Seasonal changes in the diet of the bloody cockle (

This study investigates the food sources of Senilia senilis along the Sine Saloum estuary during the monsoon and dry seasons by combining isotopic and lipid analysis. We analyzed the fatty acids (FA) and sterol composition of digestive glands, and the carbon and nitrogen isotopic composition of muscles from 180 individuals sampled at four stations distributed along the estuary and during both seasons. Our findings reveal a spatiotemporal structure of the diet of S. senilis. In the upper estuary, S. senilis relies probably more on bacteria and zooplankton (higher proportions of 17:0, anteiso 17:0 and 15:0, 20:1 and 22:1) than downstream, where it locally finds the most homogeneous habitat (lowest isotopic diversity). The sources of nitrogen and carbon supporting planktonic communities appear to be more heterogeneous upstream, as indicated by the greater isotopic diversity at station 2. During the dry season, S. senilis relies more on dinoflagellates (higher proportions of 22:6n-3 and 18:4n-3) than during monsoon. However, during the monsoon, it has a greater diversity of FA, and therefore probably of food taxa, and relies more on diatoms (higher proportions of 16:1n-7 and 20:5n-3), likely from benthic origin. Together, these results highlight the trophic plasticity of S. senilis in response to the Sine Saloum estuary's inverse dynamics. Such changes in the environment may also modify physiological need, as revealed by non-methylated interrupted (NMI) FAs present in the individuals sampled in the part of the estuary undergoing the most brutal environmental changes.