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Estimation of Microzooplankton Grazing in the Suwannee River Estuary, Florida, USA


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ESTIMATION OF MICROZOOPLANKTON GR AZING IN THE SUWANNEE RIVER ESTUARY, FLORIDA, USA By CHRISTINA JETT A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2004

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Copyright 2004 by Christina E. Jett

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To Jason, my love, and to my parents, Tom and Sally.

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ACKNOWLEDGMENTS I would like to thank my chair, Dr. Edward Phlips, for the opportunity to complete my thesis under his guidance. His help and guidance have proved to be invaluable. I also like to thank my committee members, Dr. Thomas Frazer and Dr. Thomas Crisman, for their advice and input on everything from experimental design to the final thesis. I am also very grateful to Erin Bledsoe for her guidance, help, and unending patience when answering my questions. Thanks go to Mary Cichra and Susan Badylak for taxonomic identification. Thanks go also to Carla Beals, Rob Burns, Karen Donnelly, Jessica Frost-Fajans, Katie ODonnell, and Becky Scwab for their time and effort with this project. I greatly appreciate their assistance in the field and lab. Funding for this project was provided by United States Department of Agriculture. Lastly, I would like to thank my family and fiance, Jason, for their love and support. Their patience and reassurance provided me with the confidence and motivation needed to complete this project. iv

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TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES............................................................................................................vii LIST OF FIGURES.........................................................................................................viii ABSTRACT.........................................................................................................................x CHAPTER 1 INTRODUCTION........................................................................................................1 2 MATERIALS AND METHODS.................................................................................3 Study Site and Station Description...............................................................................3 Sample Collection.........................................................................................................4 Grazing Experiment......................................................................................................4 Phytoplankton and Zooplankton Analyses...................................................................6 Nutrient Analyses.........................................................................................................7 Chlorophyll Analyses...................................................................................................7 Turbidity.......................................................................................................................7 Growth Rate and Loss Calculations.............................................................................8 Statistical Analysis........................................................................................................9 3 RESULTS...................................................................................................................11 Field Parameters.........................................................................................................11 Chemical Analysis......................................................................................................12 Microzooplankton Grazing Rates...............................................................................12 Phytoplankton Growth Rates......................................................................................13 Community Structure..................................................................................................14 4 DISCUSSION.............................................................................................................29 Compariative Phytoplankton Loss..............................................................................29 Nutrient-rich versus Ambient Nutrient Phytoplankton Growth.................................32 LIST OF REFERENCES...................................................................................................41 v

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BIOGRAPHICAL SKETCH .............................................................................................46 vi

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LIST OF TABLES Table page 3-1 Seasonal means for surface temperature (C) for each station.................................15 3-2 Seasonal means for salinity (ppt) at each station.....................................................16 3-3 Seasonal means for dissolved oxygen (mg L-1) each station...................................17 3-3 Seasonal means for total nitrogen values (mg L-1)...................................................19 3-4 Seasonal mean total phosphorous values (g L-1)....................................................20 3-5 Seasonal mean turbidity readings (ntu)....................................................................21 3-6 Seasonal mean chlorophyll readings (g L-1)..........................................................23 3-7 Grazing and growth coefficients (d-1) determined from the mesocosm experiments..............................................................................................................24 3-8 Seasonal mean percent phytoplankton standing crop lost/day.................................26 3-9 Correlation of temperature to grazing coefficient, temperature to growth coefficient and grazing coefficient to growth coefficient for each station...............26 3-10 The order of numerical dominance of the microzooplankton community structure for eight months........................................................................................28 3-11 The order of numerical dominance of the phytoplankton community structure for eight months.......................................................................................................28 3-12 The order of biovolumetric dominance (m3) of the microzooplankton community structure for eight months. ..................................................................28 4-1 Summary of percent phytoplankton standing stock removed per day for various oceanic environments. ............................................................................................36 4-2 Comparison of the different parameters for the studies examined in the discussion.................................................................................................................36 vii

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LIST OF FIGURES Figure page 2-1 Stations were monitored monthly and are located within the Suwannee Estuary. Theses stations represent the different parts of the estuary......................................10 3-1 Surface temperature for B1, C1, C4, and G1 within the Suwannee River estuary for a period of 12 months starting in February 2002................................................15 3-2 Salinity of the four stations located throughout Suwannee Estuary.........................16 3-3 Dissolved oxygen for four stations throughout the Suwannee Estuary for a period of one year, starting with February 2002......................................................17 3-4 pH of the four stations sampled for a period of one year in 2002 and 2003............18 3-5 Total nitrogen readings for stations within the Suwannee Estuary for a period of 12 months. C4 was always significantly lower than all other stations....................19 3-6 Total phosphorous readings for stations within the Suwannee Estuary for a period of 12 months. C4 was always significantly lower than all other stations...............20 3-7 Turbidity readings collected within the Suwannee Estuary for a period of 12 months, starting in February 2002............................................................................21 3-8 Initial chlorophyll levels (g L-1) for the four stations starting in February 2002 and ending in January 2003......................................................................................22 3-9 Monthly instantaneous grazing coefficients of four sites within the Suwannee estuary starting in February 2002 and ending in January 2003................................25 3-10 Monthly instantaneous phytoplankton growth coefficients of four sites within the Suwannee estuary starting in February 2002 and ending in January 2003..............25 3-11 Comparison of net phytoplankton growth in the 100% whole water mesocosms with (gray bars) and without (black bars) nutrient additions. ..................................27 4-1 A comparison of the doublings per day (open circle) and halvings per day (black box) for each station for a period of one year, February 2002 to January 2003......37 4-2 A comparison of the net doublings per day for nutrient enriched (black diamond) and non-enriched (grey box) mesocosms.................................................................38 viii

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4-3 A comparison of estimated instantaneous growth rate for non-enriched mesocosms (grey box) and instantaneous grazing rate (black triangle)...................39 4-4 An estimation of the location of the oyster reefs that run parallel to the shoreline in the Suwannee River estuary.................................................................................40 ix

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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 ESTIMATION OF MICROZOOPLANKTON GRAZING IN THE SUWANNEE RIVER ESTUARY, FLORIDA, USA By Christina Jett May 2004 Chair: Edward Phlips Major Department: Fisheries and Aquatic Science An investigation of the ecological role of microzooplankton grazing was conducted in the Suwannee River estuary, Florida, using a dilution technique. Four sites, three inshore and one offshore station, were sampled every month from February 2002 to January 2003 and brought back to the lab to conduct the experiment in temperature controlled mesocosms. The instantaneous rate of phytoplankton mortality ranged from -0.0003d-1 to 2.04d-1, corresponding to a 0 to 87% loss of phytoplankton standing crop per day. Significant seasonal differences occurred in all stations except for the offshore station. Instantaneous growth rates of phytoplankton ranged from -0.15d-1 to 3.2d-1, which is equivalent to -0.02 to 4.6 doublings per day. The microzooplankton community did not show any major spatial or temporal patterns and was mostly dominated by aloricate and loricate ciliates. Phytoplankton were numerically dominated by picoplankton, with secondary dominance alternating between centric diatom chains, centric and pennate diatoms, and cryptophytes. These results of the experiments suggest x

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that microzooplankton are important as consumers of phytoplankton production in the Suwannee River estuary. xi

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CHAPTER 1 INTRODUCTION Increasing human populations along the west coast of Florida have heightened concerns about elevated levels of nutrients in its estuaries (Bledsoe and Phlips in review,, South West Florida Water Management District (SWFWMD) 1994). Elevated nutrients can lead to increased levels of primary productivity and algal standing crops, but can also result in deleterious impacts on ecosystem integrity, such as toxic or nuisance algae blooms, periods of hypoxia (Department of Interior (DOI) 1990), changes in plankton community structure (Paerl 1988), and alterations of benthic communities (Valiela 1995). Many of these are associated with high algal standing crops or algal blooms (Richardson and Jorgensen 1996). The potentially negative impacts of algae blooms have increased interest in the factors controlling algal standing crops. Phytoplankton standing crop is dictated by gain (i.e., growth and biomass import) and loss functions (death, grazing, export, and sedimentation). Although all loss terms are potentially important, grazing by zooplankton and its link to primary productivity is often overlooked. The link between zooplankton and phytoplankton is critical to the flow of carbon from plankton to consumers (James and Hall 1998, Landry and Hassett 1982) and determining the zooplankton grazing rate is critical to understanding predator populations regulate prey populations, also known as top down control (Carrick et al. 1991). Conversely, prey availability regulates zooplankton population densities (Cyr and Pace 1992). These two elements play an important role in dictating the distribution and dynamics of carbon in estuaries. 1

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2 This study examines the importance of zooplankton grazing to phytoplankton dynamics in the Suwannee River estuary. The working hypothesis is that zooplankton grazing within the Suwannee River estuary is important in regulating phytoplankton standing crops. This role is judged as a comparison of the relative magnitude of algal growth and grazing rates in distinct regions of the Suwannee River estuary. The results are discussed in relation to key environmental factors that influence phytoplankton growth and grazing, including temperature, nutrients, and community composition.

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CHAPTER 2 MATERIALS AND METHODS Study Site and Station Description The Suwannee River system is located on the west coast of Florida in the Big Bend area. The Suwannee River originates in the Okeefenokee Swamp, Georgia, the second largest swamp in the United States (Bledsoe and Phlips 2000) and winds through northern Florida before emptying into the Gulf of Mexico near the town of Suwannee. Approximately 394km long, this black water river drains 28,500km2 of northern Florida and southern Georgia (Wolfe and Wolfe 1985, Bledsoe and Phlips 2000). It is characterized by nutrient rich waters, which are supplemented by numerous springs along the lower reaches of the river system (Bledsoe and Phlips 2000, Department of Enivronmental Protection (DEP) 1985). Four stations were picked as representatives of distinct regions within the estuary (Figure 2-1). B1 is near the mouth of the river in front of an oyster reef. A shallow station, it is exposed to tides and has periodic flushing from the river at low tides. C1 is located within Suwannee Sound and is isolated from the Gulf by two parallel oyster reefs that allow only partial inflow of seawater. This station is regularly inundated by the Suwannee River and runoff from the surrounding wetlands. C4 is a more marine environment with the least influence from the river. The last station, G1, is located by an area used for clam aquaculture and is the southern-most station. Also a shallow station, it receives some tidal influence and freshwater flushing from the river and runoff. 3

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4 Sample Collection Water samples were collected from the four stations within the Suwannee Estuary, monthly for one year. Water was taken using an integrating sampling tube that collected water from the surface to within 0.1m of the bottom. The top three meters were sampled when water depth exceeded that of the sampling tube. The latter approach was only employed at station C4, where depth was typically greater than 3.0 m. Water from a minimum of 5 pulls was combined in a tub, mixed, and sub-samples were taken for TN, TP, and turbidity analysis. An additional 20L were collected for subsequent grazing experiments. Dissolved oxygen (mg L-1), temperature (C), pH, salinity (ppt), Secchi (m), and specific conductivity (mS/cm) were measured using a Hydrolab Quanta at both 0.5m below the surface and 0.5m above the bottom. Grazing Experiment Grazing experiments in mesocosms is commonly used to estimate zooplankton grazing rates. In this study, grazing rates were determined in laboratory mesocosms using the serial dilution method developed by Landry and Hassett (1982). This method is based on four assumptions; (1) phytoplankton growth is not density dependent, (2) the probability of being consumed is directly related to the encounter rate with predators (consumption rates are linear), (3) phytoplankton are in exponential growth and (4) phytoplankton growth is not limited by nutrient availability. To correct for occasional non-linearity of grazing kinetics, the three-point method (Gallegos 1989) was applied to the data in question. This method extrapolates grazing to whole water from the two smallest dilutions in the experiment, and then re-calculates the grazing rate for the station Whole water collected in the field was filtered through 1.085mm mesh to remove large gelatinous zooplankton, e.g., jellyfish. Although this allowed grazers into the

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5 experiment that are not in the standard size range for microzooplankton (20-200m), it also allowed the passage of large chain-forming diatoms that are often found within the system. Further microscopic analysis of samples revealed that the dominant grazers on the phytoplankton fell within the standard size range category; we therefore consider this experiment an estimation of microzooplankton grazing. Dilutions were made using station water taken through a step filtration system composed of 10m, 5m, 1m, and 0.2m and were run in duplicate at 100, 75, 50, 40, and 30 percent whole water. Each treatment flask was spiked with nitrogen, phosphorous, and silica (400gN1-1 + 40g P1-1 + 400g Si 1-1) to ensure nutrient availability for phytoplankton growth (Schluter 1998). An additional 100% whole water duplicate was not spiked to compare growth rates and determine nutrient limitation over a 24hr period. Flasks (2L) were placed in a temperature-controlled mesocosms at the same temperatures measured in the field and 120Ein m-2/sec-1 of fluorescent light. Flasks were continually stirred slowly to maintain circulation. Net change in algal biomass was estimated from net change of in vivo fluorescence (IVF) of chlorophyll a using a Turner Designs Model 10 fluorometer with a l-cm path length. At the beginning and end of incubation, contents of the two flasks were combined and sub-samples for each parameter collected. Chlorophyll a was collected in duplicate by filtering 500ml of the flask contents onto Gelman A/E glass fiber and then frozen until analysis (Sartory and Grobbelaar 1984). For picoplankton estimates, 1-5ml of station water were filtered through 0.2um pore Nuclepore filters, and filters were then mounted between microscope slides and cover slips with immersion oil. These slides were stored, frozen and counted within 1 week to minimize fading of fluorescence (Sartory and

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6 Grobbelaar 1984). Zooplankton was collected by filtering 1000ml through a 41m Nitex mesh, then rinsing and preserving the samples with Lugols. Phytoplankton was collected by preserving sub-samples (to=1000ml, t24=100ml) with Lugols. Phytoplankton and Zooplankton Analyses Phytoplankton composition was determined using the Utermohl method (Utermohl 1958). Lugols-preserved samples were concentrated by settling in cylindrical counting chambers for 4 h per ml sample for phytoplankton and 30min/ml for zooplankton. Phytoplankton cells were identified and counted at 400x and 100x with a Leica phase contrast inverted microscope. At 400x, counts were terminated after reaching 100 cells of the most dominant taxon, but a minimum of 30 ocular micrometer grids were counted. Large celled taxa (>30um) were enumerated by a complete count of the settling chamber at 100x. Cell biovolumes were estimated by assigning geometric shapes to fit the characteristics of individual taxa (Smayda 1978). Specific phytoplankton dimensions were measured for at least 30 randomly selected cells. The volume was calculated for each cell, from which mean cell volume was derived. Cell counts were transformed to biovolume using the mean cell volume. Total biovolume per sample was the sum of estimated cell volumes for each species. Zooplankton were identified and enumerated from Lugols preserved samples. Concentrated samples were settled in counting chambers and enumerated at 100x with a Leica phase contrast inverted microscope. Counts were terminated after reaching 100 counts of the single most dominant taxon (Utermohl 1958). Picoplanktonic cyanobacteria and green algae were enumerated with fluorescence microscopy using filtered samples of unpreserved water (Fahnenstiel and Carrick, 1992).

