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Effects of Rapid Salinity Change on Submersed Aquatic Plants


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EFFECTS OF RAPID SALINITY CHA NGE ON SUBMERSED AQUATIC PLANTS By CHANDA JONES LITTLES 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 2005

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Copyright 2005 By Chanda Jones Littles

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This document is dedicated to my mother, L oyce, and father, Dennis, who both gave me special gifts that enable me to succeed in all of my endeavors.

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ACKNOWLEDGMENTS I thank my major advisor, Dr. Thomas Frazer, and the other members of my thesis committee for their guidance and patience throughout my thesis project. I also thank all of the graduate students in the Department of Fisheries and Aquatic Sciences who gave of their time to assist me during experimental set-up and plant analysis. Last, but certainly not least, I must thank my husband, Tony Littles, who has been extremely supportive throughout my graduate career. iv

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TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................iv LIST OF TABLES .............................................................................................................vi LIST OF FIGURES ..........................................................................................................vii ABSTRACT .....................................................................................................................viii CHAPTER 1 INTRODUCTION........................................................................................................1 2 STUDY AREA.............................................................................................................6 3 MATERIALS AND METHODS.................................................................................8 Set-up and Experimental Protocol................................................................................8 Statistical Analyses.....................................................................................................10 4 RESULTS...................................................................................................................11 Environmental Conditions..........................................................................................11 Effects of Salinity and Exposure Duration on Vallisneria americana.......................11 Effects of Salinity and Exposure Duration on Hydrilla verticillata...........................16 Effects of Salinity and Exposure Duration on Myriophyllum spicatum.....................19 Percent Mortality........................................................................................................23 5 DISCUSSION.............................................................................................................24 LIST OF REFERENCES...................................................................................................29 BIOGRAPHICAL SKETCH.............................................................................................33 v

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LIST OF TABLES Table page 1 Results for two-factor ANOVA used to test for effects of salinity and exposure duration on differences in the blade elongation (cm), number of blades (clones included), number of clones produced, above-, and below-ground biomass gain (g DW) d -1 for Vallisneria americana......................................................................13 2 Mean values for blade elongation, number of blades (all clones included), number of clones produced by Vallisneria, as well as aboveand below-ground biomass gain d -1 ........................................................................................................15 3 Results for two-factor ANOVA used to test for effects of salinity and exposure duration on differences in the mean number of branches, stem elongation, number of turions produced, aboveand below-ground biomass (g DW) d -1 for Hydrilla verticillata. An asterisk (*) indicates statistical significance at p<0.001..17 4 Mean values for the number of branches, stem elongation, turions produced by Hydrilla verticillata, as well as aboveand below-ground biomass (g DW) d -1 ......18 5 Results for two-factor ANOVA used to test for effects of salinity and exposure duration on differences in the mean number of branches, stem elongation, above-, and below-ground biomass gain (g DW) d -1 for Myriophyllum spicatum. An asterisk (*) indicates statistical significance at p<0.001....................................20 6 Mean values for the number of branches, stem elongation, aboveand below-ground biomass (g DW) d -1 of Myriophyllum spicatum..........................................22 7 Percent mortality of Vallisneria americana, Hydrilla verticillata, and Myriophyllum spicatum at each salinity/duration treatment combination after the final 28 day recovery period.....................................................................................23 vi

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LIST OF FIGURES Figure page 1 Mean ( + SD) blade elongation d -1 for Vallisneria americana at all treatment combinations............................................................................................................14 2 Mean ( + SD) stem elongation d -1 for Myriophyllum spicatum at all treatment combinations............................................................................................................21 vii

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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 EFFECTS OF RAPID SALINITY CHANGE ON SUBMERSED AQUATIC PLANTS By Chanda Jones Littles August 2005 Chair: Thomas K. Frazer Major Department: Fisheries and Aquatic Sciences Tropical storms and hurricanes affect pronounced, although acute, changes in the salinity of Floridas many tidally influenced streams and rivers. I examined the responses of Vallisneria americana, Myriophyllum spicatum and Hydrilla verticillata to rapid salinity change to better understand how a dynamic salinity regime can affect macrophyte assemblages. Though this study focused on several key plants that occur in Kings Bay, Florida, results are likely to be applicable to a large number of tidally influenced systems. Macrophytes were exposed to salinities of 5, 15 or 25 for 1, 2, or 7 days. Following exposure, plants were allowed to recover in freshwater for 28 days. Growth response measurements were then recorded. Plants subjected to salinities of 5 regardless of exposure period, exhibited no significant responses in growth related measures. Hydrilla verticillata exhibited 100% mortality at 15 and 25 irrespective of exposure duration. Relative to controls, M. spicatum and V. americana exhibited declines in growth at 15 after 1 and 2 day exposures; both exhibited significant mortality after a 7 day exposure. viii

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All three species experienced significant mortality at 25 Storm events are likely to have a marked influence on the vegetative structure of this tidally influenced system. ix

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CHAPTER 1 INTRODUCTION The structure and function of biological communities is determined by a large number of factors, biotic and abiotic, and related ecological processes. Identifying these factors and processes and understanding how they interact to influence the patterns of abundance and distribution of both plants and animals is essential to effectively manage the broad suite of biological resources which we, as humans, value and often depend on for our own well-being. With regard to aquatic ecosystems, the need for a mechanistic understanding of the processes shaping submersed aquatic plant assemblages has become increasingly important as systems worldwide have been invaded by exotic and nuisance species that threaten to displace native vegetation, thus compromising their ecological health and integrity. Some invasive aquatic plants (including both angiosperms and algae) exhibit genetic characteristics that enable them to successfully outcompete native species (i.e.,, allelopathic abilities, comparatively faster growth rates, aggressive reproduction, or other growth characteristics) (Sutton and Portier 1985, Elakovich 1989, Doyle and Smart 1995, Jones 1995). Other invasive species get a foothold in new aquatic systems as a consequence of disturbance events or more subtle changes in environmental factors (e.g., temperature, salinity, water clarity, selective herbivory) to which other species are less well adapted (Haller and Sutton 1973, Titus and Adams 1979, Van et al. 1978, Barko et al. 1991, Doyle and Smart 1995, Van et al. 1998, Van et al. 1999). Kings Bay, a tidally influenced, spring-fed system along Floridas Gulf coast, serves to highlight many of the issues noted above and provides a model systems in 1

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2 which mechanistic investigations can be carried out to better understand the processes that affect the structure of submersed plant communities. Submersed aquatic vegetation in Kings Bay, Florida was once dominated by wild celery, Vallisneria americana, based on anecdotal accounts by local residents and long-time recreational users of the bay. However, recent investigations indicate that this native plant has been largely replaced by non-native, invasive species (Notestein et al. 2005). For example, Hoyer et al. (2001) found Eurasian water milfoil, Myriophyllum spicatum, and Hydrilla verticilata to be more prevalent in Kings Bay than V. americana, occurring in 90 and 85 percent of sampled quadrats, respectively, compared to 59 percent for V. americana. Both M. spicatum and H. verticillata are invasive weeds that were introduced into the Kings Bay/Crystal River system within the past several decades (Blackburn and Weldon 1967, Haller 1978, Langeland 1990). Restoration related efforts are ongoing (Southwest Florida Water Management District, pers. comm.) and much research has been aimed at the feasibility of restoring V. americana to its earlier dominance (see, e.g., Hauxwell et al. 2004a and Hauxwell et al. 2004b), but still, M. spicatum, and H. verticilata occupy much of the area once presumably dominated by the aforementioned native species (Dick 1989, Frazer and Hale 2001, Hoyer et al. 2001, Notestein et al. 2005). Several factors have likely contributed to the displacement of V. americana in Kings Bay, including decreased water clarity and subsequent light availability, grazing by herbivores, and competitive exclusion by non-native macrophytes and proliferating macroalgae (Haller and Sutton 1973, Bowes et al. 1977, Canfield and Hoyer 1988, Barko et al. 1991, Blanch et al. 1998, Hauxwell et al. 2003, Hauxwell et al. 2004a, Hauxwell et al. 2004b). Changes in salinity (both acute and longer-term) have also been implicated as a causal

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3 factor in the altered vegetative state of the bay (see Mataraza et al.1999 and Frazer et al. 2001b). Submersed aquatic vegetation in Kings Bay/Crystal River, and other adjacent spring-fed river systems, appears to decline around a salinity of 2 to 3 (Hoyer et al. 2001; Frazer et al. 2001b), values which are only slightly above those historically reported for Kings Bay (see Yobbi and Knochenmus 1989). In fact, Yobbi and Knochenmus (1989) reported a maximum measured salinity of 2.0 near the mouth of Kings Bay which serves as the headwaters of the Crytsal River between 1984 and 1986, but never observed salinities greater than 3 Between July 2000 and June 2001, a marked drought period in north central Florida, bottom salinities of 3.6 and higher were recorded at the mouth of Kings Bay greater than 10% of the time and salinities > 5.2 were recorded greater than 2.5% of the time (Frazer et al. 2001b). These data demonstrate the potential for relatively high salinity water to enter Kings Bay during normal tidal regimes under drought conditions. Aside from salinity changes associated with tidal exchange, episodic storm events are also likely to significantly alter the salinity environment (see Mataraza et al. 1999 and Frazer et al. 2001b). There were two major storm events in Kings Bay in the 1990s, both of which had a significant impact on aquatic plant abundance and distribution (Terrell and Canfield 1996, Mataraza et al. 1999). In response to both events, M. spicatum experienced an initial die-off that was followed by rapid recovery to pre-storm biomass within a year. Hydrilla verticilata experienced a similar initial decline in biomass, but did not recover as rapidly as M. spicatum. Vallisneria americana was impacted the least, as biomass remained relatively constant throughout both events

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4 (Terrell and Canfield 1996, Mataraza et al. 1999). More recently, in 2004, back-to-back hurricanes and tropical storms swept through Florida, potentially affecting salinity and altering plant assemblages in tidally influenced systems throughout Florida and along the Gulf coast, in particular. Though no published data yet exists on the effects of these storms on the vegetative community in Kings Bay, elevated salinities were recorded and declines in vegetative biomass where observed when compared to pre-storm conditions (T. Frazer, Univ. Florida, pers. comm.). Several studies have been carried out to characterize the salinity tolerances of three of the more frequently occurring aquatic plants found in Kings Bay at present, i.e., M. spicatum, H. verticilata and V. americana (e.g., Haller et al. 1974, Stanley 1974, Twilley and Barko 1990a, Twilley and Barko 1990b, Kraemer et al. 1999, Doering et al. 2001, Doering et al. 2002). Myriophyllum spicatum and V. americana are considered salt-tolerant freshwater species while H. verticilata is not. Vallisneria americana exhibits optimal growth in freshwater, but has been reported to tolerate salinities up to 12 (Twilley and Barko 1990b). Myriophyllum spicatum appears to exhibit the highest salinity tolerance with growth observed at salinities exceeding 15 (Twilley and Barko 1990b). Twilley and Barko (1990a) observed that peak above-ground biomass for M. spicatum occurred at 12 and growth was actually reduced at lower salinities. Hydrilla verticilata, on the other hand, exhibited little growth at salinities > 4 in their study and mortality occured at approximately 6 (Twilley and Barko 1990a). Differences in salinity tolerance among these three species are likely to play an important role in their patterns of abundance and distribution in Kings Bay and other tidally influenced systems

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5 in which they co-occur and, in fact, salinity may be a primary factor mediating their competitive success. Most of the studies in which salinity tolerances of macrophytes have been reported, including many of those referenced above, have been carried out under static conditions, and may not reflect a particular plants ability to handle rapid changes in salinity, i.e., changes that occur during normal tidal cycles (during drough conditions or acute storm events in Kings Bay. Thus, the primary objective of this work was to measure the responses of the three aquatic macrophytes noted above to rapid salinity change, a potentially frequent occurrence in Kings Bay (see Frazer et al. 2001b). Doering et al. (2001) conducted a pulsed salinity experiment with V. americana in which plants were exposed to a salinity of 18 for varying durations and then returned to a base salinity of 3 for a 30-day recovery period. These investigators reported reduced shoot number and blade density for V. americana at exposure times of 20 days or longer. No such experiments have been carried out with M. spicatum (a primary competitor with V. americana; see Hauxwell et al. 2004a) or H. verticillata. This study addresses the effects of rapid salinity change on V. americana, H. verticillata, and M. spicatum in an attempt to better understand patterns of abundance and distribution for these three species in Kings Bay and similar systems with the aim of guiding future assemblage level competition experiments where salinity is a mediating factor.

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CHAPTER 2 STUDY AREA Kings Bay is a spring-fed, tidally influenced system and head water for the Crystal River, which flows westward for approximately 11 km before discharging directly into the Gulf of Mexico (Frazer et al. 2001a). The Bay is located approximately 100 km north of Tampa along the west coast of peninsular Florida. Kings Bay serves as a primary winter refuge for the endangered West Indian manatee (Trichechus manatus), and historically, the bay has been a focal area for recreational activities, including boating, diving and manatee viewing. Reduced water clarity, a decline in native aquatic vegetation and simultaneous increases in nuisance vegetation raised public concern, and in 1982, Kings Bay/Crystal River was designated as an Outstanding Florida Water in an attempt to curb further degradation of the system (Mobley 1992). Nutrient enrichment was initially believed to be the primary cause of decreased water clarity and attempts were made to improve water quality in the Bay by removal of the City of Crystal River wastewater effluent (Citrus County Chronicle: March 23, 1986). However, further diagnostic studies suggested that nutrients were likely not the cause of the observed decrease in water quality and loss of native vegetation (Citrus County Chronicle: May 14, 1986). Nevertheless, suspended solids, dominated by microalgae, were subsequently hypothesized to underlie decreased water clarity in Kings Bay, but the potential increase in algae was presumed to be the result of reduced vegetative biomass and frequent wind induced resuspension (see Hoyer et al. 1997). For the most part, however, the 6

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7 mechanisms underlying the observed changes in water clarity and submersed aquatic vegetation in Kings Bay are, at present, poorly understood.

