Assessing the Quality of Alternative Habitats Used by Grass Shrimp Palaemonetes Spp.

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Title:
Assessing the Quality of Alternative Habitats Used by Grass Shrimp Palaemonetes Spp.
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english
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Montgomery,Meredith L
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Master's ( M.S.)
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University of Florida
Degree Disciplines:
Fisheries and Aquatic Sciences
Committee Chair:
Frazer, Tom K
Committee Members:
Behringer, Donald Charles
Jacoby, Charles A

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Fisheries and Aquatic Sciences -- Dissertations, Academic -- UF
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Abstract:
The biomass of native aquatic plants continues to diminish in Florida?s freshwater and estuarine environments due to a variety of stressors. The Chassahowitzka River exemplifies this trend with remnant patches of native macrophytes interspersed among mats of filamentous algae and patches of Myriophyllum spicatum, a non-native macrophyte. The relative quality of these alternative habitats was assessed by measuring Palaemonetes spp. growth rates, reproductive output, relative survival, and relative abundance. High quality habitats should support more grass shrimp, higher survival, enhanced growth, and greater reproductive output. Growth rates were statistically equal for juveniles and adult males from all habitats in which they were collected, i.e., filamentous algae, Potamogeton pectinatus, and Vallisneria americana. Intermolt periods were significantly shorter for juveniles relative to adult males, but the time between molts did not differ significantly among for shrimp from different habitats. Reproductive output was greatest for grass shrimp in V. americana, with small females producing more numerous, small eggs. Relative survival was lower for shrimp tethered in filamentous algae than those tethered in patches of rooted macrophytes. The native V. americana yielded the greatest number of grass shrimp, and evidence suggested it provided the highest quality habitat because grass shrimp survived better and reproduced more quickly and more prolifically. Continued loss of native macrophytes, e.g.,V. americana and P. pectinatus, with a shift to algae or non-native plants will negatively affect grass shrimp populations and potentially cause detrimental effects to populations of fish and invertebrates that prey on these species.
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by Meredith L Montgomery.
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Thesis (M.S.)--University of Florida, 2011.
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Adviser: Frazer, Tom K.
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1 ASSESSING THE QUALITY OF ALTERNATIVE HABITATS USED BY THE GRASS SHRIMP PALAEMONETES SPP. By MEREDITH MONTGOMERY A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREM ENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2011

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2 2011 Meredith Montgomery

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3 To my family, human and canine

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4 ACKNOWLEDGMENTS I would like to thank Dr. F razer and Dr. Jacoby for their mentorship and support of this proje ct. A special thank you is extended to Dr. Jacoby who fit me into his very busy schedule and managed to be entertained patiently by my weekly, inevitable mistakes. This project would have never been completed without him. I would like to thank my committee for their comments, which served to greatly improve the quality of this manuscript. I would like to thank Lauren Sweet for her hard work, unfailin g laughter, and excellent story telling while scooping shrimp in the murky algae beds of the river. I dearly t hank my parents who have contributed their time, love, and free dog sitting. I would finally like to thank Nor m and Mark who kept an eye out for my safety over long field days and taught me the history of the Chassahowitzka River.

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5 TABLE OF CONTENTS pag e ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 6 LIST OF FIGURE S ................................ ................................ ................................ .......... 8 ABSTRACT ................................ ................................ ................................ ..................... 9 CHAPTER 1 INTRODUCTARY REMARKS ................................ ................................ ................. 11 2 MATERIALS AND METHODS ................................ ................................ ................ 13 Study Site ................................ ................................ ................................ ............... 13 Submerged Aquatic Vegetation ................................ ................................ .............. 13 Study Species ................................ ................................ ................................ ......... 14 Relative Abundance ................................ ................................ ................................ 17 In situ Growth Experiments ................................ ................................ ..................... 18 Reproductive Output ................................ ................................ ............................... 20 Relative Survival Rates ................................ ................................ ........................... 21 Statistical Analyses ................................ ................................ ................................ 21 3 RESULTS ................................ ................................ ................................ ............... 24 Environmental Cond itions ................................ ................................ ....................... 24 Relative Abundance ................................ ................................ ................................ 24 Relative Survival ................................ ................................ ................................ ..... 25 In situ Growth Experiments ................................ ................................ ..................... 25 Mo dal Progression Analysis ................................ ................................ .................... 27 Fecundity ................................ ................................ ................................ ................ 27 Egg Volume ................................ ................................ ................................ ............ 28 Brood Volume ................................ ................................ ................................ ......... 28 Size at Maturity ................................ ................................ ................................ ....... 28 4 DISCUSSION ................................ ................................ ................................ ......... 47 LIST OF REFERENCES ................................ ................................ ............................... 56 BIOGRAPHICAL SKETCH ................................ ................................ ............................ 61

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6 LIST OF TABLES Table page 3 1 Two way ANOVA based on log 10 transformed salinities (ppt) measured along three transects in February, May and August 2009.. ................................ .......... 30 3 2 Two way ANOVA based on log 10 transformed temperatures (C) measured along thre e transects in February, May and August 2009.. ................................ 30 3 3 One way ANOVA based on log 10 transformed grass shrimp m 3 captured from fila mentous algae, P. pectinatus V. americana and M. spicatum in July 2009.. ................................ ................................ ................................ ................. 30 3 4 Two way ANOVA based on log 10 transformed grass shrimp m 3 captured from P. pectinatus V. americana and M. spicatum in July and August 2009.. ... 30 3 5 One way ANOVA based on arcsi n transformed proportional survival rates in filamentous algae, P. pectinatus and V. americana .. ................................ .......... 31 3 6 Analysis of covariance bas ed on log 10 transformed wet weights with log 10 transformed total length as a covariate. ................................ .............................. 31 3 7 Two way ANOVA based on intermolt periods associated with positive growth for juveniles and males from filamentous algae, P. pectinatus and V. americana ................................ ................................ ................................ .......... 31 3 8 Two way ANOVA based on log 10 transformed positive instantaneous growth rates for juvenile and male shrimp from filamentous algae, P. pectinatus and V. americana .. ................................ ................................ ................................ .... 31 3 9 Two way ANOVA based on arcsin transformed percentage growth rates for juvenile and male shrimp from filamentous algae, P. pectinatus and V. americana ................................ ................................ ................................ .......... 32 3 10 Regression analysis of instantaneous growth of all shrimp by holding time. ...... 32 3 11 Regression analysis of instantaneous growth of juvenile shrimp by holding time. ................................ ................................ ................................ .................... 32 3 12 Regression analysis of instantaneous growth of adult male shrimp by holding time ................................ ................................ ................................ ..................... 32 3 13 Analysis of covariance ba sed on log 10 transformed numbers of eggs and embryos with total length as a covariate ................................ ............................. 32 3 14 Analysis of covariance based on log 10 transformed egg volumes with total length as a covariate. ................................ ................................ ......................... 33

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7 3 15 Analysis of covariance based on log 10 transformed brood volumes with total length as a covariate.. ................................ ................................ ........................ 33 3 16 Two way ANOVA based on total lengths of reproductive females from filamentous algae, P. pectinatus and V. americana in June and July 2009. ...... 33 3 17 Two way ANOVA based on total lengths of reproductive females from P. pectinatus, and V. americana in June, July, and August 2009 ........................... 34

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8 LIST OF FIGURES Figure page 2 1 Location of the Chassahowitzka River along the west coast of peninsular Florida. Diagram from Frazer et al. 2006. ................................ ........................... 23 3 1 Mean num ber of grass shrimp m 3 95% confidence limits (CL). ...................... 35 3 2 Back transformed mean proportional survival rates 95% confidence l imits (CL) for grass shrimp tethered in three habitats. ................................ ................ 36 3 3 Size frequency distributions of grass shrimp collected from filame ntous algae, P. pectinatus and V. americana in June August 2009. ............................ 37 3 4 Log 10 transformed wet weight versus log 10 transformed total length for all Palaemonetes species with and without isopods. ................................ ............... 38 3 5 Total length (mm) vs. telson length (mm) of Palaemonetes spp. ........................ 39 3 6 Mean intermolt period standard error (SE) by habitat and life history stage. ... 40 3 7 Total number of molting shrimp by life history stage and holding time (12 hour intervals, 4 d). ................................ ................................ ............................. 41 3 8 Size frequency distributions of juveniles used in modal progression analysis. ... 42 3 9 Relationships between log 10 transformed number eggs and embryos and total length for females collected in filamentous algae, P. pectinatus and V. americana ................................ ................................ ................................ .......... 43 3 10 Relationships between log 10 transformed egg volumes and total length for females collected in filamentous algae, P. pectinatus and V. americana .......... 44 3 11 Back transformed mean total lengths (mm) 95% confidence limits (CL) for mature females. ................................ ................................ ................................ .. 45 3 12 Size frequency distribution for mature female grass shrimp females from filamentous algae, P. pectinatus and V. americana ................................ ........... 46

