Despite plasticity, heatwaves are costly for a coral reef fish

Climate change is intensifying extreme weather events, including marine
heatwaves, which are prolonged periods of anomalously high sea surface
temperature that pose a novel threat to aquatic animals. Tropical animals
may be especially vulnerable to marine heatwaves because they are adapted
to a narrow temperature range. If these animals cannot acclimate to marine
heat waves, the extreme heat could impair their behavior and fitness.
Here, we investigated how marine heatwave conditions affected the
performance and thermal tolerance of a tropical predatory fish, arceye
hawkfish (Paracirrhites arcatus), across two seasons in Mo'orea,
French Polynesia. We found that the fish’s daily activities, including
recovery from burst swimming and digestion, were more energetically costly
in fish exposed to marine heatwave conditions across both seasons, while
their aerobic capacity remained the same. Given their constrained energy
budget, these rising costs associated with warming may impact how hawkfish
prioritize activities. Additionally, hawkfish that were exposed to hotter
temperatures exhibited cardiac plasticity by increasing their maximum
heart rate but were still operating within a few degrees of their thermal
limits. With more frequent and intense heatwaves, hawkfish, and other
tropical fishes must rapidly acclimate, or they may suffer physiological
consequences that alter their role in the ecosystem.