Abstract
Scenarios for climate change predict that global warming drives biogeographic boundaries polewards. However, reliable predictions of marine food web responses to climate change require understanding of the coupling mechanisms between trophic levels. The Arctic is characterized by extreme light regime (photoperiod) as well as extreme (low) temperatures, both with profound bearing on pelagic ecology but only temperature being affected by climate change. Here, I address the potential impact by the light climate on mesopelagic (mid-water) planktivorous fish and as a result their plankton prey. Mesopelagic fish abound in all oceans, except for the Arctic. I hypothesize that their lack of success in this environment is due to inferior feeding conditions imposed by the extreme light climate at high latitudes. Since photoperiod is unaffected by climate change mesopelagic fish may continue to be scarce, and large copepods such as Arctic Calanus spp. will continue to prevail even in a warmer climate. This hypothesis of photoperiod constraints on the effect of global warming in Arctic marine ecosystems may be tested in fjords with different temperatures and light conditions.