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9 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 ASSESSING THE QUALITY OF ALTERN ATIVE HABITATS USED BY GRASS SHRIMP PALAEMONETES SPP. By Meredith Montgomery August 2011 Chair: Thomas Frazer Major: Fisheries and Aquatic Sciences and estuarine environment s due to a variety of stressors. The Chassahowitzka River exemplifies this trend with remnant patches of native macrophytes interspersed among mats of filamentous algae and patches of Myriophyllum spicatum a non native macrophyte. The relative quality of these alternative habitats was assessed by measuring Palaemonetes spp. growth rates, reproductive output, relative survival, and relative abundance. High quality habitats should support more grass shrimp, higher survival, enhanced growth, and greater repro ductive output. Growth rates were statistically equal for juveniles and adult males from all habitats in which they were collected i.e., filamentous algae, Potamogeton pectinatus and Vallisneria americana Intermolt periods were significantly shorter for juveniles relative to adult male s, but the time between molts did not differ significantly among for shrimp from different habitats. Reproductive output was greatest for grass shrimp in V americana with small females producing more numerous, small eggs. Relative survival was lower for shrimp tether ed in filamentous algae than those tethered in patches of rooted macrophytes. The native V. americana yielded the greatest number of grass shrimp and evidence suggested it

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10 provided the highest quality habitat because grass shrimp survived better and reproduced more quickly and more prolifically. Continued loss of native macrophytes, e.g., V americana and P pectinatus with a shift to algae or non native plants will negatively affect grass shrimp populations and potentially cause detrimental effects to populations of fish and invertebrates that prey on these species.

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11 CHAPTER 1 INTRODUCTARY REMARKS The biomass of native aquatic plants continues to diminish in many of freshwater and estuarine environmen ts due to physical disturbance, changing salinity regimes eutrophication increased algal biomass expansion of introduced species and other stressors (Frazer, Notestein & Pine III 2006 ) Surveys have documented such changes in the Chassahowitzka River (F razer et al. 2006). Historically dominated by Vall is neria americana the river also contained other native macrophytes, e.g., Sagittaria kurziana and P otamogeton pectinatus but it now contains significant amounts of filamentous algae, including Lyngb y a s p., and M yriophyllum spicatum an introduced plant. An understanding of the relative quality of these alternative habitats would improve evaluations of costs and benefits associated with removing introduced and nuisance species or restoring native vegetati on (Beck et al. 2001; Castellanos and Rozas 2001). Efforts to evaluate habitat quality in aquatic systems have focused primarily on comparisons of vegetated and unvegetated habitats using measures of density and diversity, with higher values assumed to b e correlated with higher quality habitats (Van Horne 1983 ; Castellanos and Rozas 2001). Castellanos and Rozas (2001) pointed to the need to compare less dissimilar habitats, and Van Horne (1983) contended that density and diversity do not assess habitat quality adequately Species diversity does not always indicate habitats of highest quality, e.g., old growth forest s with relatively low diversity provide significant value to specialists (Van Horne 1983). In addition, assuming a positive correlation be tween species abundance and habitat quality can be misleading when habitats are used seasonally or when habitats of marginal quality

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12 become sinks for individuals displaced from higher quality sites resulting in unstable groups of immigrants that survive an d reproduce poorly (Van Horne 1983 ; Chockley St. Mary & Osenberg 2008). To avoid drawing misleading conclusions from diver sity and abundance data, Van Horne ( 1983 ) recommended evaluating habitat quality with a combination of density, growth, survival an d reproduction. High quality habitat would provide enhanced nutritional resources and refuge from predation, thereby supporting higher densities, survival rates, growth rates and fecundity, with resident populations gaining stability and the capacity to su rvive poor years (Van Horne 1983). Palaemonetes spp. or grass shrimp (Decapoda Palaemonidae) should yield valuable insights into the relative quality of alternative, vegetated habitats in the Chassahowitzka River. These shrimp are abundant and distributed widely in the rivers and estuaries along the Gulf and Atlantic coasts. In this study, proxy measures of fitness were compared among grass shrimp collected from alternative, vegetated habitats in the Chassahowitzka River during the summer of 2009. Measures chosen to assess the quality of available habitats were growth, reproductive output (fecundity, egg volume, and brood volume ), size at maturity, relative survival, and relative abundance.

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13 CHAPTER 2 MATERIALS AND METHOD S Study S ite This study was c onduct ed in the spring fed and tidally influenced Chassa howitzka R iver, Florida (Figure 2 1) In t h is river the submerged aquatic vegetation is changing Native macrophytes which included V americana P pectinatus and Naja s guadalupensis are being replaced by non native vascular aquatic plants ( e.g., M spicatum ) and filamentous algae ( e.g., Lyngb y a spp .) (Frazer et al. 2006) Submerged Aquatic Vegetation Submerged aquatic vegetation provides much of the habitat structure within the Chassahowitzka River V a llis neria amer icana is a rooted native aquatic macrophyte which historically dominated the Chassahowtizka River It has long, tape like leaves that grow throughout the depth of the water column is somewhat tolerant of brackish water conditions and persis ts year round Potamogeton pectinatus is thinly and extensively branched, with short and strap like associated leaves that grow to the height of the water column It was often found in fresh to brack ish, low flow areas of the Chassahowitzka and persists ye ar round The morphology of f ilamentous algae (e.g., Lyng bya spp.) varies among season s ; it is highly structured and extends throughout the water column during late fall and win ter before becoming a mat like layer in late spring and summer. It often disapp ears in late summer and early fall Myriophyllum spicatum has finely branched leaves in whorls that often reach and float on the water the Chassahowitzka River, this species creates a layer of tangled stems and whorls at with few branches or leaves persist ing below the water surface

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14 Study Species Grass shrimp, as their name implies, typically associate with seagrass or aquatic macrophytes (Anderson 1985). Aquatic macrophytes with different heights, growth forms, and de nsities create habitats with differing levels of physical complexity that mediate predation on grass shrimp to varying degrees (Coen Heck & Abele 1981 ; Bell et al. 1984 ; Orth van Montfrans & Fishman 1999 ; Castellanos and Rozas 2001). Thus, the assembl age composition of submerged aquatic vegetation will affect the survival of grass shrimp. In fact, loss or removal of aquatic vegetation (e.g., due to coastal dredging) has been shown to reduce their abundance (Anderson 1985 ; Rosas and Odum 1987). Furthe rmore, Palaemonetes spp. are euryhaline, eurythermal and capable of using sites with low dissolved oxygen as temporary refuge from predation or places to forage on detritus (Welsh 1975 ; Anderson 1985 ; Lowe and Provenzano 1990 ; Rowe et al. 2002). Theref ore, the effects of habitat quality should not be masked by variable responses to the range of salinities, temperatures or oxygen concentrations that characterize tidally influenced rivers and other downstream estuarine habitats. Grass shrimp have been cla ssified as rapid dispersers, but directional movement may be sporadic (Darcy 2003). Howard (1985) reported that 60 75% of Palaemonetes spp. remained in the same habitat patch six hours after they were stained, which indicated Palaemonetes spp. may remain in a habitat long enough for measures of fitness to reflect habitat quality. Though these species are of little interest to human consumers, they are extremely valuable in coastal ecosystems (Anderson 1985). Grass shrimp serve as important prey for fishes invertebrates, and other carnivores in these systems, including juveniles of valued species (Welsh 1975 ; Kunz Ford & Pung 2006 ; Frazer Lauretta &