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CHAPTER 3 MATERIALS AND METHODS Set-up and Experimental Protocol Pulsed salinity events were simulated in outdoor, concrete tanks in Gainesville, Fl during September 2004. Specified salinities (see below) were achieved in each of the experimental tanks by mixing synthetic sea salt, Instant Ocean (Aquarium Systems, Inc., Eastlake, OH) with ground water from an on site well. Submersible water pumps were placed in all tanks with a salt treatment to facilitate mixing and maintain a homogeneous and constant salinity environment. Each of the tanks contained a mixed assemblage of the three study plants. Translucent shade cloth placed atop each tank resulted in a 70 % reduction of ambient light and were used to adjust the light environment to one more commonly encountered by submersed plants in Kings Bay. Salinity was monitored daily to ensure that occasional rainfall events did not alter the prescribed treatments. When needed, Instant Ocean or well water was added to maintain the specified salinity. For the duration of the experiment, salinities were maintained within 1 of the prescribed treatments. Other water quality measurements, including temperature ( o C), dissolved oxygen (mg/L), and pH, were monitored daily with a YSI meter (Model 650 MDS). Whole Vallisneria americana plants, apical fragments of Myriophyllum spicatum and the female dioecious biotype of Hydrilla verticillata were collected from Kings Bay/Crystal River, Florida during August 2004. For Hydrilla and Myriophyllum, 4 cm apical sections were cut from each fragment, blotted dry and weighed, then planted with at least 2 nodes below the sediment, leaving approximately 3 cm of the stem and 8

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9 associated leaf material exposed. For Vallisneria, the blades of each plant were trimmed to 3 cm, roots were clipped to 2 cm and any rhizomes were removed at the crown and discarded. Remaining blades were then counted and each shoot was blotted dry and weighed and planted immediately thereafter. All study specimens were planted in 1-quart, plastic nursery pots lined with fabric (to prevent sand leakage from pre-drilled drainage holes) and filled with 900 g of sand fertilized with 0.1% (0.9 g) Osmocote. Forty-eight pots were designated for each species resulting in a total of 4 plants per species per treatment. Plants were then randomly placed in the outdoor tanks (2.5 m length x 1.5 m width x 1.5 m depth; 900 L volume capacity) pre-filled with ground water from an on site well (<1 salinity), and allowed to a 28 day conditioning period prior to experimentation. Two outdoor tanks were assigned to each pre-subscribed salinity treatment (i.e., 0 -control, and 5, 15 and 25 ) and six plants of each species were randomly placed in each tank with an approximate separation distance of ca. 0.5 m minimize potential plant interactions and edge effects. This set-up allowed replicate plants (n=4) to be subjected to simulated pulses of 1, 2 and 7 days at the different salinities indicated above. After being subjected to the pre-subscribed salinity treatment and exposure duration, plants were removed from treatment tanks and placed into recovery tanks, i.e., those with ground water from an on site well (<1 salinity). Plants remained in recovery for 28 days following the simulated pulse events to allow for recovery and continued monitoring of growth parameters. Harvesting was completed in October 2004, after the final recovery period. Plants were removed from pots, rinsed, and measured for number of blades and clones (Vallisneria), number of branches (Hydrilla and Myriophyllum), length

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10 of longest blade or branch (cm), and turions produced (Hydrilla). Plants were then dried at 60 o C for 48 h and weighed to the nearest g for total aboveand below-ground biomass. Statistical Analyses Measures recorded post-harvest were used for all analyses where each plant in each salinity and duration of exposure treatment was designated as a replicate. Stem/blade elongation (cm) d -1 was calculated using the difference in the length of the original plant and the length of the longest branch/blade of the original plant at the time of harvesting, and dividing by the total number of days in the experiment (treatment duration plus 28-day recovery). Aboveand below-ground biomass gain (g DW) d -1 number of branches d -1 (Hydrilla and Myriophyllum), number of blades and clones d -1 (Vallisneria) and number of turions d -1 (Hydrilla) were calculated similarly. The expression of growth related measures on a relative scale (change in dependent-variable d -1 ) ameliorates concerns over an unequal growth period for plants subjected to different exposure periods (i.e., 1, 2 and 7 d), but assumes a linear response for each over the finite study period (i.e., 29 to 35 d). Each of the aforementioned growth-related measures was treated as a separate dependent variables in a 2 X 2 factorial analysis (PROC GLM, SAS Institute, Inc. 2000), with salinity and duration of exposure as fixed effects. Tukeys Test was used as pairwise follow-up to the more general ANOVA procedures indicated above. All results were considered significant at the P <0.05 level unless indicated otherwise in the text.

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CHAPTER 4 RESULTS Environmental Conditions Incident light levels at the surface of the tanks during midday ranged between 1750 and 2000E m -2 s -1 during the study. Shade cloth placed over each of the tanks resulted in an approximate 70% light reduction (525 to 600E m -2 s -1 at midday) and effectively simulated in situ light levels near the bottom in Kings Bay (Frazer, unpublished data). Daily mean water temperatures in the tanks varied between 21 and 26 o C at midday for the duration of the experiment and were also representative of temperatures in Kings Bay during the study period (August/September; Frazer unpublished data). Salinity values in control and recovery tanks were always < 0.2 and salinities in treatment tanks were always within 1 of the prescribed 5 and 15 treatments, and within 2 for the 25 treatments. The average dissolved oxygen concentration and pH values, as measured at midday, ranged between 7.5-10 mg L -1 and 7.5-8.5, respectively. Effects of Salinity and Exposure Duration on Vallisneria americana Vallisneria americana growth characteristics, i.e., number of blades, blade elongation d -1 and number of clones produced d -1 as well as aboveand below-ground biomass gain d -1 were all significantly affected by salinity (Table 1). There were no significant main effects attributed to the duration of exposure (Table 1), although, there was a significant (p < 0.01) interaction between the main effects of salinity and exposure duration on mean blade elongation d -1 (Table 1) due largely to the decline in this metric after a 7-day exposure at 15 salinity (Figure 1). 11

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12 In follow-up pairwise tests, there were only two statistically significant differences involving control plants and plants subjected to pulsed salinities at 5 (Table 2); the mean blade elongation rate for control plants (0.596 cm d -1 ) was less than the mean blade elongation rate of plants subjected to a 5 for 1 day (0.897 cm d -1 ), and the mean above-ground biomass gain of control plants (0.0201 g DW d -1 ) was greater than that of plants subjected to a 5 for 7 days (0.0121 g DW d -1 ). Noteworthy was the fact that plants exposed to simulated salinity pulses of 15 produced fewer blades and clones d -1 and exhibited less elongation and above-ground biomass gain d -1 than controls, irrespective of exposure duration (Table 2). Below-ground biomass gain d -1 was generally lower for plants subjected to salinity pulses of 5 than control plants, though not significantly (Table 2). Mean below-ground biomass gain d -1 of plants exposed to 15 did not differ significantly from that of plants exposed to 25 (Table 2). All Vallisneria plants exposed to salinities of 25 exhibited a complete loss of above-ground leaf material regardless of exposure duration (Table 2).

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13 Table 1. Results for two-factor ANOVA used to test for effects of salinity and exposure duration on differences in the blade elongation (cm), number of blades (clones included), number of clones produced, above-, and below-ground biomass gain (g DW) d -1 for Vallisneria americana. An asterisk (*) indicates statistical significance at p < 0.01. Variable df MS F P Number of blades d -1 Salinity 3 3.372 29.24 0.0001* Duration 2 0.013 0.11 0.8942 Salinity Duration 6 0.062 0.54 0.7749 Model Error 37 0.115 Blade elongation d -1 (cm) Salinity 3 1.305 61.33 0.0001* Duration 2 0.063 2.98 0.0633 Salinity Duration 6 0.069 3.24 0.0116* Model Error 37 0.021 Number of clones d -1 Salinity 3 0.083 26.47 0.0001* Duration 2 2.2 E 4 0.07 0.9335 Salinity Duration 6 8.0 E 4 0.26 0.9538 Model Error 37 3.1 E -3 Above-ground biomass (g DW) gain d -1 Salinity 3 7.3 E 4 37.76 0.0001* Duration 2 1.7 E 5 0.88 0.4223 Salinity Duration 6 1.1 E 5 0.56 0.7581 Model Error 37 1.9 E -5 Below-ground biomass (g DW) gain d -1 Salinity 3 2.9 E 4 42.5 0.0001* Duration 2 3.2 E 7 0.4 0.6602 Salinity Duration 6 9.2 E 6 1.7 0.1477 Model Error 37 6.7 E -6

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14 00.20.40.60.811.2051525SalinityBlade elongation (cm) day -1 1 day 2 days 7 days Figure 1. Mean ( + SD) blade elongation d -1 for Vallisneria americana at all treatment combinations.

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15 Table 2. Mean values for blade elongation, number of blades (all clones included), number of clones produced by Vallisneria, as well as aboveand below-ground biomass gain d -1 (standard deviations are given in parentheses). Letters indicate results of Tukeys LSM follow-up test to the more general ANOVA (see Table 1). Means with the same letters are not statistically significant at p<0.05. Small letters compare results form salinity treatments at a given exposure time (across a row). Control 5 15 25 Number of blades d -1 1-day 1.089 a ( 0.789) 0.686 a, b ( 0.319) 0.355 a, b ( 0.171) 0.0 b 2-days 1.133 a ( 0.427) 0.625 a, b ( 0.206) 0.235 b, c ( 0.145) 0.0 c 7-days 1.251 a ( 0.546) 0.900 a ( 0.098) 0.064 b ( 0.129) 0.0 b Blade elongation d -1 (cm) 1-day 0.596 b ( 0.139) 0.897 a ( 0.214) 0.325 b ( 0.126) 0.0 c 2-days 0.480 a ( 0.091) 0.622 a ( 0.152) 0.357 a ( 0.238) 0.0 b 7-days 0.663 a ( 0.204) 0.652 a ( 0.192) 0.023 b ( 0.066) 0.0 b Number of clones d -1 1-day 0.178 a ( 0.119) 0.097 a, b ( 0.074) 0.041 a, b ( 0.031) 0.0 b 2-days 0.172 a ( 0.060) 0.109 a, b ( 0.054) 0.032 b, c ( 0.036) 0.0 c 7-days 0.189 a ( 0.082) 0.136 a ( 0.014) 0.014 b ( 0.029) 0.0 b Above-ground biomass (g DW) gain d -1 1-day 0.0156 a ( 0.0085) 0.0126 a, b ( 0.0048) 0.0039 b, c ( 0.0009) 0.0 c 2-days 0.0141 a ( 0.0072) 0.0105 a, b ( 0.0050) 0.0022 b, c ( 0.0011) 0.0 c 7-days 0.0201 a ( 0.0048) 0.0121 b ( 0.0038) 0.0028 c ( 0.0042) 0.0 c Below-ground biomass (g DW) gain d -1 1-day 0.0074 a ( 0.0035) 0.0089 a ( 0.0034) 0.0019 b ( 0.0008) 0.0 b 2-days 0.0103 a ( 0.0040) 0.0067 a ( 0.0033) 0.0011 b ( 0.0003) 0.0 b 7-days 0.0116 a ( 0.0042) 0.0074 a ( 0.0028) 0.00005 b ( 0.0001) 0.0 b

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16 Effects of Salinity and Exposure Duration on Hydrilla verticillata The mean number of branches produced d -1 stem elongation (cm d -1 ), turions produced d -1 aboveand below-ground biomass gain (g DW d -1 ) of H. verticillata were all significantly affected by salinity (Table 3). Duration of exposure did not have a significant effect on the above-mentioned parameter estimates (Table 3). The mean number of branches produced d -1 was statistically higher for plants exposed to 5 for 2 and 7 days (2.01 and 2.04 branches d -1 respectively), than control plants of equivalent duration (1.21 and 1.07 branches d -1 respectively) (Table 4). There was no significant difference between mean stem elongation d -1 for control and plants exposed to salinity pulses of 5 regardless of exposure duration, but there was a general decrease in stem elongation with increased salinity (Table 4). Though not statistically different, the mean above-ground biomass gain d -1 was higher for plants exposed to 5 salinity than control plants (i.e., 0 ) (Table 4). At 5 salinity, mean stem elongation rate (1.02 cm d -1 ) and above-ground biomass gain (0.023 g DW d -1 ) was lowest for plants exposed for 2 days (Table 4). Mean below-ground biomass was higher, though not significantly, for control vs. 5 treatment plants after 2and 7-days exposure (Table 4). Turion production was limited and highly variable among control plants and those subjected to 5 salinity, but means were generally greater for controls than treatment plants (Table 4). Hydrilla verticillata exposed to salinities of 15 or 25 regardless of duration, exhibited 100% mortality (Table 4, Table 7).

