Brittle star Photo: Norwegian Polar Institute

Benthos

Benthos is an essential component of the marine ecosystems. It can be stable in time, characterizing the local situation, and is useful to explain ecosystem dynamics in retrospect. It is also dynamic and shows pulses of new species distribution, such as the snow crab and the king crab, and changes in migrating benthic species (predatory and scavenger species such as sea stars, amphipods and snails with or without sea anemones). The changes in community structure and composition reflect natural and anthropogenic factors. There are more than 3000 species

of benthic invertebrates registered in the Barents Sea (Sirenko 2001), but here we only present the megafaunal component of the benthos collected by trawl and registered (species, abundance and biomass) during the BESS survey. This includes mainly large bodied animals with long life spans. This includes mainly large-bodied animals with long life spans. This investigation was initiated in 2005 - only a short timeline relative to investigations related to plankton and fish. Accordingly, interpretation of long-term trends for megabenthic data must be pursued with caution.

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Lab work: Photo: Norwegian Polar Institute

Phytoplankton development in the Barents Sea is typical for a high latitude region with pronounced maximum biomass and productivity during spring. During winter and early spring (January-March), both phytoplankton biomass and productivity are relatively low. Spring bloom is initiated during mid-April to mid-May and may vary strongly from year to year. Bloom duration is typically about 3-4 weeks and is followed by a reduction in phytoplankton biomass mainly due to nutrient exhaustion and grazing by zooplankton. Later in the fall when the increasing winds start to mix the upper layer and bring nutrients to the surface, a short autumn bloom can be observed. However, the timing of phytoplankton development can vary geographically. Spring bloom in the Atlantic water domain (without sea-ice) is thermocline-driven; whereas in the Arctic domain (with seasonal sea-ice), stability from ice-melt determines the bloom (Skjoldal and Rey 1989, Hunt et al. 2012). Thus, spring bloom at the ice edge can sometimes take place earlier than in the southern regions of the Barents Sea due to early stratification from ice melting.

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Polar sculpin (Cottunculus microps). Photo: Norwegian Polar Institute

Zoogeographical groups of fish species are associated with specific water masses. Rel-ative distribution and abundance of fish species belonging to different zoogeographic groups are of interest because these fish will respond differently to climate variability and change. Since they are not commercial species, fishing does not directly contribute to changes in abundance and distribution of these species. Different zoogeographic groups also tend to differ in their trophic ecology: many of the Arctic species are small, resident, and feed mainly on invertebrates; whereas, most boreal and mainly boreal species are migratory and piscivorous. Therefore, the relative abundance of these spe-cies should influence foodweb structure and dynamics. Comparing changes in relative abundance and distribution of species classified into zoogeographical groups based on established criteria from the literature, is relatively simple and does not rely on sophis-ticated statistical methods — like those used to study changes in the Barents Sea fish community, e.g. Fossheim et al., 2015 and Frainer et al., 2017.

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The deepwater redfish (Sebastes mentella). Photo: Norwegian Polar Institute

Most Barents Sea fish species are demersal (Dolgov et al., 2011); this fish community consists of about 70-90 regularly occurring species which have been classified into zoogeographical groups. About 25% are Arctic or mainly Arctic species. The commercial species are all boreal or mainly boreal (Andriashev and Chernova, 1995), except for Greenland halibut (Reinhardtius hippoglossoides) that is classified as either Arcto-boreal (Mecklenburg et al., 2013) or mainly Arctic (Andriashev and Chernova, 1995).

Distribution maps for cod, haddock, long rough dab, Greenland halibut, redfish, and six other demersal fish species can be found at: http://www.imr.no/tokt/okosystemtokt_i_barentshavet/utbredelseskart/en, and are based on data from the BESS.

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Ringed seal (Pusa hispida or Phoca hispida). Photo: Norwegian Polar Institute

3.8.1 Marine mammals

During the 20 June to 14 August 2017 period, a sighting survey was conducted in the Barents Sea east of 28°E as part of a six-year mosaic survey of the Northeast Atlantic to estimate the regional abundance of minke whales and other cetaceans during summer. Coverage was adequate, except in the southeastern area where military restrictions re-stricted survey activity. The most often observed species was minke whale, followed by white-beaked dolphins, harbour porpoises, humpback whales, and fin whales. A few observations were also made of bowhead whales and beluga whales. Data have not yet been analysed but the qualitative impression was that minke whales were abun-dant in northern and eastern areas (Figure 3.8.1.1). Harbour porpoises were observed mostly in the southern parts of the area covered, and they are associated with the coastal areas along Kola and fjord systems. Humpback whales were sighted in the northwest, which is considered an early appearance in waters where they usually occur later in autumn in association with capelin distribution. White-beaked dolphins were, as usual, observed in southern and central parts of the survey area, especially over the Central Bank. It is noteworthy that a considerable number of harp seal observations — single animals and groups — were made in open waters north of about 74°N. During summer, ime harp seals are usually closely associated with the ice edge in the north.

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Atlantic herring (Clupea harengus): Photo: Institute of Marine Research, Norway

Total biomass

Zero group fish are important consumers on plankton and are prey of other predators, and, therefore, are important for transfer of energy between trophic levels in the ecosystem. Estimated total biomass of 0-group fish species (cod, haddock, herring, capelin, polar cod, and redfish) was 1.92 million tonnes during August-September 2017; slightly above the long term mean of 1.76 million tonnes (Fig 3.5.1). Biomass was dominated by cod and haddock, and mostly distributed in central and northern-central parts of the Barents Sea.

Capelin, polar cod, young herring, and blue whiting constitute the bulk of pelagic fish biomass in the Barents Sea. Note that the acoustic target strength for blue whiting has been changed recently, and the time series has been recalculated. Total biomass of the main pelagic species (age 1 and older fish) in the Barents Sea in 1986-2017 has fluctuated between 0.5 and 9 million tonnes; mainly driven by fluctuations of the capelin stock. In 2017, cumulative biomass of capelin, herring, polar cod, and blue whiting was close to the long-term mean (Fig. 3.5.2).

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Calanus Glacialis Photo: Norwegian Polar Institute

Mesozooplankton biomasses

Mesozooplankton play a key role in the Barents Sea ecosystem by transferring energy from primary producers to animals higher in the food web. Geographic distribution patterns of total mesozooplankton biomass show similarities over time, although some inter-annual variability is apparent. Challenges in covering the same area each year are inherent in such large-scale monitoring programs, and inter-annual variation in ice-cover is one of several reasons for this. This implies that estimates of average zooplankton biomasses for different years might not be directly comparable.

In 2017, relatively high biomass (> 10 g m-2) was observed in the Bear Island Trench (southwestern region), north of Svalbard/Spitsbergen; south of Franz Josef Land, and in large parts of the easterly survey-region including the South-eastern Basin. Relatively low biomass (< 3 g m-2) was observed: in the westernmost area bordering the Norwegian Sea; in regions both south and east of Svalbard/Spitsbergen, and in the south-eastern corner of the survey area (Fig. 3.3.1). Relative to 2016, the most notable difference in 2017 was enhanced biomass in easterly parts of the Barents Sea. However, a large area just north of the Kola Peninsula was not covered in 2016, which complicates comparison.

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