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15 Pine III 2011) In fact, gra ss shrimp play a key role in transferring energy from the base of food webs to higher trophic levels (Welsh 1975). Adult Palaemonetes spp. have been classified as opportunistic, generalist feeders, and they have been documented to be detritivores, omnivores and facultative grazers on epiphytes, (Welsh 1975 ; Beck and Cowell 197 6 ; Bell and Coull 1978 ; Morgan 1980 ; Anderson 1985 ; McCall 2007). Juvenile grass shrimp have been described as obligate, planktonic carnivores and detritivores (Anderson 1985). Furthermore, Palaemonetes pugio has been documented to accelerate the brea kdown of detritus, making nutrients and carbon available to multiple trophic levels as fecal pellets which enhance production of seagrass (McCall 2007), dissolved organic matter, and shrimp biomass (Welsh 1975 ; Anderson 1985). Because of their importan t ecological role, naturally high abundances and year round availability, grass shrimp have been used as an indicator of habitat quality in studies focused on occupancy and density (Williams 1984 ; Kneib 1987 ; Glancy et al. 2003). Decapods, including Pal aemonetes spp., grow incrementally through ecdysis, which can simplify studies of their growth. Ecdysis results from decreased levels of molting inhibiting hormone (MIH) and synthesis of ecdysteroids (Fingerman 1997 ; Chang Chang & Mulder 2001 ). This hor monal cascade causes grass shrimp to shed their cuticles, enabling both growth and copulation. The relative irreversibility of the cascade makes grass shrimp suitable for short term molting experiments designed to estimate intermolt periods and growth rate s (e.g., the methods of Ross et al. 2000). Growth of Palaemonetes spp. peaks during the summer when temperatures are consistently high and resources are abundant, with growth rates estimated to reach 0.133 0.143 mm d 1 in adults (Anderson 1985). Grass sh rimp achieve maximum

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16 lengths of 42 50 mm and live 6 13 months (Anderson 1985). Parasites (like the bopyrid isopods observed on the gills of Palaemonetes spp. in the Chassahowitzka River) have not been documented to limit the growth of Gulf grass shrimp (A nderson 1985). Adult female Palaemonetes spp. brood eggs. From February to October along the C entral Gulf coast Florida females of Palaemonetes spp. grow extra setae in their abdominal brood pouches to hold eggs during this reproductive season (Anderson 1985 ; Raviv Parnes & Sagi 2008). Broods of Gulf Coast populations develop in 12 22 d, which allows a mature female to bear up to eight broods between April and September (Anderson 1985 ; Bauer and Abdalla 2000). Ecdysis, mating, and oviposition are cou pled tightly; female grass shrimp have been observed to molt soon after vitellogenesis and mating; and females will not molt later in the brooding cycle as embryos could be lost (Bauer and Abdalla 2000 ; personal observation). Females continue somatic grow th after reaching maturity at 22 44 mm, although growth rates decrease (Beck and Cowell 1976 ; Anger and Morriera 1998). In Florida, Beck and Cowell (1976) found that female Palaemonetes spp. hatched in early spring were able to reproduce in late summer a t 20 24 mm and in late winter at 35 43 mm. Overall, the tendency to brood multiple batches of eggs during the year makes grass shrimp suitable for evaluating differences in reproductive output as a metric of habitat quality. Three species of Palaemonetes i nhabit the Chassahowitzka River: Palaemonetes pugio P. intermedius and P. vulgaris These species exhibit similar morphologies, growth and reproduction (Broad 1957 ; Thorpe 1976 ; Anderson 1985). The species may partition available habitat and alleviate niche overlap through agonistic behavior or microhabitat choice based on salinity, e.g., P. vulgaris has been documented to expend

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17 more energy in low salinity habitats ( Thorpe 1976 ; Skadsheim 1984 ; Anderson 1985 ; Rowe 2002). Similar to other Gulf coas t populations, abundances and reproductive effort of grass shrimp in the Chassahowitzka River peak in summer and early fall (Beck and Cowell 1976 ; Castellanos and Rozas 2001 ) with increased availability of brooding females mak ing summer a suitable time to evaluate habitat quality. Relative A bundance In June, July and August 2009, sampling to assess the relative abundance of grass shrimp was conducted in discrete patches of V americana P pectinatus M spicatum and filamentous al gae Habitat patches of similar scale were selected according to the ir dominant vegetation and heterogeneous patches were avoided P atch dimension s to the nearest meter [ length and width ( SE) ] were 16 ( 2) m and 13 ( 1) m for V americana ; 16 ( 1) m and 6 ( 2) m for P pect inatus ; 29 ( 9) m and 5 ( 3) m for filamentous algae ; and 8 ( 1) m ; and 4 m for M spicatum Patches were located in a uniform reach of the river as delineated by temperatures and salinities measured at stations along three transects in February, May an d August 2009 as part of a complementary project documenting water quality and the distribution of vegetation R elative abun dance of grass shrimp was assessed via s tandardize d 0.14 m 3 sweeps of a hand held dip net ( 1 mm 1 mm mesh ) made at the approxima t e center of each habitat patch to avoid edge effects A minimum of 4 sweeps was made, and sweeping ceased if 150 individuals were collected (the target number for in situ growth experiments) or after 10 sweeps Shrimp were counted and held in aerated coole rs prior to growth experiments.

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18 In s itu G rowth E xperiments Upon completion of standardized sweeps, non standardized sweeps were made if additional individuals were needed for growth experiments or studies of reproduction. Collections continued until approx imately 150 individuals were captured and stored in an aerated cooler or until disturbance of the patch, high tide or sunset precluded successful sampling. Individual shrimp were transferred from the aerated cooler into separate small glass jars (6 8 oz). Aside from two initial trials in June that did not include ovigerous females shrimp were selected without regard to size, maturity or presence of eggs Mesh screens (1 mm 1 mm) affixed with rubber bands restrained the shrimp within the jar s while allo wing exchange of water Jars containing shrimp were held in a cooler (< 1 h ) until 11 50 jars with shrimp were placed in a slotted, plastic bin (60 3 8 20 cm) and returned to the river. These bins were used to organize held shrimp and did not restrict e to river water. B ins containing shrimp from all habitat types were held in a small V americana patch (28.71467 N 82.58437 W ) for approximately 96 h. The V americana patch was chosen because it had relatively high dissolved ox ygen concentrations, was located in shallow water and was protected from boat traffic S hrimp were checked for evidence of molting or mortality at approximately 12 h interval s ( 0 6:30 and 18:30) for 96 h Upon evidence of molt ing each shrimp and its exu v i a were placed in a labeled, plastic centrifuge vial containing 90% ethanol to prevent deterioration of soft shelled recently molted shrimp and frozen. S hrimp that died or did not molt during the experiment were frozen for morphometric analyses. Grass shri mp and their exuviae were processed to yield measure s of growth and morphometric relationships between telson length and total length and wet weight and

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19 total length S hrimp were lightly washed with water to remove excess debris and dirt, subsequently blot ted with paper towels to remove excess water, and weighed to the nearest 0.1 mg T he t otal length of each shrimp i.e. from the tip of its rostrum to the tip of its fully extended tail, was measured to the nearest 0. 5 mm with a ruler T otal length was not recorded if a rostrum or tail was broken Exuviae typically comprised multiple or poorly connected pieces ; therefore, growth could not be assessed by comparing the total lengths of the post molt shrimp and its exuvia. Instead, lengths of unbroken telsons w ere measured to the nearest 0.01 mm using a dissectin g microscope and ocular micrometer with growth to be assessed by comparing telson lengths from post molt shrimp and their exuviae and by using the morphometric relationship between total lengths and tel son lengths Intermolt periods instantaneous growth rates and percentage growth rates were estimated according to the methods of Ross et al. 2000 (Equations 2 1, 2 2 and 2 3): ( 2 1 ) ( 2 2 ) ( 2 3 ) During processing, g rass shrimp were classifi ed to species in accordance with W illi ams 1984. In addition, g rass shrimp were classified as being ovigerous, post ovigerous, or non ovigerous . Ovigerous and post ovigerous shrimp were considered sexually mature females The m inimum total length of these females across all samples was use d as the criterion for classifying non ovigerous shrimp as either adult males or juveniles

