Eutrophication, pollution and fragmentation: effects on parasite communities in roach (Rutilus rutilus) and perch (Perca fluviatilis) in four lakes in central Finland

Parasite communities in four study lakes in 1986 reflected the influences of eutrophication, pollution, and habitat fragmentation. Discriminant 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 polluted lakes. Changes in the density of intermediate hosts, direct effects on ectoparasites, and impaired immune systems were regarded as important mechanisms. The second contrasted communities in an oligotrophic, unpolluted lake with those from the two eutrophic lakes and was more complex, 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 loading, supported our conclusion that parasite faunas in Lake Vatia in 1986 involved the effects of pollution.