Fish and crustaceans in northeast Greenland lakes with special emphasis on interactions between Arctic charr (Salvelinus alpinus), Lepidurus arcticus and 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 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 fromlakes with fish. Adult Lepidurus aremainly 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.