The structuring role of fish in Greenland lakes: an overview based on contemporary and paleoecological studies of 87 lakes from the low and the high Arctic

Lakes in Greenland are species-poor ecosystems and many are fishless. We studied the structuring role of fish in lakes in high- and low-Arctic Greenland. Major differences were observed in the trophic structure of the 87 lakes studied. Pelagic zooplankton biomass was on average 3-4-fold higher in the fishless lakes and dominated by large-bodied taxa such as Daphnia, the phyllopod Branchinecta and the tadpole shrimp Lepidurus. In contrast, small-bodied crustaceans dominated the lakes with fish. Analysis of microcrustacean remains in the surface sediment and contemporary benthic invertebrates also showed a marked influence of fish on community structure and the size of the taxa present. The cascading effect of fish on the microbial communities was modest, and no differences were observed for chlorophyll a. The cascading effect of fish on invertebrates depended, however, on the species present, being largest between fishless lakes and lakes hosting only sticklebacks (Gasterosteus aculeatus), while lakes with both Arctic charr (Salvelinus arcticus) and stickleback revealed a more modest response, indicating that presence of charr modulates the predation effect of sticklebacks. It is predicted that more lakes in Greenland will be colonised by fish in a future warmer climate, and this will substantially alter these vulnerable ecosystems.