Seasonal occurrence of planktic Crustacea in sediment trap samples at three depth horizons in the Greenland Sea

Abstract

Zooplankton were quantitatively investigated in sediment trap samples deployed in the Greenland 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. Crustacea were composed of 45 species, mainly Copepoda, Amphipoda and Ostracoda. Each depth level showed a characteristic species composition. Diversity decreased with depth. The samples were dominted 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 emanating from the traps. Omnivores showed a distinct seasonal occurrence. During winter, when primary production 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 severly biased at this time of the year.