Short-term performance responses of an intertidal fish to sedimentation and warming

Climate change is altering coastal ecosystems by causing environmental fluctuations, such as increases in temperature and turbidity, which pose major implications for fish physiology and behaviour. Increases in temperature affect fish food intake, swimming capacity and oxygen delivery, while increases in turbidity can impair or enhance prey detection, as well as affect fish movement. Since these stressors often act together, understanding their combined effects is critical. We investigated how short-term increases in temperature and turbidity, both separately and in combination, influenced the foraging and swimming performance of the common triplefin, Forsterygion lapillum Hardy 1989, and measured oxygen consumption during acute thermal ramping to explore links between thermal tolerance and performance. Results show that F. lapillum strike speed was slower in high turbidity treatments, indicating that F. lapillum relies on visual cues to feed, and consequently, fish foraging performance is impaired in sedimented waters. Moreover, fish routine swimming speed and burst speed were unaffected by any treatment, suggesting that F. lapillum can adapt its swimming performance to the increases in temperature and turbidity that were tested. During acute thermal ramping, fish oxygen consumption rate was found to increase only at temperatures above 24°C. This can explain F. lapillum's lack of adjustment in swimming speed, burst speed and strike speed to increases in temperature during the experiment and suggests that oxygen delivery starts to be compromised at temperatures above this threshold. Our findings highlight F. lapillum resilience to moderate temperature increases but reveal vulnerability to increased sedimentation due to reduced foraging efficiency.