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7 Samples were counted with a Nikon microscope equipped with autofluorescence, including both green and blue light excitation. Numerical abundances of cells were determined by counting at least five ocular micrometer grids at 1000x. Representative samples of each cell type were measured for subsequent calculation of cellular biovolume. Counts were considered complete after reaching a minimum of 100 cells of one taxon. At least five grids were counted when cell concentration was high. Nutrient Analyses Total nitrogen was determined from frozen whole water samples using the persulfate digestion method (American Public Health Association (APHA) 1989) and analyzed with a Technicon AutoAnalyzer. Total phosphorous was also determined from frozen whole water samples using the persulfate digestion method (APHA 1989) and analyzed with a Hitachi U2000 dual beam spectrophotometer. Chlorophyll Analyses Chlorophyll a was determined from samples (500 ml) filtered onto Gelman A/E glass-fiber filters and then frozen. Filters were placed into test tubes with 8.0 ml of 95% ethanol and heated in a water bath for 5 min at 78C (Sartory and Grobbelaar 1984). After passive extraction (24 h), filters were removed and samples centrifuged to exclude particulate debris. Chlorophyll a concentrations were determined with a Hitachi U2000 dual beam spectrophotometer and corrected for phaeophytin using the acidification method (APHA 1989). Turbidity Turbidity was determined by a LaMotte 2020 Turbidimeter calibrated in a range of 0 1100 NTU.

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8 Growth Rate and Loss Calculations By tracking incubations of different dilutions of seawater, instantaneous rates of phytoplankton growth and mortality can be established. To determine change, the following equation is used: Pt = P0e(k-g)t (1) Where Pt is the phytoplankton biomass at the end of the experiment, P0 the initial concentration of phytoplankton biomass, t is the length of incubation (days), and the instantaneous coefficients of phytoplankton growth and mortality are designated by k and g, respectively. Phytoplankton biomass is estimated by chlorophyll at the beginning and end of each experiment. The regression of the results for all of the dilutions will provide a linear equation in which the y-axis intercept is phytoplankton growth rate (k), and the negative slope of the relationship is the grazing coefficient (g). A minimum of two dilutions will yield two equations with two unknowns which can be solved for g and k. The linear regression will, however, provide estimates of confidence limits for the coefficients (Landry and Hassett 1982). With the coefficient for phytoplankton mortality due to grazing (g), the percent of phytoplankton standing crop removed per day (S) can be calculated as S= (1 e (-g)) 100 (3) where g is the instantaneous grazing coefficient calculated from Eq.1. In situations where saturated feeding responses were observed, an adjusted grazing rate (K) has been calculated using a three-point method (Gallegos 1989). K = (X2rx,1 X1rx,2)/(X2 X1) (4)

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9 Where X1 and X2 are the lowest fraction of unfiltered seawater within the experiment(e.g. X2 = 0.30 and X1 = 0.40) and corresponding r (ln(Chl T24/ Chl T0). K is then used to determine g in equation 7. First, the change in the number of microzooplankton must be determined: Z = ln(zoo# T24/zoo# T0) (5) Where zoo# is the number of microzooplankton counted using light microscopy at times 0h and 24h. Z, determined from equation 5, is then used with K, to calculate a new grazing coefficient (g): g = (Chl T24/ Chl T0 expK) [(Z K) / (expZ expK)] (7) Statistical Analysis SAS and Minitab were used to carry out statistical analysis such as ANOVA and Tukeys multiple comparisons procedure. The latter was used to determine differences between means for stations and seasons. Seasons were designated as winter (January, February, and December), spring (March, April, May), summer (June, July, August), and fall (September, October, and November). A p-value of 0.01 was used as a measure of significance due to low sample size. Pearsons Correlation tests were used to determine correlation between parameters.

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10 Suwannee R iver Gulf of Mex i co Figure 2-1. Stations were monitored monthly and are located within the Suwannee Estuary. Theses stations represent the different parts of the estuary.

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CHAPTER 3 RESULTS Field Parameters Surface temperature ranged from 11C to 31C and did not vary significantly between stations during any sampling period (Figure 3-1). There were, however, significant seasonal differences in temperature at all sites (Table 3-1), with average winter temperature (11 and 15C) lower than mean values during all other seasons (>2C). Salinity ranged from 5 to 34 ppt (Figure 3-2). Among sites, no significant seasonal differences in salinity were observed. There were, however, significant differences in salinity between sites within seasons (Table 3-2). C1, nearest to the river mouth had the lowest mean salinities, while C4, the most offshore site, had the highest mean salinities (Table 3-2). Dissolved oxygen concentrations were consistently 4.9mg L-1 or higher (Figure 3-3). They tended to be lower in summer, especially June and July, and tended to be higher in early spring and late winter, mainly in January and March (Figure 3-3). Salinity at C1 was marginally different (p = 0.07) between summer and fall. pH values fell within a very narrow range (7.6 and 8.4) and did not show any apparent spatial or temporal pattern (Figure 3-4). 11

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12 Chemical Analysis Total nitrogen concentrations ranged from 0.180 to 0.897 mg L-1 (Figure 3-5). There were no obvious seasonal patterns in the data, although C4 was consistently lower in TN than all other sites (Table 3-3). Total phosphorous concentrations ranged from 0.002 to 0.200 g/L (Figure 3-6). No seasonal differences were observed at any sites, but there were significant differences in TP within seasons among sites (Table 3-4). C4 was consistently in lower TP levels than all other stations. Turbidity readings were between 0.15 and 24.0 ntu (Figure 3-7). The lowest readings were consistently observed at station C4, but no significant seasonal or station differences were found (Table 3-5). Chlorophyll a concentrations ranged from 1.2 to 64.4g L-1 (Figure 3-8). Station C4 exhibited consistently low levels of chlorophyll a, although the mean value was only significantly different from other stations in summer. For the near-shore stations, summer and winter was always significantly different (Table 3-6). Microzooplankton Grazing Rates The instantaneous rate of phytoplankton mortality (grazing coefficient) ranged from -0.0003d-1 to 2.04d-1 (Table 3-7). Percent phytoplankton standing crop lost per day ranged from 0 to 87% (Table 3-7). The lowest grazing coefficient was in June at station C4, while the highest was at C4 during March. Station C4 also had the highest grazing coefficient in March and November, but was consistently lower than all other stations for the remainder of the study (Figure 3-9). B1, C1, and G1, all had a sharp decrease in grazing during the month of November but C4 was relatively unchanged (Figure 3-9).

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13 There was seasonal variation in percent phytoplankton standing crop lost per day for all stations except C4 (Table 3-8). C1 and B1 showed a significant difference between summer and winter (p = 0.001), while G1 showed a significant difference between spring and summer (p = 0.005). On an annual average, G1 and C4 were significantly different from each other (p = 0.02) though not significantly different from the other stations; B1 and C1 were not significantly different from each other (Table 3-8). Phytoplankton Growth Rates Growth coefficients for phytoplankton ranged from -0.15d-1 to 3.2d-1 (Table 3-7), which corresponded to -0.02 to 4.6 doublings per day. The lowest growth coefficient was at station C1 in winter, while the highest was at B1 during summer. B1 and C1 showed little variation from each other and displayed the same pattern with higher phytoplankton growth rates occurring in the summer months and lower rates occurring in winter. G1 showed relatively higher growth rates throughout the year, however displayed a sharp decrease in July. C4 also had a sharp decrease in July though it showed no kind of seasonal trend with higher rates occurring in winter (Figure 3-10). There was a strong, positive correlation between growth and grazing coefficients for all stations except G1 (Table 3-9). Grazing and growth coefficients (Table 3-9) were positively and significantly correlated with temperature at stations B1 and C1, i.e. the two stations with the most influence from the river. Phytoplankton doublings per day in both nutrient addition and control mesocosms were compared for control and nutrient-added treatment groups (Figure 3-11). In all but one experiment, growth in the nutrient addition groups was greater than the control. G1 showed a strong nutrient limitation response for all months from March to October 2002.

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14 Community Structure The microscopic analyses of selected sampling sites showed a relatively stable dominance of small microzooplankton (<10 m), e.g. copepod nauplii and ciliates and small sized phytoplankton, e.g. picoplankton and cryptophytes. The numerically dominant zooplankton shifted among aloricate ciliates, loricate ciliates, and copepod nauplii (Table 3-10); while the dominant phytoplankton were picoplankton. Cryptophytes, centric, and pinnate diatoms were the major constituents of the phytoplankton community (Table 3-11). No pattern was discernable from the dominant phytoand microzooplankton in either numeric or biovolumetric dominance, although the potential importance of copepod nauplii increased in the biovolumetric comparison (Table 3-12).

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15 Surface Temperature05101520253035FM A M JJA SONDJMonthC B1 C1 C4 G1 Figure 3-1. Surface temperature for B1, C1, C4, and G1 within the Suwannee River estuary for a period of 12 months starting in February 2002. Table 3-1. Seasonal means for surface temperature (C) for each station. Seasons were described as: December, January, February for winter, March, April, and May for spring, June, July, August, for summer and September, October, November for fall. Values in bold are the means and values in parenthesis are the standard deviation. Capital letters designated differences between seasons within each station; lower case letters designate differences between stations within each season and capital letters in bold designate total average for each season. Season Station Winter Spring Summer Fall Annual A B B B B1 11.7 a 21.8 a 28.7 a 22.9 a 21.1 a (0.84) (0.74) (2.05) (2.55) (7.39) A B B B C1 11.9 a 22.2 a 29.4 a 23.0 a 21.5 a (3.27) (3.75) (3.28) (1.66) (7.67) A B B B C4 13.6 a 24.1 a 28.4 a 22.9 a 22.3 a (1.17) (2.12) (1.17) (2.27) (6.49) A B B B G1 14.1 a 26.4 a 28.7 a 23.9 a 23.2 a (7.07) (7.79) (6.40) (6.68) (6.65) Overall A B B B Seasonal 12.84 23.63 28.79 24.35 Average (1.85) (3.25) (1.55) (6.07)

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16 Salinity0510152025303540FM A M JJA SONDJMonthppt B1 C1 C4 G1 Figure 3-2. Salinity of the four stations located throughout Suwannee Estuary. Table 3-2. Seasonal means for salinity (ppt) at each station. Seasons were described as: December, January, February for winter, March, April, and May for spring, June, July, August, for summer and September, October, November for fall. Values in bold are the means and values in parenthesis are the standard deviation. Capital letters designated differences between seasons within each station; lower case letters designate differences between stations within each season and capital letters in bold designate total average for each season. Seasons Stations Winter Spring Summer Fall Annual A A A A B1 18.44 a b 17.34 b 22.87 a b 23.45 b c 20.26 b c (11.58) (6.93) (5.57) (1.88) (7.11) A A A A C1 13.29 b 18.65 b 16.93 b 19.46 c 16.87 c (6.19) (2.13) (6.24) (0.25) (4.74) A A A A C4 31.22 a 31.51 a 32.82 a 30.69 a 31.56 a (2.17) (1.03) (0.47) (3.49) (1.99) A A A A G1 23.60 a 24.40 a b 29.60 a 25.15 a b 25.69 b (1.93) (6.41) (2.72) (2.17) (4.03) Overall A A A A Seasonal 23.60 24.40 29.60 25.15 Average (1.93) (6.41) (2.72) (2.17)

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17 Dissolved Oxygen024681012FM A M JJA SONDJMonthmg L-1 B1 C1 C4 G1 Figure 3-3. Dissolved oxygen for four stations throughout the Suwannee Estuary for a period of one year, starting with February 2002. Table 3-3. Seasonal means for dissolved oxygen (mg L-1) each station. Seasons were described as: December, January, February for winter, March, April, and May for spring, June, July, August, for summer and September, October, November for fall. Values in bold are the means and values in parenthesis are the standard deviation. Capital letters designated differences between seasons within each station; lower case letters designate differences between stations within each season and capital letters in bold designate total average for each season. Stations Stations Winter Spring Summer Fall Annual A A B B B B1 8.38 a 6.78 a 5.62 a 6.80 a 6.90 a (0.57) (0.71) (0.51) (1.41) (1.25) A A A A C1 8.50 a 6.81 a 6.11 a 7.51 a 7.21 a (0.74) (1.28) (0.37) (1.36) (1.26) A A B B A C4 7.96 a 7.03 a 5.29 a 6.97 a 6.81 a (0.31) (1.38) (0.54) (0.89) (1.26) A A A A G1 8.45 a 8.74 a 6.20 a 7.83 a 7.81 a (0.79) (2.32) (0.61) (1.15) (1.57) Overall A A B A Seasonal 8.32 7.34 5.80 7.30 Average (0.58) (1.56) (0.59) (1.04)

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18 pH012345678910FM A M JJA SONDJMonth B1 C1 C4 G1 Figure 3-4. pH of the four stations sampled for a period of one year in 2002 and 2003.

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19 Total Nitrogen for Suw 20020.000.100.200.300.400.500.600.700.800.901.00FMAMJJASONDJMonthmg L-1 B1 C1 C4 G1 Figure 3-5. Total nitrogen readings for stations within the Suwannee Estuary for a period of 12 months. C4 was always significantly lower than all other stations. Table 3-3. Seasonal means for total nitrogen values (mg L-1). Seasons were described as: December, January, February for winter, March, April, and May for spring, June, July, August, for summer and September, October, November for fall. Values in bold are the means and values in parenthesis are the standard deviation. Capital letters designated differences between seasons within each station; lower case letters designate differences between stations within each season and capital letters in bold designate total average for each season. Season Station Winter Spring Summer Fall Annual A A A A B1 0.5863 a 0.5873 a 0.5943 a 0.6867 a 0.6137 a (0.18) (0.19) (0.16) (0.04) (0.14) A A A A C1 0.6434 a 0.5301 a 0.6510 a 0.6035 a 0.6070 a (0.17) (0.19) (0.16) (0.04) (0.12) A A A A C4 0.2484 b 0.2089 b 0.2457 b 0.2536 b 0.2392 b (0.06) (0.03) (0.03) (0.06) (0.04) A A A A G1 0.4495 a 0.4772 a 0.6363 a 0.6226 a 0.5464 a (0.11) (0.19) (0.12) (0.24) (0.17) Overall A A A A Seasonal 0.0603 0.0767 0.0758 0.0703 Average (0.05) (0.07) (0.04) (0.05)

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20 Total Phosphorous for Suw 20020.000.050.100.150.200.25FMAMJJASONDJMonthg L-1 B1 C1 C4 G1 Figure 3-6. Total phosphorous readings for stations within the Suwannee Estuary for a period of 12 months. C4 was always significantly lower than all other stations. Table 3-4. Seasonal mean total phosphorous values (g L-1). Seasons were described as: December, January, February for winter, March, April, and May for spring, June, July, August, for summer and September, October, November for fall. Values in bold are the means and values in parenthesis are the standard deviation. Capital letters designated differences between seasons within each station; lower case letters designate differences between stations within each season and capital letters in bold designate total average for each season. Season Station Winter Spring Summer Fall Annual A A A A B1 0.096 a 0.137 a 0.104 a 0.098 a 0.109 a (0.06) (0.07) (0.02) (0.04) (0.05) A A A A C1 0.086 a b 0.126 a 0.096 a 0.099 a 0.102 a (0.03) (0.07) (0.02) (0.04) (0.04) A A A A C4 0.011 b 0.007 b 0.020 b 0.018 b 0.014 b (0.01) (0.00) (0.01) (0.01) (0.01) A A A A G1 0.049 a b 0.037 a b 0.083 a 0.065 a b 0.059 c (0.03) (0.03) (0.04) (0.02) (0.03) Overall A A A A Seasonal 0.482 0.451 0.532 0.542 Average (0.20) (0.20) (0.20) (0.21)

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21 Suw Turbidity 20020 5 10 15 20 25 30 FMAMJJASONDJ Monthntu B1 C1 C4 G1 Figure 3-7. Turbidity readings collected w ithin the Suwannee Estuary for a period of 12 months, starting in February 2002. Table 3-5. Seasonal mean turbidity readings (ntu). Seasons were described as: December, January, February for wint er, March, April, and May for spring, June, July, August, for summer and September, October, November for fall. Values in bold are the means and valu es in parenthesis are the standard deviation. Capital letters designated differences between seasons within each station; lower case letters designate differences betw een stations within each season and capital letters in bold designa te total average for each season. Season Station Winter Spring Summer Fall Annual A A A A B1 10.85 a 9.24 a 3.32 a 14.59 a 9.04 a (6.88) (9.60) (0.62) (9.78) (7.38) A A A A C1 5.55 a 9.18 a 3.86 a 14.18 a b 7.65 a (2.44) (8.43) (0.77) (13.89) (7.05) A A A A C4 1.07 b 2.11 a 1.27 b 1.09 b 1.38 b (0.29) (2.30) (0.69) (1.47) (1.29) A A A A G1 4.71 a 4.97 a 5.45 a b 3.51 a b 4.66 a b (2.30) (1.39) (4.28) (2.00) (2.44) Overall A A A A Seasonal 5.54 6.37 3.48 7.13 Average (4.90) (6.39) (2.46) (8.56)

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22 Chlorophyll values 2002010203040506070FM A M JJA SONDJMonthug L-1 B1 C1 C4 G1 Figure 3-8. Initial chlorophyll levels (g L-1) for the four stations starting in February 2002 and ending in January 2003.