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20 Grass shrimp also were examined for the presence of bopyrid isopod s on their gills Isopod length s and width s were meas ured to the nearest 0.01 mm using Vernier cal ipers held over the carapace s of the shrimp. Subsequently, i sopods were removed with tweezers and weighed to the n earest 0. 1 m g Reproductive O utput All ovigerous females were categorized as having an open abdom inal brood pouch or a closed brood pouch C lo sed brood pouches were assumed to contain an entire brood whereas, individuals with split or open brood pouches were assumed to have lost eggs The closed brood pouches were open ed with a scalpel and the scalpel and water w ere used to free eggs and embry os Care was taken to avoid remov ing claws, legs or swimmerettes. All eggs and embryos were counted with the aid of a compound microsc ope. Embryos were distinguished from eggs by the presence of eyespots or visible cell proliferation and they were counted but not measured Inta ct eggs that were not yolked were not counted or measured. Broken eggs were assumed to be yolked and they were counted. The lengths and widths of intact, yolked elliptical eggs were measured to the nearest 0.01 mm using a n ocular micrometer fitted to a compound microscope. Egg volume (treated as the sum of the volumes of two cones Equation 2 4 ) and brood volume (Equation 2 5) were calculated a s : (2 4) (2 5)

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21 Relative S urvival R ates Tethering experiments to estimate relative survival rates were conducted in September, October and November 2009 In each of four trial s, grass shrimp were collecte d from a patch of V americana using hand held dip nets (mesh: 1 mm 1 mm). T ether s were created by using a needle to attach 30 40 cm of thread between the base of rostr u m and one of its eye stalk s Shrimp were held in an aerated cooler for app roximately 30 min to confirm the stability of tethers and absence of immediate mortality Shrimp were transported to characteristic and proximate patches of V americana (7 X 5 m; 28.71648 N, 82.57844 W), P pectinatus ( 17 X 5 m; 28.7159 N, 82.57745 W), and filamentous algae ( 7 X 6 m; 28.71638 N, 82.57689 W). Twenty five shrimp were used in all trial s except the September 30 trial in P. pectinatus where 7 shrimp were used. Each tether w as attached approximately 20 25 cm above base of a wood dowel Dowels separated by ~30 cm were forced into the sediment within the appropriate patch of habitat Once situated each shrimp was placed at the base of its dowel within the vegetation which s im ul ate d their normal daytime location. The shrimp and habitat were o bserved for 15 minutes to ensure equilibration, and then the sites were left undisturbed for 1 h After that time, t ether ed shrimp were classified as present ( whether alive or dead ) and absent Relative survival was calculated as the total number tethered grass shrimp present at the end of the trial divided by the total number grass shrimp used in the trial. Statistical A nalys e s As appropriate, the as sumptions of normality and homoscedasticity of residuals were tested with Anderson Darling ts, respectively Data were

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22 transformed where necessary, and the results of analyses based on non normal or heteroscedastic data were interpreted with due regard for potentially inflated Type I errors. Variations in temperature and salinity were analyzed w ith two way analys e s of variance (ANOVA s ). Transects and months were treated as fixed factors. Relative abundances of grass shrimp were analyzed similarly Months of sampling and habitats were treated as fixed factors. Differential survival rates among hab itats were assessed with a one way ANOVA. Habitat was considered a fixed factor Analysis of covariance (ANCOVA) was used to determine if the relationship between wet weight s and total length s differed among species and between shrimp with and without isop od parasites Species and parasitism were treated as fixed factors. Data from in situ growth experiments were analyzed in two ways. Regression was used to relate telson lengths to total lengths. Intermolt periods, instantaneous growth rates and percentage growth rates (expressed as proportions) generated from in situ growth experiments were analyzed with two way ANOVAs. Life history stage and habitat were treated as fixed factors in these analyses. In addition to estimates from the in situ experiments, mon thly changes in mean total lengths of visibly distinct cohorts of shrimp were used to estimate growth rates. Between June and August, g rowth was calculated as (Equation 2 6) : (2 6) Variation in size at maturity for females and measures of reproductive output were analyzed with ANCOVAs or ANOVA that treated months and habitats as fixed fa ctors. Variation in s ize at maturity was analyzed with a two way ANOVA. Fecundity (the

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23 number of fertilized eggs), egg volume and brood volume were analyzed with ANCOVAs treating total length as a covariate. Figure 2 1. Location of the Chassahowitzka Ri ver along the west coast of peninsular Florida. Diagram from Frazer et al. ( 2006 )

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24 CHAPTER 3 R ESULTS Environmental C onditions Salinity and temperature did not vary significantly across the three transects bracketing the habitat patches sampled in this st udy (Tables 3 1 and 3 2). S alinit ies and temperatures did vary significantly among months, with means differing by a maximum of only 2.4C and 1.6 ppt (Tables 3 1 and 3 2). Given these results, any differences in measures of abundance, relative survival, g rowth, size at maturity or reproductive output were not attributed to differences in environmental conditions among patches of habitat Relative A bundance Standardized sweeps yielded reliable data for four habitats in July V americana P pectinatus M spicatum and filamentous algae, and three habitats in July and August V americana P pectinatus and M spicatum Therefore, a one way ANOVA was conducted using data from July, and a two way ANOVA was conducted using data from July and August (Tables 3 3 and 3 4) Log 10 transformed densities (individuals m 3 ) met the assumptions of homoscedasticity and normality. In July, densities varied significantly among the four habitats and in July and August, densities varied significantly among combinations of mo nth and habitat (Tables 3 3 and 3 4). Grass shrimp were never collected in M spicatum despite similar sampling effort (Figure 3 1) In July, filamentous algae harboured 198 fewer shrimp than V americana and 3 fewer than P pectinatus (Figure 3 1). V alli sneria americana yielded 75 and 5 more shrimp than P pectinatus in July and August, respectively (Figure 3 1). In August shrimp

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25 densities in V americana decreased four fold and shrimp densities in P pectinatus increased four fold (Figure 3 1). Relativ e S urvival Significantly more grass shrimp survived when they were tethered in P pectinatus and V americana as compared to filamentous algae ( Table 3 5; Figure 3 2) T he proportion of shrimp surviving in the first two habitats was over 5 as great ( Figur e 3 2 ). N o difference in relative survival was observed in grass shrimp tethered in V. americana and P. pectinatus In situ Growth E xperiments Across June, July and August, in situ growth experiments involved 1839 grass shrimp from three species ( 1137 Pala emonetes pugio 373 P. intermedius and 217 P. vulgaris) and three habitats, V americana (786 shrimp), P pectinatus (723 shrimp) and filamentous algae (330 shrimp). Some individuals of all life history stages molted i.e. juveniles, males and females, b ut only juveniles and males regularly exhibited positive growth. Total lengths of shrimp from V americana P pectinatus and filamentous algae ranged from 11 mm to 50 mm and the size frequency distribution contained multiple modes (Figure 3 4). Smaller s hrimp were more numerous in V. americana with m ean total lengths ( standard deviations ) of 28.13 mm ( 5.63 mm ), 27.09 mm ( 5.84 mm ), and 20.70 mm ( 4.99 mm ) for shrimp from filamentous algae, P. pectinatus and V. americana respectively. The percentag e of grass shrimp infected by isopods also varied among habitats, with infection rates of 22.49%, 30.62% and 10.88% for shrimp from filamentous algae, P pectinatus and V americana respectively. Parasites were never observed on r eproductive females but they were observed on 15.19 % of juveniles and 32 .23 % of

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26 males In addition, 21.18 % of P pugio 17.42 % of P. intermedius and 20.27 % of P. vulgaris were parasitized. In an effort to determine if growth needed to be analyzed separately for species and parasi tized shrimp an ANCOVA was used to compare linear regressions based on log 10 transformed wet weight s and log 10 transformed t otal length s of infected and un infected shrimp across the three species Wet weights were related to total lengths, and the presenc e of an isopod parasite altered this relationship by increasing the intercept for wet weight by about 0.06 g ( Table 3 6 ; Figure 3 4 ) The average wet weight of removed isopods was 0.01 g. The lack of significance for the species and interaction term s indic ate d P pugio P. intermedius and P. vulgaris all exhibited similar morphometrics even if infected by an isopod These results indicated that the three species and shrimp with and without parasites could be pooled for analyses based on total length s T elso n length s reliably predicted total length s (Figure 3 5 ). Therefore, growth was expressed as change in total length, with the total lengths of pre molt shrimp estimated from the regression. Intermolt periods did not vary significantly among habitats or comb inations of habitats and months (Table 3 7 ). Mean intermolt periods were significantly shorter for juveniles (1.7), and this relationship held across all habitats (Figure 3 6 ). Only 32.19 % of the 1839 shrimp used in the growth experiments increased in siz e, with 52.52 % showing no measurable change and 15.29 % shrinking In addition, females seldom grew, so analyses were limited to data from juveniles and males. P ositive instantaneous growth rates did not vary significantly for juveniles or males from any of

