Habitat preference during overwintering and timing of seasonal vertical migration of Calanus finmarchicus

Abstract

Calanus finmarchicus (Copepoda) appears to be very flexible with respect to physical characteristics of the overwintering habitat. Data from the literature document successful overwintering at depths ranging from about 2000 m to near the surface, and temperatures ranging from -1 to +11°C. I argue that reducing encounters with predators may be a major driving force for C. finmarchicus to select their overwintering habitat. Preliminary analyses from Norwegian fjords suggest that overwintering C. finmarchicus may distribute vertically so as to reduce danger of preda-tion by mesopelagic fish. Episodic presence of planktivorous fish may influence timing of seasonal vertical migrations of Calanus populations.