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23 Table 3-6. Seasonal mean chlorophyll readings (g L-1). Seasons were described as: December, January, February for winter, March, April, and May for spring, June, July, August, for summer and September, October, November for fall. Values in bold are the means and values in parenthesis are the standard deviation. Capital letters designated differences between seasons within each station; lower case letters designate differences between stations within each season and capital letters in bold designate total average for each season. Season Stations Winter Spring Summer Fall Annual B A B A A B B1 9.03 a 17.85a 27.23a36.03 a 21.31a (4.13) (4.29) (7.61) (35.84) (15.81) C B A A B C C1 5.56 a b 19.70a 36.14a35.90 a b 23.27a (2.44) (9.00) (3.80) (35.91) (18.13) A B B A B A C4 2.59 b 1.11b 2.41b4.10 b 2.68b (1.79) (0.17) (0.87) (1.50) (1.49) B A B A A G1 7.93 a b 26.35a b 28.20a31.66 a 23.53a (4.36) (21.26) (9.38) (18.42) (15.21) Overall A A BA Seasonal 21.31 23.272.6823.53 Average (15.81) (18.13)(1.49)(15.21)

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24 Table 3-7. Grazing and growth coefficients (d-1) determined from the mesocosm experiments. Microzooplankton Phytoplankton %Phytoplankton Grazing Coeff. Growth Coeff. Standing crop/Loss Day February B1 0.42 0.24 34 C1 0.15 -0.15 14 C4 0.33 1.6 28 G1 0.44 2.5 36 March B1 0.66 1.4 49 C1 0.99 1.9 63 C4 2.0 2.4 87 G1 1.1 2.2 66 April B1 0.51 2.7 40 C1 0.70 2.0 50 C4 No data No data No data G1 1.1 2.0 67 May B1 0.61 1.8 46 C1 0.84 2.6 57 C4 0.25 1.5 22 G1 1.1 2.4 67 June B1 1.5 3.2 77 C1 0.84 1.9 57 C4 0.17 0.76 16 G1 0.88 2.2 59 July B1 1.3 2.3 73 C1 1.2 2.5 69 C4 0.21 0.23 19 G1 0.77 0.90 54 August B1 1.0 2.1 64 C1 1.3 2.3 73 C4 0.04 1.1 4 G1 0.89 1.8 59 Sept B1 No data No data No data C1 No data No data No data C4 0.73 2.0 52 G1 1.2 1.6 69 October B1 1.2 2.2 70 C1 1.2 2.1 70 C4 0.19 0.73 17 G1 0.99 1.2 63 November B1 0.00 1.1 0 C1 0.07 1.1 7 C4 0.46 1.8 37 G1 0.15 1.6 14 December B1 0.35 0.88 29 C1 0.18 0.62 16 C4 0.02 0.82 2 G1 0.69 1.8 50 January B1 0.23 0.43 21 C1 0.28 1.1 25 C4 0.38 1.1 32 G1 1.42.876

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25 Grazing Coefficient-0.500.511.522.5FMAMJJASONDJMonth B1 C1 C4 G1 Figure 3-9. Monthly instantaneous grazing coefficients of four sites within the Suwannee estuary starting in February 2002 and ending in January 2003. Growth Coefficients-0.500.511.522.533.5FMAMJJASONDJMonth B1 C1 C4 G1 Figure 3-10. Monthly instantaneous phytoplankton growth coefficients of four sites within the Suwannee estuary starting in February 2002 and ending in January 2003.

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26 Table 3-8. Seasonal mean percent phytoplankton standing crop lost/day. Seasons were described as: December, January, February for winter, March, April, and May for spring, June, July, August, for summer and September, October, November for fall. Values in bold are the means and values in parenthesis are the standard deviation. Capital letters designated differences between seasons within each station; lower case letters designate differences between stations within each season and capital letters in bold designate total average for each season. Season Station Winter Spring Summer Fall Annual C B A A B C B1 28 a b 45 b 71 a 35 a 46 a b (6.97) (4.20) (6.44) (49.63) (24.15) B A A A B C1 18 b 57 a b 66 a b 38 a 45 a b (5.60) (6.29) (8.33) (44.52) (24.96) A A A A C4 21 a b 54 a b 13 c 35 a 29 b (16.35) (46.11) (7.69) (17.48) (24.09) A B A B A B G1 54 a 67 a 57 b 49 a 57 a (20.67) (0.66) (2.89) (30.16) (17.07) Overall A B B A B Seasonal 30 56 52 40 Average (18.92) (17.25) (24.83) (28.37) Table 3-9. Correlation of temperature to grazing coefficient, temperature to growth coefficient and grazing coefficient to growth coefficient for each station. Numbers in bold are the p-value and the values on the bottom are the correlation number. Station Correlation B1 C1 C4 G1 Temperature and Grazing <.010 <.010 0.8000 0.4000 0.83 0.83 -0.09 0.27 Temperature and Growth <0.01 <.010 0.6100 0.1600 0.92 0.87 -0.17 -0.43 Grazing and Growth <.010 <.010 <.010 0.3600 0.76 0.86 0.76 0.29

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27 Station B1-1012345FMAMJJASO N D J Doublings/Day Station C1-1012345FMAMJJASO N D J Doublings/Day Station C4-1012345FMAMJJASO N D J Doublings/Day Station G1-2-101234FMAMJJASO N D J Doublings/Day Figure 3-11. Comparison of net phytoplankton growth in the 100% whole water mesocosms with (gray bars) and without (black bars) nutrient additions. In all but one (March B1) experiment, growth with nutrient addition surpassed growth in the control.

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28 Table 3-10. The order of numerical dominance of the microzooplankton community structure for eight months. Stations are presented from lowest to highest grazing rate. Dominant Secondary Dominant Month Station Microzooplankton Microzooplankton Nov B1 Aloricate Ciliates (39indv/ml) Loricate Ciliates (1 ind/ml) Aug C4 Aloricate Ciliates (9 ind/ml) Cope Nauplii (0.20ind/ml) Nov C1 Aloricate Ciliates (67 ind/ml) Loricate Ciliates (9.4ind/ml) Feb C1 Aloricate Ciliates (27ind/ml) Loricate Ciliates (2.5ind/ml) Nov G1 Aloricate/Loricate (1ind/ml) Cope Nauplii (0.19 ind/ml) Aug C1 Loricate ciliates (2.4ind/ml) Cope Nauplii (0.84ind/ml) Jan G1 Rotifer (0.27ind/ml) Cope Nauplii (0.07 ind/ml) June B1 Aloricate ciliates (149ind/ml) Loricate Ciliates (4 ind/ml) March C4 Cope Nauplii (0.17 ind/ml) Loricate Ciliates (0.6 ind/ml) Table 3-11. The order of numerical dominance of the phytoplankton community structure for eight months. Stations are presented from lowest to highest grazing rate. Dominant Secondary Dominant Month Station Phytoplankton Microzooplankton Nov B1 Picoplankton (188409 cells/ml) Cryptophytes (2358 cells/ml) Aug C4 Picoplankton (825330 cells/ml) Dactyliosolen chains (883 cells/ml) Nov C1 Picoplankton (109210 cells/ml) Cryptophytes (1935 cells/ml) Feb C1 Picoplankton (63359 cells/ml) Pennate Diatoms (851 cells/ml) Nov G1 Picoplankton (104327 cells/ml) Cryptophytes (1428 cells/ml) Aug C1 Picoplankton (1570628 cells/ml) Centric Diatoms (3628 cells/ml) Jan G1 Picoplankton (45018 cells/ml) Skeletonema chains (2031 cells/ml) June B1 Picoplankton (445178 cells/ml) Cryptophytes (3224 cells/ml) March C4 Picoplankton (78603 cells/ml) Leptocylindricus chains (34593 cells/ml) Table 3-12. The order of biovolumetric dominance (m3) of the microzooplankton community structure for eight months. Stations are presented from lowest to highest grazing rate. Secondary Dominant Month Station Dominant Species Species Nov B1 Aloricate Ciliates(39396.52) Copepod Nauplii (6241) Aug C4 Loricate Ciliates(22884.3) Copepod Nauplii (465) Nov C1 Aloricate Ciliates(53443.6) Loricate Ciliates(18087.48) Feb C1 Aloricate Ciliates(43293) Loricate Ciliates(10760) Nov G1 Copepod Nauplii (1370) Loricate Ciliates(244.35) Aug C1 Copepod Nauplii (8713) Loricate Ciliates(1382.16) Jan G1 Rotifer (5054) Copepod Nauplii (825.25) June B1 Loricate Ciliates(70164) Aloricate Ciliates(36194) March C4 Copepod Nauplii (629) Loricate Ciliates(256)

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CHAPTER 4 DISCUSSION The goal of this study was to determine the potential impact of microzooplankton grazing on phytoplankton dynamics in the Suwannee River estuary. The results demonstrate that the microzoplankton grazing rates in the Suwannee River estuary are significant. There are several different observations that led to this general conclusion, including 1. Comparisons of phytoplankton loss rates for this study with those observed in estuaries within the Gulf of Mexico and globally. 2. Comparisons of phytoplankton growth for nutrient-rich versus ambient nutrient mesocosms. Compariative Phytoplankton Loss Significance of grazing in the Suwannee River estuary can be obtained by comparing grazing estimates from other regions of the world. The grazing losses observed in this study ranged from 0 to 87% loss of phytoplankton standing crop per day, with seasonal averages from 13 to 71% among the four sampling sites. These numbers are not unlike other estimates for coastal and oceanic waters through out the world (Table 4-1). Strom and Strom (1996) observed that grazing rates in the Mississippi River delta resulted in a 26 90% loss of phytoplankton standing crop during October 1992 and May 1993. In this study grazing by microzooplankton resulted in a 17 70% loss of phytoplankton standing crop for corresponding months in the Suwannee River estuary. Several other similarities between the Mississippi delta and Suwannee River 29

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30 estuary are noteworthy. Although there were some differences in microzooplankto community structure between the two systems, ciliates were often dominant in both system. In addition, higher grazing rates were observed at higher phytoplankton standing crops, as indicated by chlorophyll a concentrations. There are also major differences between the two systems. For example, the portion of the Suwannee River estuary examined in this study exhibited a broader range in salinity and chlorophyll range than the portions of the Mississippi River delta studied by Strom and Strom (1996) (Table 4-2). In some studies of tropical open-ocean systems, grazing rates similar to those in the Suwannee River estuary have been observed. For example, Verity et al. (1996) found grazing rates in the equatorial Pacific, ranging from 14 62% loss of phytoplankton standing crop per day. The grazer community composition in the latter system is very different from that found in the Suwannee River estuary. Heterotrophic nanoplankton and dinoflagellates dominated the grazer community in the Verity et al. study, while ciliates were only a minor constituent in the microzooplankton community. Chlorophyll levels were also much lower in the latter study than in the Suwannee (Table 4-2). However, Verity et al. (1996) concluded that the grazing rates observed played a significant role in the regulation of phytoplankton standing crop. Outside the sub-tropical/tropics, Gallegos (1989) estimated 17 to 80% loss of phytoplankton standing crop per day during July, August, and October in the Rhode River estuary, Maryland. Within the Suwannee River estuary a 4 to 73% loss of phytoplankton standing crop per day was observed the same months. The Rhode River estuary is a turbid, eutrophic estuary, which receives high nutrient inputs with average

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31 chlorophyll concentrations of 50g l-1 in parts of the system (Table 4-2). The primary difference in the microzooplankton community from the Suwannee estuary was the dominance by oligotrichs and rotifers, while loricate ciliates played a minor role. Again this study suggested that microzooplankton grazing had a significant effect on phytoplankton standing crop. Not all systems exhibit as broad a range of grazing loss as the Suwannee River estuary. For example, the oligotrophic Kareiega estuary, located on the south coast of South Africa, exhibits much lower loss rates (Froneman and McQuaid 1997). With low freshwater inputs, this estuary is regarded as primarily marine; the estuary is characterized as having low chlorophyll concentrations, and is usually dominated by small ciliates and nanophytoplankton. The instantaneous grazing rate ranged between 0.010 and 0.105d-1 (1.06 8.51% loss of phytoplankton standing crop per day). Their values are much lower than those observed in the Suwannee River estuary. However, Froneman and McQuaid (1997) still concluded that the impact of grazing was significant. Their findings, in combination with those of others illustrate that the significance of grazing may not be related to the absolute grazing rate, but to the relationship between grazing rate and the growth rate of phytoplankton, which can be very low in oligotrophic systems. In the Kariega estuary, initial chlorophyll levels (0.312 1.24g l-1) and phytoplankton growth rates (0.012 0.242 doublings/day) are extremely low (Froneman and McQuaid 1997) (Table 4-2). Thus a 8.51% loss of the phytoplankton standing crop has a much greater effect on this system. Within the Suwannee River estuary, there exists a trophic gradient which may similarly affect the significance of microzooplankton grazers in the system. The most

