In the Barents Sea, the monitoring of phytoplankton abundance and species composition is carried out on the transect Fugløya–Bjørnøya and Vardø– N, and during a regional covering of the area in the autumn. This monitoring program gives important information for a better understanding of food web processes, effects of human activity, and changes due to climate changes. In 2008, the seasonal distribution of phytoplankton was more or less similar to what has been observed in earlier years.
Decreasing Levels of Zooplankton
The average zooplankton biomass measured in August–September 2008 is below the long-term mean and has dropped significantly compared to 2007 and 2006. This may be due to a lesser amount of Atlantic water being transported into area, but an increasing capelin stock grazing on zooplankton, mainly copepods and krill, may have contributed to the decrease. Atlantic water masses contain the highest biomass, stressing the importance of advective transport of zooplankton from the Norwegian Sea and the favorable higher temperatures in these waters that influence the central western part of the Barents Sea considerably. The average zooplankton abundance in 2008 and the considerable decline observed since 2006 suggest that the condition for local production is less favorable for 2009. The total production will probably depend largely on the magnitude of zooplankton advection from the Norwegian Sea, although it should be noticed that the abundance here has been declining over several years, and was for 2008 the lowest recorded since 1997. However, the increase in the capelin stock from 2006 to 2008 (from less than 1 to about 4.4 million tons) is probably the main factor causing the drop in average zooplankton biomass. Other plankton consumers like herring, juvenile cod, haddock and redfish are also important predators that will influence zooplankton biomass, although in 2008 their abundance were reduced compared to 2007, except for 0-group capelin and cod.
Species such as blue whiting and sand eel were less important in the Barents Sea in 2008 compared to previous years. Hence, the predation pressure on zooplankton from many 0-group plankton consumers has most likely been reduced. Gelatinous zooplankton like medusa and ctenophores are also important predators on zooplankton in the Barents Sea, but their quantitative assessment has not yet been undertaken for 2008.