MICROGEOGRAPHICAL VARIATIONS IN GAMETOGENESIS AND SEX-RATIOS IN THE EASTERN OYSTER AT 2 MARSH SITES IN GEORGIA

This study examined gametogenesis of the eastern oyster Crassostrea vi rginica along an intertidal gradient. Twenty eastern oysters were take n from two tidal heights (high-intertidal, HI, and low-intertidal, LI) on a mostly biweekly basis from two sites (House Creek and Skidaway R iver) in Wassaw Sound, Georgia, from June 1993 to September 1994. Game togenic condition was evaluated by histological staging of the gonads and by subsequent image analysis. No retardation in gametogenic matura tion and spawning activity was seen in the HI eastern oysters when com pared with the LI eastern oysters. Also, the HI eastern oysters tended to maintain higher gametogenic variables throughout the year than the LI eastern oysters. At the Skidaway River site, HI female eastern oys ters had significantly higher reproductive variables than the LI easte rn oysters. Multiple spawning events occurred at each tidal height. We concluded that no retardation in gametogenesis occurred in HI eastern oysters, and being located high in the intertidal zone appeared to en hance the reproductive ability of the oysters. Sex ratios differed at the different tidal heights. Female: male abundance ratios were greate r in HI areas (3.45:1 at House Creek and 3.12:1 at Skidaway River) tha n in LI areas (1.95:1 at House Creek and 1.85:1 at Skidaway River). Th e higher proportion of males and smaller-sized eastern oysters found i n the LI zone at both sites probably indicated a younger population of eastern oysters. Younger or smaller animals could have resulted from stressors on the eastern oysters induced by nonlethal predatory activi ty, siltation, and disease.