Physiological and metabolic response of the bloody cockle (Senilia senilis) to salinity in the Sine Saloum estuary, Senegal

Estuaries are unique ecosystems that experience dynamic environmental conditions. Organisms in estuaries face significant and rapid fluctuations in salinity caused by tidal variations, evaporation, rainfall, and freshwater runoff. This is especially true for bivalve mollusks, which cannot move to escape unfavorable conditions. Consequently, variations in salinity can significantly influence their life-history traits. Here, we examined the response of the bloody cockle, Senilia senilis , to variations in salinity. This bivalve is predominant in the estuaries of West Africa and supports a significant artisanal fishing activity. Experiments were conducted in an in situ laboratory to assess the behavioural (valve opening/closing), physiological (respiration, filtration) and osmoregulatory responses of the species to changes in salinity. The results help us define the species' tolerance and functional niche ranges:: (1) closing behavior occurs at salinities above 12 and 60, (2) filtration stops at salinities above 25 and 40, and (3) respiration increases on either side of an optimal salinity of 40. Analysis of internal osmolarity confirms that S. senilis is an osmoconformer, as its osmolarity strongly correlates with that of seawater. These responses underline the adaptation of this species to an estuarine habitat subject to intense salinity fluctuations, while identifying tolerance thresholds beyond which its vital functions are impaired. These results are crucial for understanding the resilience of S. senilis in the context of global change and for anticipating the effects of increased estuarine salinity on benthic biodiversity and associated ecosystem services. • Senilia senilis exhibits significant physiological responses to salinity variations. • Valve closure behavior increases under salinity stress, indicating a protective mechanism. • Filtration rate declines significantly at extreme salinity levels. • Internal fluid osmolarity closely follows external salinity, confirming osmoconforming status.