Effect of light and food on the metabolism of the Arctic copepod Calanus glacialis
Résumé
Reduction in sea-ice thickness and cover is expected to lead to earlier underwater light penetration and thus earlier onset of the spring bloom and a longer open water production in the Arctic. The goal of this study was to understand how these climate-induced changes in light and food regimes may impact the key zooplankton grazer Calanus glacialis CV. We studied this copepod's metabolic response to starvation (filtered sea water; FSW) and algal food (Food) under two different light regimes (light vs. dark) when it was in dormancy (diapause) in winter (November) and active in summer (July). Respiration was measured as indicator of metabolism and was measured for 9 days for copepods exposed to: Dark+FSW, Dark+Food, Light+FSW and Light+Food. The in situ respiration in winter was three times lower than in summer. In winter, light was the main factor to increase the copepod's metabolism to a level comparable with that of active copepods in summer, but respiration only remained high if food was present. In summer, it was the combined effect of light and Food that increased the respiration, although Food seemed more important than light with time. Copepods reduced their metabolism with time when food was absent, regardless of the light regime, probably preparing for diapause. These results suggest that C. glacialis can quickly adapt to a changing light and food regime in the Arctic, being able to wake up from diapause if light and thus food appear and postpone its diapause if the food availability is still favorable.