. (1988) Consumer Control of Lake Productivity. Bioscience, 38, 764769. Chorus I. & Bartram J. (1999) Toxic cyanobacteria in water: A guide to their public health consequences, monitoring, management E & FN Spon London, London, England. Cichr a M. (2009) Lake George Characteristics Personal communication Clark R.F., Williams S.R., Nordt S.P. & Manoguerra A.S. (1999) A review of selected seafood poisonings. Undersea & Hyperbaric Medicine, 26, 175 -184. Crisman T.L. & Beaver J.R. (1990) Applic ability of planktonic biomanipulation for managing eutrophication in the subtropics. Hydrobiologia, 200, 185. Demott W.R. & Moxter F. (1991) Foraging on Cyanobacteria by Copepods Responses to Chemical Defenses and Resource Abundance. Ecology, 72, 1820 1 834.

PAGE 72

72 Demott W.R., Zhang Q.X. & Carmichael W.W. (1991) Effects of Toxic Cyanobacteria and Purified Toxins on the Survival and Feeding of a Copepod and 3 Species of Daphnia. Limnology and Oceanography, 36, 1346 -1357. Dong L. (2010) Factors Controlling Phyt oplankton Community and Dynamics During Cyanobacterial Bloom Masters Thesis. University of Florida Elmore J.L., Cowell B.C. & Vodopich D.S. (1984) Biological Communities of 3 Sub Tropical Florida Lakes of Different Trophic Character. Archiv Fur Hydrobi ologie, 100, 455-478. Epp G.T. (1996) Grazing on filamentous cyanobacteria by Daphnia pulicaria. Limnology and Oceanography, 41, 560567. Gilbert J.J. (1996) Effect of temperature on the response of planktonic rotifers to a toxic cyanobacterium. Ecology, 77, 1174 -1180. Gillooly J.F. & Dodson S.I. (2000) Latitudinal patterns in the size distribution and seasonal dynamics of new world, freshwater cladocerans. Limnology and Oceanography, 45, 22 -30. Gliwicz Z.M. (1990) Daphnia Growth at Different Concentrat ions of Blue -Green Filaments. Archiv Fur Hydrobiologie, 120, 51 -65. Haider S., Naithani V., Viswanathan P.N. & Kakkar P. (2003) Cyanobacterial toxins: a growing environmental concern. Chemosphere, 52, 1 -21. Halliday N.C. (2001) A comparison of morphometr ic and geometric methods for the estimation of individual zooplankton volumes. Sarsia, 86, 101105. Havens K.E. & East T.L. (1997) Carbon dynamics in the 'grazing food chain' of a subtropical lake. Journal of Plankton Research, 19, 1687 -1711. Havens K.E. East T.L. & Beaver J.R. (1996) Experimental studies of zooplanktonphytoplankton -nutrient interactions in a large subtropical lake (Lake Okeechobee, Florida, USA). Freshwater Biology, 36, 579 -597. Havens K.E., Elia A.C., Taticchi M.I. & Fulton R.S. (200 9) Zooplankton-phytoplankton relationships in shallow subtropical versus temperate lakes Apopka (Florida, USA) and Trasimeno (Umbria, Italy). Hydrobiologia, 628, 165 -175. Hawkins P. & Lampert W. (1989) The Effect of Daphnia Body Size on Filtering Rate Inh ibition in the Presence of a Filamentous Cyanobacterium. Limnology and Oceanography, 34, 1084 1088.

