Investigating how zooplankton monitoring can support shellfisheries in mangrove ecosystems of West Africa

In the West African mangrove ecosystems, oysters (Crassostrea tulipa) and bloody cockles (Senilia senilis) play crucial roles both economically and in ensuring local food security. However, these bivalve species face significant threats mostly from overexploitation, environmental degradation, and climate change impacts. These challenges endanger their sustainability, and the livelihoods of the dependent local communities. Previous research detailed the ecophysiology, reproductive cycles, stock dynamics, and recruitment patterns of the two species. The present study focuses on the planktonic larval stages of C. tulipa and S. senilis in the Sine Saloum ecosystem (Senegal). This critical life phase is essential for maintaining stocks and a better understanding is key to sustain an effective management of artisanal shellfisheries. Here, we aim to describe the occurrence, distribution and development of larvae of these two species in the Sine Saloum, to assess the diversity of associated zooplankton communities and the effect of hydrological variables on the patterns observed. 

Based on the assumption that larval occurrence correlates with low salinity and high temperature, a bimonthly spatial survey across seven sites in the Sine Saloum estuary has been underway during monsoon season. Plankton samples were collected using two different nets (53µm and 100µm mesh size) and environmental parameters were measured. Plankton samples were analyzed using PlanktoScope and Zooscan at the new West African Aquatic Quantitative Imaging platform (PIQAAO) hosted at the Dakar-Thiaroye Oceanographic Research Center (CRODT), Dakar Sénégal. Based on the images acquired, a learning set is produced to develop a machine learning model for plankton classification, including bivalve larvae. After presenting the context of the study, we will share and discuss the initial results of the classification algorithm and observed changes in the plankton community in connection with hydro-climatic patterns.

This survey will establish a baseline for describing the plankton community composition in the Sine Saloum ecosystem and more generally for the West African coasts. More specifically, the results of this research will provide critical insights into the under-documented planktonic phase of two major bivalve species, contributing to scientific recommendations for sustainable management of their exploitation. These findings are also key in the context of developing aquaculture activities, especially for the oyster.