Hydrobiologia 442: 329–337, 2001. M. Boersma & K.H. Wiltshire (eds), Cladocera. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 329 Fish and crustaceans in northeast Greenland lakes with special emphasis on interactions between Arctic charr (Salvelinus alpinus), Lepidurus arcticus and benthic chydorids Erik Jeppesen 1 , Kirsten Christoffersen 2 , Frank Landkildehus 1 , Torben Lauridsen 1 , Susanne L. Amsinck 1 , Frank Riget 3 & Martin Søndergaard 1 1 National Environmental Research Institute, Department of Lake and Estuarine Ecology, P.O. Box 314, DK-8600 Silkeborg, Denmark 2 Freshwater Biological Laboratory, University of Copenhagen, Helsingørsgade 51, DK-3400 Hillerød, Denmark 3 National Environmental Research Institute, Department of Arctic Research, Tagensvej 153 4 th , DK-2200 Copenhagen N, Denmark Key words: Arctic lakes, trophic structure, Arctic charr (Salvelinus alpinus), Lepidurus, fish, zooplankton, pelagic- benthic coupling, benthic chydorids Abstract We studied the trophic structure in the pelagial and crustacean remains in the surface 1 cm of the sediment of 13 shallow, high arctic lakes in northeast Greenland (74 ◦ N). Seven lakes were fishless, while the remaining six hosted a dwarf form of Arctic charr (Salvelinus alpinus). In fishless lakes, Daphnia pulex was abundant, while no daphnids were found in the pelagial of lakes with fish. In fish lakes, the zooplankton community was dominated numerically by cyclopoid copepods and rotifers. Both lake sampling and analysis of remains in the top 1 cm of the sediment indicated that the phyllopod, Lepidurus arcticus, occurred in all fishless lakes, but was either absent or present in low densities from lakes with fish. Adult Lepidurus are mainly predators and forage in the top layer of the sediment. An analysis of surface sediment revealed low abundance of the benthic chydorids Alona sp. and Macrothrix sp. in lakes with Lepidurus, while they were abundant in lakes with fish. The low abundance in fishless lakes could not be explained by damage of crustacean remains caused by Lepidurus feeding in the sediment, because remains of the more soft-shelled, pelagic-living Daphnia were abundant in the sediment of these lakes. No significant differences between lakes with and without fish were found in chlorophyll a, total phosphorus, total nitrogen, conductivity or temperature, suggesting that the observed link between Lepidurus arcticus and the benthic crustacean community is causal. Consequently, remains of crustaceans in high arctic lake sediments may be useful for detecting the impact of past climate change on top-down control by fish. Not only remains of pelagic species, but also of Lepidurus and some benthic chydorids, may be used to detect changes in fish abundance and predation pressure in the past. Introduction Lakes in the arctic are often inhabited by few species and accordingly have simple pelagic food web struc- tures (Rigler et al., 1974; Stross et al., 1980; Hobbie, 1984). Arctic charr (Salvelinus alpinus) is the only freshwater fish species found in high arctic (Hammar, 1989). Further south in subarctic continental freshwa- ter lakes, sticklebacks (Gasterosteus aculeatus, Pun- gitius pungitius) and a number of salmonids, grayling (Thymallus spp.) and whitefish (Coregonus spp.) and smelt (Osmerus spp.) may appear (Hammar, 1989). Zooplankton community structure in arctic lakes is also simple and highly influenced by fish (O’Brien, 1975; Hobbie, 1984). In the presence of fish, large- bodied cladocerans such as Daphnia pulex and D. middendorffiana are replaced by smaller species such as D. longiremis (if present in the area) and Bosmina spp., and the mean size of Holopedium gibberum de- clines (O’Brien, 1975). Likewise, only four species of copepods have been recorded in high arctic lakes (Halvorsen & Gullestad, 1976; Stross et al. 1980;