Upper thermal limits and warming safety margins of coastal marine species – Indicator baseline for future reference

The threat of global warming has driven recent efforts of estimating upper thermal limits of ectothermic species all over the world. The investigation of thermal limits is crucial for the understanding of climate change ecology, since it provides insight into how climate will shape future species distributions. This work estimated the Critical Thermal Maxima (CTMax) of 42 coastal species (Gastropoda, Crustacea, Teleostei, Echinodermata and Cnidaria) in a tropical and a temperate area. The thermal safety margin (CTMax-Maximum Habitat Temperature) and future thermal safety margin (CTMax-(Maximum Habitat Temperature + 3 °C)) of each species was estimated for two alternative habitats, shallow coastal waters and tide pools. The CTMax of tropical species was higher than that of temperate species and no difference was found among the taxonomic groups tested. Thermal safety margins were larger for temperate species, than for tropical species, and considerably larger for shallow waters than for tide pools. Most tropical species had negative safety margins in tide pools (with only two exceptions), while most temperate species had positive safety margins (with only three exceptions). Future thermal safety margins for tide pools were negative for all tropical organisms and also for most of their temperate counterparts. This work adds to the data collection already available for the study areas, raising the number of species with known upper thermal limits to 100. These estimations do not take into account phenotypical acclimation, nor genetic adaptation, to future temperatures, which are likely to occur. However, they constitute important values for future reference, allowing insights into the adaptation capacity of coastal species, as well as basis to explain future distribution shifts and/or local extinctions.