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17 Table 3. Results for two-factor ANOVA used to test for effects of salinity and exposure duration on differences in the mean number of branches, stem elongation, number of turions produced, aboveand below-ground biomass (g DW) d -1 for Hydrilla verticillata. An asterisk (*) indicates statistical significance at p<0.001. Variable df MS F P Number of branches d -1 Salinity 3 11.07 86.92 0.0001* Duration 2 0.01 0.10 0.9045 Salinity Duration 6 0.22 1.76 0.1352 Model Error 37 0.13 Stem elongation (cm) d -1 Salinity 3 7.31 57.73 0.0001* Duration 2 0.21 1.69 0.1992 Salinity Duration 6 0.09 0.72 0.6373 Model Error 37 0.13 Number of turions d -1 Salinity 3 0.0033 10.84 0.0001* Duration 2 3.7 E -4 1.20 0.3126 Salinity Duration 6 3.2 E -4 1.04 0.4162 Model Error 37 3.1 E -4 Above-ground biomass (g DW) gain d -1 Salinity 3 0.0029 55.1 0.0001* Duration 2 1.2 E -4 2.23 0.1215 Salinity Duration 6 8.0 E -5 1.49 0.2073 Model Error 37 5.3 E -5 Below-ground biomass (g DW) gain d -1 Salinity 3 0.00025 27.86 0.0001* Duration 2 2.1 E -5 2.30 0.1142 Salinity Duration 6 9.2 E -6 1.02 0.4278 Model Error 37 9.0 E -6

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18 Table 4. Mean values for the number of branches, stem elongation, turions produced by Hydrilla verticillata, as well as aboveand below-ground biomass (g DW) d -1 (standard deviations are given in parentheses). Letters indicate results of Tukeys LSM follow-up test to the general ANOVA (see Table 3). Means with the same letters are not statistically significant at p<0.05. Small letters compare results form salinity treatments at a given exposure time (across a row). Control 5 15 25 Number of branches d -1 1-day 1.71 a ( 0.98) 1.62 a ( 0.25) 0.0 b 0.0 b 2-days 1.21 b ( 0.35) 2.01 a ( 0.26) 0.0 c 0.0 c 7-days 1.07 b ( 0.23) 2.04 a ( 0.53) 0.0 c 0.0 b Stem elongation (cm) d -1 1-day 1.77 a ( 0.99) 1.40 a (0.13) 0.0 b 0.0 b 2-days 1.39 a ( 0.69) 1.02 a ( 0.08) 0.0 b 0.0 b 7-days 1.22 a ( 0.21) 1.12 a ( 0.15) 0.0 b 0.0 b Number of turions d -1 1-day 0.016 a ( 0.0186) 0.016 a ( 0.0323) 0.0 a 0.0 a 2-days 0.047 a ( 0.0403) 0.023 a, b ( 0.0156) 0.0 b 0.0 b 7-days 0.040 a ( 0.0156) 0.0072 b ( 0.0143) 0.0 b 0.0 b Above-ground biomass (g DW) gain d -1 1-day 0.025 a ( 0.01) 0.028 a ( 0.0) 0.0 b 0.0 b 2-days 0.020 a ( 0.01) 0.023 a ( 0.01) 0.0 b 0.0 b 7-days 0.024 b ( 0.0) 0.04 a ( 0.01) 0.0 c 0.0 c Below-ground biomass (g DW) gain d -1 1-day 0.0046 a ( 0.0016) 0.0059 a ( 0.0039) 0.0 b 0.0 b 2-days 0.010 a ( 0.0064) 0.0079 a,b ( 0.0044) 0.0 b 0.0 b 7-days 0.010 a ( 0.0029) 0.0086 a ( 0.0047) 0.0 b 0.0 b

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19 Effects of Salinity and Exposure Duration on Myriophyllum spicatum The main effect of salinity on M. spicatum was significant for all measures, i.e., the mean number of branches, stem elongation (cm d -1 ), aboveand below-ground biomass gain d -1 for (Table 5). Duration of exposure (p<0.001) and the interaction between salinity and duration (p<0.001) were significant only for the final stem length in this set of analysis (Table 5). The interaction was attributed to the precipitous decline in the stem length measures for M. spicatum following a 7 day exposure at 15 salinity (Figure 2). In pairwise follow-up tests, there were no significant difference in any of the measures made for control plants and those subjected to salinity pulses of 5 regardless of duration of exposure (Table 6). Exposure to 15 salinity generally resulted in a significant decrease in branching, stem elongation rates, and biomass gain d -1 when compared to control plants. Exceptions were for plants exposed to 15 salinity for 1 day. In this case, there were no statistically significant differences in the number of branches (0.23 d -1 ), stem elongation (1.2 cm d -1 ) or below-ground biomass gain (0.0017 g DW d -1 ) when compared to control plants (0.42 d -1 1.71 cm d -1 and 0.0069 g DW d -1 respectively), though the variability in these measured values was high (Table 6). Exposure to 25 for any length of time resulted in significantly lower values for all measures when compared to control plants (Table 6). A significant effect of duration was demonstrated at the 15 salinity treatment, with plants of 1 and 2 days exposure durations exhibiting greater stem elongation rates, 1.2 and 1.16 cm d -1 than those exposed for 7 days, 0.24 cm d -1 (Table 6). Though not significant, aboveand below-ground biomass gain generally decreased as salinity increased for 2 and 7 days exposure (Table 6). Exposure to 25 for any length of time resulted in significant reductions in all measures when compared to control plants (Table 6).

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20 Table 5. Results for two-factor ANOVA used to test for effects of salinity and exposure duration on differences in the mean number of branches, stem elongation, above-, and below-ground biomass gain (g DW) d -1 for Myriophyllum spicatum. An asterisk (*) indicates statistical significance at p<0.001. Variable df MS F P Number of branches d -1 Salinity 3 0.91 46.9 0.0001* Duration 2 0.02 1.0 0.3762 Salinity Duration 6 0.02 1.1 0.3781 Model Error 37 8.3 E -5 Stem elongation (cm) d -1 Salinity 3 7.97 143.1 0.0001* Duration 2 0.48 8.7 0.0008* Salinity Duration 6 0.25 4.5 0.0016* Model Error 37 0.06 Above-ground biomass (g DW) gain d -1 Salinity 3 0.0044 52.6 0.0001* Duration 2 1.2 E -4 1.5 0.2462 Salinity Duration 6 1.0 E -4 1.2 0.3136 Model Error 37 8.3 E -5 Below-ground biomass (g DW) gain d -1 Salinity 3 4.3 E -4 25.9 0.0001* Duration 2 4.4 E -5 2.7 0.0833 Salinity Duration 6 2.2 E -5 1.3 0.2763 Model Error 37 1.7 E -5

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21 00.511.522.5051525SalinityStem elongation (cm) day-1 1 day 2 days 7 days Figure 2. Mean (+ SD) stem elongation d -1 for Myriophyllum spicatum at all treatment combinations.

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22 Table 6. Mean values for the number of branches, stem elongation, aboveand below-ground biomass (g DW) d -1 of Myriophyllum spicatum (standard deviations are given in parentheses). Letters indicate results of Tukeys LSM follow-up test to the general ANOVA (see Table 5). Means with the same letters are not statistically significant at p<0.05. Small letters compare results form salinity treatments at a given exposure time (across a row). Control 5 15 25 Number of branches d -1 1-day 0.42 a, b ( 0.20) 0.57 a ( 0.16) 0.23 b, c ( 3.0) 0.06 c ( 0.03) 2-days 0.66 a ( 0.12) 0.60 a ( 0.22) 0.19 b ( 0.08) 0.03 b ( 0.03) 7-days 0.57 a ( 0.16) 0.55 a ( 0.21) 0.09 b ( 0.12) 0.0 b Stem elongation (cm) d -1 1-day 1.71 a, b ( 0.31) 1.78 a ( 0.34) 1.20 b ( 0.42) 0.11 c ( 0.09) 2-days 1.76 a ( 0.30) 1.80 a ( 0.10) 1.16 b ( 0.24) 0.03 c ( 0.05) 7-days 1.62 a ( 0.13) 1.73 a ( 0.18) 0.24 b ( 0.28) 0.0 b Above-ground biomass (g DW) gain d -1 1-day 0.025 a ( 0.013) 0.032 a ( 0.012) 0.0063 b ( 0.0025) 0.0009 b ( 0.0006) 2-days 0.045 a ( 0.010) 0.036 a ( 0.014) 0.0053 b ( 0.0011) 0.0002 b ( 0.0003) 7-days 0.039 a ( 0.013) 0.035 a ( 0.014) 0.0040 b ( 0.0048) 0.0 b Below-ground biomass (g DW) gain d -1 1-day 0.0069 a, b ( 0.0044) 0.0074 a ( 0.0030) 0.0017 b,c ( 0.0006) 0.00085 c ( 0.0010) 2-days 0.0145 a ( 0.0014) 0.0119 a ( 0.0056) 0.0014 b ( 0.0006) 0.000050 b ( 0.0001) 7-days 0.0149 a ( 0.0066) 0.0114 a,b ( 0.0084) 0.0025 b ( 0.0034) 0.0 b

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23 Percent Mortality Control plants and plants exposed to 5 for any duration experienced 0% mortality for all three study species. Vallisneria americana exhibited 75% mortality (as indicated by a total loss of above-ground tissue) after exposure to 15 for 7 days and 100% mortality after exposure to 25 for any duration (Table 7). Hydrilla verticillata exhibited 100% mortality in the 15 or 25 treatments, regardless of exposure duration (Table 7). Myriophyllum spicatum had 0% mortality after exposure to 15 for either 1 or 2 days, but exhibited 50% mortality after 7 days. Percent mortality of M. spicatum increased with exposure duration at 25 salinity, with 25, 75, and 100% mortality after 1, 2, and 7 days exposure, respectively (Table 7). Table 7. Percent mortality of Vallisneria americana, Hydrilla verticillata, and Myriophyllum spicatum at each salinity/duration treatment combination after the final 28 day recovery period. Vallisneria Hydrilla Myriophyllum 1 day 2 days 7 days 1 day 2 days 7 days 1 day 2 days 7 days Control 0 0 0 0 0 0 0 0 0 5 0 0 0 0 0 0 0 0 0 15 0 0 75 100 100 100 0 0 50 25 100 100 100 100 100 100 25 75 100

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CHAPTER 5 DISCUSSION Marked differences in the responses of V. american, H. verticillata and M. spicatum to acute pulses in salinity as reported here provide insight into the potential effects of climate change and ephemeral tropical storm events on the vegetative character of Kings Bay (see Frazer et al. 2001b) and may help to explain the recent prevalence of invasive species in this system (see Notestein et al. 2005). Although all three species were able to tolerate 1 to 7 day exposures to 5 salinity, pulses of 15 even for short time periods, resulted in significant and often pronounced reductions in growth related measures. In fact, even a 1-day exposure to a salinity of 15 was sufficient to kill H. verticillata in this study. Pulses of higher salinity water, i.e., 25 resulted in 100% mortality of V. americana regardless of exposure duration, but only the longest exposure period (7 days) at this salinity level elicited this same response in M. spicatum. These experimental findings are consistent with field observations reported by Mataraza et al. (1999) where following a strong tropical storm event, H. verticillata in Kings Bay was noticeably reduced and failed to recover to pre-storm densities even after a year whereas M. spicatum actually increased in abundance. It is interesting to note that Mataraza et al. (1999) observed little change in the biomass of V. americana following the aforementioned storm event. These investigators did not measure changes in salinity coincident with the passing of the storm, but one might postulate that salinities did not exceed the 15 threshold value necessary to result in a decline of this species. 24

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25 Although salinity was determined be an important factor with regard to the growth and survival of the three plant species studied here, duration of exposure, in general, had little effect. This finding suggests rapid or acute changes in salinity are more detrimental to these species than are gradual changes that may occur as a consequence of longer-term climatic shifts. In fact, both V. americana and M. spicatum exhibited lower salinity thresholds when compared to results from several previous studies where plants were exposed to gradual increases in salinity (see, e.g., Haller et al. 1974, Stanley 1974, Twilley and Barko 1990a, Twilley and Barko 1990b, Kraemer et al. 1999, Doering et al. 2001, Doering et al. 2002). The need for an acclimation period for plants to adjust their physiology to increasing salinity (see Twilley and Barko 1990a), however, is a luxury seldom afforded to many plants that occupy tidally influenced systems. There are likely several mechanisms involved in the osmoregulatory response of plants needing to adjust to changes in salinity. The accumulation of antioxidative enzymes, proline and other amino acids, for example, has been demonstrated as a mechanism to achieve salt-tolerance in other plants (Rout and Shaw 1998, Rout and Shaw 2001, Mulholland and Otte 2002) and a measure of these chemical constituents might provide additional insight into the degree of salinity stress imposed on aquatic plants in Kings Bay and other tidally influenced systems. Such an approach may be particularly useful in those systems where freshwater delivery has been reduced as a consequence of climatic shifts, i.e., drought, or changing patterns of consumptive use by humans, e.g., groundwater withdrawal. With regard to species specific responses to changes in salinity, Doering et al. (2001) exposed V. americana to 18 salinity for 1, 5, 11, and 20 days, but failed to detect significant effects on blade length or number of blades per shoot. These

PAGE 35

26 investigators did observe a decreasing trend, however, in the number of blades produced and the number of clones produced with increasing duration of exposure. Similar qualitative patterns were observed in this study for V. americana exposed to 15 salinity. Interestingly, Haller et al. (1974) reported that V. americana exhibited decreased growth with increased salinity, even at relatively low salinity values, i.e., 3.33 and 6.66 The duration of exposure may have been a major contributing factor to the results found in the above study since all plants were exposed to the prescribed salinities for 4-weeks with no recovery period. Clearly, V. americana can tolerate exposure to much higher salinities, at least for short durations. In this study, V. americana was able to persist when subjected to salinities of 15 for two days or less, though decreases in growth related measures were observed relative to controls. The negative effects of exposure to 15 salinity were intensified after 7 days when compared to 1 and 2-days exposure duration. The 75% mortality of V. americana at 15 after 7 days indicates an inability to recover from rapid salinity changes near the upper-limit of its reported salinity tolerance, especially when exposure is for more than a few days. The ability of V. americana to tolerate 18 salinity for upwards of 50-days in the long-term experiments of Doering et al. (2001) may be reflective of adaptations specific to this species in the Caloosahatchee estuary (Gulf Coast, South Florida) or the result of the experimental protocol in which salinity was gradually increased to 18 over several days. The high (100%) mortality experienced by H. verticillata exposed to 15 or 25 salinity, regardless of exposure duration was not surprising. Previous studies have shown H. verticillata to grow optimally in freshwater, though results on its tolerance to saltwater