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32 offshore station within this study of the Suwannee estuary, C4, displayed relatively low nutrient levels and chlorophyll concentrations. Although the grazing rates for C4 were often lower than at the inshore sites, the grazing impact may be more important due to lower growth rates of phytoplankton. For this station, chlorophyll levels were highest in spring when grazing pressure was lower. Later in the year, however, higher grazing rates occurred and chlorophyll levels were decreased and stayed depressed. By contrast, the inshore stations, more eutrophic in nature, showed no summer depression of chlorophyll despite increased in grazing rates. Nutrient-rich versus Ambient Nutrient Phytoplankton Growth The potential importance of grazing rates observed in the controlled experiments in this study must also be discussed within the context of the factors that vary within the natural environment. One of the most critical of these is nutrient availability. For this purpose, it is useful to compare phytoplankton growth rates were always higher than instantaneous grazing rates, although a few months showed similar rates. However, the nutrient-enriched mesocosm environment removes potential limiting factors that may inhibit growth of the phytoplankton community in situ (e.g., light limitation and nutrient limitation). While this experimental environment provides a good picture of potential grazing rate, it may provide an inflated view of phytoplankton growth rates. Under optimal light and nutrient conditions in the bioassay environment, the phytoplankton growth observed is likely to be the maximal. Nutrients, such as nitrogen, are periodically limiting in the Suwannee River estuary, especially farther from shore (Bledsoe and Phlips 2000). In a similar study, Strom and Strom (1996) showed that grazing by microzooplankton resulted in an 30% average loss of phytoplankton standing crop per

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33 day in nutrient-enriched mesocosms, but losses were as high as 90% in experiments that were not nutrient-enriched. To further understand the role nutrients play in regulation of phytoplankton growth, it is useful to compare net phytoplankton growth rates between nutrient-enriched and un-enriched mesocosms. In all cases, phytoplankton growth was greater in the nutrient-enriched mesocosms, suggesting that with no nutrient addition, the grazing impact could be greater than otherwise indicated (Figure 4-2). While direct comparison of instantaneous growth rates and net growth rates is not possible, for purposes of discussion instantaneous growth rate of non-enriched mesocosms were estimated and then compared to those instantaneous grazing rates obtained from enriched mesocosms (Figure 4-3). With this estimation, the importance of nutrient availability to the phytoplankton standing crop becomes apparent. For stations nearest to the Suwannee River, B1 and C1, estimated growth rates without nutrient addition are still greater than the instantaneous grazing rates for most of the year, although August and winter, they are practically equal. The offshore station, C4, shows the same relationship as the previous stations, showing estimated growth as greater than grazing except for a few months. Differences between the two parameters, though, are relatively small, while those for B1 and C1 are periodically large. G1, however, displays strong nutrient limitation for most of the year, March through October. At this station, growth is greater than grazing in winter. From a broader perspective, a discussion of the relative impacts of microzooplankton grazing within the Suwannee River must include consideration of

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34 other controlling factors. Phytoplankton biomass may well be influenced by a number of factors other than grazing, such as nutrient and light availability. Another factor that may be regionally important is light availability. The dark waters of the river amy cause light limitation for inshore sites. Although the estuary is relatively shallow, the river input of color maybe significant enough to inhibit the introduction of light to deeper depths in the near shore regions of the estuary (Bledsoe and Phlips 2000). This may play a role in the regulation of phytoplankton and also the community structure. Another important controlling factor in the Suwannee River estuary is water residence time (Blesoe and Phlips 2004). The Suwannee River estuary is a semi-enclosed system. Although the estuary does not have specific land barriers blocking tidal flow it does contain two oyster reefs running parallel to the shoreline (Figure 4-4). While the reefs do not totally block tidal flushing, they do restrict movement of water throughout the area, especially at low tide. Monbet (1992) has shown that magnitude of tidal mixing can be important in regulation the response of phytoplankton to nutrient inputs by altering the time available for biomass accumulation. Another possible regulation factor is periodic shifts in grazer communities related to life histories of organisms. For example, there have been periodic masses of ctenophores noted throughout the Suwannee River system (per observation, communication with E. Bledsoe). Often congregating along tide lines, these large predators can alter the grazing rates on phytoplankton and the microzooplankton community with undetermined results.

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35 Beyond the planktonic domain, another possible controlling factor for phytoplankton biomass would be benthic grazers (Cloern 1982). The Suwannee River estuary contains a high population of benthic grazers, including expansive oyster and brachiopod beds (Per observation and personal communication with D. Parkyn). Considering the shallow depth of the Suwannee River estuary, the grazing activities of these organisms could have a major impact on phytoplankton biomass. An important future step in evaluating the importance of microzooplankton to phytoplankton dynamics in the Suwannee River estuary will be to define the relative importance of all aforementioned factors.

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36 Table 4-1. Summary of percent phytoplankton standing stock removed per day for various oceanic environments. Though the percentages show a high range of numbers, the rates determined within this study fall in line with their results. % standing stock Region Location removed per day Source Polar Arctic Sea, Pacific 8 15% Paranjape 1987 Marginal ice zone Bellingshausen Sea 3 24% Burkill et al 1995 Marginal ice zone stations 1 2 3.7 19.8% Froneman and Perissinotto 1996 Subartic/Subantartic Pacific Ocean 5 30% Strom and Welschmeyer 1991 Antartic Polar Front stations 3-12 5.3 44.4% Froneman and Perissinotto 1996 Coastal, Washington 6 24% Landry and Hassett 1982 Temperate Celtic Sea and Carmarthen Bay 30 65% Burkill et al. 1987 Long Island Sound 41% Capriula and Carpenter 1980 New Zealand 10 92% James and Hall 1998 Southern Ocean stations 13 -17 0 22.5% Froneman and Perissinotto 1996 Subtropical Convergence 748% Froneman and Perissinotto 1996 Kariega Estuary 1.06 8.51% Froneman and McQuaid 1997 Southern Ocean stations 18 22 10 22.7% Froneman and Perissinotto 1996 Subtropical Mississippi River Delta 30% Strom and Strom 1996 Suwannee Estuary 13 71% This study Tropical Equitorial Pacific 14 62% Verity et al 1996 Table 4-2. Comparison of the different parameters for the studies examined in the discussion. The salinity conditions for the Kariega estuary have been reported as hypersaline with episodic freshwater inputs (Bate et al. 2002). The salinity for the equatorial Pacific was also not reported specifically, except to say that it was a marine system. Chlorophyll values for the Mississippi River delta were not reported in the publication, but the system was described as containing eutrophic coastal waters. Salinity Chlorophyll Dates Sampled Study Area (ppt) (g l-1) Suwannee Estuary 5.3 33.4 0.99 61 Feb 02 Jan 03 Mississippi River Delta 31.9 36.3 na Oct 92 & May 93 Equatorial Pacific marine 0.1 0.4 March Apr 92 & Oct 92 Rhode River brackish 32.5 138.4 Kariega Estuary marine 0.312 1.21 Nov-94 Jul, Aug, Oct 88

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37 Station B1 -1012345F M A M JJA SONDJ Station C1-1012345F M A M JJA SONDJ Station C4-1012345F M A M JJA SONDJ Station G1-1012345F M A M JJA SONDJ Figure 4-1. A comparison of the doublings per day (open circle) and halvings per day (black box) for each station for a period of one year, February 2002 to January 2003.

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38 B1-2-101234FMAMJJASONDJ C1-2-101234FMAMJJASONDJ C4-2-101234FMAMJJASONDJ G1-2-101234FMAMJJASONDJ Figure 4-2. A comparison of the net doublings per day for nutrient enriched (black diamond) and non-enriched (grey box) mesocosms. Except for a few months, growth in the nutrient enriched mesocosms showed greater growth than the non-enriched mesocosms.

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39 B1-1135FMAMJJASONDJ C1-1135FMAMJJASONDJ C4-1135FMAMJJASONDJ G1-1135FMAMJJASONDJ Figure 4-3. A comparison of estimated instantaneous growth rate for non-enriched mesocosms (grey box) and instantaneous grazing rate (black triangle). This was obtained by using the absolute difference in the net growth rate for the two treatment groups and applying it to the instantaneous growth rate calculated from the enriched-treatment group.

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40 Figure 4-4. An estimation of the location of the oyster reefs that run parallel to the shoreline in the Suwannee River estuary. Though not the only oyster reefs present in the system, these two reefs are mentioned due to their major impact on tidal and river flow throughout the estuary.

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LIST OF REFERENCES Aldridge, F., E. Phlips, and C. Schelske. 1995. The use of nutrient enrichment bioassays to test for spatial and temporal distribution of limiting factors affecting phytoplankton dynamics in Lake Okeechobee, Florida. Ergenbnisse der Limnologie, 0(45): 177-190. American Public Health Association (APHA). 1989. Standard Methods for the Analysis of Water and Wastewater, 17th ed. American Public Health Association, Washington, DC pp. 1075-1077. Ayukai, T. 1996. Possible limitation of the dilution technique for estimating growth and grazing mortality rates of picoplanktonic cyanobacteria in oligotrophic tropical waters. Journal of Experimental Marine Biology and Ecology 198: 101-111. Bledsoe, E. and E. Phlips. 2000. Relationship between phytoplankton standing crop and physical, chemical, and biological gradients in the Suwannee River and Plume Region, U.S.A. Bledsoe, E. and E. Phlips. The relationships between phytoplankton biomass, nutrient loading and hydrodynamics in an inner-shelf estuary, the Suwannee River estuary, Florida, USA. In review. Boynton, W., W. Kemp, and C. Keefe. 1982. A comparative analysis of nutrients and other factors influencing phytoplankton production. In V.S. Kennedy (ed.), Estuarine Comparisons. Academic Press, New York, New York pp. 69-90. Burkill, P., E. Edwards, and M. Sleigh. 1995. Microzooplankton and their role in controlling phytoplankton growth in the marginal ice zone of the Bellingshausen Sea. Deep-Sea Research II 42: 1277-1290. Burkill, P., R. Mantoura, C. Llewellyn, and N. Owens. 1987. Microzooplankton grazing and selectivity of phytoplankton in coastal waters. Marine Biology 93: 581-590. Capriulo, G., and E. Carpenter. 1980. Grazing by 35 to 202 m micro-zooplankton in Long Island Sound. Marine Biology 56: 319-326. Carrick, H., G. Fahnenstiel, E. Stoermer, and R. Wetzel. 1991. The importance of zooplankton-protozoan trophic couplings in Lake Michigan. Limnology and Oceanography 36: 1335-1345. 41

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42 Cloern, J. 1982. Does the benthos control phytoplankton biomass in south San Francisco Bay? Marine Ecology Progress Series 9: 191-202. Cloern, J. 1987. Turbidity as a control of phytoplankton biomass and productivity in estuaries. Continental Shelf Research 7: 1367-1381. Cloern, J. 2001. Our evolving conceptual model of the coastal eutrophication problem. Marine Ecology Progress Series 210: 223-253. Cyr, H., and M. Pace. 1992. Grazing by zooplankton and its relationship to community structure. Canadian Journal of Fisheries and Aquatic Science 49: 1455-1465. Dagg, M. 1995. Ingestion of phytoplankton by the microand mesozooplankton communities in a productive subtropical estuary. Journal of Plankton Research 17: 845-847. Department of Interior. 1990. An ecological characterization of the Florida Springs coast: Pithlachascotee to Wacasassa Rivers. Biological Report 90(21). Dolan, J., C. Gallegos, and A. Moigis. 2000. Dilution effects on microzooplankton in dilution grazing experiments. Marine Ecology Progress Series 200: 127-139. Downing, J., M. McClain, R. Twilley, J. Melack, J. Elser, N Rabalais, W. Lewis Jr., R. Turner, J. Corredor, D. Soto, A. Yanez-Arancibia, J. Kopaska, and R. Howarth, 1999. The impact of accelerating land-use change on the N-Cycle of tropical aquatic ecosystems: Current conditions and projected changes. Biogeochemistry 46: 109-148. Elliott, M. and V. Jonge. 2002. The management of nutrients and potential eutrophication in estuaries and other restricted water bodies. Hydrobiologia 475/476: 513-524. Eppley, R. 1972. Temperature and phytoplankton growth in the sea. Fishery Bulletin 70: 1063-1085. Evans, G. and M. Paranjape. 1992. Precision of estimates of phytoplankton growth and microzooplankton grazing when the functional response of grazers may be nonlinear. Marine Ecology Progress Series 80: 285-290. Fahnenstiel, G. and H. Carrick. 1992. Phototrophic picoplankton in Lakes Huron and Michigan: Abundance, distribution, composition, contribution to biomass and production. Canadian Journal of Fisheries and Aquatic Sciences 49:379-388. Franks, P. 2001. Phytoplankton blooms in a fluctuating environment: The roles of plankton response time scales and grazing. Journal of Plankton Research 23: 1433-1441.

PAGE 54

43 Frazer, T., M. Hoyer, S. Notestein, D. Canfield, F. Vose, W. Leavens, S. Blitch and J. Conti. 1998. Nitrogen, Phosphorous, and Chlorophyll relations in selected rivers and near shore coastal waters along the Big Bend region of Florida. Final project report to Suwannee River Water Management District. Contract #96197-156. Froneman, P. 2001. Seasonal changes in zooplankton biomass and grazing in a temperate estuary, South Africa. Estuarine, Coastal and Shelf Science 52: 543-553. Froneman, P. 2002. Trophic cascading in an oligotrophic temperate estuary, South Africa Journal of Plankton Research 24: 807-816. Froneman, P. and C. McQuaid. 1997. Preliminary investigation of the ecological role of microzooplankton in the Kariega Estuary, South Africa. Estuarine, Coastal and Shelf Science 45: 689-695. Froneman, P. and R. Perissinotto. 1996. Microzooplankton grazing and protozooplankton community structure in the South Atlantic and in the Atlantic sector of the Southern Ocean. Deep-Sea Research I 43: 703-721. Frost, B. 1991. The role of grazing in nutrient rich area of the open sea. Limnology and Oceanography 36: 1616-1630. Gallegos, C. 1989. Microzooplankton grazing on phytoplankton in the Rhode River, Maryland: nonlinear feeding kinetics. Marine Ecology Progress Series 57: 23-33. Gaston, G., C. Cleveland, S. Brown, and C. Rakocinski. 1997. Benthic-pelagic coupling in northern Gulf of Mexico estuaries: Do benthos feed directly on phytoplankton? Gulf Research Reports 9: 231-237. Hansen, B., P. Bjornsen, and J. Hansen. 1994. The size ratio between planktonic predators and their prey. Limnology and Oceanography 39: 395-403. Landry, M.and R. Hassett. 1982. Estimating the grazing impact of marine micro-zooplankton. Marine Biology 67:283-288. James, M. and J. Hall. 1998. Microzooplankton grazing in different water masses associated with the Subtropical Convergence round the South Island, New Zealand. Deep-Sea Research I 45: 1689-1707. Jonge, V., M. Elliott, and E. Orive. 2002. Causes, historical development, effects and future challenges of a common environmental problem: eutrohpication. Hydrobiologia 475/476: 1-19. Mallin, M. and H. Paerl. 1994. Planktonic trophic transfer in an estuary: Seasonal, diel, and community structure effects. Ecology 75: 2168-2184. Monbet, Y. 1992. Control of phytoplankton biomass in estuaries: A comparative analysis of microtidal and macrotidal estuaries. Estuaries 15: 563-571.

