Thermal tolerance of nearshore fishes across seasons: implications for coastal fish communities in a changing climate

Global climate change is predicted to increase the variability in weather patterns with more extreme weather conditions occurring on a more frequent basis. Little information exists on thermal limits of fishes from highly variable environments. This study evaluated the thermal maximum and minimum of checkered puffers, yellowfin mojarra, schoolmaster snapper, and bonefish across seasons. Thermal scope (i.e., CTmax-CTmin) of nearshore fishes ranged from 24 to 28.6 degrees C across seasons, with thermal scopes typically being larger in the winter (January 1, 2012-March 22, 2012) than in the summer (June 26, 2012-November 9, 2012). Acclimatization response ratios (AZRR; Delta CTmax Delta T-1 and Delta CTmin Delta T-1) were typically greater than 0.60 for all species, a value greater than most previously reported for fish species from variable thermal environments. Present-day maximum and minimum temperatures in the nearshore environment are approximately equal to or exceed the thermal tolerance limits of the fish in this study, making thermal safety margins (TSM; i.e., the difference between thermal tolerance limit and extreme environmental temperature) very small or negative for nearshore fishes (TSM upper = -4.9 to 0.5; lower = -0.2 to 0.4). The IPCC's worse-case scenario will push maximum temperatures beyond the TSM of all nearshore fish in this study. Distribution of fishes in the nearshore environment in the future will depend on available thermal refuge, cost of migrating, and food web interactions. Overall, the thermal landscape in the nearshore environment in the future will likely benefit species with positive thermal safety margins that are capable of acclimatizing (e.g., schoolmaster snapper), while relatively intolerant species (e.g., bonefish) may inhabit these systems less frequently or will be absent in the future.