The Barents Sea is a sub-Arctic ecosystem located between 70 and 80ºN. It connects with the Norwegian Sea to the west and the Arctic Ocean to the north. The average depth is 230 m and the maximum depth is approximately 500 m at the western entrance. The general pattern of circulation (Figure 2.1.1) is strongly influenced by this topography, and is characterised by inflow of relatively warm Atlantic water, and coastal water from the west. This current divides into two branches: 1) a southern branch that flows parallel to the coast and eastwards towards Novaya Zemlya; and 2) a northern branch that flows into the Hopen Trench. The Coastal Water has more fresh-water runoff and a lower salinity than the Atlantic water; it also has a stronger seasonal temperature signal. In the northern region of the Barents Sea, fresh and cold Arctic waters flow from northeast to southwest. Atlantic and Arctic water masses are separated by the Polar Front, which is characterised 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.
In the biogeochemical cycles of the ocean, a multitude of processes are catalyzed by Bacteria and Archaea, and the functioning of these cycles in the Barents sea do not differ qualitatively from those at lower latitudes. Both bacteria and viruses show highly variable abundance in the Barents Sea, and in general, the dynamics of these groups in this area do not differ from other parts of the ocean. The situation in the ice-covered areas in the north remains to be investigated.
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.
Stratification of water masses in different areas of the Barents Sea may occur in several different ways; 1) through fresh surface water from melting ice along the marginal ice zone; 2) through solar heating of surface layers in Atlantic water masses; or 3) through lateral dispersion of waters in the southern coastal region (Rey, 1981). As in other areas, diatoms are also the dominant phytoplankton groups in the Barents Sea (Rey, 1993). Diatoms particularly dominate the first part of the spring bloom, and the concentration of diatoms can reach up to several million cells per litre. They require silicate for growing, and when this is consumed, other phytoplankton groups, such as flagellates, take over. An important flagellate species in the Barents Sea is Phaeocystis pouchetii but other species may, however, predominate the spring bloom in different years.
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 small zooplankton during other times of the year (Melle et al., 2004). Four dominant species that occupy different niches in the community of Barents Sea euphausiids are: Meganyctiphanes norvegica (neritic shelf boreal); Thysanoessa longicaudata (oceanic arcto-boreal); T. inermis (neritic shelf arcto-boreal); and T. raschii (neritic coastal arcto-boreal) (Drobysheva, 1994). The two latter species comprise 80-98% of total euphausiid abundance, but species composition may vary between years relative to climate (Drobysheva, 1994). After periods with cold climate, observed abundance of T. raschii increased while abundance of T. inermis decreased (Drobysheva, 1967). Advection from the Norwegian Sea is influenced by the intensity of Atlantic water inflow, which also influences the composition of species (Drobysheva, 1967; Drobysheva et al., 2003).
Three amphipod species were found abundant in the Barents Sea; Themisto abyssorum and T. libellula in the western and central Barents Sea, and T. compressa is found, albeit less abundant, in central and northern regions. T. abyssorum is most abundant in sub-Arctic waters. In contrast, the largest of the Themisto species, T. libellula, is largely restricted to combined Atlantic and Arctic water masses. High abundance of T. libellula was observed adjacent to the Polar Front. Amphipods feed on small zooplankton and copepods form an important component of their diet (Melle et al., 2004).
Gelatinous zooplankton” is a term often used by non-specialists in reference to classes of organism that are jelly-like in appearance. The term "jellyfish" is commonly used in reference to marine invertebrates belonging to the class Scyphozoa, phylum Cnidaria. Neither of these terms implies any systematic relationship to vertebrate fish. The term "jellyfish" is also often used in reference to relatives of true scyphozoans, particularly the Hydrozoa and the Cubozoa. Both comb-jellies (Ctenophora) 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. Some are buried in sediment, others are attached to a substrate, some are slow and sluggish, others roving and rapid. Many feed by actively or passively, sieving food particles or small organisms from the water. Others eat the bottom sediments (detritus feeders), eat carrion (scavengers) or hunt other animals (carnivores). The high diversity among bottom animals is presumed to be due to the abundance of micro-habitats that organisms can adapt. In shallow waters, kelp forests are feeding and nursery habitats for several many species of fish, birds, and mammals. Below the sublittoral zone, sea anemones, sponges, hydrozoans, tunicates, echinoderms, crustaceans, molluscs and many other animal groups abound on hard substrates. These large conspicuous animals are not abundant on sand or muddy bottoms, and in fact some of these habitats may at first look rather lifeless. However, most of the benthic animals in these habitats live buried in the sediments. Polychaete worms, crustaceans and bivalves are found in the sediments well as a myriad of other taxa. Some muddy areas might have dense aggregations of brittle stars, sea stars or bivalves.