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44 Nixon, S. 1995. Coastal marine eutrophication: A definition, social causes, and future concerns. Ophelia 41:199-219. Paranjape, M. 1987. Grazing by microzooplankton in the eastern Canadian Arctic summer. Marine Ecology Progress Series 40: 239-246. Phlips, E., S. Badylak, and T. Grosskopf. 2002. Factors affecting the abundance of phytoplankton in a restricted subtropical lagoon, the Indian River Lagoon, Florida, USA. Estuarine, Coastal and Shelf Science 55: 385-402. Pearl, H. 1988. Nuisance phytoplankton blooms in coastal, estuarine and inland waters. Limnology and Oceanography 33: 823-847. Richardson, K. and B. Jorgensen. 1996. Eutrophication, definition, history and effects. In Eutrophication in Coastal Marine Ecosystems. American Geophysical Union, Washington, D.C. pp. 1-20. Sartory, D. and Grobbelaar, J. 1984. Extraction of chlorophyll a from freshwater phytoplankton for spectrophotometric analysis. Hydrobiologia 114: 177. Schlter, L. 1998. The influence of nutrient addition on growth rates of phytoplankton groups, and microzooplankton grazing rates in a mesocosm experiment. Journal of Experimental Marine Biology and Ecology 228: 53-71. Sherr, E. and B. Sherr. 2002. Significance of predation by protests in aquatic microbial food webs. Antonie van Leeuwenhoek 81: 293-308. Smayda, T. 1978. Estimating Cell Numbers. What to Count In, A. Sournia [ed.] Phytoplankton Manual, UNESCO Monographs on Oceanographic Methodology Paris, France No. 6. pp. 165-166. Southwest Florida Water Management District. 1994. Weekie Watchie River Diagnostic/Feasibility Study. Tallahassee, Florida 2022A-01.01. State of Florida Department of Environmental Programs. 1985. Limnology of the Suwannee River, FL., Tallahasee, FL. Strom, S. and M. Strom. 1996. Microplankton growth, grazing, and community structure in the northern Gulf of Mexico. Marine Ecology Progress Series. 130: 229-240. Strom S. and N. Welschmeyer. 1991. Pigment specific r4ates of phytoplankton growth and microzooplankton in the open subarctic Pacific Ocean. Limnology and Oceanography 3: 50-63. Utermohol, H. 1985. ZurVervollkommnung der quantitativen Phytoplankton-Methodik. Mitteilungen-Internationale Vereinigrung fur Theoretische und Angewandte Limnologie 9: 1-38.

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45 Valiela, I. 1995. Marine Ecological Processes 2nd ed. Springer-Verlag. New York Inc. New York, New York. Verity, P., D. Stoecker, M. Sierack, and J. Nelson. 1996. Microzooplankton grazing of primary production at 140W in the equatorial Pacific. Deep-Sea Research II 43:1227-1255. Waterhouse, T. and N. Welschmayer. 1995. Taxon-specific analysis of microzooplankton grazing rates and phytoplankton growth rates. Limnology and Oceanography 40: 827-834. Wolfe, L. and S. Wolfe. 1985. The ecology of the Suwannee River Estuary: An analysis of ecological data from the Suwannee River Water Management District Study of the Suwannee River estuary, 1982-1983. Florida Department of Environmental Regulation, Tallahassee, Florida.

PAGE 57

BIOGRAPHICAL SKETCH Christina E. Jett was born on November 2, 1975, in St. Petersburg, Florida, the daughter of Tom and Sally Jett. She was raised in Ft. Myers, Florida, with seven brothers and sisters, Monica, Karen, Kathleen, Michael, Steven, and Sarah. She then graduated from the University of Florida with a BS in wildlife ecology and conservation and a minor in zoology in May 1997. She worked for Dr. Phlips as a field technician for two and a half years before being offered an opportunity to pursue her masters. She then started her work on primary trophic interactions within the Suwannee River estuary at the University of Florida in the Fall of 2000. In May 2004, she will graduate with her Master of Science degree. Her future plans include getting married in May 2004 and pursuing a career in marine ecology. 46


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Title: Estimation of Microzooplankton Grazing in the Suwannee River Estuary, Florida, USA
Physical Description: Mixed Material
Copyright Date: 2008

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ESTIMATION OF MICROZOOPLANKTON GRAZING IN THE SUWANNEE RIVER
ESTUARY, FLORIDA, USA
















By

CHRISTINA JETT


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


2004

































Copyright 2004

by

Christina E. Jett

































To Jason, my love, and to my parents, Tom and Sally.















ACKNOWLEDGMENTS

I would like to thank my chair, Dr. Edward Phlips, for the opportunity to complete

my thesis under his guidance. His help and guidance have proved to be invaluable.

I also like to thank my committee members, Dr. Thomas Frazer and Dr. Thomas

Crisman, for their advice and input on everything from experimental design to the final

thesis.

I am also very grateful to Erin Bledsoe for her guidance, help, and unending

patience when answering my questions.

Thanks go to Mary Cichra and Susan Badylak for taxonomic identification.

Thanks go also to Carla Beals, Rob Burns, Karen Donnelly, Jessica Frost-Fajans, Katie

O'Donnell, and Becky Scwab for their time and effort with this project. I greatly

appreciate their assistance in the field and lab.

Funding for this project was provided by United States Department of Agriculture.

Lastly, I would like to thank my family and fiancee, Jason, for their love and

support. Their patience and reassurance provided me with the confidence and motivation

needed to complete this project.
















TABLE OF CONTENTS

page

A C K N O W L E D G M E N T S ................................................................................................. iv

LIST OF TABLES ....................................................... ............ .............. .. vii

LIST OF FIGURES .............. ................................. ............. ........... viii

A B STR A C T ................................................. ..................................... .. x

CHAPTER

1 INTRODUCTION ............... ................. ........... ................. ... .... 1

2 M ATERIALS AND M ETHOD S ........................................... ........... ............... 3

Study Site and Station D description .................................................................... .... .3
S am ple C collection ........... ..................................................................... ....... .. .. ...
G razing Experim ent........................................................................4
Phytoplankton and Zooplankton Analyses .........................................................6
N utrient A analyses ................. ........ .......................... ...... ........ .......... ...... .
Chlorophyll Analyses .................................. ............ ................7
Turbidity ............... ...... .................................... 7
G row th R ate and Loss Calculations ........................................ ........................ 8
Statistical A nalysis.................................................... 9

3 R E S U L T S .......................................................................................... 1 1

Field Parameters .............. ......... ........ ...... ...............11
C hem ical A naly sis.......... ................................................ .............. .......... ....... 12
M icrozooplankton G razing R ates.................................................... ... ................. 12
Phytoplankton Growth Rates .............. ......... .................... 13
Com munity Structure .................. ............................. .. ........ ................. 14

4 DISCUSSION ....................................................... ........... .............. 29

Com pariative Phytoplankton Loss....................... .... ............. ............... .... 29
Nutrient-rich versus Ambient Nutrient Phytoplankton Growth ..............................32

L IST O F R E FE R E N C E S ......... ................. ................. ................................................ 4 1









B IO G R A PH IC A L SK E TCH ...................................................................... ..................46















LIST OF TABLES


Table p

3-1 Seasonal means for surface temperature (C) for each station..............................15

3-2 Seasonal means for salinity (ppt) at each station. ............. ..................................... 16

3-3 Seasonal means for dissolved oxygen (mg L-1) each station. ................................17

3-3 Seasonal means for total nitrogen values (mg L1) ............... ........................19

3-4 Seasonal mean total phosphorous values (gg L1)............................ .................20

3-5 Seasonal mean turbidity readings (ntu). ........................................ ............... 21

3-6 Seasonal mean chlorophyll readings (gg L ). ................................................. 23

3-7 Grazing and growth coefficients (d-1) determined from the mesocosm
experim ents. ....................................................... ................. 24

3-8 Seasonal mean percent phytoplankton standing crop lost/day.............................26

3-9 Correlation of temperature to grazing coefficient, temperature to growth
coefficient and grazing coefficient to growth coefficient for each station...............26

3-10 The order of numerical dominance of the microzooplankton community
structure for eight m months. ............................................. .............................. 28

3-11 The order of numerical dominance of the phytoplankton community structure
for eight m months. ......................................................................28

3-12 The order of biovolumetric dominance (rim3) of the microzooplankton
community structure for eight m months. ........... ............................ ............... 28

4-1 Summary of percent phytoplankton standing stock removed per day for various
oceanic environm ents. ........................ ................ ............ ..... ........36

4-2 Comparison of the different parameters for the studies examined in the
discu ssion ...........................................................................36















LIST OF FIGURES


Figure page

2-1 Stations were monitored monthly and are located within the Suwannee Estuary.
Theses stations represent the different parts of the estuary.............................. 10

3-1 Surface temperature for B1, Cl, C4, and G1 within the Suwannee River estuary
for a period of 12 months starting in February 2002.................................... 15

3-2 Salinity of the four stations located throughout Suwannee Estuary.......................16

3-3 Dissolved oxygen for four stations throughout the Suwannee Estuary for a
period of one year, starting with February 2002. ............................................... 17

3-4 pH of the four stations sampled for a period of one year in 2002 and 2003............18

3-5 Total nitrogen readings for stations within the Suwannee Estuary for a period of
12 months. C4 was always significantly lower than all other stations....................19

3-6 Total phosphorous readings for stations within the Suwannee Estuary for a period
of 12 months. C4 was always significantly lower than all other stations. .............20

3-7 Turbidity readings collected within the Suwannee Estuary for a period of 12
m months, starting in February 2002....................................... ......................... 21

3-8 Initial chlorophyll levels (tg L1) for the four stations starting in February 2002
and ending in January 2003 ............................................... ........................... 22

3-9 Monthly instantaneous grazing coefficients of four sites within the Suwannee
estuary starting in February 2002 and ending in January 2003.............................25

3-10 Monthly instantaneous phytoplankton growth coefficients of four sites within the
Suwannee estuary starting in February 2002 and ending in January 2003..............25

3-11 Comparison of net phytoplankton growth in the 100% whole water mesocosms
with (gray bars) and without (black bars) nutrient additions. ................................27

4-1 A comparison of the doublings per day (open circle) and halvings per day (black
box) for each station for a period of one year, February 2002 to January 2003. .....37

4-2 A comparison of the net doublings per day for nutrient enriched (black diamond)
and non-enriched (grey box) mesocosms......... .......... ...... ................38









4-3 A comparison of estimated instantaneous growth rate for non-enriched
mesocosms (grey box) and instantaneous grazing rate (black triangle)...................39

4-4 An estimation of the location of the oyster reefs that run parallel to the shoreline
in the Suw annee River estuary ......................................................... ............... 40















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

ESTIMATION OF MICROZOOPLANKTON GRAZING IN THE SUWANNEE RIVER
ESTUARY, FLORIDA, USA

By

Christina Jett

May 2004

Chair: Edward Phlips
Major Department: Fisheries and Aquatic Science

An investigation of the ecological role of microzooplankton grazing was conducted

in the Suwannee River estuary, Florida, using a dilution technique. Four sites, three

inshore and one offshore station, were sampled every month from February 2002 to

January 2003 and brought back to the lab to conduct the experiment in temperature

controlled mesocosms. The instantaneous rate of phytoplankton mortality ranged from

-0.0003d-1 to 2.04d1, corresponding to a 0 to 87% loss of phytoplankton standing crop

per day. Significant seasonal differences occurred in all stations except for the offshore

station. Instantaneous growth rates of phytoplankton ranged from -0.15d- to 3.2d1,

which is equivalent to -0.02 to 4.6 doublings per day. The microzooplankton community

did not show any major spatial or temporal patterns and was mostly dominated by

aloricate and loricate ciliates. Phytoplankton were numerically dominated by

picoplankton, with secondary dominance alternating between centric diatom chains,

centric and pennate diatoms, and cryptophytes. These results of the experiments suggest









that microzooplankton are important as consumers of phytoplankton production in the

Suwannee River estuary.














CHAPTER 1
INTRODUCTION

Increasing human populations along the west coast of Florida have heightened

concerns about elevated levels of nutrients in its estuaries (Bledsoe and Phlips in review,,

South West Florida Water Management District (SWFWMD) 1994). Elevated nutrients

can lead to increased levels of primary productivity and algal standing crops, but can also

result in deleterious impacts on ecosystem integrity, such as toxic or nuisance algae

blooms, periods of hypoxia (Department of Interior (DOI) 1990), changes in plankton

community structure (Paerl 1988), and alterations of benthic communities (Valiela 1995).

Many of these are associated with high algal standing crops or algal blooms (Richardson

and Jorgensen 1996). The potentially negative impacts of algae blooms have increased

interest in the factors controlling algal standing crops. Phytoplankton standing crop is

dictated by gain (i.e., growth and biomass import) and loss functions (death, grazing,

export, and sedimentation). Although all loss terms are potentially important, grazing by

zooplankton and its link to primary productivity is often overlooked.

The link between zooplankton and phytoplankton is critical to the flow of carbon

from plankton to consumers (James and Hall 1998, Landry and Hassett 1982) and

determining the zooplankton grazing rate is critical to understanding predator populations

regulate prey populations, also known as top down control (Carrick et al. 1991).

Conversely, prey availability regulates zooplankton population densities (Cyr and Pace

1992). These two elements play an important role in dictating the distribution and

dynamics of carbon in estuaries.






2


This study examines the importance of zooplankton grazing to phytoplankton

dynamics in the Suwannee River estuary. The working hypothesis is that zooplankton

grazing within the Suwannee River estuary is important in regulating phytoplankton

standing crops. This role is judged as a comparison of the relative magnitude of algal

growth and grazing rates in distinct regions of the Suwannee River estuary. The results

are discussed in relation to key environmental factors that influence phytoplankton

growth and grazing, including temperature, nutrients, and community composition.














CHAPTER 2
MATERIALS AND METHODS

Study Site and Station Description

The Suwannee River system is located on the west coast of Florida in the "Big

Bend" area. The Suwannee River originates in the Okeefenokee Swamp, Georgia, the

second largest swamp in the United States (Bledsoe and Phlips 2000) and winds through

northern Florida before emptying into the Gulf of Mexico near the town of Suwannee.

Approximately 394km long, this black water river drains 28,500km2 of northern Florida

and southern Georgia (Wolfe and Wolfe 1985, Bledsoe and Phlips 2000). It is

characterized by nutrient rich waters, which are supplemented by numerous springs along

the lower reaches of the river system (Bledsoe and Phlips 2000, Department of

Enivronmental Protection (DEP) 1985).

Four stations were picked as representatives of distinct regions within the estuary

(Figure 2-1). B1 is near the mouth of the river in front of an oyster reef. A shallow

station, it is exposed to tides and has periodic flushing from the river at low tides. Cl is

located within Suwannee Sound and is isolated from the Gulf by two parallel oyster reefs

that allow only partial inflow of seawater. This station is regularly inundated by the

Suwannee River and runoff from the surrounding wetlands. C4 is a more marine

environment with the least influence from the river. The last station, G1, is located by an

area used for clam aquaculture and is the southern-most station. Also a shallow station, it

receives some tidal influence and freshwater flushing from the river and runoff.









Sample Collection

Water samples were collected from the four stations within the Suwannee Estuary,

monthly for one year. Water was taken using an integrating sampling tube that collected

water from the surface to within 0. Im of the bottom. The top three meters were sampled

when water depth exceeded that of the sampling tube. The latter approach was only

employed at station C4, where depth was typically greater than 3.0 m. Water from a

minimum of 5 pulls was combined in a tub, mixed, and sub-samples were taken for TN,

TP, and turbidity analysis. An additional 20L were collected for subsequent grazing

experiments. Dissolved oxygen (mg L-l), temperature (C), pH, salinity (ppt), Secchi

(m), and specific conductivity (mS/cm) were measured using a Hydrolab Quanta at both

0.5m below the surface and 0.5m above the bottom.

