Experimental Evaluation of Chronic Hyposalinity on Three Intertidal Venerid Bivalves

Abstract

Salinity is a key environmental factor in estuarine and intertidal ecosystems. It decreases with freshwater inputs from rivers or intense rainfall. It is essential to investigate the effects of salinity on bivalves to understand their adaptive capacity to highly variable conditions. Long-term experiments over several weeks are particularly valuable, as they allow the detection of acclimation processes that are not apparent in short-term studies spanning a few days, which mainly reflect acute stress responses. Such knowledge is crucial for predicting species resilience under climate change scenarios and for supporting their conservation and sustainable management. This study evaluated the responses of three venerid bivalves – Ruditapes decussatus, Ruditapes philippinarum, and Chamelea gallina – to different salinity treatments over a 21-day period. At 15 and 20 psu, mortality patterns markedly shifted with survival patterns emerged. Mortality decreased significantly above these salinities, although tolerance differed among species and exposure durations. After 7 days, R. decussatus and C. gallina were more resistant, showing no mortality at 20 psu, whereas 77.8% of R. philippinarum individuals survived at this salinity. After 21 days, mortality exceeded 80% for all species at ≤ 15 psu. Ruditapes decussatus survival was 90% at 20 psu, while there was comparable survival for R. philippinarum and C. gallina at 25 and 35 psu, respectively. Median lethal concentration analysis indicated that C. gallina exhibited lower tolerance to prolonged hyposalinity. Overall, R. decussatus demonstrated superior survival under low-salinity conditions, indicating greater resilience to environmental fluctuations, a trait likely to be critical for its conservation under future climate change scenarios.