Oyster Monitoring Network for the Caloosahatchee Estuary 2007-2010 Final Report Submitted to the South Florida Water Management District Project Manager: Patricia Goodman September 2010 Aswani K. Volety, S. Gregory Tolley, Ai Ning Loh, and Holly Abeels 10501 FGCU Blvd Fort Myers, FL 33965 EXECUTIVE SUMMARY The hydrology and watershed of the Caloosahatchee River and Estuary located on the southwest coast of Florida has been altered since the 1880’s. The river has also been straightened, deepened and three water control structures have been added. The last, Structure S-79, was completed in 1966 to act, in part, as a salinity barrier. These alterations have resulted in huge fluctuations in freshwater input into the estuary resulting in extreme salinities with near freshwater conditions in the wet summer months and saline to hypersaline conditions in the winter months. The transition between the two states can be rapid, sometimes requiring less than a week. As part of the Comprehensive Everglades Restoration Plan (CERP), several storage facilities are being planned to retain freshwater during high flow periods, with subsequent release to the estuary during drier times thereby reducing high discharges during the wet season and provide a base flow during the dry season. The premise of CERP is that restoring hydrology in Caloosahatchee Estuary will improve the health and survival of the Eastern oyster (Crassostrea virginica) and promote the development of healthy oyster reefs. The status of oyster beds in the Caloosahatchee comprises one of the performance measures which will assess the success of CERP. The goals of this project are to establish the temporal and spatial variability of oyster responses in the Caloosahatchee River and Estuary (CRE) and to examine the effect of freshwater inflows into the estuary on oyster responses and habitat use of oyster reefs by decapods crustaceans and fishes. Dissolved oxygen, salinity, conductivity, pH, density of living oysters, prevalence and intensity of Perkinsus marinus, gonadal condition, oyster spat recruitment, and growth & survival of juvenile oysters were measured at 6 sampling locations in the CRE along a salinity gradient. Habitat use of oyster reefs was determined by examining the spatial variation of the reef-resident community and trophic transfer within the reef using stable isotopes compositions. Spatial variation of habitat use of oyster reefs by decapod crustaceans and fishes was determined using changes in community metrics at three locations in the Caloosahatchee estuary. Stable carbon and nitrogen isotope compositions were used to establish food sources of different species that make use of oyster reefs as habitat and that may consume the oysters themselves. While temperature followed a typical seasonal pattern and ranged between 17 - 32°C, salinities fluctuated drastically at various sampling locations (0 – 44 ppt). There was a very good 2 correlation between freshwater inflows from S-79 lock and dam, and salinities at various sampling locations (R2 = 58 – 73%). Prevalence and intensity of P. marinus infection increased with increasing distance and salinities downstream. Condition index of oysters showed a seasonal pattern with higher indices during cooler winter months and decreased with late spring / early summer months, a period that coincides with oyster reproduction. Densities of living oysters fluctuated over the sampling years and varied significantly between sampling years, but remained high, overall (>1000 oysters / sq. m). Changes in living oyster densities may be related to seasonal rainfall and water management practices that have influence on larval recruitment and survival. Juvenile oysters showed good growth at all of the locations, but predation resulting from higher salinities was significant, resulting in 100% mortality at some locations. Oysters in the CRE were reproductively active between May – October, a period that coincides with regulatory releases and /or watershed runoff resulting from seasonal rainfall. High freshwater inflows into the CRE will flush the larvae downstream where limited substrate is available and/or create unfavorable salinities resulting in mortality and poor recruitment of oyster larvae. In addition, oyster reproduction seemed to be negatively affected by high salinities. Flows between 500 and 3000 CFS will result in optimal salinity regime for the growth, survival and proliferation of oysters in the estuary. Examination of habitat use by various decapods crustaceans and trophodynamics with the oyster reef suggests that oyster reefs serve as essential fish habitat for many resident and ransient species, including those that are recreationally and commercially important (e.g. Farfantepenaeus sp., Florida stone crab