EFFECTS OF SALINITY AND OTHER STRESSORS ON EASTERN OYSTER (CRASSOSTREA VIRGINICA) HEALTH AND A DETERMINATION OF RESTORATION POTENTIAL IN NAPLES BAY, FLORIDA. A Thesis Presented to The Faculty of the College of Arts and Sciences Florida Gulf Coast University In Partial Fulfillment Of the Requirement for the Degree of Master of Science By Katie Sue Laakkonen 2014 2 APPROVAL SHEET This thesis is submitted in partial fulfillment of the requirements for the degree of Masters of Science _____________________________ Katie S. Laakkonen Approved: May 2014 _____________________________ Aswani K. Volety, Ph.D. Committee Chair/Advisor _____________________________ Michael Savarese, Ph.D. _____________________________ Michael Bauer, Ph.D. The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline. 3 ACKNOWLEDGMENTS This research would not have been possible without the support of many people. First, I would like to thank my committee members, Dr. Aswani Volety, Dr. Michael Bauer, and Dr. Michael Savarese for their guidance, advice, and expertise that they provided throughout this process. Dr. Aswani Volety’s expertise and foundation of oyster research in Southwest Florida lead to my thesis work in Naples Bay and made all of this possible. A special thank you goes to Dr. Michael Bauer for the numerous hours helping me in the field collecting data, cleaning oysters, and enduring many cuts from oyster shells. This research project could not have been completed without all of his efforts and guidance. Thank you to Dr. Michael Savarese for his thorough review of my thesis work and invaluable advise. I would also like to thank Monique Barnhart and Lacey Smith for assistance in the field collecting data. Thanks to Lesli Haynes and Lacey Smith for their lab assistance at FGCU, training me on processing procedures and Perkinsus marinus microscopic ID, and always being available to answer my questions. A big thank you and appreciation to Dr. Brian Bovard for the willingness and perseverance in helping me analyze my data. And finally, I am grateful for the support of my family and friends, especially my loving husband Keith, for their encouragement and moral support through this challenging journey. 4 ABSTRACT Naples Bay, a highly urbanized estuary, has lost an estimated 80% of its oyster reefs since the 1950s due to dredging and development activities. Artificial canals, primarily the Golden Gate Canal, have increased freshwater flows into Naples Bay causing extreme swings in salinity. This study characterizes the health of the eastern oyster, Crassostrea virginica, at four sites along a salinity gradient by investigating and correlating various oyster responses to salinity, dissolved oxygen, and temperature. Prevalence and intensity of Perkinsus marinus infection varied significantly among sites, with the northernmost upstream Site 1 showing the lowest infection. Condition index varied significantly among sampling months and sites, and decreased during the spawning period, April through October. Sites 1 and 2, with more optimal salinities for the first 8 months of the study, had the highest mean condition index. Significant differences were found among sampling months for spat recruitment and sites and peaked in August. Spat recruitment was greatest at the southernmost Site 4 which is located furthest from the freshwater influence and therefore has less extremes in salinity. Living densities (# live oysters m-2) also varied significantly among sampling months and sites, with living densities increasing when moving downstream. Higher living densities were found in the wet season than the dry season reflecting recruitment occurring onto the reefs. The wet season is when extreme swings in salinities result upstream which corresponds with oyster reproduction. Site 1 experienced a 31 ppt drop in salinity within a few days in July when significant rainfall began. This is a tremendous stressor on oysters and could result in mortality of juvenile oysters and the flushing of spat downstream due to high freshwater flows. This study highlights that freshwater flows and resulting salinities are a 5 driving force for oyster reef health and distribution in Naples Bay. It also provides a baseline assessment of the oyster population that will allow for future comparisons when water quality improves due to diversions of freshwater from the Golden Gate Canal. These diversions are planned for the near future by the South Florida Water Management District. This study also assists resource managers in determining potential oyster restoration sites in the bay. Management recommendations include focusing oyster restoration sites at the downstream locations due to less salinity extremes, high oyster living densities, and higher spat recruitment. 