Ice amphipod distribution relative to ice density and under-ice topographyin the northern Barents Sea

Arctic ice amphipods are part of the sympagic macrofauna in the Marginal Ic e Zone of the northern Barents Sea and represent an important link from low er to higher trophic levels in some Arctic marine food chains. The species diversity in this area (1995/1996) consisted of four species: Gammarus wilk itzkii, Apherusa glacialis, Onisimus nanseni and Onisimus glacialis. The la rger ice amphipod, G. wilkitzkii, was the most abundant with the highest bi omass (>90%), whereas A. glacialis was abundant, but contributed little to the total biomass (<4%). The other two species were found only in small num bers. Both abundance and biomass of ice amphipods decreased along a latitud inal gradient from north to south across the Marginal Ice Zone. Their distr ibution was also related to the under-ice topography with regard to mesosca le structures (edge, flat area, dome and ridge). Overall, the abundance and biomass on ridges were much higher in comparison to other mesoscale struct ures, although edges also showed high abundance, but low biomass. The large G. wilkitzkii was consistently abundant on ridges. The small A. glacialis was predominately associated with edges, but also showed high numbers in do me-shaped areas. The Onisimus species were present in low numbers at all st ructures, and their biomass contributed <10% on any one structure. The reas ons for different distribution patterns of the dominant amphipod species un der Arctic sea ice are probably related to different requirements of the sp ecies, especially for food, shelter and physiological conditions.