Menippe mercenaria, gray snapper Lutjanus griseus, sheepshead Archosargus probatocephalu). Organism abundance varied with season and was greater at the upper and middle stations during the dry season but was greater at the middle stations during wet months; biomass was greater at the lower stations, at least during the dry season. Measures of biodiversity (H’ and % dominance) suggested that diversity increased downstream. It appears that assemblages of fishes and decapod crustaceans inhabiting oyster reefs in the Caloosahatchee River and Estuary are shaped partly by salinity, with distinct communities occurring at different locations along the salinity gradient. Reduced salinities occurring upstream or as a result of high freshwater inflow, have the potential to alter the habitat value of oyster reefs for commensal organisms by increasing oyster mortality and reducing oyster density. Such changes would not only affect microhabitat within oyster clusters (e.g., availability of oyster boxes) but also increase the patchiness of oyster reef habitat. 3 The organic matter sources, amphipods, and worms were at the lowest level and were consumed by oysters, resident crabs, shrimp, and fishes. The oysters, crabs and shrimp were then consumed by other resident crabs and fish species. Transient fish species such as Lutjanus sp. came to the reef to feed on the reef resident crab, shrimp, and fish species. Alterations in freshwater flow and watershed changes over time caused differences in the isotope compositions of the organisms on oyster reefs. Samples from locations that receive freshwater showed a difference in carbon isotopic compositions compared to the more estuarine samples indicating that carbon sources from upstream could change the energy transfer within the oyster reef communities. This may cause areas with higher freshwater flow to have a decrease in higher quality food, abundance of food, or diversity of food compared to more natural areas. The abundance and diversity of organisms at sites that encounter greater freshwater input were lower compared to more estuarine / marine sites indicating that freshwater flow did influence food sources available for the organisms at this site. Given the severity of predation, future studies should examine the role of predation with appropriate replication. The effect of various salinity regimes and inflow patterns on the early life stages of oysters (e.g., veliger, umbo, pediveliger) is not clear and should be investigated further. Continuous salinity measurements at the sampling locations are necessary to capture episodic events and better understand the changes in oyster responses. This will result in better tools for freshwater inflow management by resource managers. Minimizing extreme flows into the estuary during this period may minimize flushing of larvae to downstream locations and retain larvae within the estuary, while creating optimal salinity conditions for larvae and juvenile oysters. Future work could look at the quality and diversity of food sources on oyster reefs especially in altered and natural areas to determine if species in altered systems do receive a lower quality food compared to natural systems. 4 TABLE OF CONTENTS Acknowledgements 6 Chapter 1: Seasonal and Spatial Variation of Oyster Responses in the Caloosahatchee Estuary 7 Introduction and Background 7 Project Goals and Objectives 11 Approach 12 Materials and Methods 13 Statistical Analyses 16 Data deposition and Utilization 17 Results 17 Discussion 21 Summary and Future Directions 26 Chapter 2: Habitat Use of Oyster Reefs by Decapods Crustaceans and Fishes 28 Introduction and Background 28 Research Goals and Objectives 35 Materials and Methods 36 Statistical Analyses 40 Results 42 Discussion 50 Summary and Future Studies 58 References Cited 61 Tables 76 Figures 92 5 ACKNOWLEDGMENTS This project was funded through a grant from the South Florida Water Management District (SFWMD; award #4600000815). We are grateful to Ms. Patricia Goodman, project manager for her support, technical input, and guidance on the project. We thank Ms. Patricia Gorman for her support and technical guidance and Ms. Darlene Marlene for her assistance with data management. Thanks are also due to Mr. Julio Fanjul who served as the contract manager and provided guidance, support and input. Flow data was generously provided by Dr. Peter Doering and Ms. Kathy Haunert (SFWMD). Cover page design was generously provided by Mr. James Greco. Many people helped with the field and laboratory work associated with this project. First and foremost, we thank our laboratory managers, Ms. Lesli Haynes and Ms. Lacey Smith for their dedication, hard work, planning, and help with both field and laboratory tasks. Ms. Christal Niemeyer was invaluable