The Barents Sea is a sub‐Arctic ecosystem located between 70 and 80°N. It connects with the Norwegian Sea to the west and the Arctic Ocean to the north, all water masses with different characteristics when it comes to salinity, temperature and origin. The average depth is 230 m and the maximum depth is approximately 500 m at the western entrance. The general pattern of circulation is strongly influenced by topography. Atlantic and Arctic water masses are separated by the Polar Front, which is characterized by strong
gradients in both temperature and salinity. There is large inter‐annual variability in ocean climate related to variable strength of the Atlantic water inflow, and exchange of cold Arctic water. Thus, seasonal variations in hydrographic conditions can be quite large.
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, with the retracting ice, and there may also be a high inter‐annual variability. By 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. Stratification of water masses in different areas of the Barents Sea may occur in several different ways:
- Fresh surface water from melting ice along the marginal ice zone.
- Solar heating of surface layers in Atlantic water masses.
- Lateral dispersion of waters in the southern coastal region (Rey, 1981).
Same as in other areas, diatoms are also the dominant phytoplankton groups in the Barents Sea (Rey, 1993).
In the Barents Sea ecosystem, zooplankton forms a link between phytoplankton (primary producers) and fish, mammals and other organisms at higher trophic levels. Zooplankton biomass in the Barents Sea can vary significantly between years and crustaceans are important. The calanoid copepods of the genus Calanus play a key role in this ecosystem. Calanus finmarchicus, is most abundant in Atlantic waters and C. glacialis is most abundant in Arctic waters. Both form the largest component of zooplankton biomass. Calanoid copepods are largely herbivorous, and feed particularly on diatoms (Mauchline, 1998). Krill (euphausiids), another group of crustaceans, also play a significant role in the Barents Sea ecosystem as food for fish, seabirds, and marine mammals. Krill species are believed to be omnivorous: filter‐feeding on phytoplankton during the spring bloom; while feeding on smaller zooplankton during other times of the year (Melle et al., 2004). Several amphipod species were found abundant in the Barents Sea. The term "jellyfish" is commonly used in reference to marine invertebrates belonging to the class Scyphozoa, phylum Cnidaria. Both comb‐jellies (Ctenophora sp.) and "true" jellyfish are predators, and they compete with plankton‐eating fish, because copepods often are significant prey items.
The sea floor is inhabited by a wide range of organisms. The high diversity among bottom animals is presumed to be due to the abundance of microhabitats that organisms can adapt to. More than 3050 species of benthic invertebrates inhabit the Barents Sea (Sirenko, 2001). The benthic ecosystems in the Barents Sea have considerable value, both in direct economic terms and in their ecosystem functions. Scallops, shrimp, king crab, and snow crab are benthic residents which are harvested in the region. Many species of benthos are also interesting for bio‐prospecting or as a future food resource, such as sea cucumber, snails and bivalves. Several of them are crucial to the ecosystem. Important fish species such as haddock, catfish and most flatfishes primarily feed on benthos.
More than 200 fish species are registered in trawl catches during surveys of the Barents Sea, and nearly 100 of them occur regularly. Even so, the Barents Sea is a relatively simple ecosystem, with few fish species of potentially high abundance. Commercially important fish species include Northeast Arctic cod, Northeast Arctic haddock, Barents Sea capelin, polar cod and immature Norwegian spring‐spawning herring. Species distribution largely depends on positioning of the Polar Front. Variation in recruitment of species, including cod and herring, has been linked to changes in influx of Atlantic waters. Cod, capelin, and herring are key species in the Barents Sea trophic system. Cod prey on capelin, herring, and smaller cod; while herring prey on capelin larvae. Cod is the most important predator fish species in the Barents Sea, and feeds on a wide range of prey, including larger zooplankton, most available fish species and shrimp. Capelin feed on zooplankton produced near the ice edge. Further south, capelin is the most important prey species in the Barents Sea as it transports biomass from northern to southern regions (von Quillfeldt and Dommasnes, 2005). Herring, another prey species for cod, has similar abundance, and high energy content. Herring is also a major predator on zooplankton.
