Synergistic effect of salinity and temperature on the survival of the bloody cockle Senilia senilis in the Sine Saloum estuary (Senegal)

Estuarine ecosystems are characterized by strong temporal and spatial variability in environmental conditions, particularly temperature and salinity. These parameters often fluctuate simultaneously, potentially generating combined stress that may affect the physiological performance and survival of resident organisms. In the context of climate change, understanding how estuarine species respond to such interacting stressors has become increasingly important. This study investigates the effects of temperature and salinity, and their interaction, on the survival and metabolic response of the bloody cockle Senilia senilis , a key benthic species of the Sine Saloum estuary (Senegal). Experiments were conducted in situ using the mobile laboratory Galou Xam Xam, allowing controlled ecophysiological measurements close to natural environmental conditions. First, thermal tolerance was assessed by exposing individuals to increasing temperatures to determine the median lethal temperature (LT₅₀). Second, respiration rates were measured across a thermal gradient to evaluate metabolic sensitivity to temperature. Finally, survival was monitored under different combinations of temperature (30–39 °C) and salinity (12–62) to examine their combined effects. Results indicate that S. senilis exhibits relatively high thermal tolerance, with an LT₅₀ of 39.6 °C after 24 h. Respiration rates increased with temperature, indicating strong metabolic sensitivity (Arrhenius temperature T A = 6925 K). Survival analyses revealed significant effects of temperature, salinity, and their interaction, with marked reductions in survival under extreme thermohaline conditions. An optimal thermohaline window was identified between 30 and 35 °C and salinities of 20–40. These findings highlight the vulnerability of S. senilis to extreme environmental conditions and provide key physiological parameters for predicting the responses of estuarine populations to future climate-driven hydroclimatic changes.