Distribution of benthic megafauna in the Barents Sea: baseline for an ecosystem approach to management

Abstract

Benthos plays a significant role as substrate, refuge from predation and food for a wide variety of fish and invertebrates of all life stages and should therefore be considered in the ecosystem approach (EA) to management. Epibenthos from trawl catches, used in annual assessments of commercial fish stocks, was identified and measured on-board. The 2011 dataset present the baseline mapping for monitoring and included 354 taxa (218 to species level) analysed with multivariate statistical methods. This revealed four main megafaunal regions: southwestern (SW), banks/slopes in southeast and west (SEW), northwestern (NW), and northeastern (NE) which were significantly related to depth, temperature, salinity, and number of ice-days. The SW region was dominated by filter-feeders (sponges) in the inflow area of warm Atlantic water while the deeper trenches had a detritivorous fauna (echinoderms). In the SEW region, predators (sea stars, anemones and snow crabs) prevailed together with filtrating species (sea cucumber and bivalves) within a mosaic of banks and slopes. Plankton-feeding brittlestars were common in the NW and NE region, but with increasing snow crab population in NE. Climate change, potentially expanding trawling activity, and increasing snow and king crab populations might all have impacts on the benthos. Benthos should therefore be a part of an integrated assessment of a changing sea, and national agencies might consider adding benthic taxonomic expertise on-board scientific research vessels to identify the invertebrate “by-catch” as part of routine trawl surveys.

Large-scale patterns in community structure of benthos and fish in the Barents Sea

“…From the spatial variation in functional traits (size, motility, feeding types, etc.) of the fishes (Wiedmann et al 2014) and benthos species (Jørgensen et al 2015 and below), we can infer how the nature of the fish and benthos interactions varies in space and contributes to the observed spatial co-variation. In deeper areas in the Barents Sea, with relative warm, saline waters, the large-bodied Geodia barretti and G. macandrewii are forming dense populations referred to as ''sponge ground''.…”

“…Depth and temperature influence species composition of fish and benthos (Johannesen et al 2012;Jørgensen et al 2015). Temperature and salinity are used to distinguish different water masses in the Barents Sea.…”

“…Recently, there have been large-scale studies (*1.5 million km 2 ) identifying demersal fishes and megabenthos assemblages and relating these to abiotic factors (Anisimova et al 2011;Dolgov et al 2011a;Johannesen et al 2012;Jørgensen et al 2015). For both fishes and benthos, temperature and depth were found to be the most important structuring factors (Johannesen et al 2012;Jørgensen et al 2015). However, fishes and benthic invertebrates differ in many traits that can affect how the assemblages are structured in space.…”

“…The survey covers the whole Barents Sea shelf. In 2011, the megabenthos species identification was sufficiently standardised to qualify to baseline mapping (Jørgensen et al 2015) and to compare with the fish data. During the survey, a Campelen 1800 shrimp bottom trawl towed on double warps and a rockhopper ground gear was used throughout.…”

“…The mesh size was 80 mm (stretched) in the front and 16-22 mm in the codend, allowing the capture and retention of small-sized fish and megabenthos. The trawl catches of fishes and megabenthos were sorted to the lowest possible taxonomic level on board (for details on species identification see Wienerroither et al 2011;Jørgensen et al 2015). The trawl configuration and bottom contact were monitored remotely by Scanmar trawl sensors.…”