Unveiling Seasonal Variability in Crassostrea tulipa Larval Dispersal in Gulf of Guinea Coastal Waters: Foundations for Sustainable shellfish farming

Yaovi ZOUNON^1,2*Dogbè Clément Adjahouinou³Pierrick Barbier⁴Sènakpon Emmanuel Wanou³Théophile Godome⁵Francina Moya Ruiz⁶Manuel Vargas-Yáñez⁷M. Carmen García Martínez⁷Zacharie SOHOU^5,8

• ¹Department of Zoology, Faculty of Science and Technology, University of Abomey-Calavi, Cotonou, Benin
• ²Institut de Recherches Halieutiques et Océanologiques du Bénin (IRHOB), Cotonou, Benin
• ³Universite Nationale d'Agriculture, Ketou, Benin
• ⁴Centre pour l’Aquaculture, la Pêche et l’Environnement de Nouvelle-Aquitaine (CAPENA), Le Château d’Ol´eron, France
• ⁵Universite d'Abomey-Calavi, Cotonou, Benin
• ⁶Instituto Español de Oceanografia (IEO), Malaga, Spain
• ⁷Instituto Español de Oceanografia (IEO), Málaga, Spain
• ⁸Institut de Recherches Halieutiques et Océanologiques et Océanologiques du Bénin, Cotonou, Benin

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 Dand veliger larvae was noted in the Djondji area, whereas pediveliger larvae were more prevalent in the Ahouandji production zone. Larval indices showed that the days of highest larval density at Ahouandji and Dégouè corresponded to the 84th day of the year (19,583.3 larvae/m³ for Ahouandji and 8,340.0 larvae/m³ for Dégouè), while in Djondji, this occurred on the 112th day (17,416.7 larvae/m³). 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 favourable survival conditions for larvae. The production areas of Ahouandji and Dégouè may offer more favourable environments for larval development. These results provide valuable data that can be used to improve oyster farming and management in Benin's coastal waters.