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. Many benthic animals, primarily bivalves, filter particles from the ocean and effectively clean it up. Others scavenge on dead organisms, returning valuable nutrients to the water column. Detritius feeders and other active diggers regularly move the bottom sediments around and therefore increase sediment oxygen content and overall productivity – much like earthworms on land.
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. Different species of fish are not evenly distributed throughout the Barents Sea. Rather, they exhibit highest abundance in areas with suitable environmental conditions. Commercially important fish species include Northeast Arctic cod, Northeast Arctic haddock, Barents Sea capelin, polar cod and immature Norwegian spring-spawning herring. In years, increased numbers of young blue whiting have migrated into the Barents Sea. 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. Farther 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 use temperate areas for mating, calving, and feeding (e.g. minke whale Balaenoptera acutorostrata). Others reside in the Barents Sea all year round (e.g. white-beaked dolphin Lagenorhynchus albirostris, and harbour 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); its 20 million seabirds harvest annually approximately 1.2 million tonnes 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.
There are 10 types of parasites found in the fish of the Barents Sea, but it is hard to determine which groups of parasitic organisms that play an important role in the population dynamics of their hosts. The Barents Sea parasites considered to be most damaging to the human health are larvae stages of Cestoda (Diphyllobothrium and Pyramicocephalus genera), Nematoda (Anisakis and Pseudoterranova genera) and Palaeacanthocephala (Corynosoma genera). 82 species of helminthes are recorded from 18 bird species. The Barents Sea birds’ helminthofauna mostly consists of the species with the life cycle dependent on coastal ecosystems. Invertebrates and fish from the littoral and upper sub littoral complex serve as their intermediate hosts.
The Barents Sea includes species that either have very small populations or species that have recently undergone considerable population decline (or are expected to do so in the close future). The assessments are done by use of the IUCN criteria (IUCN, 2001; 2003), but the Global, the Russian and the Norwegian lists available can not be directly compared. All these lists are closely related and have high relevance for the conservation of biodiversity, and the list from the Barents Sea include a total of 56 species comprising of 28 fish species, 9 bird species, and 18 mammal species.
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 can be natural movement associated with the population dynamics and climatic changes, intentional introduction and reintroduction, and accidental introduction with the ballast waters and 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 involve transportation of goods, oil and gas, tourism and aquaculture. In the last years interest has increases on the evaluation of the most likely response of the Barents Sea ecosystem to the future climate changes due to anthropogenic effect on climate warming.
Fishing is the largest human impact to the fish stocks in the Barents Sea, and thereby the functioning of the whole ecosystem. However, the observed variation in both fish species and ecosystem is also impacted by other effects such as climate and predation. The most widespread gear used in the central Barents Sea is bottom trawl, but also long line and gillnets are used in the demersal fisheries. The pelagic fisheries use purse seine and pelagic trawl.
The Barents Sea remains relatively clean, however, when compared to marine areas in many industrialized parts of the world. Major sources of contaminants in the Barents Sea are natural processes, long-range 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 significant impact on commercially important stocks and on the Barents ecosystem as a whole.
Traditionally, fishing having been the most important and far-reaching human activity in the ecosystem has been given most of the attention with analyses of impacts and risks. This need has increased in importance as oil- and gas industries have begun to develop new off-shore fields in the Barents Sea, and ship transport of oil and gas from the region has increased exponentially over the last 5 years.
The Barents Sea can become an important region for oil and gas development. Currently offshore development is limited both in the Russian and Norwegian economic zones (to the Snøhvit field north of Hammerfest in the Norwegian zone), but this may increase in the future with development of new oil- and gas fields. In Russia there are plans for the development of Stochkman, a large gas-field west of Novaya Zemlja. 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.
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. In a five-ten years perspective, the total available capacity from Russian arctic oil export terminals can reach the level of 100 million tons/year (Bambulyak and Frantsen, 2009). Therefore, the risk of large accidents with oil tankers will increase in the years to come, unless considerable measures are imposed to reduce such risk.
Tourism is one of the largest and steadily growing economic sectors world-wide. Travels to the far north have increased considerable during the last 15 years, and there are currently nearly one million tourists annually.
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. Researchers from several nations are currently engaged in research that could be characterised as bio-prospecting.
Aquaculture is growing along the coasts of northern Norway and Russia, and there are several commercial fish farms producing salmonids (salmon, trout), white fish (mainly cod) and shellfish.
Ocean acidification is greater and happening faster than any previous acidification process experienced in millions of years. The absorption of CO2 generally goes faster in colder waters and thus will rapidly affect the Barents Sea.