Horizontal distribution of cladocerans in arctic Greenland lakes - impact of macrophytes and fish

Submerged macrophytes may play an important role as a refuge for zooplankto n against predators. However, a recent study suggests that their importance depends on the trophic state of the lake. We studied the impact of fish an d macrophytes on the horizontal distribution of pelagic cladocerans in 56 o ligotrophic arctic Greenland lakes. In north-east and western Greenland, zo oplankton was sampled in the near-shore (littoral) and central (pelagial) p art of all lakes and fish were sampled with multiple mesh-sized gill nets. Macrophytes were visually estimated in the littoral. In north-east Greenlan d, 5 taxa of cladocerans were found, while 14 taxa were recorded in western Greenland. Daphnia pulex occurred only in fishless lakes in both northeast and western Greenland and avoided the near-shore areas in the shallow and deep lakes. Bosmina spp. and Holopedium gibberum were evenly distributed be tween the littoral and the pelagial in the deep and shallow fishless lakes. However, their near-shore density was lowest in the presence of fish. Macr ophyte-related and benthic cladocerans concentrated either in the littoral or were evenly distributed between the littoral and the pelagial, irrespect ive of depth and fish presence or absence. Macrophytes had no impact on the horizontal distribution of pelagic cladocerans. Thus, it is concluded that horizontal heterogeneity of Bosmina spp. and Holopedium gibberum might be affected by the presence of fish.