Fish and crustaceans in northeast Greenland lakes with special emphasis oninteractions between Arctic charr (Salvelinus alpinus), Lepidurus arcticusand benthic chydorids

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 northe ast Greenland (74 degrees N). Seven lakes were fishless, while the remainin g six hosted a dwarf form of Arctic charr (Salvelinus alpinus). In fishless lakes, Daphnia pulex was abundant, while no daphnids were found in the pel agial of lakes with fish. In fish lakes, the zooplankton community was domi nated numerically by cyclopoid copepods and rotifers. Both lake sampling an d analysis of remains in the top 1 cm of the sediment indicated that the ph yllopod, Lepidurus arcticus, occurred in all fishless lakes, but was either absent or present in low densities from lakes with fish. Adult Lepidurus a re mainly predators and forage in the top layer of the sediment. An analysi s of surface sediment revealed low abundance of the benthic chydorids Alona sp. and Macrothrix sp. in lakes with Lepidurus, while they were abundant i n lakes with fish. The low abundance in fishless lakes could not be explain ed by damage of crustacean remains caused by Lepidurus feeding in the sedim ent, 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 cau sal. Consequently, remains of crustaceans in high arctic lake sediments may be useful for detecting the impact of past climate change on top-down cont rol 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 an d predation pressure in the past.