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.

Summertime plankton ecology in Fram Strait—a compilation of long- and short-term observations

“…Accordingly, we have already observed a decrease in polar species and an increase in boreal species in the swimmer fraction of sediment trap samples from Fram Strait (Kraft et al 2011;Kraft et al 2012;Kraft et al 2013;Bauerfeind et al 2014). However, in summer 2011 the observed mesozooplankton community structure*with a pronounced numerical dominance of copepods*was in accordance with results reported from earlier investigations (e.g., Richter 1995;Hop et al 2006;Blachowiak-Samolyk et al 2007), although detailed studies of changing zooplankton communities are rare.…”

First evidence of reproductive success in a southern invader indicates possible community shifts among Arctic zooplankton

“…From the beginning of observations in September 2000, pelagic amphipods of the genus Themisto (Hyperiidae) have dominated the amphipod community in the traps in terms of biomass (Kraft et al 2011(Kraft et al , 2012. In July 2004, we first observed the appearance of the North Atlantic hyperiid amphipod Themisto compressa at 79°N in the European Arctic (Kraft et al 2011). The number of collected individuals over time increased until June 2012 (Fig.…”

Arctic pelagic amphipods: lipid dynamics and life strategy

“…A limited number of investigations of T. compressa suggested a free-swimming life-style, with sporadic occurrences in North Atlantic water masses in sub-arctic regions (Brandt, 1997;Weigmann-Haass, 1997;Dalpadado et al, 2001;Dalpadado, 2002). Since 2004, we regularly observed this species in the Fram Strait, with its northernmost distribution at 818N (Kraft et al, 2011(Kraft et al, , 2012.…”

“…Three hyperiid amphipod species comprise the genus Themisto in northern latitudes: T. libellula, a large Arctic species associated with cold, polar water masses, its subarctic congener T. abyssorum, which is transported to the Arctic by inflowing North Atlantic water masses and T. compressa, a North Atlantic species with its major distribution area in the southern Norwegian Sea (Kraft et al, 2011). Themisto libelulla and T. abyssorum have been studied over the past decade with regard to their food sources, variations in distribution, reproductive strategies, abundances and summer lipid compositions, while little is known about the deepwater species Cyclocaris guilelmi (Bousfield, 1951;Percy, 1993;Koszteyn et al, 1995;Auel et al, 2002;Dalpadado et al, 2008;Marion et al, 2008;Noyon et al, 2009Noyon et al, , 2011Noyon et al, , 2012Kraft et al, 2011Kraft et al, , 2012Kraft et al, , 2013b.…”