The role of krill and other zooplankton in the Barents Sea ecosystem based on long-term monitoring
In the Barents Sea ecosystem, zooplankton form a link between phytoplankton and fish, mammals and other organisms at higher trophic levels. An example of a short and efficient energy transfer is phytoplankton → herbivorous zooplankton → capelin → cod. The most abundant species e.g. calanoid copepods, krill and hyperiid amphipods form the diet of key fish species such as capelin, polar cod, and herring. The Polar Front in the Barents Sea marks the boundary between the Arctic zooplankton species (Calanus glacialis, Themisto libellula) and the Atlantic/subarctic species (Calanus finmarchicus, Thysanoessa inermis, Meganyctiphanes norvegica). Favourable conditions for the phytoplankton bloom close to the ice edge, as it temporarily retracts during summer and autumn, supports large concentrations of crustaceans. Blooms in the Atlantic waters are not so intense as blooms at the ice edge. However, they occur over a longer time period and thus have a higher phytoplankton production. The spring bloom in the Atlantic waters is of particular importance to predominant herbivores such copepod, C. finmarchicus and krill (T. inermis). Carnivorous zooplankton such as hyperiid amphipods (Themisto spp.) may feed on copepods, and may compete with fish that consume zooplankton. Long-term monitoring data indicate substantial year to year variation in the biomass and abundance of zooplankton in the Barents Sea.