Spatially Distinct Life Stages Leave a Tropical Fish Species More Susceptible to Climate Change

The Intergovernmental Panel on Climate Change predicts sea surface temperatures will increase by 1-2°C over the next century.  Many species inhabit thermally dynamic environments during early life stages and migrate to stable ecosystems as adults, yet little is known about how the same species will respond to elevated temperatures across ontogeny.  This study investigates the tolerance of multiple life stages of Lutjanus apodus to elevated temperatures that coincide with and surpass IPCC projections.  A peak in aerobic scope (AS) was identified for juveniles with no net change from control to extreme treatments, while a slight yet continual increase in AS was found in adults, indicating potentially different thermal performance curves or physiological response mechanisms across life stages.  Critical swimming speed (U_crit) significantly decreased for both groups as temperatures increased.  Critical thermal maximum (CT_max) was significantly higher in juveniles than adults.  CT_max of juveniles was only 3°C higher than the maximum environmental temperature measured at the site from which they were collected, whereas the CT_max for adults was 9.4°C above its environmental maximum.  Extreme thermal events, combined with hindered performance factors such as lower U_crit, may leave this ecologically and economically important group of fish highly susceptible to foreseen warming conditions.