The progress of gametogenesis was studied in oysters Crassostrea gigas having the same origin (Tremblade), but cultured during 1 year in two distinctive French marine areas, the Baie des Veys and Marennes-Oléron. We assessed seasonal changes in the reproduction cycle on the basis of stereological techniques to estimate reproductive investment and measurement of gonad evolution area by quantitative histology. From a qualitative point of view, both oyster groups presented typical reproductive stages, but showed differential timing, in particular during the sequence of spawning and duration of the re-absorption stage. Oysters in Baie des Veys had a single partial spawning in August and a re-absorption stage that extended until winter. Oysters in Merennes-Oléron had a partial spawning in July and massive release of gametes during August. Spawnings in both the areas were related to maximum temperature (19°C). The quantitative analysis showed, on an annual basis, a higher reproductive investment by oysters from Baie des Veys, 86% against 53% in the other group. Larger gonads, higher gamete production, and more intensive spawning were the characteristics of oysters in Baie des Veys. Recently, the reproduction pattern and investment has been related with summer mortalities; therefore, a quantitative understanding of reproductive processes becomes necessary for C. gigas. Environmental conditions at each site may explain differences in the progress and intensity of gametogenesis. While temperature regulated the time and speed of gametogenesis, results suggest that the intensity was influenced by the quantity of available food but may need further research. However, nutrient recycling from unreleased gametes in the gonads of oysters from Baie des Vey is a factor to be considered in the results of this study.

Queen conch, Strombus gigas (Linnaeus, 1758), is a species of significant economic importance in the Caribbean Sea, exploited mainly for consumption by a ravenous export market in the USA and French West Indies. Because populations have been depleted throughout the Caribbean region by overfishing, present conservation efforts are focused on regional harmonization of conch management to improve its sustainability. In the present study, we compare the reproductive cycle of S. gigas from eight sites (Florida Keys, Alacranes Reef, Chinchorro Bank, San Pedro, San Andrés Archipelago, Guadeloupe, Martinique, and Barbados) to consider the biological rationale for a harmonized closed fishing season. A framework recognizing four reproductive stages for males and females is proposed for use in future studies. Significant differences were found in the timing and intensity of reproductively active stages between conch from western and eastern sites in the wider Caribbean region. Two distinct reproductive strategies were observed: (1) continuous and low level of reproduction throughout the year (Alacranes Reef, San Pedro, and San Andrés Archipelago); and (2) a discrete and intense reproductive period with rapid gametogenesis (Guadeloupe, Martinique, and Barbados). Queen conch required a temperature of ≥27.7 °C to initiate gametogenesis; and were found in the resting stage below 27.5 °C. Based on a comparison of spawning seasons across the reproductive strategies observed, we suggest that the most "biologically meaningful" period for a closed season for the entire western central Atlantic would need to incorporate the months of June to September, at a minimum, to offer regional protection for spawners.

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