Oocyte cohort analysis: reproductive patterns of Crassostrea virginica (Bivalvia) in tropical lagoons of the Gulf of Mexico

Abstract

The Eastern oyster, Crassostrea virginica, was collected during 2004 from two tropical lagoons (1 – Laguna Tamiahua; Tantalamos, LT-1 and La Dalia, LT-2; and 2 – Laguna Grande; Vega de Alatorre, LG) in the Gulf of Mexico to document sexual and reproductive changes. Evolution of oocyte cohorts was described by analyzing frequency distributions of oocyte diameters and sex ratios. Each population (LT-1, LT-2, and LG) showed a distinct pattern in the number of cohorts, eight at LT-1 and LG, and five at LT-2. The main reproductive period was January through September with continuous spawning events and peaks in March and July. From modal analysis, oysters at LT-1 and LG, sites with a mean annual temperature >27°C, produced oocytes at a rate three times faster than oysters at LT-2, a site with a lower mean annual temperature. This suggests, apart from differences in spawning intensity among sites, a threshold temperature to attain maximum reproductive activity. Energy reserves were stored during lower temperatures, and it appears that the reserves are used later for gametogenesis. Higher frequency of hermaphrodites occurred throughout the reproduction cycle, suggesting continuous changes of sex from male to female, likely to be a reproductive strategy to maintain high rates of gametogenesis. These findings provide a better understanding of the reproductive biology of C. virginica in tropical areas.