Salinity narrows thermal tolerance while sediment burial buffers temperature stress in the common cockle Cerastodermaedule

Climate change is altering environmental conditions through raising air temperatures and changing precipitation patterns, threatening species and ecosystem functioning. Intertidal species are particularly vulnerable, and in this study, we analyzed long-term climate data and investigated the thermal tolerance of the common cockle (Cerastoderma edule) under simulated emersion conditions. Climate data spanning 150 years (1875-2024) show that, when comparing 25-year averages from 1875 to 1899 to 2000-2024, annual maximum air temperature increased by 2.44 °C, the number of days with sub-zero air temperatures decreased by 25.1 days, and annual precipitation increased by 168.0 mm (25.8%) to 2000-2020. Cerastoderma edule demonstrated considerable tolerance to both sub-zero (LLT₅₀ = -7.5 °C) and high (ULT₅₀ = 38.2 °C) air temperatures. Burial in sediments provided effective thermal buffering, reducing body temperature fluctuations and was associated with high survival, particularly during sub-zero exposure. Acute exposure to reduced interstitial salinity (0-25 PSU) had no detectable effect on thermal tolerance. In contrast, prolonged exposure to low seawater salinity significantly reduced both upper and lower thermal limits and increased susceptibility to high temperature stress through a synergistic interaction. These findings indicate that while C. edule can tolerate current and projected temperature extremes in isolation, future increases in freshwater input and associated salinity changes may substantially constrain its thermal tolerance. This highlights the importance of accounting for interacting climate-driven stressors when assessing species vulnerability and resilience in intertidal ecosystems.