Abstract
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 2 stressors affect respiration rates. We tested 2 very different copepod species: the large, pelagic calanoid Calanus finmarchicus and the small, semibenthic 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 2 species differed in their responses. We found no clear effects of either stressor in C. finmarchicus. In T. brevicornis, predation risk increased respiration rates, whereas 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 because female-biased T. brevicornis replicates were more sensitive to both predation risk (increased respiration rates) and Cu exposure (reduced respiration rates). The present study provides further evidence that predation risk can interact with copepod responses toward Cu exposure. Interactive effects of biotic stressors ought to be considered to improve future marine environmental monitoring. Environ Toxicol Chem 2020;39:1765-1773. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.
Highlights
All organisms are continuously exposed to a combination of multiple natural and anthropogenic stressors
The weight‐specific respiration rates in control groups were lower for C. finmarchicus (0.054 ± 95% CI 0.007 nmol O2 μg dry wt−1 h−1) than for T. brevicornis (0.099 ± 0.053 nmol O2 μg dry wt−1 h−1), but variation was higher in T. brevicornis (Figure 2)
No effects were found for predation risk or Cu exposure on respiration rates in C. finmarchicus when analyzed for the full 12‐h exposure period
Summary
All organisms are continuously exposed to a combination of multiple natural and anthropogenic stressors. Effects of multiple stressors may range from antagonistic to synergistic compared to single‐stressor exposure (Holmstrup et al 2010). Synergistic interactions are generally expected from combined‐ stressor exposure in marine systems (Crain et al 2008; Gunderson et al 2016). Previous multiple‐stressor studies of marine systems and species have mainly focused on abiotic factors such as temperature, salinity, and pH (Crain et al 2008; Gunderson et al 2016). Few have looked at combined effects with biotic factors such as predation risk or competition (e.g., Linke‐Gamenick et al 1999; Lode et al 2018).
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