Structure, biomass distribution, and energetics of the pelagic ecosystem in the Barents Sea: A synopsis

Abstract

Biomass distribution and energetics of trophic levels in the pelagic ecosystem of the Barents Sea are presented as averages over several years for the whole Barents Sea using data from the research programme Pro Mare in 1984–1989 and mathematical ecosystem models. Average biomasses range from more than 3 tonnes carbon km−2 (zooplankton) to 0.1 kg C km−2 (polar bears) and P/B ratios from 300 (bacteria) to 0.035 (minke whales). However, the Barents Sea ecosystem is in a far from steady state with, for instance, capelin stocks ranging from 30–700 kg C km−2 between years and cod stocks from 150–700 kg C km−2. As a general rule, the various fish stocks grow adequately, albeit at different rates, in “warm” years characterized by large influxes of Atlantic water and high zooplankton productivity. The skewed populations distribution which arises in “warm” years may lead to grave imbalances in “cold” years and even to the “collapses” of stocks, such as of capelin in the eighties. The food requirements of average-sized stocks of cod, seabirds and marine mammals correspond to more than twice the average productivity of capelin. Thus other species of pelagic fish (herring, polar cod) and zooplankton obviously play major roles as prey for these animals.