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27 the three habitats that yielded shrimp (Table 3 8 ). Overall, the mean positive instantaneous growth rate ( standard error) for all juvenile and male shrimp was 0.44 ( 0.11) mm d 1 Similarly, instantaneous growth expressed as a percentage increase in si ze did not vary significantly for juveniles and males from the three habitats (Table 3 9). The overall m ean ( standard error) instantaneous percent age growth rate was 2.34 ( 0.73 ) % d 1 Juvenile and adult male m olting predominately occurred during overni ght holding time intervals (12, 36, 60, 8 4 hr) (Figure 3 7) a nd decreased from 12 to 96 h r. A regression of instantaneous growth versus holding time for all shrimp was not significant ( F 1 453 = 0.7 2 p = 0. 39 7 ) (Table 3 10). Similar regression s were not significant for juveniles (F 1 265 = 0.7 1 p = 0. 401 ) (Table 3 11 ) or adult m ales ( F 1 186 = 1.55 p = 0. 215 ) (Table 3 12 ) Modal P rogression A nalysis Only one cohort of shrimp could be clearly identified, with those shrimp captured in V americana (Figure 3 8 ) Therefore; juvenile growth rate s from June to August 2009 were estimated with modal progression analysis of total length s for thi s cohort of shrimp In addition, the cohort was distinguished most easily in June and August The analysis indicated tha t these juveniles grew 0.05 mm d 1 Fecundity Available data supported analysis of fecundity, i.e., numbers of eggs and embryos, for females captured in filamentous algae, P. pectinatus and V americana during June and July 2009. Analysis indicated that f ecundity varied significantly with total length and among habitats ( Table 3 13 ; Figure 3 9 ) The lack of a significant interaction indicated that fecundity increased similarly with total length for shrimp from the three habitats and

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28 two months, with regres sions for shrimp from different habitats indicating increases of 0.01 0.03 eggs per mm increase in total length (Figure 3 9 ) The regressions also indicated that shrimp from V americana carried more eggs and embryos (Figure 3 9 ) with back transformed mea ns and 95% confidence limits of 99.1 23.1 and 425.1 in June and 87.8, 66.0 and 116.8 in July for V americana ; 48.0 28.3 and 81.4 in June and 43.2, 13.9 and 134.6 in July for P pectinatus ; and 46.7 32.5 and 67.1 in June and 43.3, 21.4 and 87.6 in July for filamentous algae. Egg V olume An ANCOVA indicated that the relationship between egg volumes and total length varied according to the month of sampling and habitat sampled (Table 3 14 ; Figure 3 1 0 ). Variation among habitats was of primary interest. B ack transformed least squares mean egg volumes (i.e., mean egg volume s for females captured in each habitat with total length and month held constant) were 1.6 6 mm 3 for filamentous algae, 1.6 4 mm 3 for P pectinatus and 1.21 mm 3 for V americana Brood V olume An ANCOVA indicated that the relationship between brood volumes and total length s varied according to the combination of month of sampling and habitat sampled (Table 3 15 ). Variation among habitats the measure of primary interest, was approximately 1 mm 3 B ack transformed l east squares mean brood volumes were 9.90 mm 3 for filamentous algae, 9.72 mm 3 for P pectinatus and 1 0.73 mm 3 for V americana Size at M aturity Mature female grass shrimp were defined as females brooding eggs or embryos and females with extended brood pouch es indicating recent hatching of eggs. Available data supported two analyses. One analysis focused on shrimp collected from

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29 filamentous algae, P pectinatus and V americana in June and July, and the other analysis focused on shrimp co llected from P pectinatus and V americana in June July and August. In both cases, m ean total length s of mature females varied significantly among combinations of months and habitats (Tables 3 16 and 3 17 ). On average, mature females from V americana we re smaller, with the difference ranging from 2.0 mm in June to 6.3 mm in J uly (Figure 3 1 1 ). In addition, size frequency distributions for mature females separated by habitats showed the presence of numerous small mature females in samples from V americ ana (Figure 3 12 ).

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30 Table 3 1 Two way ANOVA based on log 10 transformed salinities (ppt) measured along three transects in February, May and August 2009. According to an Anderson the dat a were normal (p > 0.01) and homoscedastic (p > 0.01). Factor df Sum of squares Mean square F value p value Month 2 0.0092 9 0.00464 170.12 < 0.00 1 Transect 2 0.00018 0.00009 3.35 0.058 Month T ransect 4 0.00028 0.00007 2.58 0.073 Error 18 0.00049 0.00 003 Table 3 2. Two way ANOVA based on log10 transformed temperatures (C) measured along three transects in February, May and August 2009. According to an Anderson the data were norma l (p > 0.01) and homoscedastic (p > 0.01). Factor df Sum s of squares Mean square F value p value Month 2 0.38184 0.19092 11.23 0.001 Transect 2 0.04892 0.02446 1.44 0.263 Month T ransect 4 0.01267 0.00317 0.19 0.942 Error 18 0.30599 0.01700 Table 3 3 One way ANOVA based on log 10 transformed grass shrimp m 3 captured from filamentous algae, P pectinatus V americana and M spicatum in July 2009 According to an Anderson for homoscedasticity, the data were normal (p > 0.05) and homoscedastic (p > 0.05). Factor df Sums of squares Mean square F value p value Habitat 3 8.0596 2.6865 323.89 < 0.00 1 Error 4 0.0332 0.0083 Table 3 4 Two way ANOVA based on log 10 transformed grass shrimp m 3 captured fr om P pectinatus V americana and M spicatum in J uly and August 2009 According to an Anderson homoscedasticity, the data were normal (p > 0.05) and homoscedastic (p > 0.05). Factor df Sum of squares Mean square F value p value Month 1 0.0006 0.0006 0.05 0.83 5 Habitat 2 10.2357 5.1179 388.45 < 0.00 1 Month Habitat 2 0.7273 0.3636 27.60 0.00 1 Error 6 0.0791 0.0132

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31 Table 3 5. One way ANOVA based on arcsin transformed proportional survival rates i n filamentous algae, P pectinatus and V americana According to an Anderson the data were normal (p > 0.05) and homoscedastic (p > 0.05). Factor df Sum s of square s Mean square F value p value Habitat 2 1.116 0. 55 8 22.13 < 0.001 Error 9 0.227 0. 025 Table 3 6. Analysis of covariance based on log 10 transformed wet weight s with log 10 transformed total leng th as a covariate. According to an Anderson Darling test for normality and Cochra normal (p < 0.01) and heteroscedastic (p < 0.01). Factor df Sums of squares Mean square F value p value L ength 1 213.190 213.190 22000.00 < 0.001 Species 2 0.016 0.008 0.83 0.436 Isopod 1 0.241 0.241 24.5 0 < 0.001 Species I sopod 2 0.005 0.002 0.25 0.778 Error 1676 16.521 0.010 Table 3 7. Two way ANOVA based on i ntermolt period s associated with positive growth for juveniles and males from filamentous algae, P pectinatus and V americana According to an Anderson Darling test for normality and homoscedastic (p > 0.05). Factor df Sum s of squares Mean square F value p value Life history stage 1 116.392 116.392 12.69 0.006 Habit at 2 1.30 1 0.650 0.07 0.932 Life history stage Habitat 2 0.982 0.491 0.05 0.948 Error 9 82.557 9.17 3 Table 3 8. Two way ANOVA based on log 10 transformed positive instantaneous growth rates for juvenile and male shrimp from filamentous algae, P pe ctinatus and V americana According to an Anderson Darling test for normality and homoscedastic (p > 0.05). Factor df Sums of squares Mean square F value p value Life history stage 1 0.0742 0.0742 0.62 0.455 Habitat 2 0.0825 0.0413 0.34 0.720 Life history stage Habitat 2 0.0468 0.0234 0.19 0.827 Error 8 0.9634 0.1204