Marine mammals, as top predators, are keystone species, significant components of the Barents Sea ecosystem. About 25 species of marine mammals regularly occur in the Barents Sea, including: 7 pinnipeds (seals and walruses); 12 large cetaceans (large whales); 5 small cetaceans (porpoises and dolphins); and the polar bear (Ursus maritimus). Some of these species are not full‐time residents in the Barents Sea, and migrate between temperate areas and the Polar Regions. Others reside in the Barents Sea all year round (e.g. white‐beaked dolphin Lagenorhynchus albirostris, and harbor porpoise Phocoena phocoena). Some marine mammals are naturally rare, such as the beluga whale Delphinapterus leucas. Others are rare due to historic high exploitation, such as bowhead whale Balaena mysticetus and blue whale Balaenoptera musculus. Marine mammals may consume up to 1.5 times the amount of fish caught in fisheries. Minke whales and harp seals may each year consume 1.8 million and 3‐5 million tons of prey of crustaceans, capelin, herring, polar cod, and gadoid fish respectively (Folkow et al., 2000; Nilssen et al., 2000). Functional relationships between marine mammals and their prey seem closely related to fluctuations in marine ecosystems. Both minke whales and harp seals are thought to switch between krill, capelin and herring depending on availability of the different prey species (Lindstrøm et al., 1998; Haug et al., 1995; Nilssen et al., 2000). Fish and mammals have seasonal feeding migrations so that the stocks in the area will have their most northern and eastern distribution in August‐September and be concentrated in the Southern and south‐western areas in February‐March.
The Barents Sea has one of the largest concentrations of seabirds in the world (Norderhaug et al., 1977; Anker‐Nilssen et al., 2000; Gabrielsen, 2009); its 20 million seabirds harvest annually approximately 1.2 million tons of biomass from the area (Barrett et al., 2002). Nearly 40 species are thought to breed regularly in northern regions of the Norwegian Sea and the Barents Sea. Abundant species belong to the auk and gull families. Seabirds play an important role in transporting organic matter and nutrients from the sea to the land (Ellis, 2005). This transport is of great importance especially in the Arctic, where lack of nutrients is an important limiting factor.
Factors Influencing the Barents Sea Ecosystem
Invasions of alien species – spread of the representatives of various groups of living organisms beyond their primary habitats – are global in nature. Their introduction and further spread often leads to the undesirable environmental, economic and social consequences. Different modes of biological invasions include a natural movement associated with the population dynamics and climatic changes, intentional introduction and reintroduction, and accidental introduction with the ballast waters or along with the intentionally introduced species, etc. The best known examples of introduced species in the Barents Sea are red king crab (Paralithodes camtschaticus) and snow crab (Chionoecetes opilio).
The Barents Sea is strongly influenced by human activity historically involving the fishing and hunting of marine mammals. More recently, human activities also include transportation of goods, oil and gas, tourism and aquaculture. Industrial development in the Arctic demands a closer look at its impact on the ecosystem. During the last years there has been a growing interest in evaluation of ecosystem response to anthropogenic impact in light of the climate change. Fisheries are considered to be the strongest human impact on the fish stocks in the Barents Sea, and thereby for the functioning of the whole ecosystem. However, the observed variation in both fish species and ecosystem is also influenced by other factors such as climate and predation.
The Barents Sea remains relatively clean when compared to marine areas in many industrialized parts of the world. Major sources of contaminants in the Barents Sea are natural processes, longrange transport, accidental releases from local activities, and ship fuel emissions. Results of recent studies indicate low level of contaminants in the Barents Sea marine environment and confirm results of earlier studies on bottom sediments in the same areas. In the near‐term, observed levels of contaminants in the marine environment should not have any significant impact on commercially important stocks or on the Barents Sea ecosystem.
The Barents Sea holds a large potential as an important region for oil and gas development. Currently, offshore development is limited both in the Russian and Norwegian economic zones but it is gradually increasing with the discoveries and development of new oil‐ and gas fields. In the Norwegian zone production is limited to the Snøhvit field (as of 2009 when the status report was finished, ref www.barentsportal.com). There is however increasing petroleum activity in the Barents Sea, related to among other things exploration drilling. Transport of oil and other petroleum products from ports and terminals in NW‐Russia have been increasing over the last decade. In 2002, about 4 million tons of Russian oil was exported along the Norwegian coastline, in 2004, the volume reached almost 12 million tons, but the year after it dropped, and from 2005 to 2008 was on the levels between 9,5 and 11,5 million tons per year (Bambulyak and Frantsen, 2009).
The environmental risk of oil and gas development in the region has been evaluated several times, and is a key environmental question facing the region. The risk of large accidents with oil tankers will increase in the years to come, unless considerable measures are imposed to reduce such risk.
The high biodiversity of the oceans represents a correspondingly rich source of chemical diversity, and there is a growing scientific and commercial interest in the biotechnology potential of Arctic biodiversity. Scientists from several nations are currently engaged in research that can be characterized as bio‐prospecting (systematic search for interesting and unique genes, molecules and organisms from the marine environment with features that may be of value for commercial development).
Ocean acidification is greater and happening faster than at any other time during the entire period of observation. The absorption of CO2 seems to generally go faster in colder waters and thus might affect the Barents Sea ecosystem.