Unveiling seasonal variability in Crassostrea tulipa larval dispersal in Gulf of Guinea coastal waters: foundations for sustainable shellfish farming

The coastal zone of the Gulf of Guinea holds significant natural potential for the production of the mangrove oyster Crassostrea tulipa . This study assessed the larval dispersal of C. tulipa in the Benin’s coastal lagoon. Oyster larvae were sampled monthly from January to December 2023 in three traditional oyster production areas (Ahouandji, Dégouè, and Djondji) using a 50 µm mesh plankton net. The larvae samples collected, were analyzed under a light microscope, and the different larval stages (D-, veliger, and pediveliger larvea) of C. tulipa were identified and counted. The results show a major larvae abundance period extending from November to April, with maximum density occurring in March and/or April, depending on the site. A secondary phase of larvae abundance production was observed from May to July, although it was characterized by a very low presence of advanced larval stages (pediveliger). A dominance of D- and veliger larvae was noted in the Djondji area, whereas pediveliger larvae were more prevalent in the Ahouandji production zone. The highest cumulative number of larvae (56,220.0) was recorded in the Djondji area, compared to 35,586.7 in Dégouè and 36,160.0 in Ahouandji. In terms of larval survival, the lowest rate (0.1%) was observed in Djondji, compared to 0.2% in Ahouandji and 0.4% in Dégouè. Therefore, the high larval abundance observed in the Djondji production area does not necessarily reflect favorable survival conditions for larvae. The production areas of Ahouandji and Dégouè may offer more favorable environments for larval development. These results provide valuable data that can be used to improve oyster farming and management in Benin’s coastal waters.