Zooplankton in the Polar Night

Pelagic communities play a key role in Arctic ecosystems. Although zooplankton occupy several different trophic levels in the food chain, their primary niche is often considered that of a link between pelagic and ice-associated primary production on one side and higher trophic levels on the other. In fact, most of the biological energy (organic carbon) ending up in top predators such as seabirds, fish and marine mammals have been funnelled through one or more zooplankton species. As such, zooplankton ecology is often viewed and understood in relation to primary production regimes. However, recent research has showed that processes occurring in the zooplankton community during winter are crucial for our understanding of Polar Night ecology. As a group, they are active throughout the entire year, they conduct various forms of vertical migration in relation to both the moon and solar background illumination and some species utilize the Polar Night for reproduction. Evidence of reproduction among short-lived omnivorous zooplankton species during Polar Night suggests that production is sustained by feeding opportunistically throughout winter and Polar Night and that life history strategies are tuned to support fast turnover rates and not on building up large lipid reserves. This chapter provides an overview of the main zooplankton taxa inhabiting Arctic waters during the Polar Night and describes the main processes typical for zooplankton taxa during the Polar Night.