PAGE 36

27 are somewhat conflicted. Haller et al. (1974) transplanted Hydrilla into indoor mesocosms of differing salinities and observed no growth at salinities 6.66 Twilley and Barko (1990b) increased salinity gradually and found that Hydrilla showed little productivity at salinities above 4 In stark contrast to the reports by Haller et al. (1974) and Twilley and Barko (1990b), and also the findings reported herein, Steward and Van (1987) present data indicating growth of H. verticillata at salinities up to 13 The variability in the findings may be explained partly by differing methodologies (gradual increase vs. rapid changes in salinity), but may also be explained by differences in the genetic makeup or physiological characteristics of plants from different environments. Plants from estuarine and brackish habitats, such as Kings Bay, may experience subtle and possibly frequent salinity changes that have resulted in their ability to adapt to higher salinities. This may explain the fact that H. verticillata in the current study seemed to tolerate and almost favor 5 salinity, as there was a slight trend for greater branching and higher biomass when compared to control plants. Myriophyllum spicatum, in this study, exhibited successful growth and productivity at 5 salinity. However, a significant decrease in branching, growth, and biomass gain d -1 at 15 regardless of exposure duration, was observed. This result is consistent with the decrease in growth of M. spicatum exposed to a 13.32 reported by Haller et al. (1974). The findings reported here and those reported by Haller et al. (1974) conflict with the results of Twilley and Barko (1990b) who observed a general increase in M. spicatum biomass with increasing salinity, up to 12 However, Twilley and Barko (1990b) gradually increased the salinity over several days, which may have allowed more time for physiological adjustment to the environment. Myriophyllum spicatum was the

PAGE 37

28 only species in this study to exhibit any tolerance to 25 salinity, although each of the growth-related measures were significantly less than those of control plants. Its seeming tolerance at 1 and 2 days exposure could give it a competitive advantage over the other two species. While the current study does not directly address competition between these species, it does help to understand how salinity might possibly mediate competition and provides a foundation for further investigation of this important topic. Results of this study may also be used in conjunction with salinity monitoring efforts in Kings Bay and other estuarine areas to predict where submersed plants are likely to occur and may also be used to develop conservation strategies and help guide restoration efforts. It is possible, based on the findings reported here, that the dynamic nature of Kings Bay (which includes the occurrence of frequent storm events) precludes large-scale restoration efforts of V. americana as the system may be episodically reset allowing for rapid colonization and persistence of invasive species such as M. spicatum and H. verticillata. Longer-term data that characterizes variability in the vegetative structure in relation to salinity is essential as managers seek to understand and predict the impacts of water use activities (ground water withdrawals in particular) and storm events on the ecology Kings Bay.

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LIST OF REFERENCES Barko, J. W., Smart, R. M. and D. G. McFarland. 1991. Interactive effects of environmental conditions on the growth of submersed aquatic macrophytes. Journal of Freshwater Ecology 6(2):199-207. Blackburn, R. D. and L. W. Weldon. 1967. Eurasian watermilfoil Floridas new underwater menace. Hyacinth Control Journal 6:15-18. Blanch, S. J., Ganf, G. G. and K. F. Walker. 1998. Growth and recruitment in Vallisneria americana as related to average irradiance in the water column. Aquatic Biology 61:181-205. Bowes, G., Van, T. K., Garrard, L. A. and W. T. Haller. 1977. Adaptation to low light levels by Hydrilla. Journal of Aquatic Plant Management 15:32-35. Canfield, D. E. and M. V. Hoyer. 1988. Influence of nutrient enrichment and light availability on the abundance of aquatic macrophytes in Florida streams. Canadian Journal of Fisheries and Aquatic Sciences 45:1467-1472. Citrus County Chronicle. March 23, 1986 (3A). Crystal River wants to clean up canals. Iverness, FL. Citrus County Chronicle. May 14, 1986. Study says wastewater not the cause of water weed problem. Iverness, FL. Dick, T. H. 1989. Crystal River: A No Win situation. Aquatics 11(2):10-13. Doering, P. H., Chamberlain, R. H. and J. M. McMunigal. 2001. Effects of simulated saltwater intrusions on the growth and survival of Wild Celery, Vallisneria americana, from the Caloosahatchee Estuary (South Florida). Estuaries 24(6A):894-903. Doering, P. H., R. H. Chamberlain, and D. E. Haunert. 2002. Using submerged aquatic vegetation to establish minimum and maximum freshwater inflows to the Caloosahatchee Estuary, Florida. Estuaries 25(6B):1343-1354. Doyle, R. D. and R. M. Smart. 1995. Potential use of native aquatic plants for long-term control of problem aquatic plants in Guntersville Reservoir, Alabama: Report 2. Competitive interactions between beneficial and nuisance species. Technical Report A-93-6, US Army Corps Engineers, Waterways Experiment Station, Aquatic Plant Control Research Program, Vicksburg, MS, 52pp. 29

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30 Elakovich, S. D. 1989. Allelopathic aquatic plants for aquatic weed management. Biologia Planatarum (Praha) 31(6):479-486. Frazer, T. K. and J. A. Hale. 2001. An atlas of submersed aquatic vegetation in Kings Bay (Citrus County Florida). Final Report. Southwest Florida Water Management District. Brooksville, Florida. Frazer, T. K., Notestein, S. K., Hoyer, M. V., Hale, J. A. and D. E. Canfield, Jr. 2001a. Physical, chemical and vegetative characteristics of five Gulf coast rivers. Final Report. Southwest Florida Water Management District, Brooksville, Florida Frazer, T. K., Notestein, S. K., Hoyer, M. V., Hale, J. A. and D. E. Canfield, Jr. 2001b. Frequency and duration of pulsed salinity events in Kings Bay. Final Report. Southwest Florida Water Management District, Brooksville, Florida. Haller, W. T. 1978. Hydrilla: A new and rapidly spreading aquatic weed problem. Agriculture Experiment Stations/IFAS/Gainesville, Florida/ Agronomy Department, University of Florida. Haller, W. T. and D. L. Sutton. 1973. Community structure and competition between Hydrilla and Vallisneria. Hyacinth Control Journal 13:48-50. Haller, W. T., Sutton, D. L. and W. C. Barlowe. 1974. Effects of salinity on growth of several aquatic macrophytes. Ecology 55(4):891-894. Hauxwell, J. A, Frazer, T. K. and C. W. Osenberg. 2003. Effects of herbivores and competing primary producers on Vallisneria americana in Kings Bay: Iimplications for restoration and management. Final Report. Southwest Florida Water Management District, Brooksville, Florida. Hauxwell, J. A., Osenburg, C. W. and T. K. Frazer. 2004a. Conflicting management goals: Manatees and invasive competitors inhibit restoration of a native macrophyte. Ecological Applications 14(2):571-586. Hauxwell, J. A., Osenburg, C. W. and T. K. Frazer. 2004b. Grazing by manatees excludes both new and established wild celery transplants: Implications for restoration in Kings Bay, FL, USA. Journal of Aquatic Plant Management 42:49-53. Hoyer, M. V., Mataraza, L. K., Munson, A. B. and D. E. Canfield, Jr. 1997. Water Clarity in Kings Bay/Crystal River. Final Report. SWIM Department, Southwest Florida Water Management District, Brooksville, Florida. Hoyer, M. V., Frazer, T. K., Canfield, D.E., Jr. and J. M. Lamb. 2001. Vegetation evaluation in Kings Bay/Crystal River. Final Report. Southwest Florida Water Management District, Brooksville, Florida.

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31 Jones, H. L. 1995. Allelopathic ability of various aquatic plants to inhibit the growth of Hydrilla verticillata (L.f.) Royle and Myriophyllum spicatum L. Final Report. U.S. Army Corps of Engineers. Technical Report A-95-1. Washington, D.C. Kraemer, G. P., Chamberlain, R. H., Doering, P. H., Steinman, A. D. and M. D. Hanisak. 1999. Physiological responses of the freshwater angiosperm Vallisneria americana along a salinity gradient in the Caloosahatchee Estuary (Southwestern Florida). Estuaries 22(1):138-148. Langeland, K. A. 1990. Hydrilla (Hydrilla verticillata (L.f.) Royle): A continuing problem in Florida waters. Circ. No. 884. Coop. Ext. Serv., IFAS, Univ. of Florida, Gainesville, 21pp. Mataraza, L. K., Terrell, J. B., Munson, A. B. and D. E. Canfield, Jr. 1999. Changes in submersed macrophytes in relation to tidal storm surges. Journal of Aquatic Plant Management 37:3-12. Mobley, A. 1992. Kings Bay/Crystal River: Charting a course to rehabilitation. Hydroscope 23(1):10-11. Mulholland, M. M. and M. L. Otte. 2002. The effects of nitrogen supply and salinity on DMSP, glycine betaine and proline concentrations in leaves of Spartina anglica. Aquatic Botany 72:193-200. Notestein, S. K., Frazer, T. K., Keller, S. R. and R. A. Swett. 2005. Crystal River/Kings Bay vegetation evaluation 2004. Annual Report. Southwest Florida Water Management District, Brooksville, Florida. Rout, N. P. and B. P. Shaw. 1998. Salt tolerance in aquatic macrophytes: probable role of proline, the enzymes involved in its synthesis and C 4 type of metabolism. Plant Science 136:121-130. Rout, N. P. and B. P. Shaw. 2001. Salt tolerance in aquatic macrophytes: possible involvement of the antioxidative enzymes. Plant Science 160:415-423. Stanley, R. A. 1974. Effect of 2,4-D and various salts on Eurasian Watermilfoil. Weed Science 22:591-594. Steward, K. K. and T. K. Van. 1987. Comparative studies of monoecious and dioecious Hydrilla (Hydrilla verticillata) biotypes. Weed Science 35:204-210. Sutton, D. L. and K. M. Portier. 1985. Density of tubers and turions of Hydrilla in South Florida. Journal of Aquatic Plant Management 23:64-67. Terrell, J. B. and D. E. Canfield, Jr. 1996. Evaluation of the effects of nutrient removal and the Storm of the Century on submersed vegetation in Kings Bay-Crystal River, Florida. Journal of Lake and Reservoir Management 12(3):394-403.

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32 Titus, J. E. and M. S. Adams. 1979. Coexistence and the comparative light relations of the submersed macrophytes Myriophyllum spicatum L. and Vallisneria americana Michx.. Oecologia (Berl.) 40:273-286. Twilley, R. R. and J. W. Barko. 1990a. Effects of salinity and irradiance conditions on the growth, morphology, and chemical composition of submersed aquatic macrophytes. Final Report. US Army Corps of Engineers, Aquatic Plant Control Research Program. Technical Report A-90-5, 25pp. Twilley, R. R. and J. W. Barko. 1990b. The growth of submersed macrophytes under experiment salinity and light conditions. Estuaries 13(3):311-321. Van, T. K., W. T. Haller, and G. Bowes. 1978. Some aspects of the competitive biology of Hydrilla. Pages 117-125 of Proceedings of the EWRS 5 th Symposium on Aquatic Weeds. Van, T. K., Wheeler, G. S. and T. D. Center. 1998. Competitive interactions between Hydrilla (Hydrilla verticillata) and Vallisneria (Vallisneria americana) as influenced by insect herbivory. Biological Control 11:185-192. Van, T. K., Wheeler, G. S. and T. D. Center. 1999. Competition between Hydrilla verticillata and Vallisneria americana as influenced by soil fertility. Aquatic Botany 62:225-233. Yobbi, D. K. and L. A. Knochenmus. 1989. Effects of river discharge and high-tide stage on salinity intrusion in the Weeki Wachee, Crystal, and Withlacoochee River estuaries, southwest Florida: U.S. Geological Survey Water-Resources Investigations Report 88-4116, 63pp.

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BIOGRAPHICAL SKETCH I pursued my undergraduate degree at Texas A&M University Corpus Christi and received a B.S. in biology: Marine Emphasis along with a minor in public relations in May 2003. As an undergraduate, I participated in several research projects through the AMP (Alliance for Minority Participation) Program at TAMU-CC. I was also involved in REU (Research Experience for Undergraduates) programs at Rice University, University of Oregon-Hatfield Marine Science Center, and Western Washington University-Shannon Point Marine Center. My experience has been diverse, ranging from tallow tree invasion of coastal prairies, to crab larvae ingestion of toxic dinoflagellates, to use of the lateral line by juvenile walleye Pollock while feeding. I also worked three years as a research assistant with USGS looking at the habitat selection and feeding behavior of wintering burrowing owls, Athene cunicularia, in South Texas. However, my loyalty remains with aquatic ecosystems, and more specifically to conservation and management. My most recent experience at the University of Florida as an M.S. candidate under Dr. Thomas Frazer has been a step in the right direction and results of my research will hopefully contribute to future management strategies for submersed plants. 33


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Title: Effects of Rapid Salinity Change on Submersed Aquatic Plants
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Copyright Date: 2008

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EFFECTS OF RAPID SALINITY CHANGE ON SUBMERSED AQUATIC PLANTS


By

CHANDA JONES LITTLE


















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


2005

































Copyright 2005

By

Chanda Jones Littles

































This document is dedicated to my mother, Loyce, and father, Dennis, who both gave me
special gifts that enable me to succeed in all of my endeavors.















ACKNOWLEDGMENTS

I thank my major advisor, Dr. Thomas Frazer, and the other members of my thesis

committee for their guidance and patience throughout my thesis project. I also thank all

of the graduate students in the Department of Fisheries and Aquatic Sciences who gave of

their time to assist me during experimental set-up and plant analysis. Last, but certainly

not least, I must thank my husband, Tony Littles, who has been extremely supportive

throughout my graduate career.
















