The timing of reproductive events of Calanus glacialis is closely coupled to the two major marine primary production events in the Arctic: the ice algal and phytoplankton blooms. Reproductive strategies vary between different physical and biological environments of the European and Canadian Arctic. In the Canadian Beaufort Sea and the high Arctic Rijpfjorden on Svalbard, C. glacialis utilized the ice algae bloom to fuel spawning in spring, while growth and development of the new generation was primarily supported by the phytoplankton bloom. In the predominantly ice-free Arctic Kongsfjorden (Svalbard), C. glacialis was mainly a capital breeder spawning early in the season in the absence of food. This enabled the offspring to synchronize their growth and development with the phytoplankton bloom and, thus, reproduce successfully despite the lack of an early ice algal bloom. The variability in life history traits observed in the Canadian and European Arctic is compared with data from other Arctic regions to present a pan-Arctic perspective on life cycle strategies of C. glacialis.

High-latitude environments show extreme seasonal variation in physical and biological variables. The classic paradigm of Arctic marine ecosystems holds that most biological processes slow down or cease during the polar night. One key process that is generally assumed to cease during winter is diel vertical migration (DVM) of zooplankton. DVM constitutes the largest synchronized movement of biomass on the planet, and is of paramount importance for marine ecosystem function and carbon cycling. Here we present acoustic data that demonstrate a synchronized DVM behaviour of zooplankton that continues throughout the Arctic winter, in both open and ice-covered waters. We argue that even during the polar night, DVM is regulated by diel variations in solar and lunar illumination, which are at intensities far below the threshold of human perception. We also demonstrate that winter DVM is stronger in open waters compared with ice-covered waters. This suggests that the biologically mediated vertical flux of carbon will increase if there is a continued retreat of the Arctic winter sea ice cover.