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Seasonal Changes in Fecundity of Oysters Crassostrea Virginica (Gmelin): from Four Oyster Reefs in the James River, Virginia

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Seasonal Changes in Fecundity of Oysters Crassostrea Virginica (Gmelin): from Four Oyster Reefs in the James River, Virginia W&M ScholarWorks Dissertations, Theses, and Masters Projects Theses, Dissertations, & Master Projects 1988 Seasonal Changes in Fecundity of Oysters Crassostrea virginica (Gmelin): From Four Oyster Reefs in the James River, Virginia Carrollyn Cox College of William and Mary - Virginia Institute of Marine Science Follow this and additional works at: https://scholarworks.wm.edu/etd Part of the Fresh Water Studies Commons, Oceanography Commons, and the Zoology Commons Recommended Citation Cox, Carrollyn, "Seasonal Changes in Fecundity of Oysters Crassostrea virginica (Gmelin): From Four Oyster Reefs in the James River, Virginia" (1988). Dissertations, Theses, and Masters Projects. Paper 1539617594. https://dx.doi.org/doi:10.25773/v5-h6wd-y692 This Thesis is brought to you for free and open access by the Theses, Dissertations, & Master Projects at W&M ScholarWorks. It has been accepted for inclusion in Dissertations, Theses, and Masters Projects by an authorized administrator of W&M ScholarWorks. For more information, please contact [email protected]. SEASONAL CHANGES IN FECUNDITY OF OYSTERS CRASSOSTREA VIRGINICA (GMELIN) FROM FOUR OYSTER REEFS IN THE JAMES RIVER, VIRGINIA. A Thesis Presented to The Faculty of the School of Marine Science The College of William and Mary in Virginia In Partial Fulfillment Of the Requirements for the Degree of Master of Arts by / Carrollyn Cox APPROVAL SHEET This thesis is submitted in partial fulfillment of the requirements for the degree of Master of Arts Oij, Carrollyn^ Cox Approved: May, 1988 Roger L.^Mann, Ph.D. Committee Chairman/Advisor Mark W. Luckenbach, Ph.D. Morris H. Roberts, Jr., ^h.D Michael Castagna, M. Evon P. Ruzecki, Ph.D DEDICATION To Kevin J . McCarthy and Bernardita Campos for the times shared during the summer of 1986 TABLE OF CONTENTS Page ACKNOWLEDGMENTS................................................ v LIST OF TABLES .................................................... vi LIST OF FIGURES....................................................... vii ABSTRACT ............................................................ viii INTRODUCTION .................................................... 2 LITERATURE REVIEW.................................................. 5 Historical D a t a .............................................. 5 Life History ................................................ 6 F e c u n d i t y .................................................... 12 Condition Index .............................................. 15 OBJECTIVES ....................................................... 18 MATERIALS AND METHODS.............................................. 19 Sample Collection ............................................ 19 Temperature, Salinity, and Dissolved Oxygen ............... 19 Fecundity .................................................. 21 Condition Index .............................................. 22 Sex Ratios.................................................... 24 Abundance and Size-Frequency .............................. 24 Total Egg Production......................................... 25 Spawning and Larval Viability ............................... 25 RESULTS............................................................. 28 Temperature, Salinity, and Dissolved Oxygen ............... 28 F e c u n d i t y ................. 31 Condition Index .............................................. 39 Sex Ratios.................................................... 45 Abundance and Size-Frequency................................ 49 Total Egg Production................ 49 Spawning and Larval Viability ............................... 52 DISCUSSION ................................................ 57 LITERATURE CITED ......................................... 65 VITA ................................................ 74 iv ACKNOWLEDGMENTS I wish to express my gratitude to all of those who have helped to make this thesis a reality. My major professor, Roger Mann, and my thesis committee, Michael Castagna, Mark Luckenbach, Morris Roberts, and Evon Ruzecki, supported and encouraged me. Mark Luckenbach spent countless hours making sense of the statistics. Jean Watkinson gave me the benefit of her expertise in bivalve spawning techniques. Bernardita Campos listened. Kevin McCarthy, James Whitcomb, David Eggleston, Julia Wilcox, Curtis Roegner, and especially Kenneth Walker assisted in the field. Jan Hodges digitized reef areas. Diane Walker proof read sections of the manuscript. The VIMS Computer Center Staff, especially Gary Anderson and Kevin Kiley, and many others assisted me with my computer work. Distilled water was provided by Betty Salley and the VIMS Nutrient Analysis Laboratory. Kenneth Kurkowski and the VIMS Oyster Hatchery Staff provided oyster larvae, filtered water and advice. This work was funded in part by a grant from the Virginia General Assembly, and in part by two minor research grants to me from the Virginia Institute of Marine Science, School of Marine Science of the College of William and Mary. v LIST OF TABLES Table Page 1. Multiple Comparisons of Fecundity Among Stations. 