Grazing Experiment

Grazing experiments in mesocosms is commonly used to estimate zooplankton

grazing rates. In this study, grazing rates were determined in laboratory mesocosms

using the serial dilution method developed by Landry and Hassett (1982). This method is

based on four assumptions; (1) phytoplankton growth is not density dependent, (2) the

probability of being consumed is directly related to the encounter rate with predators

(consumption rates are linear), (3) phytoplankton are in exponential growth and (4)

phytoplankton growth is not limited by nutrient availability. To correct for occasional

non-linearity of grazing kinetics, the three-point method (Gallegos 1989) was applied to

the data in question. This method extrapolates grazing to whole water from the two

smallest dilutions in the experiment, and then re-calculates the grazing rate for the station

Whole water collected in the field was filtered through 1.085mm mesh to remove

large gelatinous zooplankton, e.g., jellyfish. Although this allowed grazers into the









experiment that are not in the standard size range for microzooplankton (20-200im), it

also allowed the passage of large chain-forming diatoms that are often found within the

system. Further microscopic analysis of samples revealed that the dominant grazers on

the phytoplankton fell within the standard size range category; we therefore consider this

experiment an estimation of microzooplankton grazing.

Dilutions were made using station water taken through a step filtration system

composed of 10tm, 5[tm, ltm, and 0.2[tm and were run in duplicate at 100, 75, 50, 40,

and 30 percent whole water. Each treatment flask was spiked with nitrogen,

phosphorous, and silica (400[tgNl1- + 40[tg P1-1 + 400[tg Si 1-1) to ensure nutrient

availability for phytoplankton growth (Schluter 1998). An additional 100% whole water

duplicate was not spiked to compare growth rates and determine nutrient limitation over a

24hr period. Flasks (2L) were placed in a temperature-controlled mesocosms at the same

temperatures measured in the field and 120tEin m-2/sec-1 of fluorescent light. Flasks

were continually stirred slowly to maintain circulation. Net change in algal biomass was

estimated from net change of in vivo fluorescence (IVF) of chlorophyll a using a Turner

Designs Model 10 fluorometer with a 1-cm path length.

At the beginning and end of incubation, contents of the two flasks were combined

and sub-samples for each parameter collected. Chlorophyll a was collected in duplicate

by filtering 500ml of the flask contents onto Gelman A/E glass fiber and then frozen until

analysis (Sartory and Grobbelaar 1984). For picoplankton estimates, 1-5ml of station

water were filtered through 0.2um pore Nuclepore filters, and filters were then mounted

between microscope slides and cover slips with immersion oil. These slides were stored,

frozen and counted within 1 week to minimize fading of fluorescence (Sartory and









Grobbelaar 1984). Zooplankton was collected by filtering 1000ml through a 41 m Nitex

mesh, then rinsing and preserving the samples with Lugols. Phytoplankton was collected

by preserving sub-samples (to=1000ml, t24=100ml) with Lugols.

Phytoplankton and Zooplankton Analyses

Phytoplankton composition was determined using the Utermohl method (Utermohl

1958). Lugols-preserved samples were concentrated by settling in cylindrical counting

chambers for 4 h per ml sample for phytoplankton and 30min/ml for zooplankton.

Phytoplankton cells were identified and counted at 400x and 100x with a Leica phase

contrast inverted microscope. At 400x, counts were terminated after reaching 100 cells of

the most dominant taxon, but a minimum of 30 ocular micrometer grids were counted.

Large celled taxa (>30um) were enumerated by a complete count of the settling chamber

at 100x.

Cell biovolumes were estimated by assigning geometric shapes to fit the

characteristics of individual taxa (Smayda 1978). Specific phytoplankton dimensions

were measured for at least 30 randomly selected cells. The volume was calculated for

each cell, from which mean cell volume was derived. Cell counts were transformed to

biovolume using the mean cell volume. Total biovolume per sample was the sum of

estimated cell volumes for each species.

Zooplankton were identified and enumerated from Lugols preserved samples.

Concentrated samples were settled in counting chambers and enumerated at 100x with a

Leica phase contrast inverted microscope. Counts were terminated after reaching 100

counts of the single most dominant taxon (Utermohl 1958).

Picoplanktonic cyanobacteria and green algae were enumerated with fluorescence

microscopy using filtered samples of unpreserved water (Fahnenstiel and Carrick, 1992).









Samples were counted with a Nikon microscope equipped with autofluorescence,

including both green and blue light excitation. Numerical abundances of cells were

determined by counting at least five ocular micrometer grids at 1000x. Representative

samples of each cell type were measured for subsequent calculation of cellular

biovolume. Counts were considered complete after reaching a minimum of 100 cells of

one taxon. At least five grids were counted when cell concentration was high.

Nutrient Analyses

Total nitrogen was determined from frozen whole water samples using the

persulfate digestion method (American Public Health Association (APHA) 1989) and

analyzed with a Technicon AutoAnalyzer. Total phosphorous was also determined from

frozen whole water samples using the persulfate digestion method (APHA 1989) and

analyzed with a Hitachi U2000 dual beam spectrophotometer.

Chlorophyll Analyses

Chlorophyll a was determined from samples (500 ml) filtered onto Gelman A/E

glass-fiber filters and then frozen. Filters were placed into test tubes with 8.0 ml of 95%

ethanol and heated in a water bath for 5 min at 780C (Sartory and Grobbelaar 1984).

After passive extraction (24 h), filters were removed and samples centrifuged to exclude

particulate debris. Chlorophyll a concentrations were determined with a Hitachi U2000

dual beam spectrophotometer and corrected for phaeophytin using the acidification

method (APHA 1989).

Turbidity

Turbidity was determined by a LaMotte 2020 Turbidimeter calibrated in a range of

0 1100 NTU.









Growth Rate and Loss Calculations

By tracking incubations of different dilutions of seawater, instantaneous rates of

phytoplankton growth and mortality can be established. To determine change, the

following equation is used:

Pt = Poe(k-g)t (1)

Where Pt is the phytoplankton biomass at the end of the experiment, Po the initial

concentration of phytoplankton biomass, t is the length of incubation (days), and the

instantaneous coefficients of phytoplankton growth and mortality are designated by k and

g, respectively. Phytoplankton biomass is estimated by chlorophyll at the beginning and

end of each experiment.

The regression of the results for all of the dilutions will provide a linear equation in

which the y-axis intercept is phytoplankton growth rate (k), and the negative slope of the

relationship is the grazing coefficient (g). A minimum of two dilutions will yield two

equations with two unknowns which can be solved for g and k. The linear regression

will, however, provide estimates of confidence limits for the coefficients (Landry and

Hassett 1982).

With the coefficient for phytoplankton mortality due to grazing (g), the percent of

phytoplankton standing crop removed per day (S) can be calculated as

S= (1 e ())* 100 (3)

where g is the instantaneous grazing coefficient calculated from Eq. 1.

In situations where saturated feeding responses were observed, an adjusted grazing

rate (K) has been calculated using a three-point method (Gallegos 1989).

K = (X2rx, Xirx,2)/(X2 X) (4)









Where X1 and X2 are the lowest fraction of unfiltered seawater within the

experiment(e.g. X2 = 0.30 and X1 = 0.40) and corresponding r (ln(Chl T24/ Chl TO). K is

then used to determine g in equation 7. First, the change in the number of

microzooplankton must be determined:

Z = In(zoo# T24/ZOO# TO) (5)

Where zoo# is the number of microzooplankton counted using light microscopy at

times Oh and 24h. Z, determined from equation 5, is then used with K, to calculate a new

grazing coefficient (g):

g = (Chl T24/ Chl TO- expK) [(Z K) / (expz expK)] (7)

Statistical Analysis

SAS and Minitab were used to carry out statistical analysis such as ANOVA and

Tukey's multiple comparisons procedure. The latter was used to determine differences

between means for stations and seasons. Seasons were designated as winter (January,

February, and December), spring (March, April, May), summer (June, July, August), and

fall (September, October, and November). A p-value of 0.01 was used as a measure of

significance due to low sample size. Pearson's Correlation tests were used to determine

correlation between parameters.














2Sn2O 29n2O
Suwannee River





B1
C1 S




C4

291 o0 G1 2G 9 o
Gulf of Mexico

0 9
Kilometers

8310 83'10



Figure 2-1. Stations were monitored monthly and are located within the Suwannee
Estuary. Theses stations represent the different parts of the estuary.














CHAPTER 3
RESULTS

Field Parameters

Surface temperature ranged from 110C to 310C and did not vary significantly

between stations during any sampling period (Figure 3-1). There were, however,

significant seasonal differences in temperature at all sites (Table 3-1), with average

winter temperature (11 and 150C) lower than mean values during all other seasons

(>20C).

Salinity ranged from 5 to 34 ppt (Figure 3-2). Among sites, no significant seasonal

differences in salinity were observed. There were, however, significant differences in

salinity between sites within seasons (Table 3-2). Cl, nearest to the river mouth had the

lowest mean salinities, while C4, the most offshore site, had the highest mean salinities

(Table 3-2).

Dissolved oxygen concentrations were consistently 4.9mg L-1 or higher (Figure 3-

3). They tended to be lower in summer, especially June and July, and tended to be higher

in early spring and late winter, mainly in January and March (Figure 3-3). Salinity at Cl

was marginally different (p = 0.07) between summer and fall. pH values fell within a

very narrow range (7.6 and 8.4) and did not show any apparent spatial or temporal pattern

(Figure 3-4).









Chemical Analysis

Total nitrogen concentrations ranged from 0.180 to 0.897 mg L-1 (Figure 3-5).

There were no obvious seasonal patterns in the data, although C4 was consistently lower

in TN than all other sites (Table 3-3).

Total phosphorous concentrations ranged from 0.002 to 0.200 tg/L (Figure 3-6).

No seasonal differences were observed at any sites, but there were significant differences

in TP within seasons among sites (Table 3-4). C4 was consistently in lower TP levels

than all other stations.

Turbidity readings were between 0.15 and 24.0 ntu (Figure 3-7). The lowest

readings were consistently observed at station C4, but no significant seasonal or station

differences were found (Table 3-5).

Chlorophyll a concentrations ranged from 1.2 to 64.4[ig L-1 (Figure 3-8). Station

C4 exhibited consistently low levels of chlorophyll a, although the mean value was only

significantly different from other stations in summer. For the near-shore stations,

summer and winter was always significantly different (Table 3-6).

Microzooplankton Grazing Rates

The instantaneous rate of phytoplankton mortality (grazing coefficient) ranged

from -0.0003d-1 to 2.04d-1 (Table 3-7). Percent phytoplankton standing crop lost per day

ranged from 0 to 87% (Table 3-7). The lowest grazing coefficient was in June at station

C4, while the highest was at C4 during March. Station C4 also had the highest grazing

coefficient in March and November, but was consistently lower than all other stations for

the remainder of the study (Figure 3-9). B1, Cl, and G1, all had a sharp decrease in

grazing during the month of November but C4 was relatively unchanged (Figure 3-9).









There was seasonal variation in percent phytoplankton standing crop lost per day

for all stations except C4 (Table 3-8). Cl and B showed a significant difference

between summer and winter (p = 0.001), while G1 showed a significant difference

between spring and summer (p = 0.005). On an annual average, G1 and C4 were

significantly different from each other (p = 0.02) though not significantly different from

the other stations; B and Cl were not significantly different from each other (Table 3-8).

Phytoplankton Growth Rates

Growth coefficients for phytoplankton ranged from -0.15d-1 to 3.2d-1 (Table 3-7),

which corresponded to -0.02 to 4.6 doublings per day. The lowest growth coefficient was

at station C1 in winter, while the highest was at B1 during summer. B1 and Cl showed

little variation from each other and displayed the same pattern with higher phytoplankton

growth rates occurring in the summer months and lower rates occurring in winter. G1

showed relatively higher growth rates throughout the year, however displayed a sharp

decrease in July. C4 also had a sharp decrease in July though it showed no kind of

seasonal trend with higher rates occurring in winter (Figure 3-10).

There was a strong, positive correlation between growth and grazing coefficients

for all stations except G1 (Table 3-9). Grazing and growth coefficients (Table 3-9) were

positively and significantly correlated with temperature at stations B1 and C1, i.e. the two

stations with the most influence from the river.

Phytoplankton doublings per day in both nutrient addition and control mesocosms

were compared for control and nutrient-added treatment groups (Figure 3-11). In all but

one experiment, growth in the nutrient addition groups was greater than the control. G1

showed a strong nutrient limitation response for all months from March to October 2002.









Community Structure

The microscopic analyses of selected sampling sites showed a relatively stable

dominance of small microzooplankton (<10 pm), e.g. copepod nauplii and ciliates and

small sized phytoplankton, e.g. picoplankton and cryptophytes. The numerically

dominant zooplankton shifted among aloricate ciliates, loricate ciliates, and copepod

nauplii (Table 3-10); while the dominant phytoplankton were picoplankton.

Cryptophytes, centric, and pinnate diatoms were the major constituents of the

phytoplankton community (Table 3-11). No pattern was discernable from the dominant

phyto- and microzooplankton in either numeric or biovolumetric dominance, although the

potential importance of copepod nauplii increased in the biovolumetric comparison

(Table 3-12).











Surface Temperature


35
30
25
20
15
10
5
0


- B1
---- C1
-- C4
-- G1


F M A M J J A S O N D J
Month


Figure 3-1. Surface temperature for B1, Cl, C4, and G1 within the Suwannee River
estuary for a period of 12 months starting in February 2002.



Table 3-1. Seasonal means for surface temperature (oC) for each station. Seasons were
described as: December, January, February for winter, March, April, and May
for spring, June, July, August, for summer and September, October,
November for fall. Values in bold are the means and values in parenthesis are
the standard deviation. Capital letters designated differences between seasons
within each station; lower case letters designate differences between stations
within each season and capital letters in bold designate total average for each
season.
Season


Station Winter
A
B1 11.7
(0.84)


Overall
Seasonal
Average


A
11.9
(3.27)

A
13.6
(1.17)

A
14.1
(7.07)

A
12.84
(1.85)


Spring
B
a 21.8
(0.74)


Summer
B
28.7
(2.05)


B
22.2
(3.75)

B
24.1
(2.12)

B
26.4
(7.79)

B
23.63
(3.25)


B
29.4
(3.28)

B
28.4
(1.17)

B
28.7
(6.40)

B
28.79
(1.55)


Fall
B
a 22.9
(2.55)

B
a 23.0
(1.66)

B
a 22.9
(2.27)

B
a 23.9
(6.68)


Annual


a 21.1
(7.39)


a 21.5
(7.67)


a 22.3
(6.49)


a 23.2
(6.65)


B
24.35
(6.07)











Salinity

40
35




25 -----------------------
30
25 B 1
20
15 G1
10
5

F M A M J J A S N D J
Month

Figure 3-2. Salinity of the four stations located throughout Suwannee Estuary.