TABLE OF CONTENTS



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

LIST OF TABLES ................... ..... ....... ......... ............. vi

LIST OF FIGURE S ......... ....................... ............. ........... vii

A B S T R A C T .......................................... .................................................. v iii

CHAPTER

1 IN TRODU CTION ................................................. ...... .................

2 STUDY AREA .............. .................. ............ ....................... .... 6

3 M ATERIALS AND M ETHOD S ........................................... ........... ............... 8

Set-up and Experim ental Protocol .................................................................... ..... 8
Statistical A analyses .................................................... ...... ............... 10

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

Environm ental Conditions ......................... ...................... ................. 11
Effects of Salinity and Exposure Duration on Vallisneria americana.....................11
Effects of Salinity and Exposure Duration on Hydrilla verticillata...........................16
Effects of Salinity and Exposure Duration on Myriophyllum spicatum....... ........ 19
Percent M mortality .................................. .. .......... .. ............23

5 DISCUSSION ............................ .. .............. ............... .........24

LIST OF REFEREN CES ..................................................................... ............... 29

B IO G R A PH IC A L SK E TCH ..................................................................... ..................33










v















LIST OF TABLES


Tablege

1 Results for two-factor ANOVA used to test for effects of salinity and exposure
duration on differences in the blade elongation (cm), number of blades (clones
included), number of clones produced, above-, and below-ground biomass gain
(g DW) d-1 for Vallisneria americana............. ........... ............. .. ............... 13

2 Mean values for blade elongation, number of blades (all clones included),
number of clones produced by Vallisneria, as well as above- and below-ground
biom ass gain d-1 .......................................................................15

3 Results for two-factor ANOVA used to test for effects of salinity and exposure
duration on differences in the mean number of branches, stem elongation,
number ofturions produced, above- and below-ground biomass (g DW) d-1 for
Hydrilla verticillata. An asterisk (*) indicates statistical significance at p<0.001. .17

4 Mean values for the number of branches, stem elongation, turions produced by
Hydrilla verticillata, as well as above- and below-ground biomass (g DW) d1 ......18

5 Results for two-factor ANOVA used to test for effects of salinity and exposure
duration on differences in the mean number of branches, stem elongation,
above-, and below-ground biomass gain (g DW) d-1 for Myriophyllum spicatum.
An asterisk (*) indicates statistical significance at p<0.001 ..................................20

6 Mean values for the number of branches, stem elongation, above- and below-
ground biomass (g DW) d-1 of Myriophyllum spicatum ........................................22

7 Percent mortality of Vallisneria americana, Hydrilla verticillata, and
Myriophyllum spicatum at each salinity/duration treatment combination after the
final 28 day recovery period ......... .................. .. .. ............... 23















LIST OF FIGURES

Figure page

1 Mean (+ SD) blade elongation d-1 for Vallisneria americana at all treatment
com bination s. ...................................................... ................. 14

2 Mean (+ SD) stem elongation d-1 for Myriophyllum spicatum at all treatment
com bination s. ...................................................... ................. 2 1















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

EFFECTS OF RAPID SALINITY CHANGE ON SUBMERSED AQUATIC PLANTS

By

Chanda Jones Littles

August 2005

Chair: Thomas K. Frazer
Major Department: Fisheries and Aquatic Sciences

Tropical storms and hurricanes affect pronounced, although acute, changes in the

salinity of Florida's many tidally influenced streams and rivers. I examined the responses

of Vallisneria americana, Myriophyllum spicatum and Hydrilla verticillata to rapid

salinity change to better understand how a dynamic salinity regime can affect macrophyte

assemblages. Though this study focused on several key plants that occur in Kings Bay,

Florida, results are likely to be applicable to a large number of tidally influenced systems.

Macrophytes were exposed to salinities of 5, 15 or 25 %o for 1, 2, or 7 days. Following

exposure, plants were allowed to recover in freshwater for 28 days. Growth response

measurements were then recorded. Plants subjected to salinities of 5 %o, regardless of

exposure period, exhibited no significant responses in growth related measures. Hydrilla

verticillata exhibited 100% mortality at 15 and 25 %o, irrespective of exposure duration.

Relative to controls, M. spicatum and V. americana exhibited declines in growth at 15 %o

after 1 and 2 day exposures; both exhibited significant mortality after a 7 day exposure.









All three species experienced significant mortality at 25 %o. Storm events are likely to

have a marked influence on the vegetative structure of this tidally influenced system.














CHAPTER 1
INTRODUCTION

The structure and function of biological communities is determined by a large

number of factors, biotic and abiotic, and related ecological processes. Identifying these

factors and processes and understanding how they interact to influence the patterns of

abundance and distribution of both plants and animals is essential to effectively manage

the broad suite of biological resources which we, as humans, value and often depend on

for our own well-being. With regard to aquatic ecosystems, the need for a mechanistic

understanding of the processes shaping submersed aquatic plant assemblages has become

increasingly important as systems worldwide have been invaded by exotic and nuisance

species that threaten to displace native vegetation, thus compromising their ecological

health and integrity. Some invasive aquatic plants (including both angiosperms and

algae) exhibit genetic characteristics that enable them to successfully outcompete native

species (i.e.,, allelopathic abilities, comparatively faster growth rates, aggressive

reproduction, or other growth characteristics) (Sutton and Portier 1985, Elakovich 1989,

Doyle and Smart 1995, Jones 1995). Other invasive species get a foothold in new aquatic

systems as a consequence of disturbance events or more subtle changes in environmental

factors (e.g., temperature, salinity, water clarity, selective herbivory) to which other

species are less well adapted (Haller and Sutton 1973, Titus and Adams 1979, Van et al.

1978, Barko et al. 1991, Doyle and Smart 1995, Van et al. 1998, Van et al. 1999).

Kings Bay, a tidally influenced, spring-fed system along Florida's Gulf coast,

serves to highlight many of the issues noted above and provides a model systems in









which mechanistic investigations can be carried out to better understand the processes

that affect the structure of submersed plant communities. Submersed aquatic vegetation

in Kings Bay, Florida was once dominated by wild celery, Vallisneria americana, based

on anecdotal accounts by local residents and long-time recreational users of the bay.

However, recent investigations indicate that this native plant has been largely replaced by

non-native, invasive species (Notestein et al. 2005). For example, Hoyer et al. (2001)

found Eurasian water milfoil, Myriophyllum spicatum, and Hydrilla verticilata to be

more prevalent in Kings Bay than V. americana, occurring in 90 and 85 percent of

sampled quadrats, respectively, compared to 59 percent for V. americana. Both M

spicatum and H. verticillata are invasive weeds that were introduced into the Kings

Bay/Crystal River system within the past several decades (Blackburn and Weldon 1967,

Haller 1978, Langeland 1990). Restoration related efforts are ongoing (Southwest

Florida Water Management District, pers. comm.) and much research has been aimed at

the feasibility of restoring V americana to its earlier dominance (see, e.g., Hauxwell et

al. 2004a and Hauxwell et al. 2004b), but still, M. spicatum, and H. verticilata occupy

much of the area once presumably dominated by the aforementioned native species (Dick

1989, Frazer and Hale 2001, Hoyer et al. 2001, Notestein et al. 2005). Several factors

have likely contributed to the displacement of V americana in Kings Bay, including

decreased water clarity and subsequent light availability, grazing by herbivores, and

competitive exclusion by non-native macrophytes and proliferating macroalgae (Haller

and Sutton 1973, Bowes et al. 1977, Canfield and Hoyer 1988, Barko et al. 1991, Blanch

et al. 1998, Hauxwell et al. 2003, Hauxwell et al. 2004a, Hauxwell et al. 2004b).

Changes in salinity (both acute and longer-term) have also been implicated as a causal









factor in the altered vegetative state of the bay (see Mataraza et al.1999 and Frazer et al.

2001b).

Submersed aquatic vegetation in Kings Bay/Crystal River, and other adjacent

spring-fed river systems, appears to decline around a salinity of 2 to 3 %o (Hoyer et al.

2001; Frazer et al. 2001b), values which are only slightly above those historically

reported for Kings Bay (see Yobbi and Knochenmus 1989). In fact, Yobbi and

Knochenmus (1989) reported a maximum measured salinity of 2.0 %o near the mouth of

Kings Bay which serves as the headwaters of the Crytsal River between 1984 and 1986,

but never observed salinities greater than 3 %o. Between July 2000 and June 2001, a

marked drought period in north central Florida, bottom salinities of 3.6 %o and higher

were recorded at the mouth of Kings Bay greater than 10% of the time and salinities > 5.2

%o were recorded greater than 2.5% of the time (Frazer et al. 2001b). These data

demonstrate the potential for relatively high salinity water to enter Kings Bay during

normal tidal regimes under drought conditions.

Aside from salinity changes associated with tidal exchange, episodic storm events

are also likely to significantly alter the salinity environment (see Mataraza et al. 1999 and

Frazer et al. 2001b). There were two major storm events in Kings Bay in the 1990's,

both of which had a significant impact on aquatic plant abundance and distribution

(Terrell and Canfield 1996, Mataraza et al. 1999). In response to both events, M.

spicatum experienced an initial die-off that was followed by rapid recovery to pre-storm

biomass within a year. Hydrilla verticilata experienced a similar initial decline in

biomass, but did not recover as rapidly as M. spicatum. Vallisneria americana was

impacted the least, as biomass remained relatively constant throughout both events









(Terrell and Canfield 1996, Mataraza et al. 1999). More recently, in 2004, back-to-back

hurricanes and tropical storms swept through Florida, potentially affecting salinity and

altering plant assemblages in tidally influenced systems throughout Florida and along the

Gulf coast, in particular. Though no published data yet exists on the effects of these

storms on the vegetative community in Kings Bay, elevated salinities were recorded and

declines in vegetative biomass where observed when compared to pre-storm conditions

(T. Frazer, Univ. Florida, pers. comm.).

Several studies have been carried out to characterize the salinity tolerances of three

of the more frequently occurring aquatic plants found in Kings Bay at present, i.e., M.

spicatum, H. verticilata and V. americana (e.g., Haller et al. 1974, Stanley 1974, Twilley

and Barko 1990a, Twilley and Barko 1990b, Kraemer et al. 1999, Doering et al. 2001,

Doering et al. 2002). Myriophyllum spicatum and V americana are considered salt-

tolerant freshwater species while H. verticilata is not. Vallisneria americana exhibits

optimal growth in freshwater, but has been reported to tolerate salinities up to 12 %o

(Twilley and Barko 1990b). Myriophyllum spicatum appears to exhibit the highest

salinity tolerance with growth observed at salinities exceeding 15 %o (Twilley and Barko

1990b). Twilley and Barko (1990a) observed that peak above-ground biomass forM

spicatum occurred at 12 %o and growth was actually reduced at lower salinities. Hydrilla

verticilata, on the other hand, exhibited little growth at salinities > 4 %o in their study and

mortality occurred at approximately 6 %o (Twilley and Barko 1990a). Differences in

salinity tolerance among these three species are likely to play an important role in their

patterns of abundance and distribution in Kings Bay and other tidally influenced systems









in which they co-occur and, in fact, salinity may be a primary factor mediating their

competitive success.

Most of the studies in which salinity tolerances of macrophytes have been

reported, including many of those referenced above, have been carried out under static

conditions, and may not reflect a particular plants ability to handle rapid changes in

salinity, i.e., changes that occur during normal tidal cycles (during drough conditions or

acute storm events in Kings Bay. Thus, the primary objective of this work was to

measure the responses of the three aquatic macrophytes noted above to rapid salinity

change, a potentially frequent occurrence in Kings Bay (see Frazer et al. 2001b).

Doering et al. (2001) conducted a pulsed salinity experiment with V. americana in which

plants were exposed to a salinity of 18 %o for varying durations and then returned to a

base salinity of 3 %o for a 30-day recovery period. These investigators reported reduced

shoot number and blade density for V americana at exposure times of 20 days or longer.

No such experiments have been carried out with M. spicatum (a primary competitor with

V. americana; see Hauxwell et al. 2004a) or H. verticillata. This study addresses the

effects of rapid salinity change on V americana, H. verticillata, and M spicatum in an

attempt to better understand patterns of abundance and distribution for these three species

in Kings Bay and similar systems with the aim of guiding future assemblage level

competition experiments where salinity is a mediating factor.














CHAPTER 2
STUDY AREA

Kings Bay is a spring-fed, tidally influenced system and head water for the Crystal

River, which flows westward for approximately 11 km before discharging directly into

the Gulf of Mexico (Frazer et al. 2001a). The Bay is located approximately 100 km north

of Tampa along the west coast of peninsular Florida. Kings Bay serves as a primary

winter refuge for the endangered West Indian manatee (Trichechus manatus), and

historically, the bay has been a focal area for recreational activities, including boating,

diving and manatee viewing. Reduced water clarity, a decline in native aquatic

vegetation and simultaneous increases in nuisance vegetation raised public concern, and

in 1982, Kings Bay/Crystal River was designated as an Outstanding Florida Water in an

attempt to curb further degradation of the system (Mobley 1992). Nutrient enrichment

was initially believed to be the primary cause of decreased water clarity and attempts

were made to improve water quality in the Bay by removal of the City of Crystal River

wastewater effluent (Citrus County Chronicle: March 23, 1986). However, further

diagnostic studies suggested that nutrients were likely not the cause of the observed

decrease in water quality and loss of native vegetation (Citrus County Chronicle: May 14,

1986). Nevertheless, suspended solids, dominated by microalgae, were subsequently

hypothesized to underlie decreased water clarity in Kings Bay, but the potential increase

in algae was presumed to be the result of reduced vegetative biomass and frequent wind

induced resuspension (see Hoyer et al. 1997). For the most part, however, the






7


mechanisms underlying the observed changes in water clarity and submersed aquatic

vegetation in Kings Bay are, at present, poorly understood.














