Thermal response of ingestion and egestion rates in the Arctic copepod Calanus glacialis and possible metabolic consequences in a warming ocean

Climate change is particularly rapid in the Arctic, where water temperatures are predicted to increase substantially with implications for Arctic marine organisms, especially ectotherms such as the calanoid copepod Calanus glacialis, a key herbivore in the Arctic marine ecosystem. Feeding depends on temperature, and recent studies indicate different thermal responses in ingestion and respiration implying a possible metabolic mismatch with increasing temperatures. We investigated the thermal response of ingestion and faecal pellet production as an indicator of egestion of the Arctic copepod C. glacialis in incubation experiments at five temperatures ranging from 0 to 10 A degrees C and compared the obtained data with published results on temperature dependence of respiration. Copepods were fed ad libitum with the diatom Thalassiosira gravida, and algae concentration was assessed prior and after 4 h feeding experiments. Egested faecal pellets were collected and counted. Ingestion and faecal pellet production rates increased linearly (Q (10) coefficient similar to 1.4-1.7 and similar to 1.8-4.1, respectively). No pronounced effect of feeding history (fed vs. starved for 3 days prior to experiment) was found, but responses in both rates were generally less dependent on temperature in the pre-starved experiment. Q (10) values for ingestion rates were lower than Q (10) values for published respiration rates (similar to 1.8-4.6), indicating that metabolic losses increase stronger with increasing temperature than metabolic gains by ingestion. A persistent imbalance between metabolic losses and energy uptake could lead to reduced fitness for C. glacialis, thereby affecting the population dynamics and distribution of this important species in the Arctic.