Structure, biomass distribution, and energetics of the pelagic ecosystem in the Barents Sea: A synopsis (original) (raw)
Related papers
Food webs and carbon flux in the Barents Sea
Progress in Oceanography, 2006
Within the framework of the physical forcing, we describe and quantify the key ecosystem components and basic food web structure of the Barents Sea. Emphasis is given to the energy flow through the ecosystem from an end-to-end perspective, i.e. from bacteria, through phytoplankton and zooplankton to fish, mammals and birds. Primary production in the Barents is on average 93 g C m À2 y À1 , but interannually highly variable (±19%), responding to climate variability and change (e.g. variations in Atlantic Water inflow, the position of the ice edge and low-pressure pathways). The traditional focus upon large phytoplankton cells in polar regions seems less adequate in the Barents, as the cell carbon in the pelagic is most often dominated by small cells that are entangled in an efficient microbial loop that appears to be well coupled to the grazing food web. Primary production in the ice-covered waters of the Barents is clearly dominated by planktonic algae and the supply of ice biota by local production or advection is small. The pelagic-benthic coupling is strong, in particular in the marginal ice zone. In total 80% of the harvestable production is channelled through the deep-water communities and benthos. 19% of the harvestable production is grazed by the dominating copepods Calanus finmarchicus and C. glacialis in Atlantic or Arctic Water, respectively. These two species, in addition to capelin (Mallotus villosus) and herring (Clupea harengus), are the keystone organisms in the Barents that create the basis for the rich assemblage of higher trophic level organisms, facilitating one of the worlds largest fisheries (capelin, cod, shrimps, seals and whales). Less than 1% of the harvestable production is channelled through the most dominating higher trophic levels such as cod, harp seals, minke whales and sea birds. Atlantic cod, seals, whales, birds and man compete for harvestable energy with similar shares. Climate variability and change, differences in recruitment, variable resource availability, harvesting restrictions and management schemes will influence the resource exploitation between these competitors, that basically depend upon the efficient energy transfer from primary production to highly successful, lipid-rich zooplankton and pelagic fishes.
FOOD WEBS AND PRIMARY PRODUCTION IN THE BARENTS SEA (Twelfth Symposium on Polar Biology)
This summary paper describes the food webs in the Barents Sea and deals with the seasonal changes in the phytoplankton stock and productivity. The pelagic food web is, as elsewhere, based mainly on unicellular algae (phytoplankton) as the primary producers. Temperatures of -1.8 to 5OC set an upper limit of about 0.6-0.8 d-I for the growth rate of diatoms in the Barents Sea. Phytoplankton biomass may reach as high as 10-1 5 mg m-3 in terms of Chlorophyll a or 300-600 mg m-3 in terms of carbon at the peak of the spring bloom. During most of the productive season, Chl a concentrations are 0.2-1 .O mg m-3 in the upper layers and 5-20mg m-3 at and near the pycnocline. Typical daily rates for primary production are 10-60mgC m-3; during the peak of the spring bloom up to 300-600 mgC m-3.
Climate effects on Barents Sea ecosystem dynamics
ICES Journal of Marine Science, 2012
Effects of climate variability and change on sea temperature, currents, and water mass distribution are likely to affect the productivity and structure of high-latitude ecosystems. This paper focuses on the Barents Sea (BS), a productive Arcto-boreal shelf ecosystem sustaining several ecologically and economically important fish species. The water masses in the region are classified as Atlantic, Arctic, and mixed, each having a distinct ecological signature. The pronounced increase in temperature and a reduction in the area covered by Arctic water that has taken place during the past decade have affected the ecology of the region. An increase in biomass of lipid-rich euphausiids in recent years, possibly linked to the temperature increase, has apparently provided good feeding and growth conditions for several species, including capelin and young cod. The observed reduction in Arctic zooplankton may on the other hand have negative implications for polar cod and other zooplankton predators linked to the Arctic foodweb. Despite these changes, the BS at present seems to maintain relatively stable levels of boreal zooplankton biomass and production, with no significant changes in the abundances of Calanus finmarchicus or the episodic immigrant C. helgolandicus.
Polar Biology, 1996
The at-sea distribution of seabirds and marine mammals in the eastern Barents Sea was determined using standardized transect counts during three cruises of R» ''Dalnie Zelentsy'' (Murmansk) in late summer 1991, 1992 and 1993. Totals of 32,268 seabirds, 485 pinnipeds, 25 cetaceans and 4 polar bears were counted during 554 half-hour counts. Numbers were converted into densities, total biomass and calculated daily food intake. Mean total food intake in kg fresh weight/km.day was 3.1 for the entire zone and all years; fish eaters dominated the whole region, with an intake of 1.3 (mainly Bru¨nnich's guillemot, ºria lomvia, and harp seal, Phoca groenlandica), followed by zooplankton eaters (0.85, mainly fulmar, Fulmarus glacialis) and mixed zooplankton and fish feeders (0.75, mainly minke whale, Balaenoptera acutorostrata, and kittiwake, Rissa tridactyla). Year-to-year variations were of little importance, while geographic differences were obvious between Norwegian coastal, Atlantic and Barents Sea water masses, both quantitatively and qualitatively (relative importance of main diets). Within each zone, a strong geographic heterogeneity was noted, with high local concentrations at fronts between water masses and at ice edges.