Table 3-2. Seasonal means for salinity (ppt) at each station. Seasons were described as:
December, January, February for winter, March, April, and May for spring,
June, July, August, for summer and September, October, November for fall.
Values in bold are the means and values in parenthesis are the standard
deviation. Capital letters designated differences between seasons within each
station; lower case letters designate differences between stations within each
season and capital letters in bold designate total average for each season.
Seasons
Stations Winter Spring Summer Fall Annual
A A A A
B1 18.44 a b 17.34 b 22.87 a b 23.45 bc 20.26 b c
(11.58) (6.93) (5.57) (1.88) (7.11)

A A A A
C1 13.29 b 18.65 b 16.93 b 19.46 c 16.87 c
(6.19) (2.13) (6.24) (0.25) (4.74)

A A A A
C4 31.22 a 31.51 a 32.82 a 30.69 a 31.56 a
(2.17) (1.03) (0.47) (3.49) (1.99)

A A A A
G1 23.60 a 24.40 a b 29.60 a 25.15 a b 25.69 b
(1.93) (6.41) (2.72) (2.17) (4.03)

Overall A A A A
Seasonal 23.60 24.40 29.60 25.15
Average (1.93) (6.41) (2.72) (2.17)










Dissolved Oxygen


-- B1

-C4
-B-G1


F M A M J J A S O N D J
Month
Figure 3-3. Dissolved oxygen for four stations throughout the Suwannee Estuary for a
period of one year, starting with February 2002.


Table 3-3. Seasonal means for dissolved oxygen (mg L-1) each station. Seasons were
described as: December, January, February for winter, March, April, and May
for spring, June, July, August, for summer and September, October,
November for fall. Values in bold are the means and values in parenthesis are
the standard deviation. Capital letters designated differences between seasons
within each station; lower case letters designate differences between stations
within each season and capital letters in bold designate total average for each
season.
Stations


Stations Winter
A
B1 8.38
(0.57)

A
C1 8.50
(0.74)

A
C4 7.96
(0.31)

A
G1 8.45
(0.79)


Overall
Seasonal
Average


A
8.32
(0.58)


Spring
A B
6.78
(0.71)

A
6.81
(1.28)

A B
7.03
(1.38)

A
8.74
(2.32)

A
7.34
(1.56)


Summer
B
5.62
(0.51)


A
6.11
(0.37)

B
5.29
(0.54)

A
6.20
(0.61)

B
5.80
(0.59)


Annual


B
6.80
(1.41)

A
7.51
(1.36)

A
6.97
(0.89)

A
7.83
(1.15)

A
7.30
(1.04)


a 6.90
(1.25)



a 7.21
(1.26)



a 6.81
(1.26)



a 7.81
(1.57)





























F M A M J


-o- B1
-- C1
-- C4
--- G1


J A S 0 N D J


Month


Figure 3-4. pH of the four stations sampled for a period of one year in 2002 and 2003.


- j I ~o







19



Total Nitrogen for Suw 2002

1.00
0.90
0.80
0. 70- B1
060 / \ -C
J 0.50 -- C4
040 G- 1G
0.30
0.20 -
0.10
0.00
F M A M J J A S O N D J
Month



Figure 3-5. Total nitrogen readings for stations within the Suwannee Estuary for a period
of 12 months. C4 was always significantly lower than all other stations.




Table 3-3. Seasonal means for total nitrogen values (mg L-1). Seasons were described
as: December, January, February for winter, March, April, and May for
spring, June, July, August, for summer and September, October, November
for fall. Values in bold are the means and values in parenthesis are the
standard deviation. Capital letters designated differences between seasons
within each station; lower case letters designate differences between stations
within each season and capital letters in bold designate total average for each
season.
Season
Station Winter Spring Summer Fall Annual
A A A A
B1 0.5863 a 0.5873 a 0.5943 a 0.6867 a 0.6137 a
(0.18) (0.19) (0.16) (0.04) (0.14)

A A A A
C1 0.6434 a 0.5301 a 0.6510 a 0.6035 a 0.6070 a
(0.17) (0.19) (0.16) (0.04) (0.12)

A A A A
C4 0.2484 b 0.2089 b 0.2457 b 0.2536 b 0.2392 b
(0.06) (0.03) (0.03) (0.06) (0.04)

A A A A
G1 0.4495 a 0.4772 a 0.6363 a 0.6226 a 0.5464 a
(0.11) (0.19) (0.12) (0.24) (0.17)

Overall A A A A
Seasonal 0.0603 0.0767 0.0758 0.0703
Average (0.05) (0.07) (0.04) (0.05)










Total Phosphorous for Suw 2002


0.25

0.20

0.15

0.10

0.05

0.00


-- B1
C C1
-- C4
-- G1


F M A M J J A SO N D J
Month

Figure 3-6. Total phosphorous readings for stations within the Suwannee Estuary for a
period of 12 months. C4 was always significantly lower than all other
stations.


Table 3-4. Seasonal mean total phosphorous values (.g L1). Seasons were described as:
December, January, February for winter, March, April, and May for spring,
June, July, August, for summer and September, October, November for fall.
Values in bold are the means and values in parenthesis are the standard
deviation. Capital letters designated differences between seasons within each
station; lower case letters designate differences between stations within each
season and capital letters in bold designate total average for each season.
Season


Station Winter
A
B1 0.096
(0.06)


Overall
Seasonal
Average


A
0.086
(0.03)

A
0.011
(0.01)

A
0.049
(0.03)

A
0.482
(0.20)


Spring
A
a 0.137
(0.07)


a b


Summer
A
0.104
(0.02)


A
0.126
(0.07)


A
0.096
(0.02)

A
0.020
(0.01)


A
b 0.007
(0.00)


a b


A
0.037
(0.03)

A
0.451
(0.20)


A
b 0.083
(0.04)

A
0.532
(0.20)


Fall
A
a 0.098
(0.04)

A
a 0.099
(0.04)

A
b 0.018
(0.01)

A
a 0.065
(0.02)


Annual


a 0.109
(0.05)


a 0.102
(0.04)


b 0.014
(0.01)


a b 0.059
(0.03)


A
0.542
(0.21)











Suw Turbidity 2002


30
25
20

* 15

10
5

0


S -- -
J A S 0
Month


Figure 3-7. Turbidity readings collected within the Suwannee Estuary for a period of 12
months, starting in February 2002.


Table 3-5. Seasonal mean turbidity readings (ntu). Seasons were described as:
December, January, February for winter, March, April, and May for spring,
June, July, August, for summer and September, October, November for fall.
Values in bold are the means and values in parenthesis are the standard
deviation. Capital letters designated differences between seasons within each
station; lower case letters designate differences between stations within each
season and capital letters in bold designate total average for each season.
Season


Station Winter
A
B1 10.85
(6.88)


Overall
Seasonal
Average


A
5.55
(2.44)

A
1.07
(0.29)

A
4.71
(2.30)

A
5.54
(4.90)


Spring
A
9.24
(9.60)

A
9.18
(8.43)

A
2.11
(2.30)

A
4.97
(1.39)

A
6.37
(6.39)


Summer
A
3.32
(0.62)

A
3.86
(0.77)

A
1.27
(0.69)


5.45
(4.28)

A
3.48
(2.46)


A
a 14.59
(9.78)

A
a 14.18
(13.89)

A
b 1.09
(1.47)


ab


3.51
(2.00)

A
7.13
(8.56)


F M A M J


-- B1
-- C1
--- C4
--- G1


N D J


Annual

9.04
(7.38)


7.65
(7.05)


1.38
(1.29)


4.66
(2.44)


ab


ab


ab












Chlorophyll values 2002


-- B1
--C1
-- C4
-E- G1


F M A M J


J A S 0 N D J
Month


Figure 3-8. Initial chlorophyll levels (tg L1) for the four stations starting in February
2002 and ending in January 2003.










Table 3-6. Seasonal mean chlorophyll readings ([g L-'). Seasons were described as:
December, January, February for winter, March, April, and May for spring,
June, July, August, for summer and September, October, November for fall.
Values in bold are the means and values in parenthesis are the standard
deviation. Capital letters designated differences between seasons within each
station; lower case letters designate differences between stations within each
season and capital letters in bold designate total average for each season.
Season


Stations Winter
B
B1 9.03
(4.13)


Overall
Seasonal
Average


C
5.56
(2.44)

AB
2.59
(1.79)

B
7.93
(4.36)

A
21.31
(15.81)


Spring
A B
a 17.85
(4.29)


a b


a b


B
19.70
(9.00)

B
1.11
(0.17)

AB
26.35
(21.26)

A
23.27
(18.13)


Summer
A
27.23
(7.61)


A
36.14
(3.80)

AB
2.41
(0.87)


a b


Fall
A B
a 36.03
(35.84)

ABC
a 35.90
(35.91)


A
4.10
(1.50)


28.20 a 31.66
(9.38) (18.42)


B
2.68
(1.49)


Annual

a 21.31
(15.81)


23.27
(18.13)


2.68
(1.49)


a 23.53
(15.21)


A
23.53
(15.21)











Table 3-7. Grazing and growth coefficients (d-1) determined from the mesocosm
experiments.


February B1
C1
C4
G1
March B1
C1
C4
G1
April B1
C1
C4
G1
May B1
C1
C4
G1
June B1
C1
C4
G1
July B1
C1
C4
G1
August B1
C1
C4
G1
Sept B1
C1
C4
G1
October B1
C1
C4
G1
November B1
C1
C4
G1
December B1
C1
C4
G1
January B1
C1
C4
G1


Microzooplankton
Grazing Coeff.
0.42
0.15
0.33
0.44
0.66
0.99
2.0
1.1
0.51
0.70
No data
1.1
0.61
0.84
0.25
1.1
1.5
0.84
0.17
0.88
1.3
1.2
0.21
0.77
1.0
1.3
0.04
0.89
No data
No data
0.73
1.2
1.2
1.2
0.19
0.99
0.00
0.07
0.46
0.15
0.35
0.18
0.02
0.69
0.23
0.28
0.38
1.4


Phytoplankton
Growth Coeff.
0.24
-0.15
1.6
2.5
1.4
1.9
2.4
2.2
2.7
2.0
No data
2.0
1.8
2.6
1.5
2.4
3.2
1.9
0.76
2.2
2.3
2.5
0.23
0.90
2.1
2.3
1.1
1.8
No data
No data
2.0
1.6
2.2
2.1
0.73
1.2
1.1
1.1
1.8
1.6
0.88
0.62
0.82
1.8
0.43
1.1
1.1
2.8


%Phytoplankton
Standing crop/Loss Day
34
14
28
36
49
63
87
66
40
50
No data
67
46
57
22
67
77
57
16
59
73
69
19
54
64
73
4
59
No data
No data
52
69
70
70
17
63
0
7
37
14
29
16
2
50
21
25
32
76












Grazing Coefficient


-- B1
-- C1
-A-C4
--G1


F M A M J


J A S O N D J

Month


Figure 3-9. Monthly instantaneous grazing coefficients of four sites within the Suwannee
estuary starting in February 2002 and ending in January 2003.





Growth Coefficients


F M A


M J J A S


O N D J


Month


Figure 3-10. Monthly instantaneous phytoplankton growth coefficients of four sites
within the Suwannee estuary starting in February 2002 and ending in January
2003.


3
2.5
2
1.5
1
0.5
0
-0.5


- B1
- C14
-- C4
--G1


-A


J










Table 3-8. Seasonal mean percent phytoplankton standing crop lost/day. Seasons were
described as: December, January, February for winter, March, April, and May
for spring, June, July, August, for summer and September, October,
November for fall. Values in bold are the means and values in parenthesis are
the standard deviation. Capital letters designated differences between seasons
within each station; lower case letters designate differences between stations
within each season and capital letters in bold designate total average for each
season.


Season


Station Winter
C
B1 28
(6.97)


Overall
Seasonal
Average


B
18
(5.60)

A
21
(16.35)

A B
54
(20.67)

A
30
(18.92)


Spring
B
a b 45
(4.20)


b




a b




a


A
57
(6.29)

A
54
(46.11)

A
67
(0.66)

B
56
(17.25)


a b




a b




a


Summer
A
71
(6.44)

A
66
(8.33)

A
13
(7.69)

B
57
(2.89)

B
52
(24.83)


A B
b 49
(30.16)


Table 3-9. Correlation of temperature to grazing coefficient, temperature to growth
coefficient and grazing coefficient to growth coefficient for each station.
Numbers in bold are the p-value and the values on the bottom are the
correlation number.


Station
B1 C1


C4 G1


Annual


a




a b




c


Fall
ABC
35
(49.63)

A B
38
(44.52)

A
35
(17.48)


a 46
(24.15)



a 45
(24.96)



a 29
(24.09)



a 57
(17.07)


a b




a b




b




a


A B
40
(28.37)


Correlation


Temperature and Grazing <.010 <.010 0.8000 0.4000
0.83 0.83 -0.09 0.27

Temperature and Growth <0.01 <.010 0.6100 0.1600
0.92 0.87 -0.17 -0.43

Grazing and Growth <.010 <.010 <.010 0.3600
0.76 0.86 0.76 0.29












Station B1


F M A M J J A S O N D



Station C1


JI]Ph ,ire


F M A M J J A S


N D J


5
4
3
- 2


0
-1


Station C4











F M A M J J A S N D


Station G1


4
3
0 2

0


-1
-2
F M A M J J A S O N D J

Figure 3-11. Comparison of net phytoplankton growth in the 100% whole water
mesocosms with (gray bars) and without (black bars) nutrient additions. In all
but one (March B1) experiment, growth with nutrient addition surpassed
growth in the control.


- 2


0
-1


5
4

3 2


0
-1










Table 3-10. The order of numerical dominance of the microzooplankton community
structure for eight months. Stations are presented from lowest to highest
grazing rate.


Dominant
Microzooplankton
Aloricate Ciliates (39indv/ml)
Aloricate Ciliates (9 ind/ml)
Aloricate Ciliates (67 ind/ml)
Aloricate Ciliates (27ind/ml)
Aloricate/Loricate (1 ind/ml)
Loricate ciliates (2.4ind/ml)
Rotifer (0.27ind/ml)
Aloricate ciliates (149ind/ml)
Cope Nauplii (0.17 ind/ml)


Secondary Dominant
Microzooplankton
Loricate Ciliates (1 ind/ml)
Cope Nauplii (0.20ind/ml)
Loricate Ciliates (9.4ind/ml)
Loricate Ciliates (2.5ind/ml)
Cope Nauplii (0.19 ind/ml)
Cope Nauplii (0.84ind/ml)
Cope Nauplii (0.07 ind/ml)
Loricate Ciliates (4 ind/ml)
Loricate Ciliates (0.6 ind/ml)


Table 3-11. The order of numerical dominance of the phytoplankton community
structure for eight months. Stations are presented from lowest to highest
grazing rate.


Station
B1
C4
C1
C1
G1
C1
G1
B1
C4


Dominant
Phytoplankton
Picoplankton (188409 cells/ml)
Picoplankton (825330 cells/ml)
Picoplankton (109210 cells/ml)
Picoplankton (63359 cells/ml)
Picoplankton (104327 cells/ml)
Picoplankton (1570628 cells/ml)
Picoplankton (45018 cells/ml)
Picoplankton (445178 cells/ml)
Picoplankton (78603 cells/ml)


Secondary Dominant
Microzooplankton
Cryptophytes (2358 cells/ml)
Dactyliosolen chains (883 cells/ml)
Cryptophytes (1935 cells/ml)
Pennate Diatoms (851 cells/ml)
Cryptophytes (1428 cells/ml)
Centric Diatoms (3628 cells/ml)
Skeletonema chains (2031 cells/ml)
Cryptophytes (3224 cells/ml)
Leptocylindricus chains (34593 cells/ml)


Table 3-12. The order of biovolumetric dominance (um3) of the microzooplankton
community structure for eight months. Stations are presented from lowest to
highest grazing rate.