CHAPTER 3
MATERIALS AND METHODS

Set-up and Experimental Protocol

Pulsed salinity events were simulated in outdoor, concrete tanks in Gainesville, Fl

during September 2004. Specified salinities (see below) were achieved in each of the

experimental tanks by mixing synthetic sea salt, Instant Ocean (Aquarium Systems, Inc.,

Eastlake, OH) with ground water from an on site well. Submersible water pumps were

placed in all tanks with a salt treatment to facilitate mixing and maintain a homogeneous

and constant salinity environment. Each of the tanks contained a mixed assemblage of

the three study plants. Translucent shade cloth placed atop each tank resulted in a 70 %

reduction of ambient light and were used to adjust the light environment to one more

commonly encountered by submersed plants in Kings Bay. Salinity was monitored daily

to ensure that occasional rainfall events did not alter the prescribed treatments. When

needed, Instant Ocean or well water was added to maintain the specified salinity. For the

duration of the experiment, salinities were maintained within 1%o of the prescribed

treatments. Other water quality measurements, including temperature (C), dissolved

oxygen (mg/L), and pH, were monitored daily with a YSI meter (Model 650 MDS).

Whole Vallisneria americana plants, apical fragments ofMyriophyllum spicatum

and the female dioecious biotype ofHydrilla verticillata were collected from Kings

Bay/Crystal River, Florida during August 2004. For Hydrilla and Myriophyllum, 4 cm

apical sections were cut from each fragment, blotted dry and weighed, then planted with

at least 2 nodes below the sediment, leaving approximately 3 cm of the stem and









associated leaf material exposed. For Vallisneria, the blades of each plant were trimmed

to 3 cm, roots were clipped to 2 cm and any rhizomes were removed at the crown and

discarded. Remaining blades were then counted and each shoot was blotted dry and

weighed and planted immediately thereafter. All study specimens were planted in 1-

quart, plastic nursery pots lined with fabric (to prevent sand leakage from pre-drilled

drainage holes) and filled with 900 g of sand fertilized with 0.1% (0.9 g) Osmocote.

Forty-eight pots were designated for each species resulting in a total of 4 plants per

species per treatment. Plants were then randomly placed in the outdoor tanks (2.5 m

length x 1.5 m width x 1.5 m depth; 900 L volume capacity) pre-filled with ground water

from an on site well (<1 %o salinity), and allowed to a 28 day conditioning period prior to

experimentation.

Two outdoor tanks were assigned to each pre-subscribed salinity treatment (i.e., 0

%o -control, and 5, 15 and 25 %o) and six plants of each species were randomly placed in

each tank with an approximate separation distance of ca. 0.5 m minimize potential plant

interactions and edge effects. This set-up allowed replicate plants (n=4) to be subjected

to simulated pulses of 1, 2 and 7 days at the different salinities indicated above. After

being subjected to the pre-subscribed salinity treatment and exposure duration, plants

were removed from treatment tanks and placed into recovery tanks, i.e., those with

ground water from an on site well (<1 %o salinity). Plants remained in recovery for 28

days following the simulated pulse events to allow for recovery and continued monitoring

of growth parameters. Harvesting was completed in October 2004, after the final

recovery period. Plants were removed from pots, rinsed, and measured for number of

blades and clones (Vallisneria), number of branches (Hydrilla and Myriophyllum), length









of longest blade or branch (cm), and turions produced (Hydrilla). Plants were then dried

at 60 C for 48 h and weighed to the nearest g for total above- and below-ground

biomass.

Statistical Analyses

Measures recorded post-harvest were used for all analyses where each plant in each

salinity and duration of exposure treatment was designated as a replicate. Stem/blade

elongation (cm) d-1 was calculated using the difference in the length of the original plant

and the length of the longest branch/blade of the original plant at the time of harvesting,

and dividing by the total number of days in the experiment (treatment duration plus 28-

day recovery). Above- and below-ground biomass gain (g DW) d-1, number of branches

d-1 (Hydrilla and Myriophyllum), number of blades and clones d-1 (Vallisneria) and

number of turions d-1 (Hydrilla) were calculated similarly. The expression of growth

related measures on a relative scale (change in dependent-variable d-1) ameliorates

concerns over an unequal growth period for plants subjected to different exposure periods

(i.e., 1, 2 and 7 d), but assumes a linear response for each over the finite study period

(i.e., 29 to 35 d). Each of the aforementioned growth-related measures was treated as a

separate dependent variables in a 2 X 2 factorial analysis (PROC GLM, SAS Institute,

Inc. 2000), with salinity and duration of exposure as fixed effects. Tukey's Test was used

as pairwise follow-up to the more general ANOVA procedures indicated above. All

results were considered significant at the P <0.05 level unless indicated otherwise in the

text.














CHAPTER 4
RESULTS

Environmental Conditions

Incident light levels at the surface of the tanks during midday ranged between 1750

and 2000pE m-2 s-1 during the study. Shade cloth placed over each of the tanks resulted

in an approximate 70% light reduction (525 to 600iE m-2 s-1 at midday) and effectively

simulated in situ light levels near the bottom in Kings Bay (Frazer, unpublished data).

Daily mean water temperatures in the tanks varied between 21 and 26 C at midday for

the duration of the experiment and were also representative of temperatures in Kings Bay

during the study period (August/September; Frazer unpublished data). Salinity values in

control and recovery tanks were always < 0.2 %o and salinities in treatment tanks were

always within 1%o of the prescribed 5 %o and 15 %o treatments, and within 2 %o for the 25

%o treatments. The average dissolved oxygen concentration and pH values, as measured

at midday, ranged between 7.5-10 mg L-1 and 7.5-8.5, respectively.

Effects of Salinity and Exposure Duration on Vallisneria americana

Vallisneria americana growth characteristics, i.e., number of blades, blade

elongation d-1 and number of clones produced d-1, as well as above- and below-ground

biomass gain d-1 were all significantly affected by salinity (Table 1). There were no

significant main effects attributed to the duration of exposure (Table 1), although, there

was a significant (p < 0.01) interaction between the main effects of salinity and exposure

duration on mean blade elongation d-1 (Table 1) due largely to the decline in this metric

after a 7-day exposure at 15 %o salinity (Figure 1).









In follow-up pairwise tests, there were only two statistically significant differences

involving control plants and plants subjected to pulsed salinities at 5 %o (Table 2); the

mean blade elongation rate for control plants (0.596 cm d-1) was less than the mean blade

elongation rate of plants subjected to a 5 %o for 1 day (0.897 cm d-1), and the mean

above-ground biomass gain of control plants (0.0201 g DW d-1) was greater than that of

plants subjected to a 5 %o for 7 days (0.0121 g DW d-1). Noteworthy was the fact that

plants exposed to simulated salinity pulses of 15 %o produced fewer blades and clones d-1

and exhibited less elongation and above-ground biomass gain d-1 than controls,

irrespective of exposure duration (Table 2). Below-ground biomass gain d-1 was

generally lower for plants subjected to salinity pulses of 5 %o than control plants, though

not significantly (Table 2). Mean below-ground biomass gain d-1 of plants exposed to 15

%o did not differ significantly from that of plants exposed to 25 %o (Table 2). All

Vallisneria plants exposed to salinities of 25 %o exhibited a complete loss of above-

ground leaf material regardless of exposure duration (Table 2).









Table 1. Results for two-factor ANOVA used to test for effects of salinity and exposure
duration on differences in the blade elongation (cm), number of blades (clones
included), number of clones produced, above-, and below-ground biomass gain
(g DW) d-1 for Vallisneria americana. An asterisk (*) indicates statistical
significance at pO.01.
Variable df MS F P
Number of blades d1
Salinity 3 3.372 29.24 0.0001*
Duration 2 0.013 0.11 0.8942
Salinity Duration 6 0.062 0.54 0.7749
Model Error 37 0.115
Blade elongation d 1 (cm)
Salinity 3 1.305 61.33 0.0001*
Duration 2 0.063 2.98 0.0633
Salinity Duration 6 0.069 3.24 0.0116*
Model Error 37 0.021
Number of clones d-1
Salinity 3 0.083 26.47 0.0001*
Duration 2 2.2 E -4 0.07 0.9335
Salinity Duration 6 8.0 E -4 0.26 0.9538
Model Error 37 3.1 E -3
Above-ground biomass (g
DW) gain d1
Salinity 3 7.3 E -4 37.76 0.0001*
Duration 2 1.7 E -5 0.88 0.4223
Salinity Duration 6 1.1 E-5 0.56 0.7581
Model Error 37 1.9 E -5
Below-ground biomass (g
DW) gain d1
Salinity 3 2.9 E -4 42.5 0.0001*
Duration 2 3.2 E 7 0.4 0.6602
Salinity Duration 6 9.2 E -6 1.7 0.1477
Model Error 37 6.7 E -6











- 1 day
- *2 days
7 days


0%o 5%o 15%o 25%o


Salinity


Figure 1. Mean (+ SD) blade elongation d-1 for Vallisneria americana at all treatment
combinations.


"7 1.2


1

0.8

0.6

0.4

0.2

0










Table 2. Mean values for blade elongation, number of blades (all clones included),
number of clones produced by Vallisneria, as well as above- and below-ground
biomass gain d'1 (standard deviations are given in parentheses). Letters indicate
results of Tukey's LSM follow-up test to the more general ANOVA (see Table
1). Means with the same letters are not statistically significant at p<0.05. Small
letters compare results form salinity treatments at a given exposure time (across
a row).
Control 5%o 15%o 25%o
Number of blades d-1


Blade elongation d 1


Number of clones d-


Above-ground biom;
DW) gain d-1


Below-ground bioma
DW) gain d'


1-day 1.089 a
( 0.789)
2-days 1.133 a
( + 0.427)
7-days 1.251 a
( 0.546)
(cm)
1-day 0.596 b
(+0.139)
2-days 0.480 a
( 0.091)
7-days 0.663 a
( + 0.204)

1-day 0.178 a
(+0.119)
2-days 0.172 a
(+ 0.060)
7-days 0.189 a
(+0.082)
ass (g

1-day 0.0156 a
(+ 0.0085)
2-days 0.0141 a
( 0.0072)
7-days 0.0201 a
( 0.0048)
ss (g

1-day 0.0074 a
( 0.0035)
2-days 0.0103 a
(+ 0.0040)
7-days 0.0116 a
(+ 0.0042)


0.686 a, b
( 0.319)
0.625 a, b
( 0.206)
0.900 a
( 0.098)

0.897 a
( 0.214)
0.622 a
(+0.152)
0.652 a
( 0.192)

0.097 a, b
(+ 0.074)
0.109 a, b
(+ 0.054)
0.136 a
( 0.014)


0.0126 a, b
(+ 0.0048)
0.0105 a, b
( 0.0050)
0.0121 b
(+ 0.0038)


0.0089 a
(+ 0.0034)
0.0067 a
( 0.0033)
0.0074 a
( 0.0028)


0.355 a, b
( 0.171)
0.235 b, c
( 0.145)
0.064 b
( 0.129)

0.325 b
( 0.126)
0.357 a
( 0.238)
0.023 b
( 0.066)

0.041 a, b
( 0.031)
0.032 b, c
(+ 0.036)
0.014 b
( 0.029)


0.0039 b, c
(+ 0.0009)
0.0022 b, c
( 0.0011)
0.0028 c
( 0.0042)


0.0019 b
( 0.0008)
0.0011 b
(+ 0.0003)
0.00005 b
( 0.0001)


0.0 b

0.0 c

0.0 b


0.0 c

0.0 b

0.0 b


0.0 b

0.0 c

0.0 b




0.0 c

0.0 c

0.0 c




0.0 b

0.0 b

0.0 b









Effects of Salinity and Exposure Duration on Hydrilla verticillata

The mean number of branches produced d-1, stem elongation (cm d-1), turions

produced d-1, above- and below-ground biomass gain (g DW d-1) ofH. verticillata were

all significantly affected by salinity (Table 3). Duration of exposure did not have a

significant effect on the above-mentioned parameter estimates (Table 3).

The mean number of branches produced d-1 was statistically higher for plants

exposed to 5 %o for 2 and 7 days (2.01 and 2.04 branches d-1, respectively), than control

plants of equivalent duration (1.21 and 1.07 branches d-1, respectively) (Table 4). There

was no significant difference between mean stem elongation d-1 for control and plants

exposed to salinity pulses of 5 %o regardless of exposure duration, but there was a general

decrease in stem elongation with increased salinity (Table 4). Though not statistically

different, the mean above-ground biomass gain d-1 was higher for plants exposed to 5 %o

salinity than control plants (i.e., 0 %o) (Table 4). At 5 %o salinity, mean stem elongation

rate (1.02 cm d-1) and above-ground biomass gain (0.023 g DW d-1) was lowest for plants

exposed for 2 days (Table 4). Mean below-ground biomass was higher, though not

significantly, for control vs. 5 %o treatment plants after 2- and 7-days exposure (Table 4).

Turion production was limited and highly variable among control plants and those

subjected to 5 %o salinity, but means were generally greater for controls than treatment

plants (Table 4). Hydrilla verticillata exposed to salinities of 15 or 25 %o, regardless of

duration, exhibited 100% mortality (Table 4, Table 7).