Overexploitation, Recovery, and Warming of the Barents Sea Ecosystem During 1950–2013
Frontiers in Marine Science, 2021
The Barents Sea (BS) is a high-latitude shelf ecosystem with important fisheries, high and historically variable harvesting pressure, and ongoing high variability in climatic conditions. To quantify carbon flow pathways and assess if changes in harvesting intensity and climate variability have affected the BS ecosystem, we modeled the ecosystem for the period 1950–2013 using a highly trophically resolved mass-balanced food web model (Ecopath with Ecosim). Ecosim models were fitted to time series of biomasses and catches, and were forced by environmental variables and fisheries mortality. The effects on ecosystem dynamics by the drivers fishing mortality, primary production proxies related to open-water area and capelin-larvae mortality proxy, were evaluated. During the period 1970–1990, the ecosystem was in a phase of overexploitation with low top-predators’ biomasses and some trophic cascade effects and increases in prey stocks. Despite heavy exploitation of some groups, the basic ...
Deep Sea Research Part Ii Topical Studies in Oceanography, 2007
The principal features of the marine ecosystems in the Barents and Norwegian Seas and some of their responses to climate variations are described. The physical oceanography is dominated by the influx of warm, high-salinity Atlantic Waters from the south and cold, low-salinity waters from the Arctic. Seasonal ice forms in the Barents Sea with maximum coverage typically in March-April. The total mean annual primary production rates are similar in the Barents and Norwegian Seas (80-90 g C m -2), although in the Barents, the production is higher in the Atlantic than in the ice covered Arctic Waters. The zooplankton is dominated by Calanus species, C. finmarchicus in the Atlantic Waters of the Norwegian and Barents Seas, and C. glacialis in the Arctic Waters of the Barents Sea. The fish species in the Norwegian Sea are mostly pelagics such as herring ( Clupea harengus) and blue whiting ( Micromesistius poutassou), while in the Barents Sea there are both pelagics (capelin ( Mallotus villosus Mülle r), herring, and polar cod ( Boreogadus saida Lepechin)) and demersals (cod ( Gadus morhua L.) and haddock ( Melanogrammus aeglefinus)). The latter two species spawn in the Norwegian Sea along the slope edge (haddock) or along the coast (cod) and drift into the Barents Sea. Marine mammals and seabirds, although comprising only a relatively small percentage of the biomass and production in the region, play an important role as consumers of zooplankton and small fish. While top-down control by predators certainly is significant within the two regions, there is also ample evidence of bottom-up control. Climate variability influences the distribution of several fish species, such as cod, herring and blue whiting, with northward shifts during extended warm periods and southward movements during cool periods. Climate-driven increases in primary and secondary production also lead to increased fish production through higher abundance and improved growth rates.
Modelling the ecosystem dynamics of the Barents Sea including the marginal ice zone
Journal of Marine Systems, 2006
An upgraded and revised physically-biologically coupled, nested 3D model with 4 km grid size is applied to investigate the seasonal carbon flux and its interannual variability. The model is validated using field data from the years for which the carbon flux was modelled, focussing on its precision in space and time, the adequacy of the validation data, suspended biomass and vertical export. The model appears to reproduce the space and time (F 1 week and 10 nautical miles) distribution of suspended biomass well, but it underestimates vertical export of carbon at depth. The modelled primary production ranges from 79 to 118 g C m À 2 year À 1 (average 93 g C m À 2 year À 1 ) between 4 different years with higher variability in the ice-covered Arctic (F 26%) than in the Atlantic (F 7%) section. Meteorological forcing has a strong impact on the vertical stratification of the regions dominated by Atlantic water and this results in significant differences in seasonal variability in primary production. The spatially integrated primary production in the Barents Sea is 42-49% greater during warm years than the production during the coolest and most icecovered year. D
The code of the long-term biomass cycles in the Barents Sea
2003
Barents Sea capelin (Mallotus villosus), Norwegian spring-spawning herring (Cluea harengus), and Northeast Arctic cod (Gadus morhua) have been associated with large fluctuations of biomass growth. The cause of these large fluctuations has been poorly understood and led to problems in biomass management. The identification of a deterministic cause would provide the possibility of forecasting future biomass fluctuations. In this investigation, the Kola Section sea temperature and the biomasses of capelin, herring, and cod have been analyzed by a wavelet transform to identify the source of the long-term cycles. The wavelet analysis shows that the Kola Section temperature has dominant cycles at the lunar-nodal tide cycles of 3! 18:6 ¼ 55:8, 18.5 and 18:6=3 ¼ 6:2 years. The recruitment of Barents Sea capelin, Norwegian spring-spawning herring, and Northeast Arctic cod has adopted an optimal recruitment cycle close to the stationary 6.2 years Kola temperature cycle. Long-term biomass grow...
Pelagic Fish and the Ecological Impact of the Modern Fishing Industry in the Barents Sea
ARCTIC, 1995
The Barents Sea/Norwegian Sea ecosystem is inhabited by two large pelagic fish stocks, the Norwegian spring spawning herring and the Barents Sea capelin. The herring stock feeds in the high-production polar front area in the western Norwegian Sea, and spawns at the Norwegian coast. The larvae are transported into the Barents Sea, where they spend the first two to four years of life. The capelin stock spends its whole life in the Barents Sea, spawning along the southern coasts and feeding in the nutrient-rich areas in the northern parts of the sea.