PAGE 73

73 Jakher G.R. (1984) Diurnal Rhythm of Zooplankton and Certain Abiotic Factors in Lake Balsamand Jodhpur India. Oikoassay, 1, 32 -36. Kaebernick M. & Neilan B.A. (2001) Ecological and molecular investigations of cyanotoxin production. FEMS microbiology ecology, 35, 1 -9. Kotak B.G., Kenefick S.L., Fritz D.L., Rousseaux C.G., Prepas E.E. & Hrudey S.E. (1993) Occurrence and toxicological evaluation of cyanobacterial toxins in Alberta lakes and farm dugouts Water Research, 27, 495506. Landsberg J.H. (2002) The effects of harmful algal blooms on aquatic organisms. Reviews in Fisheries Science, 10, 113390. Lawton L.A. & Codd G.A. (1991) Cyanobacterial (Blue-Gre enAlgal) Tox ins and their Significance in UK and European Waters. Journal of the Institution of Water and Environmental Management, 5, 460465. Li R., Carmichael W.W., Brittain S., Eaglesham G.K., Shaw G.R., Mahakhant A., Noparatnaraporn N., Yongmanitchai W., Kaya K. & Watanabe M.M. (2001) Isolation and identification of the cyanotoxin cylindrospermopsin and deoxy -cylindrospermopsin from a Thailand strain of Cylindrospermopsis raciborskii (Cyanobacteria). Toxicon, 39, 973 980. Liu Y., Xie P. & Wu X.P. (2 006) Effects of toxic and nontoxic Microcystis aeruginosa on survival, populationincrease, and feeding of two small cladocerans. Bulletin of environmental contamination and toxicology, 77, 566573. Martin A. & Cooke G.D. (1994) Health risks in eutrophic water supplies Lake Line, 14, 2426. McComb A.J. & Davis J.A. (1993) Eutrophic waters of southwestern Australia. Fertilizer Research, 36, 104114. Mitra A. & Flynn K.J. (2005) Predator -prey interactions: is 'ecological stoichiometry' sufficient when goo d food goes bad? Journal of Plankton Research, 27, 393399. Namikoshi M. & Rinehart K.L. (1996) Bioactive compounds produced by cyanobacteria. Journal of industrial microbiology & biotechnology, 17, 373 -384. Nixon S.W. (1995) Coastal marine eutrophication: a definition, causes, and future concerns Ophelia, 41, 119219. Obertegger U., Flaim G. & Sommaruga R. (2008) Multifactorial nature of rotifer water layer preferences in an oligotrophic lake. Journal of Plankton Research, 30, 633643.

PAGE 74

74 Paerl H.W., Ful ton R.S.,III, Moisander P.H. & Dyble J. (2001) Harmful freshwater algal blooms, with an emphasis on cyanobacteria. TheScientificWorld, 1, 76 -113. Phlips E.J. (2002) Algae and eutrophication. In: Encyclopedia of Environmental Microbiology (Ed G. Bitton). W iley. Phlips E.J., Hendrickson J., Quinlan E.L. & Cichra M. (2007) Meteorological influences on algal bloom potential in a nutrient -rich blackwater river. Freshwater Biology, 52, 21412155. Piehler M.F., Dyble J., Moisander P.H., Chapman A.D., Hendrickson J. & Paerl H.W. (2009) Interactions between nitrogen dynamics and the phytoplankton community in Lake George, Florida, USA. Lake and Reservoir Management, 25, 1 14. Porter K.G. (1977) Plant -Animal Interface in Freshwater Ecosystems. American Scientist, 65, 159-170. Rivkin R.B. & Legendre L. (2001) Biogenic carbon cycling in the upper ocean: Effects of microbial respiration. Science, 291, 2398 2400. Sarkar S. & Jana B.B. (1985) Biomass Determination in some Species using a Geometric Equivalent Technique of Plankton Organisms. Acta Hydrochimica et Hydrobiologica, 13, 217221. Sartory D.P. & Grobbelaar J.U. (1984) Extraction of Chlorophyll a from Fresh-Water Phytoplankton for Spectrophotometric Analysis. Hydrobiologia, 114, 177-187. Shireman J.V. & Marti n R.G. (1978) Seasonal and Diurnal Zoo Plankton Investigations of a South Central Florida Usa Lake. Florida Scientist, 41, 193201. SJRWMD (2010) Historical records in zooplankton in Lake George. Personal communication SJRWMD (2008) A Story of the St. Johns River. Personal communication Smith V.H. (1998) Cultural eutrophication of inland, estuarine, and costal waters In: Successes, limitations, and frontiers in ecosystem science (Eds M.L. Pace & P.M. Groffman). Springer -Verlag, New York City, New York, U.S.A. Smith V.H., Tilman G.D. & Nekola J.C. (1999) Eutrophication: impacts of excess nutrient inputs on freshwater, marine, and terrestrial ecosystems Environmental Pollution, 100, 179196. Soares M.C.S., Lurling M., Panosso R. & Huszar V. (2009) Effec ts of the cyanobacterium Cylindrospermopsis raciborskii on feeding and life history

