EUTROPHICATION, POLLUTION, AND FRAGMENTATION - EFFECTS ON PARASITE COMMUNITIES IN ROACH (RUTILUS-RUTILUS) AND PERCH (PERCA-FLUVIATILIS) IN 4 LAKES IN CENTRAL FINLAND

Parasite communities in four study lakes in 1986 reflected the influen ces of eutrophication, pollution, and habitat fragmentation. Discrimin ant analyses of communities at the individual host level revealed two major axes. One contrasted communities in a lake affected by chemical pollution from a pulp mill with those from two eutrophic, less pollute d lakes. Changes in the density of intermediate hosts, direct effects on ectoparasites, and impaired immune systems were regarded as importa nt mechanisms. The second contrasted communities in an oligotrophic, u npolluted lake with those from the two eutrophic lakes and was more co mplex, reflecting habitat fragmentation (the absence of glochidia and some digeneans) and pollution or eutrophication, probably mediated by the same mechanisms as above. Changes in some index parasites in Lake Vatia monitored in 1994, following 8 years of reduced pollutant loadin g, supported our conclusion that parasite faunas in Lake Vatia in 1986 involved the effects of pollution.