Barents Sea - Ecology

The Barents Sea is a spring bloom system. During winter, primary production is close to zero. Timing of the phytoplankton bloom varies throughout the Barents Sea and there may also be a high inter-annual variability. The spring bloom starts in the south-western areas and spreads north and east with the retracting ice. In early spring, the water is mixed from surface to bottom. Despite adequate nutrient and light conditions for production, the main bloom does not occur until the water becomes stratified.
The Barents Sea is home to one of the largest concentrations of seabirds in the world, a diverse assemblage of marine mammals, including polar bears, and several commercially important fish stocks, the largest of which are Northeast Arctic cod, capelin and haddock. In addition, the Barents Sea is a nursery area for Norwegian spring spawning herring, one of the largest fish stocks in the world. There is also a rich community of benthic animals in the Barents Sea, numbering more than 3000 species, as well as a diverse community of zooplankton. There are distinct differences in plankton composition and communities, with Calanus finmarchicus being a dominant copepod in the Atlantic water while Calanus glacialis is its counterpart in the Arctic water. Large fish populations including cod, haddock, Greenland halibut, capelin and polar cod contribute to the system characteristics of the LME. Capelin performs a seasonal feeding migration north into the cold waters to feed on zooplankton in summer, causing a strong ecological linkage between the northern and southern parts. Seasonal migrations are also characteristic for most other fish populations (Skjoldal & Mundy 2013).

The Barents Sea LME contains a large population of harp seals that whelp at the entrance to the White Sea. The LME is also home to the Barents Sea subpopulation of polar bears and two populations of walrus, the Svalbard-Franz Josef Land population and the Kara Seasouthern Barents Sea-Novaya Zemlya population which extends into the Kara Sea LME. Several subpopulations of belugas or white whales are found in the White Sea and the eastern and northern parts of the Barents Sea (Skjoldal & Mundy 2013).

Planktonic algae and algae attached to the sea ice both contribute to primary production in the region. Infectious organisms and free-living bacteria and virus may be important groups, but their role for the overall dynamics of the system has received little research attention. The ecosystem has been invaded by several alien species, such as the red king crab; the influence of which is being studied currently, but is still largely unknown.
Capelin is a key species in the Barents Sea ecosystem (Wienerroither et al. 2011). This fish species feeds in the marginal ice zone and spawns near the coast in the southern part of the Barents Sea and thus transports large amounts of energy from the north to the south. It is important as prey for several species of seabirds, mammals and commercially important fish stocks, in particular Northeast Arctic cod and juvenile herring. Capelin is an important predator of zooplankton that can actually suppress the biomass of zooplankton in the Barents Sea. Capelin stock size has varied considerably in recent decades and has undergone three population collapses during the last 25 years. There is at present no consensus among scientists about the causes of the observed capelin recruitment failures leading to capelin stock collapses. While no one holds the view that the causes are all known, some suggest that the collapses are mainly a consequence of predation on capelin larvae from increased amounts of juvenile herring, others suggest several factors as likely to cause capelin collapses, including climatic fluctuations, predation from fish and marine mammals and fisheries. What-ever the cause, these collapses have had far reaching consequences for other species in the ecosystem, including a severe food shortage for the Northeast Arctic cod stock, collapses of seabird populations and food shortage and massive migration in seal populations. It should, however, be noted that the ecosystem consequences of the first collapse (late 1980s) was much more severe than during the two later collapses, probably because more alternative prey were available for the predators during the latter collapses.