Nitrification in the Course of Ecological Succession

tivorous fishes), serious disruption of the previous community structure, and a rapid shift toward smaller-bodied zooplankton. The morphological changes seen in Bosmina are not peculiar to Frains Lake. The occurrence of longer mucro spines on late-glacial Bosmina or Eubosmina has been reported in sediment from Langsee, Austria (Frey 1955), Esthwaite Water, England (Goulden 1964), the Grosser Segeberger See, West Germany (Hoffman 1977), Linsley Pond and Rogers Lake, Connecticut (Austin 1942, Deevey 1942, 1969). According to Thienemann (1950), the long-spined Eubosmina longispina was a typical member of the European glacial "mischfauna." Subsequently, this species was replaced by a sequence of forms, Eubosmina longispina to E. coregoni kessleri to E. c. coregoni, which progressively moved toward mucrones. As in the case of Bosmina, since the modern analogs of the Eubosmina occur in lakes of different trophic status, with Eubosmina characteristic of oligotrophic conditions and E. c. coregoni characteristic of eutrophic conditions (Patalas and Patalas 1966), the replacement sequence has generally been interpreted as representing succession toward eutrophication. Yet the same sequence can be interpreted to reflect a gradual increase of planktivorous fish activity, which results in the reduction or removal of large-bodied predatory copepods.