MANIPULATIONS OF PLANKTIVORE FAUNA AND DEVELOPMENT OF CRUSTACEAN ZOOPLANKTON AFTER RESTORATION OF THE ACIDIFIED LAKE GARDSJON

Major changes occurred in the crustacean community both after liming o f the originally acidified and fishless Lake Gardsjon and after benthi vorous brown trout stocking four seasons later. Species diversity incr eased after liming, but decreased after fish introduction. The dominan t copepod, Eudiaptomus gracilis, was relatively unaffected by the mani pulations. Several cladoceran species, and especially Diaphanosoma bra chyurum, were positively influenced by liming. After fish introduction , first Bosmina longirostris and Ceriodaphnia quadrangula and, some ye ars later, Daphnia longispina, became the dominant zooplankton. The ch anges in the crustacean community are discussed in relation to plankti vore fauna. During the limed and fishless condition, high densities of phantom midge larvae (Chaoborus spp.) and waterboatmen (Corixidae) su ppressed susceptible prey species. When these predators were reduced a fter fish introduction, the efficient herbivore D. longispina expanded and ultimately limited the abundance of other crustaceans. Thus, limi ng creates the potential for the development of a diverse fauna but th e actual development of crustaceans in limed lakes is strongly influen ced by predation and competition patterns.