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32 Table 3 9 Two way ANOVA based on arcsin transformed percentage growth rates for juvenile and male shrimp fro m filamentous algae, P pectinatus and V americana According to an Anderson Darling test for normality and heteroscedastic (p < 0.01). Factor df Sum s of squares Mean square F value p value Life history stage 1 0.0066 0.0066 1.06 0.333 Habitat 2 0.0107 0.0053 0.80 0.457 Life history stage Habitat 2 0.0009 0.0005 0.08 0.928 Error 8 0.0493 0.0062 Table 3 10. Regression analysis of instantaneous growth of all shrimp by holding time (Instantaneous growth w/ month TL = 0.00282 0.000037 Holding time). Source DF SS MS F P Regression 1 0.0005208 0.0005208 0.72 0.397 Residual Error 453 0.3284688 0.0007251 Table 3 11. Regression analysis of instantaneous growth of juvenile s hrimp by holding time (Instantaneous growth w/ month TL = 0.00698 +0.000039 Holding time). Source DF SS MS F P Regression 1 0.0003393 0.0003393 0.71 0.401 Residual Error 265 0.1268240 0.0004786 Table 3 12. Regression analysis of instantaneous gr owth of adult male shrimp by holding time (Instantaneous growth w/ month TL = 0.0144 0.000098 Holding time). Source DF SS MS F P Regression 1 0.0014377 0.0014377 1.55 0.215 Residual Error 186 0.1729565 0.0009299 Table 3 13 Analysis of covariance based on log 10 transformed numbers of eggs and embryos with total leng th as a covariate. According to an Anderson Darling normal (p < 0.01) and homoscedastic (p > 0.05). Factor df Sum s of squares Mean square F value p value Total length 1 0.5193 0.5193 20.78 < 0.001 Month 1 0.0039 0.0039 0.16 0.693 Habitat 2 1.5736 0.7868 31.49 < 0.001 Month Habitat 2 0.0027 0.0014 0.05 0.947 Error 96 2.3984 0.0250

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33 Table 3 1 4 Analy sis of covariance based on log 10 transformed egg volumes with total leng th as a covariate. According to an Anderson Darling test for normality and normal (p < 0.01) and heteroscedastic (p < 0.01). Fact or df Sums of squares Mean square F value p value Total length 1 50.381 50.381 1366.94 < 0. 001 Month 1 5.183 5.183 140.63 < 0. 001 Habitat 2 49.801 24.900 675.60 < 0. 001 Month Habitat 2 14.786 7.393 200.59 < 0. 001 Error 6523 240.415 0.037 Table 3 1 5 Analysis of covariance based on log 10 transformed brood volumes with total length as a covariate. According to an Anderson Darling test for 0.05) and heteroscedastic (p < 0. 01). Factor df Sums of squares Mean square F value p value Total length 1 0.043 0.043 2.59 0.116 Month 1 0.024 0.024 1.44 0.238 Habitat 2 0.046 0.023 1.40 0.261 Month Habitat 2 0.130 0.065 3.89 0.030 Error 35 0.584 0.017 Table 3 1 6 Two way ANO VA based on total length s of reproductive females from filamentous algae, P. pectinatus and V americana in June and July 2009. According to an Anderson homoscedasticity, the data were non normal (p < 0.01 ) and homoscedastic (p > 0.05). Factor df Sum s of squares Mean square F value p value Month 1 0.016 0.016 9.13 0.003 Habitat 2 0.274 0.137 78.26 < 0.001 Month Habitat 2 0.060 0.030 17.03 < 0.001 Error 35 8 0.628 0.002

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34 Table 3 1 7 Two way ANOVA b ased on total lengths of reproductive females from P. pectinatus, and V. americana in June, July and August 2009. According to an Anderson the data were non normal (p < 0.01) and homosced astic (p > 0.05). Factor df Sums of squares Mean square F value p value Month 2 0.045 0.022 10.35 < 0.001 Habitat 1 0.210 0.210 98.64 < 0.001 Month Habitat 2 0.021 0.010 4.87 0.008 Error 27 2 0.590 0.002

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35 Figure 3 1. Mean number of grass shrim p m 3 95% confidence limits ( CL ).

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36 Figure 3 2. Back transformed mean proportional survival rates 95% confidence limits (CL) for grass shrimp tethered in three habitats.

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37 Figure 3 3. Size frequency distributions of grass shrimp collected from fila mentous algae, P pectinatus and V americana in June August 2009.

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38 Figure 3 4. Log 10 transformed w et weight v ersu s log 10 transformed total length for all Palaemonetes species with and without isopods.

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39 Figure 3 5. Total length (mm) vs. telson length (mm) of Palaemonetes spp 0 5 10 15 20 25 30 35 40 45 50 0 1 2 3 4 5 6 Telson length (mm) Total length (mm) Total length=7.2356 x (Telson length) + 1.0069 r 2 = 0.8879

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40 Figure 3 6. Mean intermolt period standard error (SE) by habitat and life history stage.

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41 Figure 3 7 Total number of molting shrimp by life history stage and hold ing time (12 hour intervals, 4 d).

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42 Figure 3 8 Size frequency distributions of juveniles used in modal progression analysis. 0 20 40 60 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 June Number of shrimp 0 20 40 60 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 July Number of shrimp 0 20 40 60 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 August Total length (mm) Number of shrimp

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43 Figure 3 9 R elationship s between log 10 transformed number eggs and embryos and total length for females collected in filamentous algae, P pectinatus and V americana

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44 Figure 3 1 0 R elationship s between log 10 transformed egg volumes and total length for females collected in filamentous algae, P pectinatus and V americana

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45 Figure 3 1 1 Back transformed mean total lengths (mm) 95% confidence limits (CL) for mat ure females.

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46 Figure 3 1 2 Size frequency distribution for mature female grass shrimp females from filamentous algae, P pectinatus and V americana

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47 CHAPTER 4 DISCUSSION Following the recommendation of Van Horne (1983), the relative quality of four h abitats vegetated habitats in the Chassahowitzka River was compared by combining measures of abundance with proxy measures of grass shrimp fitness. Myriophyllum spicatum served as the poorest habitat, and it never yielded shrimp for measurements of growth or reproductive output despite equivalent collection effort during the peak of grass shrimp abundance. Nearby (within 5 50 m) patches of other habitats did yield shrimp. Filamentous algae also was considered to provide poor habitat as it supporte d relative ly low numbers of grass shrimp compared to rooted plants. Shrimp associated with filamentous algae also had the lowest relative survival rate, and exhibited lower reproductive output than shrimp from V americana Potamogeton pectinatus served as habitat o f intermediate quality, with abundance of grass shrimp and their reproductive output second only to collections from V americana In addition, relative survival rates for grass shrimp tethered in P pectinatus were not different from those of grass shrimp tethered in V americana Vallisneria americana provided the highest quality habitat, with higher densities of shrimp collected from this native macrophyte exhibiting high survival rates and the greatest reproductive output due to production of smaller an d more numerous eggs at a smaller size. Intermolt intervals and growth rates were variable and did not differ significantly for grass shrimp from all habitats. Each measure of habitat quality yielded some insight, and each had associated challenges. Relati ve abundance can be a misleading metric of habitat quality when used in isolation (Van Horne 1983 ; Heinrichs et al. 2010 ). Competition among life history stages within a species and among different species for limited space and resources in

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48 quality habit ats may force animals into lesser quality habitat (Van Horne 1983 ; Pulliam and Danielson 1991 ) Abundances also yield only a snapshot of distributions without information on past events leading to or future effects arising from the observed distributions (Van Horne 1983 ; Pulliam and Danielson 1991 ; Chockley et al. 2008 ; Heinrichs et al. 2010 ). In addition, differential capture efficiencies can bias estimates of relative abundance ( Pierce et al. 1990 ; Bayley and Austen 2002 ). The habitats in this stud y did differ in form Nevertheless, the larger differences in relative abundance (75 198) were unlikely to arise solely from gear bias. Differences in the structure of habitats probably affected relative survival rates, an important metric of fitness, as evidenced by the results of tethering experiments. Palaemonetes spp. commonly face strong predation pressure, and they seek refuge in structurally complex habitats ( Khan Merchant & Knowton 1997). For example, P pugio remained closer to and made greater use of refuge in t he presence of predators ( Davis, Metcalfe & Hines 2003). Therefore, the evaluation of relative percent survival by habitat In the Chassahowitzka River, grass s hrimp survived better in habitats where structure extended throughout the water column, in contrast to mat like filamentous algae. Filamentous algae may prove to be a better refuge in late fall and early winter when patches are more extensive and deeper (C amp u npublished data ) Even if filamentous algae can provide a habitat of suitable quality, its tendency to wane during periods of peak grass shrimp abundances and reproduction in the Chassahowitzka River (Camp. unpublished data) leads to a mismatch betwe en the need ed refuge and its availability, with potentially detrimental consequences for grass shrimp.

