Thermal tolerance and potential impacts of climate change on coastal and estuarine organisms

The study of thermal tolerance is the first step to understanding species vulnerability to climate warming. This work aimed to determine the upper thermal limits of various fish and crustaceans in a temperate estuarine ecosystem and an adjacent coastal area. Species were ranked in terms of thermal tolerance and intraspecific variability was evaluated. The method used was the Critical Thermal Maximum (CTMax). The CTMax was found to be higher for species typically found in thermally unstable environments, e.g. intertidal, supratidal, southern distributed species and species that make reproduction migrations because they are exposed to extreme temperatures. Subtidal, demersal and northern distributed species showed lower CTMax values because they live in colder environments. Species from different taxa living in similar habitats have similar CTMax values which suggests that they have evolved similar stress response mechanisms. This study showed that the most vulnerable organisms to sea warming were those that occur in thermally unstable environments because despite their high CTMax values, they live closer to their thermal limits and have limited acclimation plasticity. Among the demersal species studied, two sea-breams (Diplodus bellottii and Diplodus vulgaris) are potentially threatened by sea warming because their CTMax values are not far from the mean water temperature and they are already under thermal stress during current heat waves.