Table 3. Results for two-factor ANOVA used to test for effects of salinity and exposure
duration on differences in the mean number of branches, stem elongation,
number ofturions produced, above- and below-ground biomass (g DW) d-1 for
Hydrilla verticillata. An asterisk (*) indicates statistical significance at p<0.001.
Variable df MS F P
Number of branches d-1
Salinity 3 11.07 86.92 0.0001*
Duration 2 0.01 0.10 0.9045
Salinity Duration 6 0.22 1.76 0.1352
Model Error 37 0.13
Stem elongation (cm) d-1
Salinity 3 7.31 57.73 0.0001*
Duration 2 0.21 1.69 0.1992
Salinity Duration 6 0.09 0.72 0.6373
Model Error 37 0.13
Number of turions d-1
Salinity 3 0.0033 10.84 0.0001*
Duration 2 3.7 E -4 1.20 0.3126
Salinity Duration 6 3.2 E -4 1.04 0.4162
Model Error 37 3.1 E -4
Above-ground biomass (g DW)
gain d-1
Salinity 3 0.0029 55.1 0.0001*
Duration 2 1.2 E -4 2.23 0.1215
Salinity Duration 6 8.0 E -5 1.49 0.2073
Model Error 37 5.3 E -5
Below-ground biomass (g DW)
gain d-1
Salinity 3 0.00025 27.86 0.0001*
Duration 2 2.1 E-5 2.30 0.1142
Salinity Duration 6 9.2 E -6 1.02 0.4278
Model Error 37 9.0 E -6










Table 4. Mean values for the number of branches, stem elongation, turions produced by
Hydrilla verticillata, as well as above- and below-ground biomass (g DW) d1
(standard deviations are given in parentheses). Letters indicate results of
Tukey's LSM follow-up test to the general ANOVA (see Table 3). Means with
the same letters are not statistically significant at p<0.05. Small letters compare
results form salinity treatments at a given exposure time (across a row).
Control 5%o 15%o 25%o
Number of branches d-1


1-day 1.71 a
( 0.98)
2-days 1.21b
( 0.35)
7-days 1.07b
( 0.23)
Stem elongation (cm) d1


Number of turions d-1







Above-ground biomas
DW) gain d'







Below-ground biomas
DW) gain d'


1-day 1.77 a
(+ 0.99)
2-days 1.39 a
(+ 0.69)
7-days 1.22 a
(+0.21)

1-day 0.016 a
(+ 0.0186)
2-days 0.047 a
(+ 0.0403)
7-days 0.040 a
( 0.0156)
s (g

1-day 0.025 a
(+0.01)
2-days 0.020 a
(+0.01)
7-days 0.024 b
(+0.0)
s (g

1-day 0.0046 a
(+ 0.0016)
2-days 0.010 a
( 0.0064)
7-days 0.010 a
( 0.0029)


1.62 a
(+ 0.25)
2.01 a
(+ 0.26)
2.04 a
(+ 0.53)

1.40 a
(+0.13)
1.02 a
(+ 0.08)
1.12a
(+0.15)

0.016 a
(+ 0.0323)
0.023 a, b
( 0.0156)
0.0072 b
(+ 0.0143)



0.028 a
(+0.0)
0.023 a
(+0.01)
0.04 a
(+0.01)



0.0059 a
(+ 0.0039)
0.0079 a,b
(+ 0.0044)
0.0086 a
(+ 0.0047)


0.0 b

0.0 c

0.0 c


0.0 b

0.0 b

0.0 b


0.0 a

0.0 b

0.0 b




0.0 b

0.0 b

0.0 c




0.0 b

0.0 b

0.0 b


0.0 b

0.0 c

0.0 b


0.0 b

0.0 b

0.0 b


0.0 a

0.0 b

0.0 b




0.0 b

0.0 b

0.0 c




0.0 b

0.0 b

0.0 b









Effects of Salinity and Exposure Duration on Myriophyllum spicatum

The main effect of salinity on M spicatum was significant for all measures, i.e., the

mean number of branches, stem elongation (cm d-1), above- and below-ground biomass

gain d-1 for (Table 5). Duration of exposure (p<0.001) and the interaction between

salinity and duration (p<0.001) were significant only for the final stem length in this set

of analysis (Table 5). The interaction was attributed to the precipitous decline in the stem

length measures for M. spicatum following a 7 day exposure at 15 %o salinity (Figure 2).

In pairwise follow-up tests, there were no significant difference in any of the

measures made for control plants and those subjected to salinity pulses of 5 %o, regardless

of duration of exposure (Table 6). Exposure to 15 %o salinity generally resulted in a

significant decrease in branching, stem elongation rates, and biomass gain d-1 when

compared to control plants. Exceptions were for plants exposed to 15 %o salinity for 1

day. In this case, there were no statistically significant differences in the number of

branches (0.23 d-1), stem elongation (1.2 cm d-1) or below-ground biomass gain (0.0017 g

DW d-1) when compared to control plants (0.42 d-1, 1.71 cm d-1 and 0.0069 g DW d-1,

respectively), though the variability in these measured values was high (Table 6).

Exposure to 25 %o for any length of time resulted in significantly lower values for all

measures when compared to control plants (Table 6). A significant effect of duration was

demonstrated at the 15 %o salinity treatment, with plants of 1 and 2 days exposure

durations exhibiting greater stem elongation rates, 1.2 and 1.16 cm d-1, than those

exposed for 7 days, 0.24 cm d-1 (Table 6). Though not significant, above- and below-

ground biomass gain generally decreased as salinity increased for 2 and 7 days exposure

(Table 6). Exposure to 25 %o for any length of time resulted in significant reductions in

all measures when compared to control plants (Table 6).









Table 5. Results for two-factor ANOVA used to test for effects of salinity and exposure
duration on differences in the mean number of branches, stem elongation,
above-, and below-ground biomass gain (g DW) d-1 for Myriophyllum spicatum.
An asterisk (*) indicates statistical significance at p<0.001.
Variable df MS F P
Number of branches d1
Salinity 3 0.91 46.9 0.0001*
Duration 2 0.02 1.0 0.3762
Salinity Duration 6 0.02 1.1 0.3781
Model Error 37 8.3 E -5
Stem elongation (cm) d-1
Salinity 3 7.97 143.1 0.0001*
Duration 2 0.48 8.7 0.0008*
Salinity Duration 6 0.25 4.5 0.0016*
Model Error 37 0.06
Above-ground biomass (g DW)
gain d 1
Salinity 3 0.0044 52.6 0.0001*
Duration 2 1.2 E -4 1.5 0.2462
Salinity Duration 6 1.0 E -4 1.2 0.3136
Model Error 37 8.3 E -5
Below-ground biomass (g DW)
gain d-1
Salinity 3 4.3 E -4 25.9 0.0001*
Duration 2 4.4 E -5 2.7 0.0833
Salinity Duration 6 2.2 E -5 1.3 0.2763
Model Error 37 1.7 E -5











-E 1 day
- -2 days
7 days


0%0 5%o 15%o 25%o


Salinity


Figure 2. Mean (+ SD) stem elongation d-1 for Myriophyllum spicatum at all treatment
combinations.


2.5


2


1.5


1


0.5


0









Table 6. Mean values for the number of branches, stem elongation, above- and below-
ground biomass (g DW) d1 ofMyriophyllum spicatum (standard deviations are
given in parentheses). Letters indicate results of Tukey's LSM follow-up test to
the general ANOVA (see Table 5). Means with the same letters are not
statistically significant at p<0.05. Small letters compare results form salinity
treatments at a given exposure time (across a row).
Control 5%o 15%o 25%o
Number of branches d-1
1-day 0.42 a, b 0.57 a 0.23 b, c 0.06 c
( 0.20) ( 0.16) ( 3.0) ( 0.03)
2-days 0.66 a 0.60 a 0.19 b 0.03 b
( 0.12) ( 0.22) ( 0.08) ( 0.03)
7-days 0.57 a 0.55 a 0.09 b 0.0 b
(+0.16) (+0.21) (+0.12)
Stem elongation (cm) d 1
1-day 1.71 a,b 1.78 a 1.20 b 0.11 c
( 0.31) ( 0.34) ( 0.42) ( 0.09)
2-days 1.76 a 1.80 a 1.16b 0.03 c
( 0.30) (0.10) ( 0.24) ( 0.05)
7-days 1.62 a 1.73 a 0.24 b 0.0 b
(+0.13) (+0.18) (+0.28)
Above-ground biomass (g
DW) gain d-1
1-day 0.025 a 0.032 a 0.0063 b 0.0009 b
( 0.013) ( 0.012) ( 0.0025) ( 0.0006)
2-days 0.045 a 0.036 a 0.0053 b 0.0002 b
(+0.010) (0.014) (0.0011) (0.0003)
7-days 0.039 a 0.035 a 0.0040 b 0.0 b
(+0.013) (+0.014) (+0.0048)
Below-ground biomass (g
DW) gain d1
1-day 0.0069 a, b 0.0074 a 0.0017 b,c 0.00085 c
( 0.0044) (+ 0.0030) (+ 0.0006) (+ 0.0010)
2-days 0.0145 a 0.0119 a 0.0014 b 0.000050 b
( 0.0014) ( 0.0056) ( 0.0006) ( 0.0001)
7-days 0.0149 a 0.0114 a,b 0.0025 b 0.0 b
( 0.0066) (+ 0.0084) (+ 0.0034)









Percent Mortality

Control plants and plants exposed to 5 %o for any duration experienced 0%

mortality for all three study species. Vallisneria americana exhibited 75% mortality (as

indicated by a total loss of above-ground tissue) after exposure to 15 %o for 7 days and

100% mortality after exposure to 25 %o for any duration (Table 7). Hydrilla verticillata

exhibited 100% mortality in the 15 or 25 %o treatments, regardless of exposure duration

(Table 7). Myriophyllum spicatum had 0% mortality after exposure to 15 %o for either 1

or 2 days, but exhibited 50% mortality after 7 days. Percent mortality ofM spicatum

increased with exposure duration at 25 %o salinity, with 25, 75, and 100% mortality after

1, 2, and 7 days exposure, respectively (Table 7).

Table 7. Percent mortality of Vallisneria americana, Hydrilla verticillata, and
Myriophyllum spicatum at each salinity/duration treatment combination after the
final 28 day recovery period.
Vallisneria Hydrilla Myriophyllum
1 day 2 days 7 days 1 day 2 days 7 days 1 day 2 days 7 days
Control 0 0 0 0 0 0 0 0 0
5 %o 0 0 0 0 0 0 0 0 0
15 %o 0 0 75 100 100 100 0 0 50
25 %o 100 100 100 100 100 100 25 75 100














CHAPTER 5
DISCUSSION

Marked differences in the responses of V american, H. verticillata and M.

spicatum to acute pulses in salinity as reported here provide insight into the potential

effects of climate change and ephemeral tropical storm events on the vegetative character

of Kings Bay (see Frazer et al. 2001b) and may help to explain the recent prevalence of

invasive species in this system (see Notestein et al. 2005). Although all three species

were able to tolerate 1 to 7 day exposures to 5 %o salinity, pulses of 15 %o, even for short

time periods, resulted in significant and often pronounced reductions in growth related

measures. In fact, even a 1-day exposure to a salinity of 15 %o was sufficient to kill H.

verticillata in this study. Pulses of higher salinity water, i.e., 25 %o, resulted in 100%

mortality of V. americana regardless of exposure duration, but only the longest exposure

period (7 days) at this salinity level elicited this same response in M spicatum. These

experimental findings are consistent with field observations reported by Mataraza et al.

(1999) where following a strong tropical storm event, H. verticillata in Kings Bay was

noticeably reduced and failed to recover to pre-storm densities even after a year whereas

M. spicatum actually increased in abundance. It is interesting to note that Mataraza et al.

(1999) observed little change in the biomass of V. americana following the

aforementioned storm event. These investigators did not measure changes in salinity

coincident with the passing of the storm, but one might postulate that salinities did not

exceed the 15 %o threshold value necessary to result in a decline of this species.









Although salinity was determined be an important factor with regard to the growth

and survival of the three plant species studied here, duration of exposure, in general, had

little effect. This finding suggests rapid or acute changes in salinity are more detrimental

to these species than are gradual changes that may occur as a consequence of longer-term

climatic shifts. In fact, both V. americana and M spicatum exhibited lower salinity

thresholds when compared to results from several previous studies where plants were

exposed to gradual increases in salinity (see, e.g., Haller et al. 1974, Stanley 1974,

Twilley and Barko 1990a, Twilley and Barko 1990b, Kraemer et al. 1999, Doering et al.

2001, Doering et al. 2002). The need for an acclimation period for plants to adjust their

physiology to increasing salinity (see Twilley and Barko 1990a), however, is a luxury

seldom afforded to many plants that occupy tidally influenced systems. There are likely

several mechanisms involved in the osmoregulatory response of plants needing to adjust

to changes in salinity. The accumulation of antioxidative enzymes, proline and other

amino acids, for example, has been demonstrated as a mechanism to achieve salt-

tolerance in other plants (Rout and Shaw 1998, Rout and Shaw 2001, Mulholland and

Otte 2002) and a measure of these chemical constituents might provide additional insight

into the degree of salinity stress imposed on aquatic plants in Kings Bay and other tidally

influenced systems. Such an approach may be particularly useful in those systems where

freshwater delivery has been reduced as a consequence of climatic shifts, i.e., drought, or

changing patterns of consumptive use by humans, e.g., groundwater withdrawal.

With regard to species specific responses to changes in salinity, Doering et al.

(2001) exposed V. americana to 18 %o salinity for 1, 5, 11, and 20 days, but failed to

detect significant effects on blade length or number of blades per shoot. These









investigators did observe a decreasing trend, however, in the number of blades produced

and the number of clones produced with increasing duration of exposure. Similar

qualitative patterns were observed in this study for V. americana exposed to 15 %o

salinity. Interestingly, Haller et al. (1974) reported that V. americana exhibited decreased

growth with increased salinity, even at relatively low salinity values, i.e., 3.33 and 6.66

%o. The duration of exposure may have been a major contributing factor to the results

found in the above study since all plants were exposed to the prescribed salinities for 4-

weeks with no recovery period. Clearly, V. americana can tolerate exposure to much

higher salinities, at least for short durations. In this study, V. americana was able to

persist when subjected to salinities of 15 %o for two days or less, though decreases in

growth related measures were observed relative to controls. The negative effects of

exposure to 15 %o salinity were intensified after 7 days when compared to 1 and 2-days

exposure duration. The 75% mortality of V. americana at 15 %o after 7 days indicates an

inability to recover from rapid salinity changes near the upper-limit of its reported

salinity tolerance, especially when exposure is for more than a few days. The ability of

V. americana to tolerate 18 %o salinity for upwards of 50-days in the long-term

experiments of Doering et al. (2001) may be reflective of adaptations specific to this

species in the Caloosahatchee estuary (Gulf Coast, South Florida) or the result of the

experimental protocol in which salinity was gradually increased to 18 %o over several

days.

