Amphipod abundance in sediment trap samples at the long-term observatory HAUSGARTEN (Fram Strait, ∼79°N/4°E). Variability in species community patterns

Abstract

Since 2000, sediment traps have been deployed at the HAUSGARTEN (a long-term observatory established by the Alfred-Wegener-Institute for Polar and Marine Research in 1999) in the Fram Strait, (west of Spitsbergen at a water depth of 2,500 m, located in the confluence zone of the warm saline Atlantic water and water masses of polar origin) in order to investigate seasonal and inter-annual fluctuation of particle flux and the various contribution of zooplankton swimmers. Amongst these swimmers, amphipods are regularly observed occurring in a recurrent pattern and they dominate the biomass. Thus, we present data on amphipods regarding their seasonal and regional distribution pattern throughout the period 2000–2007. The most frequently observed amphipod species are Themisto libellula, T. abyssorum and T. compressa. While Themisto libellula is considered a true Arctic species associated to polar water masses, the boreal-Atlantic species Themisto abyssorum is imported into the Arctic by Atlantic water. A third species, Themisto compressa, occurred in 2004 and has been continually observed in the samples since then. The latter species has its main distribution in the warm regions of the North Atlantic and its occurrence in the Fram Strait points to the increased influence of warm Atlantic water masses. During 2000–2007, the amphipod composition in the samples has changed in favor of T. abyssorum and T. compressa. These shifts could suggest a northward movement of Atlantic species in the seasonally ice-covered area, a region of the ocean anticipated to react very sensitively to global warming.