Additive and non-additive effects of artificial light at night and ocean warming on the physiology and behavior of an intertidal fish

Coastal organisms are increasingly subjected to simultaneous anthropogenic stressors, yet the extent to which these drivers interact remains poorly understood. Here, we experimentally tested the combined influence of artificial light at night (ALAN) and ocean warming (OW) on the physiology and behavior of juveniles of the intertidal fish Girella laevifrons . Individual fish were exposed to a factorial design manipulating light regime (darkness vs ALAN) and temperature (19 °C vs 23 °C) to assess their influence on locomotor activity, metabolism, food consumption, and absorption efficiency rates. Our results showed that OW caused an increase in activity, while ALAN reduced food consumption rates relative to darkness. In addition, both ALAN and OW independently raised metabolic rates and absorption efficiency, indicating that metabolic and digestive processes were responsive to each stressor in isolation. When both predictors were significant, we found some evidence of one factor modulating the influence of the other, particularly upon absorption efficiency. These findings also reveal that light pollution and warming each impose energetic costs through altered behavior, metabolism, and feeding performance. Given the rapid expansion of ALAN and the predicted intensification of OW, our results underscore the ecological significance of further studies examining multiple stressors impacts on coastal organisms.