Dominant Species
Aloricate Ciliates(39396.52)
Loricate Ciliates(22884.3)
Aloricate Ciliates(53443.6)
Aloricate Ciliates(43293)
Copepod Nauplii (1370)
Copepod Nauplii (8713)
Rotifer (5054)
Loricate Ciliates(70164)
Copepod Nauplii (629)


Secondary Dominant
Species
Copepod Nauplii (6241)
Copepod Nauplii (465)
Loricate Ciliates(18087.48)
Loricate Ciliates(10760)
Loricate Ciliates(244.35)
Loricate Ciliates(1382.16)
Copepod Nauplii (825.25)
Aloricate Ciliates(36194)
Loricate Ciliates(256)


Month
Nov
Aug
Nov
Feb
Nov
Aug
Jan
June
March


Station
B1
C4
C1
C1
G1
C1
G1
B1
C4


Month
Nov
Aug
Nov
Feb
Nov
Aug
Jan
June
March


Month
Nov
Aug
Nov
Feb
Nov
Aug
Jan
June
March


Station
B1
C4
C1
C1
G1
C1
G1
B1
C4














CHAPTER 4
DISCUSSION

The goal of this study was to determine the potential impact of microzooplankton

grazing on phytoplankton dynamics in the Suwannee River estuary. The results

demonstrate that the microzoplankton grazing rates in the Suwannee River estuary are

significant. There are several different observations that led to this general conclusion,

including

1. Comparisons of phytoplankton loss rates for this study with those observed in
estuaries within the Gulf of Mexico and globally.

2. Comparisons of phytoplankton growth for nutrient-rich versus ambient nutrient
mesocosms.


Compariative Phytoplankton Loss

Significance of grazing in the Suwannee River estuary can be obtained by

comparing grazing estimates from other regions of the world. The grazing losses

observed in this study ranged from 0 to 87% loss of phytoplankton standing crop per day,

with seasonal averages from 13 to 71% among the four sampling sites. These numbers

are not unlike other estimates for coastal and oceanic waters through out the world (Table

4-1). Strom and Strom (1996) observed that grazing rates in the Mississippi River delta

resulted in a 26 90% loss of phytoplankton standing crop during October 1992 and May

1993. In this study grazing by microzooplankton resulted in a 17 70% loss of

phytoplankton standing crop for corresponding months in the Suwannee River estuary.

Several other similarities between the Mississippi delta and Suwannee River









estuary are noteworthy. Although there were some differences in microzooplankto

community structure between the two systems, ciliates were often dominant in both

system. In addition, higher grazing rates were observed at higher phytoplankton standing

crops, as indicated by chlorophyll a concentrations.

There are also major differences between the two systems. For example, the

portion of the Suwannee River estuary examined in this study exhibited a broader range

in salinity and chlorophyll range than the portions of the Mississippi River delta studied

by Strom and Strom (1996) (Table 4-2).

In some studies of tropical open-ocean systems, grazing rates similar to those in the

Suwannee River estuary have been observed. For example, Verity et al. (1996) found

grazing rates in the equatorial Pacific, ranging from 14 62% loss of phytoplankton

standing crop per day. The grazer community composition in the latter system is very

different from that found in the Suwannee River estuary. Heterotrophic nanoplankton

and dinoflagellates dominated the grazer community in the Verity et al. study, while

ciliates were only a minor constituent in the microzooplankton community. Chlorophyll

levels were also much lower in the latter study than in the Suwannee (Table 4-2).

However, Verity et al. (1996) concluded that the grazing rates observed played a

significant role in the regulation of phytoplankton standing crop.

Outside the sub-tropical/tropics, Gallegos (1989) estimated 17 to 80% loss of

phytoplankton standing crop per day during July, August, and October in the Rhode

River estuary, Maryland. Within the Suwannee River estuary a 4 to 73% loss of

phytoplankton standing crop per day was observed the same months. The Rhode River

estuary is a turbid, eutrophic estuary, which receives high nutrient inputs with average









chlorophyll concentrations of 50gg 1-1 in parts of the system (Table 4-2). The primary

difference in the microzooplankton community from the Suwannee estuary was the

dominance by oligotrichs and rotifers, while loricate ciliates played a minor role. Again

this study suggested that microzooplankton grazing had a significant effect on

phytoplankton standing crop.

Not all systems exhibit as broad a range of grazing loss as the Suwannee River

estuary. For example, the oligotrophic Kareiega estuary, located on the south coast of

South Africa, exhibits much lower loss rates (Froneman and McQuaid 1997). With low

freshwater inputs, this estuary is regarded as primarily marine; the estuary is

characterized as having low chlorophyll concentrations, and is usually dominated by

small ciliates and nanophytoplankton. The instantaneous grazing rate ranged between

0.010 and 0.105d-1 (1.06 8.51% loss of phytoplankton standing crop per day). Their

values are much lower than those observed in the Suwannee River estuary. However,

Froneman and McQuaid (1997) still concluded that the impact of grazing was significant.

Their findings, in combination with those of others illustrate that the significance of

grazing may not be related to the absolute grazing rate, but to the relationship between

grazing rate and the growth rate of phytoplankton, which can be very low in oligotrophic

systems. In the Kariega estuary, initial chlorophyll levels (0.312 1.24gg 1-1) and

phytoplankton growth rates (0.012 0.242 doublings/day) are extremely low (Froneman

and McQuaid 1997) (Table 4-2). Thus a 8.51% loss of the phytoplankton standing crop

has a much greater effect on this system.

Within the Suwannee River estuary, there exists a trophic gradient which may

similarly affect the significance of microzooplankton grazers in the system. The most









offshore station within this study of the Suwannee estuary, C4, displayed relatively low

nutrient levels and chlorophyll concentrations. Although the grazing rates for C4 were

often lower than at the inshore sites, the grazing impact may be more important due to

lower growth rates of phytoplankton. For this station, chlorophyll levels were highest in

spring when grazing pressure was lower. Later in the year, however, higher grazing rates

occurred and chlorophyll levels were decreased and stayed depressed. By contrast, the

inshore stations, more eutrophic in nature, showed no summer depression of chlorophyll

despite increased in grazing rates.

Nutrient-rich versus Ambient Nutrient Phytoplankton Growth

The potential importance of grazing rates observed in the controlled experiments in

this study must also be discussed within the context of the factors that vary within the

natural environment. One of the most critical of these is nutrient availability. For this

purpose, it is useful to compare phytoplankton growth rates were always higher than

instantaneous grazing rates, although a few months showed similar rates. However, the

nutrient-enriched mesocosm environment removes potential limiting factors that may

inhibit growth of the phytoplankton community in situ (e.g., light limitation and nutrient

limitation). While this experimental environment provides a good picture of potential

grazing rate, it may provide an inflated view of phytoplankton growth rates. Under

optimal light and nutrient conditions in the bioassay environment, the phytoplankton

growth observed is likely to be the maximal. Nutrients, such as nitrogen, are periodically

limiting in the Suwannee River estuary, especially farther from shore (Bledsoe and Phlips

2000). In a similar study, Strom and Strom (1996) showed that grazing by

microzooplankton resulted in an 30% average loss of phytoplankton standing crop per









day in nutrient-enriched mesocosms, but losses were as high as 90% in experiments that

were not nutrient-enriched.

To further understand the role nutrients play in regulation of phytoplankton growth,

it is useful to compare net phytoplankton growth rates between nutrient-enriched and un-

enriched mesocosms. In all cases, phytoplankton growth was greater in the nutrient-

enriched mesocosms, suggesting that with no nutrient addition, the grazing impact could

be greater than otherwise indicated (Figure 4-2).

While direct comparison of instantaneous growth rates and net growth rates is not

possible, for purposes of discussion instantaneous growth rate of non-enriched

mesocosms were estimated and then compared to those instantaneous grazing rates

obtained from enriched mesocosms (Figure 4-3). With this estimation, the importance of

nutrient availability to the phytoplankton standing crop becomes apparent. For stations

nearest to the Suwannee River, B and C1, estimated growth rates without nutrient

addition are still greater than the instantaneous grazing rates for most of the year,

although August and winter, they are practically equal. The offshore station, C4, shows

the same relationship as the previous stations, showing estimated growth as greater than

grazing except for a few months. Differences between the two parameters, though, are

relatively small, while those for B and Cl are periodically large. G1, however, displays

strong nutrient limitation for most of the year, March through October. At this station,

growth is greater than grazing in winter.

From a broader perspective, a discussion of the relative impacts of

microzooplankton grazing within the Suwannee River must include consideration of









other controlling factors. Phytoplankton biomass may well be influenced by a number of

factors other than grazing, such as nutrient and light availability.

Another factor that may be regionally important is light availability. The dark

waters of the river amy cause light limitation for inshore sites. Although the estuary is

relatively shallow, the river input of color maybe significant enough to inhibit the

introduction of light to deeper depths in the near shore regions of the estuary (Bledsoe

and Phlips 2000). This may play a role in the regulation of phytoplankton and also the

community structure.

Another important controlling factor in the Suwannee River estuary is water

residence time (Blesoe and Phlips 2004). The Suwannee River estuary is a semi-enclosed

system. Although the estuary does not have specific land barriers blocking tidal flow it

does contain two oyster reefs running parallel to the shoreline (Figure 4-4). While the

reefs do not totally block tidal flushing, they do restrict movement of water throughout

the area, especially at low tide. Monbet (1992) has shown that magnitude of tidal mixing

can be important in regulation the response of phytoplankton to nutrient inputs by

altering the time available for biomass accumulation.

Another possible regulation factor is periodic shifts in grazer communities related

to life histories of organisms. For example, there have been periodic masses of

ctenophores noted throughout the Suwannee River system (per observation,

communication with E. Bledsoe). Often congregating along tide lines, these large

predators can alter the grazing rates on phytoplankton and the microzooplankton

community with undetermined results.









Beyond the planktonic domain, another possible controlling factor for

phytoplankton biomass would be benthic grazers (Cloem 1982). The Suwannee River

estuary contains a high population of benthic grazers, including expansive oyster and

brachiopod beds (Per observation and personal communication with D. Parkyn).

Considering the shallow depth of the Suwannee River estuary, the grazing activities of

these organisms could have a major impact on phytoplankton biomass.

An important future step in evaluating the importance of microzooplankton to

phytoplankton dynamics in the Suwannee River estuary will be to define the relative

importance of all aforementioned factors.










Table 4-1. Summary of percent phytoplankton standing stock removed per day for
various oceanic environments. Though the percentages show a high range of
numbers, the rates determined within this study fall in line with their results.
% standing stock
Region Location removed per day Source


Polar


Subartic/Subantartic





Temperate












Subtropical

Tropical


Arctic Sea, Pacific
Marginal ice zone
Bellingshausen Sea
Marginal ice zone stations 1 -
2

Pacific Ocean
Antartic Polar Front stations
3-12

Coastal, Washington
Celtic Sea and Carmarthen
Bay

Long Island Sound
New Zealand
Southern Ocean stations 13 -
17

Subtropical Convergence

Kariega Estuary
Southern Ocean stations 18 -
22
Mississippi River Delta
Suwannee Estuary
Equitorial Pacific


8- 15%


Paranjape 1987


3 24%

3.7-19.8%

5 30%

5.3 44.4%

6 24%

30 65%

541%
10-92%

0 22.5%

7- 48%

1.06 8.51%

10-22.7%
<30%
13-71%
14 62%


Burkill et al 1995
Froneman and
Perissinotto 1996
Strom and
Welschmeyer 1991
Froneman and
Perissinotto 1996
Landry and Hassett
1982

Burkill et al. 1987
Capriula and Carpenter
1980
James and Hall 1998
Froneman and
Perissinotto 1996
Froneman and
Perissinotto 1996
Froneman and
McQuaid 1997
Froneman and
Perissinotto 1996
Strom and Strom 1996
This study
Verity et al 1996


Table 4-2. Comparison of the different parameters for the studies examined in the
discussion. The salinity conditions for the Kariega estuary have been reported
as "hypersaline" with episodic freshwater inputs (Bate et al. 2002). The
salinity for the equatorial Pacific was also not reported specifically, except to
say that it was a marine system. Chlorophyll values for the Mississippi River
delta were not reported in the publication, but the system was described as


containing eutrophic coastal waters.
Salinity Chlorophyll
Study Area (ppt) (uQ I11)


Dates Sampled


Suwannee Estuary 5.3 33.4 0.99 61 Feb 02 Jan 03
Mississippi River Delta 31.9 36.3 na Oct 92 & May 93
Equatorial Pacific marine 0.1 -0.4 March Apr 92 & Oct 92
Rhode River brackish 32.5 138.4 Jul, Aug, Oct 88
Kariega Estuary marine 0.312-1.21 Nov-94













Station B1


3



0
0 ---- i l ---------i i i

1 F M A M J J A S O N D J


Station C1

5
4
3-
2-
0


-1 F M A M J J A S O N D J


Station C4

5
4
3
2


0
1 F M A M J J A S O N D J


Station G1

5
4
3
2

0 -
-1


F M A M


J J A S O N D J


Figure 4-1. A comparison of the doublings per day (open circle) and halvings per day
(black box) for each station for a period of one year, February 2002 to January
2003.






















F M A M J J A S O N D J

C1









F M A M J J A S O N D J

C4









FM A M J J A S O N D

G1




\ ~~ ^^^/^


F M A M J J A S O


N D J


Figure 4-2. A comparison of the net doublings per day for nutrient enriched (black
diamond) and non-enriched (grey box) mesocosms. Except for a few months,
growth in the nutrient enriched mesocosms showed greater growth than the
non-enriched mesocosms.
























F M A M J J A S 0 N D J

C1










F M A M J J A S O N D J


C4











F M A M J J A S O N D J

G1


F M A M J J A S O


N D J


Figure 4-3. A comparison of estimated instantaneous growth rate for non-enriched
mesocosms (grey box) and instantaneous grazing rate (black triangle). This
was obtained by using the absolute difference in the net growth rate for the
two treatment groups and applying it to the instantaneous growth rate
calculated from the enriched-treatment group.













29020 A 29c20

N











2910 2 T1 0


0 9


8ao1 8310



Figure 4-4. An estimation of the location of the oyster reefs that run parallel to the
shoreline in the Suwannee River estuary. Though not the only oyster reefs
present in the system, these two reefs are mentioned due to their major impact
on tidal and river flow throughout the estuary.















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BIOGRAPHICAL SKETCH

Christina E. Jett was born on November 2, 1975, in St. Petersburg, Florida, the

daughter of Tom and Sally Jett. She was raised in Ft. Myers, Florida, with seven brothers

and sisters, Monica, Karen, Kathleen, Michael, Steven, and Sarah. She then graduated

from the University of Florida with a BS in wildlife ecology and conservation and a

minor in zoology in May 1997. She worked for Dr. Phlips as a field technician for two

and a half years before being offered an opportunity to pursue her master's. She then

started her work on primary trophic interactions within the Suwannee River estuary at the

University of Florida in the Fall of 2000. In May 2004, she will graduate with her Master

of Science degree. Her future plans include getting married in May 2004 and pursuing a

career in marine ecology.