Climate change is imposing constant and more severe environmental challenges to coastal and marine species. Using fiddler crabs as a model, I present the effects of increasing temperature (or heatwaves) and decreasing pH on ecological, behavioral and physiological responses. The combined effect (increase in temperature and decrease in pH) on embryonic and larval development reduced survival at higher temperatures; embryo development and larval physiology were synergistically affected by both stressors. Acidification seems to affect the chemosensation of planktonic larvae, leading them to not distinguish between a non-harmful stimulus and a potential predator and potentially bringing a cascade of ecological impairments. Fiddler crabs have an amphibious life cycle and during the planktonic phase it is the coldest water temperature that defines the limits of species distribution. As temperature increases, species can expand their distribution ranges. An increase of 0.9°C in mean sea surface temperature over the past 37 years, for the coast of South America, may explain the recent expansion of Leptuca cumulanta. Fiddler crabs grow less, reach sexual maturity earlier, and have lower survival rates in response to the high metabolic costs imposed by higher temperatures. In the adult stage, physiological and behavioral responses differ between species. Species that inhabit vegetated areas are more vulnerable to increased temperature, with greater water loss (decrease survival) and may change their geographical distribution due to high temperature; species that inhabit non-vegetated areas are more tolerant to temperature increase, despite physiological changes (osmotic control) and may have a competitive advantage in a warming scenario. With heatwaves becoming more frequent, hotter and longer lasting in the coastal region of SP, we can expect potential reductions in larval recruitment and stocks, with negative effects on coastal habitats.
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