34 2. Multiple Comparisons of Egg Number Among Dog Shoal Collections ....................................................... 36 3. Multiple Comparisons of Egg Number Among Thomas Rock Collections .............................................. 37 4. Multiple Comparisons of Egg Number Among Wreck Shoal Collections ................. 38 5. Multiple Comparisons of Egg Number Among Horsehead Collections ....................................................... 40 6. Sex Ratios of James River Oysters ...............................48 7. Number of Oysters per 0.25 square m e te r ........................ 50 8. Estimate of Total Egg Production per R e e f ...................... 53 9. Results of Spawning Trials....................................... 54 10. Results of Successful Spawning of Horsehead Oysters..... 55 vi LIST OF FIGURES Figure Page 1. The James River, Virginia ...................................... 3 2. Study sites in the James River Seed A r e a ...................... 20 3. Temperature and salinity at each study site from June to October, 1986 .................................................. 29 4. Percent Oxygen Saturation ..................................... 30 5. Regression of Egg Number and Shell Length ...................... 32 6. Mean Egg Number in James River Oysters.......................... 33 7. Regression of Cl(grav) and Shell Length ........................ 41 8. Mean Cl(grav) of James River Oysters............................ 42 9. Regression of Cl(afdw) and Shell Length ........................ 43 10. Mean Cl(afdw) of James River Oysters............................ 44 11. Correlation of Mean Egg Number and Mean Cl(grav)................ 46 12. Correlation of Mean Egg Number and Mean Cl(afdw)................ 47 13. Mean Abundance of James River Oysters ....................... 51 vii ABSTRACT Oysters Crassostrea virginica (Gmelin) were examined during the reproductive season of 1986, to determine variation in fecundity among individuals from four different reefs, Dog Shoal, Thomas Rock, Wreck Shoal, and Horsehead, in the seed area of the James River, Virginia. Factors potentially affecting reproductive potential, sex ratio, oyster abundance, mean shell length, and larval viability, were also examined. Additionally, fecundity was compared with gravimetric and ash-free dry weight condition indices to determine if fecundity and condition index were correlated. Fecundity of female oysters was found to be highly variable, both within and among locations. The large variation was attributed to a combination of factors including time since last spawning, oyster size, disease, parasitism, and temperature and salinity regimes. As a group, oysters from Thomas Rock produced 3-4 times as many eggs as those from the other 3 reefs. The production of eggs on Horsehead was greater than that on Wreck Shoal due to the great abundance of oysters on Horsehead, and a more nearly equal sex ratio. In sum, Dog Shoal oysters produced the fewest eggs. Results indicate that seed area oysters are potentially capable of providing for the large settlement of larvae in that area. Theories to account for the settlement failure of 1986 are discussed. SEASONAL CHANGES IN FECUNDITY OF OYSTERS CRASSOSTREA VIRGINICA (GMELIN) FROM FOUR OYSTER REEFS IN THE JAMES RIVER, VIRGINIA INTRODUCTION The Chesapeake Bay estuary (Fig. 1) supports one of the largest Crassostrea virginica (Gmelin, 1791) fisheries in North America (Thompson, 1986). Located centrally within the geographic range of the American oyster, the Chesapeake offers a favorable climate for oyster growth (Andrews, 1970). In addition, the subestuaries of the Chesapeake contain large areas of low salinity water which provide oysters with a refuge from predators and diseases (Andrews, 1982). The James River (Fig. 1) is the third largest and southernmost major tributary of the Chesapeake Bay (Wolman, 1968). The James is an important oyster producing area because recruitment there is high and mortality of oysters older than one year is low (Haven and Fritz, 1985). The James River has traditionally been used as an oyster seed area because, despite high recruitment and low mortality, growth rates are retarded by low salinity and meat quality of the oysters is poor (Haven and Fritz, 1985). Oysters less than 76 mm in length (seed) are harvested from the James and replanted elsewhere in the bay where growth rate is higher (Wood and Hargis, 1971; Haven and Fritz,
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