Contrasting effects of predation risk and copper on copepod respiration rates

Natural biotic and anthropogenic stressors can interact to alter contaminant toxicity. Energetic restrictions are potential mechanisms causing this pattern. To identify processes underlying observed effects of predation risk and copper (Cu) on delayed copepod age at maturity, we examined how these two stressors affect respiration rates. We tested two very different copepod species: the large, pelagic calanoid Calanus finmarchicus, and the small, semi-benthic harpacticoid Tigriopus brevicornis. Adult individuals were exposed for 12 h to the treatments: predation risk, Cu (23 µg L-1 ), combined predation risk and Cu (23 µg L-1 ), or control. Oxygen concentrations were monitored continuously. The two species differed in their responses. We found no clear effects of either stressor in C. finmarchicus. In T. brevicornis, predation risk increased respiration rates, while Cu alone had little impact. In contrast, combined exposure to predation risk and Cu interacted to reduce respiration rates to less than expected. We further observed an effect of sex, as female-biased T. brevicornis replicates were more sensitive to both predation risk (increased respiration rates) and Cu exposure (reduced respiration rates). This study provides further evidence that predation risk can interact with copepod responses towards Cu exposure. Interactive effects of biotic stressors ought to be considered to improve future marine environmental monitoring. This article is protected by copyright. All rights reserved.