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49 Survival rates as assessed by tethering experiments come with caveats. In this study, the selection of similarly sized and co located patches of filament ous algae, P. pectinatus, and V. americana reduced confounding effects from variation in type and density of predators, as well as variation in access due to differing perimeter to area ratios (Darcy 2003 ; Kneib and Scheele 2000 ; Moore and Hovel 2010). In fact, experiments were performed in the centers of patches to further diminish the effect of increased predation along perimeters (Darcy 2003 ; Moore and Hovel 2010). In an effort to control for differences in visibility and movement of the grass shrim p prey (Davis 2003 ; Paine 1976), tethering experiments were limited to non ovigerous grass shrimp with total lengths of 25 35 mm and no evidence of isopod infection. Nevertheless, tethering of grass shrimp did involve suturing, and this process may have resulted in the release of body fluids possibly altering predator behavior (Peterson & Black 1994). It is unlikel y, however, that a release of body fluids would have led to differential predation across habitats because the patches were co located and sub ject to similar assemblages of mobile predators. Tethers may limit or alter movement of shrimp if they become entangled (Aronson and Heck 1995), but entanglement of tether s would likely increase in complex habitat s leading to decrease d avoidance of predat ors and lower estimates of relative survival. Unlike tethering, experimental assessments of growth rates using standard techniques (Ross et al. 2000) did not yield significant insights into habitat quality. Growth rate s expressed as either instantaneous c hange in total length or percentage change in total length, and components of these measures, i.e. intermolt period and growth increment, were variable with no statistically significant differences among

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50 habitats. Despite efforts to minimize stress on shri mp in this study (i.e., short elapsed time from collection to maintenance, in situ maintenance, and four day holding period), approximately 56% of the shrimp that molted did not grow or became smaller. Fewer juveniles grew (31%) despite molting more freque ntly than adult males (64% grew). Mean intermolt periods did not vary significantly among shrimp from alternative habitats, but intermolt periods for juveniles were consistently shorter, which indicated that experiments yielded useful data. In addition, me an intermolt periods ( standard error ) in this study were similar to those documented for P. pugio in Vernberg and Piyatiratitivorakul ( 1998 ) : i.e., for males 12.3 ( 1.0) d in this study compared to 11.2 ( 3.9) d an d for juveniles 8.1 ( 0.6) d in th is study compared to 7 days. Another method to estimate growth was applied to j uveniles collected from V americana M odal progression analysis of a c ohort yielded 0.05 mm d 1 as an estimate of instantaneous growth, which was less than the estimate of 0.44 mm d 1 obtained from positive results of molting experiments. Th e difference in these estimates may be due to size dependent mortality, overlap ping cohorts and the differential treatment of shrimp that shrink or do not grow Grass shrimp experience differ ent predation rates at different sizes (Kneib 1987) so cohorts can be disrupted. Grass shrimp demonstrate the capacity to grow or shrink in response to environmental conditions, so cohort s could overlap In addition, the estimate from molting experiments excluded shrimp that did not grow, which would lead to a larger mean value Intermolt period and growth are affected by temperature and salinity (Quetin et al. 2003 ; Tarling et al. 2006 ; Vernberg and Piyatiratitivorakul ; 1998). Intermolt periods tend to be shorter where resources are at their peak (Ross 2000) and water is warm er,

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51 within the physiological limits of the species (Vernberg and Piyatiratitivorakul 1998). For any given species, g rowth tends to be maximized at optimal salinit ies and temperatu res determined by the energetic demands associated with maintaining homeostasis, and such demands increas e either side of th is range As temperature and salinity were similar among habitats in this study these influences should not have generated differen ces in intermolt period s or growth. M olting frequency from growth experiments will be an accurate estimate of readiness to molt at the population level only if molting is random (Hoenig and Restrepo 1989 ; Miller, Huntley & Brooks 1984 ; Quentin et al. 20 03 ; Ross et al. 2000 ; Tarling et al. 2006). Crustaceans have been shown to exhibit synchronicity in molting related to inter individual, tidal, diel, and lunar cues which may serve to protect newly molted individuals by swamping potential predators (Mil ler et al. 1984). For example, c than those predicted by stage determination (Miller et al. 1984). Therefore, synchrony may have affected the evaluation of intermolt period s for grass shrimp collected from alternative habitats, although t he effect of synchrony was diminished by using results from multiple experiments conducted over three months to calculate intermolt period s Molting experiments have been used to evaluate shr imp and krill growth (Quetin and Ross 1991 ; Ross et al. 2000 ; Kneib 1987). The method assumes that the physiological basis for ecdysis and growth are set a few days before molting when the reached, then intermolt period and growth increment are assumed to be independent of collection and incubation (Ross et al. 2000). However, t he validity of these assumptions

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52 is drawn into question by the results of various studies. Fo r example, growth increment decreased rapidly after capture and isolation in one study of krill (Tarling et al. 2006). Furthermore, both metrics intermolt period and growth increment, were affected by food supply (Buchholz et al. 1991 ; Gorokhova 2002 ; Ikeda and Dixon 1982 ; Tarling et al. 2006). In Buchholz et al. ( 1991 ) doubling food availability in the laboratory increased the growth rate of krill and addition of natural phytoplankton produced the highest 82), krill starved for 211 consecutive days experienced no greater mortality than controls, continued to molt, and demonstrated negative growth (up to 50% wet weight). Negative growth increment s may increase survival of crustaceans that do not sequester l ipids during periods of limited food. In addition, Tarling et al. ( 2006 ) observed s imilar patter ns with growth increment s of krill f alling by 26% and 50% and negative growth at days 3 and 5 of their experiment. G rowth increment s decreased most in individu als that had been growing the fastest (Tarling et al. 2006) which would equate to juveniles in this study. I n comparison to adult males t h e high percentage of grass shrimp juveniles that did not grow suggested that smaller grass shrimp have less metabol ic reserves to cope with collection and isolation. T he grass shrimp in this experiment were held in situ but they were isolated from their natural food sources, which could have affected their growth (Kneib 1987) Differences in growth among life history stages also may be related to differences in metabolism. Molting and s omatic growth along with ingestion, assimilation, respiration, excretion and locomotion represent the key metabolic demands for grass shrimp that must be met by nutrition (Tarling et al. 2006). J uvenile and adult life history stages have different metabolic demands with respirat ory demands increas ing from

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53 25% to 52% as shrimp increase in size from juveniles to adults. E nergy in juveniles is devoted predominately to somatic growth (14% of total metabolism), while energy in adults is divided between reproducti on (14%) and growth (5%). The energetic cost of molting remains similar for adult s and juveniles and it is estimated to be only 2% of their overall metabolism (Vernberg and Piyatir atitivorakul 1998). Given t his relatively low metabolic cost shrimp could be expected to molt in respo n s e to physiological and other cues, even if they do not have the reserves needed to yield growth. Fortunately other proxy measures of fitness i. e ., r elative survival and reproductive output, were used to evaluate habitat quality in this study In combination with survival, reproductive output appeared to represent a good proxy for fitness. Grass shrimp from V americana brooded smaller and more numerou s eggs than shrimp collected from filamentous algae and P pectinatus Gulf coast grass shrimp have been estimated to produce up to eight broods between April and October (Bauer and Abdalla 2000). At this rate, grass shrimp from V. americana would have mo re than double the reproductive output of grass shrimp from filamentous algae or P. pectinatus The n umber of eggs and size of eggs produced by Palaemonetes spp. in this study were consistent with literature reports (Beck and Cowell 1975 ; Broad 1957 ; Cor ey and Reid 1991) ranging from 47 99 eggs per brood. A trade off seem ed to exist between egg size and number of eggs per brood. Limits to reproductive output include anatomic al constraints and energetic resources (Hines 1982). In numerous studies of crus tacean reproduction, female body size has proven to be an important factor in determining reproductive output, brood weight, number of eggs per brood, and gonad

