Polar Biol (1997) 17: 337—349 ( Springer-Verlag 1997 ORIGINAL PAPER Dan Seiler · Angelika Brandt Seasonal occurrence of planktic Crustacea in sediment trap samples at three depth horizons in the Greenland Sea Received: 24 January 1996/Accepted: 28 June 1996 Abstract Zooplankton were quantitatively investi- gated in sediment trap samples deployed in the Green- land Sea at three locations (72°00.7@ N, 7°02.5@ W, 72°23.0@ N, 7°42.7@ W and 72°22.9@ N, 7°42.7@ W). Overall samples covered a period of three annual cycles (July 1989 to July 1992). The investigation of zooplankton, consisting almost exclusively of Crustacea ('99%), shows that the majority of the species must be regarded as ‘‘swimmers’’, which actively invaded the traps. Crus- tacea were composed of 45 species, mainly Copepoda, Amphipoda and Ostracoda. Each depth level showed a characteristic species composition. Diversity de- creased with depth. The samples were dominated by Copepoda in terms of abundance and by Amphipoda with respect to biomass. The seasonal occurrence of Crustacea showed a maximum during winter and a minimum during summer. Carnivores were regularly found in the collected material, indicating that they had been actively attracted by the organic matter emanat- ing from the traps. Omnivores showed a distinct seasonal occurrence. During winter, when primary pro- duction is low, omnivores change to a predatory way of life and they were consequently also found in increasing numbers. Herbivores were always rare. Due to the high number of ‘‘swimmers’’ found in winter, when particle flux is at its minimum, particle flux measurements may be severely biased at this time of the year. Introduction The vertical particle flux in the northern North Atlantic has been investigated using sediment traps since 1986 D. Seiler ( ) · A. Brandt1 Institute for Polar Ecology, Wischhofstrasse. 1-3, D-24148 Kiel, Germany Present address: 1 Zoological Institute and Zoological Museum, Martin-Luther-King-Platz 3, D-20146 Hamburg, Germany (Zeitzschel et al. 1978; Bodungen et al. 1991). Live zooplankton actively entering the sediment traps are, in the literature, named ‘‘swimmers’’ (Knauer et al. 1979; Fellows et al. 1981; Harbison and Gilmer 1986; Knauer and Asper 1989; Silver 1989) and represent an active flux of material into the traps. ‘‘Swimmers’’ greatly bias the measurement of particle flux. Fluxes calculated from sediment traps in the eu- photic zone suggest that at least 40—50% of the amino acids material is collected by accidental capture and mortality of ‘‘swimmers’’ (Lee et al. 1988). Since amino acids contribute with 10— 25% to the overall organic carbon in sinking particles in surface waters, estimates of carbon flux, and consequently estimates of new production based on vertical flux measurements, would result in a carbon overestimate of 5— 10% (Lee et al. 1988). In addition, other organic compounds such as lipids and carbohydrates augment this error (Lee et al. 1988). To date, most measurements of sediment trap material have focused on particles. However, it is well-known that a finite but variable percentage of the biogenic materials collected by sediment traps may partition into the solute phase, which led to investigations taking the solute phase into account (Karl and Knauer 1989). If ‘‘swimmers’’ are present, the solute phase will be contaminated by ma- terials that exuded from the carcasses and this will consequently lead to an overestimate of the passive downward flux of biogenic matter. A removal of ‘‘swim- mers’’ from the sample does not take into account the ‘‘swimmers’’— derived solutes, which are rich in C, N and P (Karl and Knauer 1989; Hansell and Newton 1994). This is the first continuous record over three annual cycles on the occurrence of zooplankton in sediment trap samples from the Greenland Sea. In the Greenland Sea sediment trap samples of zooplankton consisted almost exclusively of crustaceans (Bodungen et al. 1991). In order to determine whether the collected crustaceans went into the traps actively or fell into the