PAGE 75

75 characteristics of the grazer Daphnia magna. Ecotoxicology and environmental safety, 72, 1183 -1189. Thys I. & Hoffmann L. (2005) Diverse responses of planktonic crustaceans to fish predation by shifts in depth selection and size at maturity. Hydrobiologia, 551, 8798. Tranvik L.J. (1992) Allochthonous Dissolved Organic -Matter as an Energy -Source for Pelagic Bacteria and the Concept of the Microbial Loop. Hydrobiologia, 229, 107-114. Utermohl H. (1958) Zur Vervollkommnung der quantitiven Phytoplanktonmethodik. Mitteilungen Internationale Vereinigung fur Theoretische und Angewandte Limnologie, 9, 1 -38. Vinyard G.L. & Obrien W.J. (1976) Effects of Light and Turbidity on Reactive Distance of Bluegill (Lepomis Macrochirus). Journal of the Fisheries Research Board of Canada, 33, 2845 -2849. Wellington C.G., Mayer C.M., Bossenbroek J.M. & Stroh N.A. (2010) Effects of turbidity and prey density on the foraging success of age 0 ye ar yellow perch Perca flavescens. Journal of fish biology, 76, 1729 -1741. Williamson C.E., Salm C., Cooke S.L. & Saros J.E. (2010) How do UV radiation, temperature, and zooplankton influence the dynamics of alpine phytoplankton communities? Hydrobiologia, 648, 7381. Work K., Havens K., Sharfstein B. & East T. (2005) How important is bacterial carbon to planktonic grazers in a turbid, subtropical lake? Journal of Plankton Research, 27, 357372. Work K.A. & Havens K.E. (2003) Zooplankton grazing on bacter ia and cyanobacteria in a eutrophic lake. Journal of Plankton Research, 25, 13011306. World Health Organization. (2006) Guidelines for drinking -water quality [electronic resour ce] : incorporating first addendum. Vol. 1, Recommendations Yilmaz M., Phlip s E.J., Szabo N.J. & Badylak S. (2008) A comparative study of Florida strains of Cylindrospermopsis and Aphanizomenon for cylindrospermopsin production. Toxicon, 51, 130 -139.

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76 BIOGRAPHICAL SKETCH Akeapot Srifa was born in Surat Thani, Thailand in November, 1984. He was graduated from Mahidol Wittayanusorn School in Nakhon Pathom, Thailand, before started his undergraduate study, majoring in Biology, at Mahidol University, Bangkok, Thailand in 2003. He has a wide range of interests in aquatic, marine and environmental sciences. He got a scholarship from the universitys distinction program to experience international research career and fulfill his undergraduate thesis at the Center for Environmental Research (UFZ) in Leipzig, Germany in 2007. His undergraduate thesis was on the topic of the effectiveness of constructed wetlands in arsenic removal from contaminated water. Upon his graduation, he got a scholarship from the Royal Thai Government to pur sue further graduate studies. He came to University of Florida in 2008 and started his Masters research under the supervision of Professor Edward J. Phlips. His research has been focusing with the interrelationship between phytoplanktonzooplankton and wat er quality.