Contrasting Effects of Predation Risk and Copper on Copepod Respiration Rates

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.

Density‐Dependent Metabolic Costs of Copper Exposure in a Coastal Copepod

“…We found no effect of Cu exposure at the highest incubation density when analysed for the full 12-h exposure period. Lode et al (2020) similarly found no effect of Cu (23 µg L -1 ) on T. brevicornis respiration when exposing 10 individuals per replicate (corresponding to 3125 individuals L -1 ) for 12 h.…”

“…We found no effect of Cu exposure at the highest incubation density when data were analyzed for the full 12‐h exposure period. Lode et al (2020) similarly found no effect of Cu (23 µg L –1 ) on T. brevicornis respiration when exposing 10 individuals per replicate (corresponding to 3125 individuals L –1 ) for 12 h. The density‐dependent respiratory response to Cu exposure suggests a behavioral stress response in T. brevicornis to low conspecific densities.…”

“…We added Cu by a two-step dilution series of 0.1 M CuSO 4 equivalent to a nominal exposure concentration of 23 µg Cu L -1 . Previous studies with T. brevicornis have found comparable Cu concentrations to delay development to maturity (Lode et al 2018) and to interact with respiratory responses to predation risk exposure (Lode et al 2020). We prepared the control exposure solution similarly but without added Cu.…”

“…To quantify the metabolic costs of Cu exposure and potential density-dependency in response we carried out a respiration experiment on November 13 and 15, 2018. The method was similar as in Lode et al (2020). We placed readied OxoDish OD24 well plates on SensorDish® Reader (SDR) units (PreSens Precision Sensing) submerged in a water bath.…”

“…Lode et al (2020) similarly found no effect of Cu (23 µg L -1 ) on T. brevicornis respiration when exposing 10 individuals per…”