The high (100%) mortality experienced by H. verticillata exposed to 15 or 25 %o

salinity, regardless of exposure duration was not surprising. Previous studies have shown

H. verticillata to grow optimally in freshwater, though results on its tolerance to saltwater









are somewhat conflicted. Haller et al. (1974) transplanted Hydrilla into indoor

mesocosms of differing salinities and observed no growth at salinities >6.66 %o. Twilley

and Barko (1990b) increased salinity gradually and found that Hydrilla showed little

productivity at salinities above 4 %o. In stark contrast to the reports by Haller et al.

(1974) and Twilley and Barko (1990b), and also the findings reported herein, Steward

and Van (1987) present data indicating growth of H. verticillata at salinities up to 13 %o.

The variability in the findings may be explained partly by differing methodologies

(gradual increase vs. rapid changes in salinity), but may also be explained by differences

in the genetic makeup or physiological characteristics of plants from different

environments. Plants from estuarine and brackish habitats, such as Kings Bay, may

experience subtle and possibly frequent salinity changes that have resulted in their ability

to adapt to higher salinities. This may explain the fact that H. verticillata in the current

study seemed to tolerate and almost favor 5 %o salinity, as there was a slight trend for

greater branching and higher biomass when compared to control plants.

Myriophyllum spicatum, in this study, exhibited successful growth and productivity

at 5 %o salinity. However, a significant decrease in branching, growth, and biomass gain

d-1 at 15 %o, regardless of exposure duration, was observed. This result is consistent with

the decrease in growth ofM spicatum exposed to a 13.32 %o reported by Haller et al.

(1974). The findings reported here and those reported by Haller et al. (1974) conflict

with the results of Twilley and Barko (1990b) who observed a general increase in M.

spicatum biomass with increasing salinity, up to 12 %o. However, Twilley and Barko

(1990b) gradually increased the salinity over several days, which may have allowed more

time for physiological adjustment to the environment. Myriophyllum spicatum was the









only species in this study to exhibit any tolerance to 25 %o salinity, although each of the

growth-related measures were significantly less than those of control plants. Its seeming

tolerance at 1 and 2 days exposure could give it a competitive advantage over the other

two species.

While the current study does not directly address competition between these

species, it does help to understand how salinity might possibly mediate competition and

provides a foundation for further investigation of this important topic. Results of this

study may also be used in conjunction with salinity monitoring efforts in Kings Bay and

other estuarine areas to predict where submersed plants are likely to occur and may also

be used to develop conservation strategies and help guide restoration efforts. It is

possible, based on the findings reported here, that the dynamic nature of Kings Bay

(which includes the occurrence of frequent storm events) precludes large-scale restoration

efforts of V. americana as the system may be episodically reset allowing for rapid

colonization and persistence of invasive species such as M spicatum and H. verticillata.

Longer-term data that characterizes variability in the vegetative structure in relation to

salinity is essential as managers seek to understand and predict the impacts of water use

activities (ground water withdrawals in particular) and storm events on the ecology Kings

Bay.















LIST OF REFERENCES


Barko, J. W., Smart, R. M. and D. G. McFarland. 1991. Interactive effects of
environmental conditions on the growth of submersed aquatic macrophytes.
Journal of Freshwater Ecology 6(2): 199-207.

Blackburn, R. D. and L. W. Weldon. 1967. Eurasian watermilfoil Florida's new
underwater menace. Hyacinth Control Journal 6:15-18.

Blanch, S. J., Ganf, G. G. and K. F. Walker. 1998. Growth and recruitment in
Vallisneria americana as related to average irradiance in the water column.
Aquatic Biology 61:181-205.

Bowes, G., Van, T. K., Garrard, L. A. and W. T. Haller. 1977. Adaptation to low light
levels by Hydrilla. Journal of Aquatic Plant Management 15:32-35.

Canfield, D. E. and M. V. Hoyer. 1988. Influence of nutrient enrichment and light
availability on the abundance of aquatic macrophytes in Florida streams. Canadian
Journal of Fisheries and Aquatic Sciences 45:1467-1472.

Citrus County Chronicle. March 23, 1986 (3A). Crystal River wants to clean up canals.
Iverness, FL.

Citrus County Chronicle. May 14, 1986. Study says wastewater not the cause of water
weed problem. Iverness, FL.

Dick, T. H. 1989. Crystal River: A "No Win" situation. Aquatics 11(2):10-13.

Doering, P. H., Chamberlain, R. H. and J. M. McMunigal. 2001. Effects of simulated
saltwater intrusions on the growth and survival of Wild Celery, Vallisneria
americana, from the Caloosahatchee Estuary (South Florida). Estuaries
24(6A):894-903.

Doering, P. H., R. H. Chamberlain, and D. E. Haunert. 2002. Using submerged aquatic
vegetation to establish minimum and maximum freshwater inflows to the
Caloosahatchee Estuary, Florida. Estuaries 25(6B):1343-1354.

Doyle, R. D. and R. M. Smart. 1995. Potential use of native aquatic plants for long-term
control of problem aquatic plants in Guntersville Reservoir, Alabama: Report 2.
Competitive interactions between beneficial and nuisance species. Technical
Report A-93-6, US Army Corps Engineers, Waterways Experiment Station,
Aquatic Plant Control Research Program, Vicksburg, MS, 52pp.









Elakovich, S. D. 1989. Allelopathic aquatic plants for aquatic weed management.
Biologia Planatarum (Praha) 31(6):479-486.

Frazer, T. K. and J. A. Hale. 2001. An atlas of submersed aquatic vegetation in Kings
Bay (Citrus County Florida). Final Report. Southwest Florida Water Management
District. Brooksville, Florida.

Frazer, T. K., Notestein, S. K., Hoyer, M. V., Hale, J. A. and D. E. Canfield, Jr. 2001a.
Physical, chemical and vegetative characteristics of five Gulf coast rivers. Final
Report. Southwest Florida Water Management District, Brooksville, Florida

Frazer, T. K., Notestein, S. K., Hoyer, M. V., Hale, J. A. and D. E. Canfield, Jr. 2001b.
Frequency and duration of pulsed salinity events in Kings Bay. Final Report.
Southwest Florida Water Management District, Brooksville, Florida.

Haller, W. T. 1978. Hydrilla: A new and rapidly spreading aquatic weed problem.
Agriculture Experiment Stations/IFAS/Gainesville, Florida/ Agronomy
Department, University of Florida.

Haller, W. T. and D. L. Sutton. 1973. Community structure and competition between
Hydrilla and Vallisneria. Hyacinth Control Journal 13:48-50.

Haller, W. T., Sutton, D. L. and W. C. Barlowe. 1974. Effects of salinity on growth of
several aquatic macrophytes. Ecology 55(4):891-894.

Hauxwell, J. A, Frazer, T. K. and C. W. Osenberg. 2003. Effects of herbivores and
competing primary producers on Vallisneria americana in Kings Bay:
implications for restoration and management. Final Report. Southwest Florida
Water Management District, Brooksville, Florida.

Hauxwell, J. A., Osenburg, C. W. and T. K. Frazer. 2004a. Conflicting management
goals: Manatees and invasive competitors inhibit restoration of a native
macrophyte. Ecological Applications 14(2):571-586.

Hauxwell, J. A., Osenburg, C. W. and T. K. Frazer. 2004b. Grazing by manatees
excludes both new and established wild celery transplants: Implications for
restoration in Kings Bay, FL, USA. Journal of Aquatic Plant Management 42:49-
53.

Hoyer, M. V., Mataraza, L. K., Munson, A. B. and D. E. Canfield, Jr. 1997. Water
Clarity in Kings Bay/Crystal River. Final Report. SWIM Department, Southwest
Florida Water Management District, Brooksville, Florida.

Hoyer, M. V., Frazer, T. K., Canfield, D.E., Jr. and J. M. Lamb. 2001. Vegetation
evaluation in Kings Bay/Crystal River. Final Report. Southwest Florida Water
Management District, Brooksville, Florida.









Jones, H. L. 1995. Allelopathic ability of various aquatic plants to inhibit the growth of
Hydrilla verticillata (L.f) Royle and Myriophyllum spicatum L. Final Report.
U.S. Army Corps of Engineers. Technical Report A-95-1. Washington, D.C.

Kraemer, G. P., Chamberlain, R. H., Doering, P. H., Steinman, A. D. and M. D. Hanisak.
1999. Physiological responses of the freshwater angiosperm Vallisneria americana
along a salinity gradient in the Caloosahatchee Estuary (Southwestern Florida).
Estuaries 22(1):138-148.

Langeland, K. A. 1990. Hydrilla (Hydrilla verticillata (L.f.) Royle): A continuing
problem in Florida waters. Circ. No. 884. Coop. Ext. Serv., IFAS, Univ. of Florida,
Gainesville, 21pp.

Mataraza, L. K., Terrell, J. B., Munson, A. B. and D. E. Canfield, Jr. 1999. Changes in
submersed macrophytes in relation to tidal storm surges. Journal of Aquatic Plant
Management 37:3-12.

Mobley, A. 1992. Kings Bay/Crystal River: Charting a course to rehabilitation.
Hydroscope 23(1): 10-11.

Mulholland, M. M. and M. L. Otte. 2002. The effects of nitrogen supply and salinity on
DMSP, glycine betaine and proline concentrations in leaves of Spartina anglica.
Aquatic Botany 72:193-200.

Notestein, S. K., Frazer, T. K., Keller, S. R. and R. A. Swett. 2005. Crystal River/Kings
Bay vegetation evaluation 2004. Annual Report. Southwest Florida Water
Management District, Brooksville, Florida.

Rout, N. P. and B. P. Shaw. 1998. Salt tolerance in aquatic macrophytes: probable role
of proline, the enzymes involved in its synthesis and C4 type of metabolism. Plant
Science 136:121-130.

Rout, N. P. and B. P. Shaw. 2001. Salt tolerance in aquatic macrophytes: possible
involvement of the antioxidative enzymes. Plant Science 160:415-423.

Stanley, R. A. 1974. Effect of 2,4-D and various salts on Eurasian Watermilfoil. Weed
Science 22:591-594.

Steward, K. K. and T. K. Van. 1987. Comparative studies of monoecious and dioecious
Hydrilla (Hydrilla verticillata) biotypes. Weed Science 35:204-210.

Sutton, D. L. and K. M. Portier. 1985. Density of tubers and turions of Hydrilla in South
Florida. Journal of Aquatic Plant Management 23:64-67.

Terrell, J. B. and D. E. Canfield, Jr. 1996. Evaluation of the effects of nutrient removal
and the "Storm of the Century" on submersed vegetation in Kings Bay-Crystal
River, Florida. Journal of Lake and Reservoir Management 12(3):394-403.









Titus, J. E. and M. S. Adams. 1979. Coexistence and the comparative light relations of
the submersed macrophytes Myriophyllum spicatum L. and Vallisneria americana
Michx.. Oecologia (Berl.) 40:273-286.

Twilley, R. R. and J. W. Barko. 1990a. Effects of salinity and irradiance conditions on
the growth, morphology, and chemical composition of submersed aquatic
macrophytes. Final Report. US Army Corps of Engineers, Aquatic Plant Control
Research Program. Technical Report A-90-5, 25pp.

Twilley, R. R. and J. W. Barko. 1990b. The growth of submersed macrophytes under
experiment salinity and light conditions. Estuaries 13(3):311-321.

Van, T. K., W. T. Haller, and G. Bowes. 1978. Some aspects of the competitive biology
of Hydrilla. Pages 117-125 of Proceedings of the EWRS 5th Symposium on
Aquatic Weeds.

Van, T. K., Wheeler, G. S. and T. D. Center. 1998. Competitive interactions between
Hydrilla (Hydrilla verticillata) and Vallisneria (Vallisneria americana) as
influenced by insect herbivory. Biological Control 11:185-192.

Van, T. K., Wheeler, G. S. and T. D. Center. 1999. Competition between Hydrilla
verticillata and Vallisneria americana as influenced by soil fertility. Aquatic
Botany 62:225-233.

Yobbi, D. K. and L. A. Knochenmus. 1989. Effects of river discharge and high-tide
stage on salinity intrusion in the Weeki Wachee, Crystal, and Withlacoochee River
estuaries, southwest Florida: U.S. Geological Survey Water-Resources
Investigations Report 88-4116, 63pp.















BIOGRAPHICAL SKETCH

I pursued my undergraduate degree at Texas A&M University Corpus Christi and

received a B.S. in biology: Marine Emphasis along with a minor in public relations in

May 2003. As an undergraduate, I participated in several research projects through the

AMP (Alliance for Minority Participation) Program at TAMU-CC. I was also involved in

REU (Research Experience for Undergraduates) programs at Rice University, University

of Oregon-Hatfield Marine Science Center, and Western Washington University-

Shannon Point Marine Center. My experience has been diverse, ranging from tallow tree

invasion of coastal prairies, to crab larvae ingestion of toxic dinoflagellates, to use of the

lateral line by juvenile walleye Pollock while feeding. I also worked three years as a

research assistant with USGS looking at the habitat selection and feeding behavior of

wintering burrowing owls, Athene cunicularia, in South Texas. However, my loyalty

remains with aquatic ecosystems, and more specifically to conservation and management.

My most recent experience at the University of Florida as an M.S. candidate under Dr.

Thomas Frazer has been a step in the right direction and results of my research will

hopefully contribute to future management strategies for submersed plants.