6 TABLE OF CONTENTS ACKNOWLEDGMENTS………………………………………………………..….3 ABSTRACT…………………………………………………………….....................4-5 TABLE OF CONTENTS…………………………………………………………….6 LIST OF FIGURES…………………………………………………………………..7-9 INTRODUCTION…………………………………………………………………....10-23 RESEARCH OBJECTIVES…………………………………………………………24 METHODS…………………………………………………………………………...25-31 RESULTS…………………………………………………………………………….32-37 DISCUSSION……………………………………………………………………….. 38-52 REFERENCES……………………………………………………………………….53-62 FIGURES…………………………………………………………………………….63-78 7 LIST OF FIGURES Figure 1. This map shows the study area and the four sampling locations in the Naples Bay/Gordon River Estuary and the long term City and County water quality locations. Figure 2. This map shows a comparison of historical Naples Bay (1953) and current day Naples Bay (2010). The channelized neighborhood seen today on the left side of the photo is Port Royal and used to be mangrove wetlands as observed in the 1953 photo. Note the oyster bars throughout the bay in the 1953 aerial. Figure 3. This map shows the Golden Gate Canal Weirs #1 and #2, and the 4 USGS datasonde locations. Figure 4. This map shows both the historical (10 sq mile) watershed and the expanded watershed (120 sq mile) that resulted from the dredging of the Golden Gate Canal (South Florida Water Management District). Figure 5. This map shows a habitat comparison between 1953 and 2003 and the approximate historic versus present day oyster and seagrass coverage (Schmid et al. 2005). Figure 6: Monthly salinities (ppt) at each site showed a delayed start to the rainy season, which typically begins in June. Site 1 had the most extreme salinity swing and dropped 31 ppt within a few days. Figure 7: Mean salinities (ppt) from long term water quality sites adjacent to oyster research sites were recorded from 2005-2011. Salinities varied significantly among sites (p < 0.0001). Statistically significant differences are denoted by letters above data results where matching letters indicate results that are statistically similar. Error bars represent one standard deviation. Figure 8: Mean salinities (ppt) from long term water quality sites varied significantly among sites and between seasons (p < 0.5). Dry season salinities were significantly higher than the wet season. Statistically significant differences are denoted by letters above data results where matching letters indicate results that are statistically similar. Error bars represent one standard deviation. Figure 9: Monthly temperatures (oC) at each site showed a typical increasing trend into the summer months. Temperature values were similar among sites (within 2 oC) for a given month. 8 Figure 10: Mean temperatures (oC) from long term water quality sites were approximately 25 oC for all sites. Error bars represent one standard deviation. Figure 11. Monthly dissolved oxygen values at each site were similar for a given month and stayed within 2 mg/l of each other (with the exception of July). Due to equipment failure, data were not recorded for September or October 2011. Figure 12. Mean dissolved oxygen values from long term water quality sites were all within the range of 5-6 mg/l. Error bars represent one standard deviation. Figure 13. Monthly mean condition index of oysters from all sampling sites varied significantly among sampling months (p < 0.0001) and sites (p < 0.0001). Error bars represent one standard deviation. Figure 14. Mean condition index of oysters for each site varied significantly among sites (p < 0.0001). Statistically significant differences are denoted by letters above data results where matching letters indicate results that are statistically similar. Error bars represent one standard deviation. Figure 15. Monthly mean infection intensity of P. marinus from all sampling sites varied significantly among sampling months (p < 0.0001) and sampling sites (p < 0.001). Error bars represent one standard deviation. Figure 16. Mean infection intensity of P. marinus for each site varied significantly among sampling sites (p < 0.001). Statistically significant differences are denoted by letters above data results where matching letters indicate results that are statistically similar. Error bars represent one standard deviation. Figure 17. Monthly mean prevalence (%) of infected oysters did not vary significantly among months, but did vary significantly among sampling sites (p = 0.005). Error bars are too small to show on graph. Figure 18. Mean prevalence (%) of infected oysters varied significantly among sampling sites (p = 0.005). Statistically significant differences are denoted by letters above data results where matching letters