Cumulative Impacts of Oil Pollution, Ocean Warming, and Coastal Freshening on the Feeding of Arctic Copepods.

The Arctic is undergoing rapid changes, and biota are exposed to multiple stressors, including pollution and climate change. Still, little is known about their joint impact. Here, we investigated the cumulative impact of crude oil, warming, and freshening on the copepod species Calanus glacialis and Calanus finmarchicus . Adult females were exposed to ambient conditions (control; 0 °C + 33 psu) and combined warming and freshening: 5 °C + 27 psu (Scenario 1), 5 °C + 20 psu (Scenario 2) for 6 days. All three conditions were tested with and without dispersed crude oil. In Scenario 1, fecal pellet production (FPP) significantly increased by 40-78% and 42-122% for C. glacialis and C. finmarchicus , respectively. In Scenario 2, FPP decreased by 6-57% for C. glacialis , while it fluctuated for C. finmarchicus . For both species, oil had the strongest effect on FPP, leading to a 68-83% reduction. This overshadowed the differences between climatic scenarios. All variables (temperature, salinity, and oil) had significant single effects and several joint effects on FPP. Our results demonstrate that Arctic copepods are sensitive to environmentally realistic concentrations of crude oil and climate change. Strong reductions in feeding can reduce the copepods' energy content with potential large-scale impacts on the Arctic marine food web.