Exposure of an intertidal fish to simulated heatwaves and suspended sediment - a multistressor approach.

Extreme climatic events, such as marine heatwaves (MHW) and increased suspended sediment concentration (SSC), are increasing in frequency and intensity, resulting in sudden changes to coastal environments, especially intertidal zones. Intertidal animals experience conditions that substantially fluctuate over temporal and spatial scales and therefore require the ability to physiologically tolerate these fluctuations. Since multiple stressors often co-occur and natural populations tend to respond to local environmental fluctuations, we aimed to investigate individual and combined effects of MHW and increased suspended sedimentation in Forsterygion lapillum from two neighbouring coastal areas with distinct water temperatures and wave current regimes by assessing fish oxygen consumption rate, mortality and weight loss. Results showed that in both F. lapillum populations, oxygen consumption rate and survival probability were unaffected by any treatment. However, fish from both populations lost weight during heatwave and multistressor treatments (i.e. heatwave and sedimentation), while fish from the sedimentation treatment alone did not lose weight. Although a direct effect on fish respiration was not found, our results indicate that F. lapillum performance is reduced when exposed to heatwaves individually and in combination with increased sediment suspension. Weight loss indicates that fish experiencing these stressors were unable to meet their metabolic demands.