Crude awakening: Crude oil exposure under warming scenarios alters escape performance and metabolic enzyme activity in Pomacentrus amboinensis

Marine environments are experiencing intensifying and overlapping stressors driven by climate change and anthropogenic pollution. Among these, exposure to petroleum-derived contaminants, such as heavy crude oil, remains a persistent threat, particularly as warming conditions have the potential to exacerbate pollutant toxicity through elevated metabolic demand. Here, we investigated the independent and combined effects of oil exposure and elevated temperatures on behavioural performance and metabolic enzyme activity in a common coral reef fish. Recruits of Pomacentrus amboinensis (ambon damselfish) were exposed to one of four treatments: control (ambient temperature, no oil), elevated temperature (no oil), oil (ambient temperatures), or combined (elevated temperature and oil). Using high speed videography, we quantified routine swimming and fast start escape responses, key indicators of performance and predator evasion under environmental stress. In addition, white muscle samples were analysed for lactate dehydrogenase (LDH) and citrate synthase (CS) enzyme activity to assess potential metabolic costs associated with exposure to oil and elevated temperatures. Fish exposed to crude oil alone exhibited longer response latencies during escape responses compared to elevated temperature treatments but not the ambient control treatment. LDH activity was significantly higher in fish exposed to the crude oil and elevated temperature treatment, indicating a synergistic effect of these stressors on anaerobic metabolism. By contrast, CS activity was significantly lower following crude oil exposure but not due to temperature. Together, these findings demonstrate that crude oil pollution and ocean warming can interact to alter specific components of metabolic physiology, with potential consequences for escape performance and survival of coral reef fishes in a changing environment.