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54 capacity (Clarke 1993; Lara & Wehrtmann 2009 ; Hines 1982 ; Tallack 2007). Brood weight and consequently brood volume often was constrained to approximately 10% of total body weight due to these allometric constraints and constraints on penetration of dissolved oxygen into egg masses (Hines 1982 ; Fernandez et al. 2006). Such restriction s creat e a tradeoff between egg volume and the number of eggs per brood with t otal brood volume being relatively constant. An inverse relationship between egg size and egg number per brood was seen in this study and reported for amphipods, mysid s fairy shrimp, and brach y urans (H ines 1982). In decapods, larger egg size and decreased egg number indicative of greater parental investment in each egg, have been documented to decrease the number of zoeal stages and associated predation proceeding metamorphosis to th e first juvenile stage ( Broad 1957 ; Hines 1982). In fact, female s may be able to read environmental cues and adjust the ir investment in each egg (Fox and Czesak 2004 ; Plaistow et al. 2004). In environments where food is scarce or of poor quality, femal e s may invest more energy or yolk per egg to improve growth and survival of the resulting embryos (Clarke 1993). I n this study, Palaemonetes spp. from V americana produced more and smaller eggs, which may indicate the presence of enhanced nutritional res ources that will support development through all zoeal and juvenile stages. In fact, grass shrimp in alternative habitats within the Chassahowitzka River may be using the plasticity associated with egg size and egg number to create reproductive strategies that maximiz e fitness Size at maturity is influenced by relative growth rates and nutritional resources (Anger and Moreira 1998). Size at maturity in Palaemonetes spp. is described by Plaistow (2004) as being an overhead threshold: grass shrimp reach a m inimum size or

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55 state of maturity after which total body length exerts minimal effect on reproduction. The results of this study were consistent with this theory, because brood volume did not differ significantly for shrimp from different habitats although females from V americana exhibited a smaller mean total length at maturity. Hines (1982) describe d the possibility that a crustacean can at low latitudes by producing many broods of many small eggs as long as limitations of small s ize and seasonality are counter balanced. G rass shrimp collected from V americana brood ed more eggs, with smaller volume s at a smaller mean total length than shrimp collected from alternative habitats. G rass shrimp from V americana extend their reproduc tive season and overall reproductive output by maturing more rapidly This pattern of early maturity and increased fecundity could increase fitness (Bertness 1981) Few g rass shrimp survive their first winter, in large part because they are vulnerable to predation across all life histor y s tages and body lengths so shrimp benefit from maturing and reproduc ing quickly and prolifically. This study indicates that w ide scale habitat change from the native macrophyte V americana to nuisance levels of filamento us algae and M spicatum could generate negative consequences for population s of grass shrimp in the Chassahowitzka River. L ower abundance s decreased reproductive output, and reduced survival especially during the critical summer months may obviate the s in the trophic ecology of the Chassahowitzka R iver, resulting in detrimental effects on predators, including commercially and recreationally important fish species. Thus, those responsible for managing or restoring vegetation in the Chassahowi tzka River and other systems undergoing similar changes in vegetation should be concerned about such trends.

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59 Lowe, B.T. and Provenzano, A.J. (1990) Survival and reproduction of Pala emonetes paludosus (Gibbes, 1850) (Decapodas: Palaemonidae) in saline water. The Journal of Crustacean Biology 10 (4), 639 647. Mc Call, D.D. and Rakocinski, C.F. (2007) Grass shrimp ( Palaemonetes spp.) play a pivotal trophic role in enhancing Ruppia marit ime Ecology 88 (3), 618 624. Miller, C. B., Huntley, M.E. & Brooks, E.R. (1984) Post collection molting rates of planktonic, marine copepods: Measurement, application, probl ems. Limnology and Oceanography 29 (6), 1274 1289. Moore, E. C. and Hovel K. A. (2010) Relative influence of habitat complexity and proximity to patch edges on seagrass epifaunal communities. Oikos 119 1299 1311. Morgan, M.D. (1980) Grazing and predation of the grass shrimp Palaemonetes pugio Limnology and Oceanography 25 (5) 896 902. Paine, R.T. (1976) Size limited predation: An observational and experimental approach with the Mystilus Pisaster interaction. Ecology 57 858 873. Peterson, C.H. and Black, R. (1994) interventio n i nteract with treatments. Marine Ecol ogical Progress Ser ies 111 289 297. Pie rce, C.L., Rasmussen, J.B., & Leggett, W.C. (1990) Sampling littoral fish with a seine: Corrections for variable capture efficiency. Canadian Journal of Fisheries and Aquatic Sci ences 47 1004 1010. Plaistow, S.J., Lap sley, C.T., Beckerman, A.P. & Benton, T.G. (2004) Age and size at maturity: sex, environmental variability and development thresholds. Proceedings of the Royal Society London B 271 919 924. Pu lliam, H.R. and Dani elson, B.J. (1991) Sources, sinks, and habitat selection: A landscape perspective on population dynamics. The American Naturalist 137 Supplement S50 S66. Orth, R.J., van Montfrans J., & Fishman J. (1999) Virginia Institute of Marine Science. Report to the Virginia Marine Resources Commission : A preliminary study of predation on blue crabs by three fish predators in a seagrass bed. http://web.vims.edu/bio/sav/bluecrabpred/?=www Accessed 12 May, 201 1. Quetin, L.B. and Ross, R.M. (2003) Episodic recruitment in Antarctic krill Euphausia superba in the Palmer LTER study region. Marine Ecology Progress Series 259 185 200.

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60 Raviv, S., Parnes, S. & Sagi, A. ( 2008) Coordination of reproduction an d molt in decapods. In: Reproductive Biology of Crustaceans (Ed E. Mente), pp. 365 390. : Science Publishers Enfielied, New Hampshire Rosas L.P. and Odum W.E. (1987) Use of tidal freshwater marshes by fishes and macrofaunal crustaceans along a marsh st ream order gradient. Estuaries 10 36 43. Ross, R.M., Queti n, L.B., Baker, K.S., Vernet, V. & Smith, R.C. (2000) Growth limitation in young Euphausia superba under field conditions. Limnology and Oceanography 45 31 43. Rowe, C.L. (2002) Differences in maintenance energy expenditure by two estuarine shrimp ( Palaemonetes pugio and P. vulgaris ) that may permit partitioning of habitats by salinity. Comparative Biochemistry and Physiology Part A 132 341 351. Skadsheim, A. (1984) Coexistence and reproduct ive adaptations of amphipods: T he role of environmental heterogeneity. Oikos 43 94 103. Tallack, S.M.L. (2007) Size fecundity relationships for Cancer pagurus and Necora puber in t he Shetland Islands, Scotland: H ow is reproductive capacity facilitated? Journal of the Marine Biological As sociation of the United Kingdom 87 507 515. Tarling, G.A., Shreeve, R.S., Hirst, A.G., Atkinson A., Pond, D.W., Murphy, E.J. & Watkins, J.L. ( 2006 ) Natural growth rates in Antarctic krill ( Euphausia superba ): I. Impr oving methodology and predicting intermolt period. Limnology and Oceanography 51 959 972. Thorpe, J. H. (1976) Interference competition as a mechanism of coexistence between two sympatric species of the grass shrimp Palaemonetes (Decapoda: Palaemonidae). Journal of Experimental Marine Biology and Ecology 25 19 35. Van Horne, B. (1983) Density as a misleading indicator of habitat quality. The Journal of Wildlife Management 47 (4) 893 901. Vernberg, F.J. a nd Piyatiratitivorakul, S. (1998) Effects of sal inity and temperature on the bioenergetics of adult stages of the grass shrimp ( Palaemonetes pugio Holthius) from the North Inlet Estuary, South Carolina. Estuaries 21 (1), 176 193. Welsh, B.L. (1975) The role of grass shrimp, Palaemon e tes pugio in a tidal marsh ecosystem. Ecology 56 (3), 513 530. Williams, A.B. (1984) Shrimps, Lobsters, and Crabs of the Atlantic Coast of the Easter United States, Maine to Florida Smithsonian Institution Press Washington D.C.

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61 BIOGRAPHICAL SKETCH Meredith Mo ntgomery was born and raised in Gainesville, Florida. After graduating from high school in 2001, she head ed to Duke University to study b iology and Spanish, study abroad as much as possible, and sleep in a few tents in Krzyzewskiville. After a n influential semester and summer studying marine science at the Duke University Marine lab and graduating in May 2005, Meredith took job opportunities in the marine sciences that offered new skills, adventure, and travel; working on projects varying from marine mammal and sea turtle ecology to seagrass and water quality projects. Finding employment and a home in the Frazer laboratory at the University of Florida, Meredith decided to stay at UF to begin graduate school. While in graduate school, she spent a great deal o f time taking a brief departure to study lionfish ecology in the mangroves and patch reefs of San Salvador, Bahamas Meredith has decided to return to her two first loves: animals and medicine. She will enroll at