Deformiteter hos oligochaeter i Vänern

Benthic oligochaetes are sensitive indicators of the water quality and various kindsof stress caused by hazardous substances. In a previous study from the early1970's, grave external morphological deformities had been found in oligochaetesfrom three bays in the northern part of Lake Vänern, Sweden. In the present follow-up a new series of samples obtained from the same localities in 1975-1988 have been analyzed the same way. These samples represent a period of reducedanthropogenic impact from nutrients as well as various metals. However, largeamounts of various environmental pollutants are still deposited in the sedimentswhere benthic organisms like oligochaetes live.The results show that the presence of the most severe malformations, i.e. gravelydeformed ventral chaetae, have been reduced with time. Nevertheless, there are nogeneral signs of reduced presence of more moderate deformities, even though therehave locally been some reductions. In addition to the deformed ventral chaetaefound in earlier investigations, this study has also revealed malformations of thedorsal pectinate chaetae (so-called crotchets) in the dominant oligochaete speciesPotamothrix hammoniensis in all three investigated bays. Previously malformationsin dorsal chaetal bundles ranging from slight to severe abnormalities haveonly rarely been found in the lake. The study has also revealed that a second oligochaetespecies mostly characteristic of oligotrophic conditions, Spirosperma ferox,had a high proportion of deformed ventral chaetae.Although the presence of severely malformed chaetae has been reduced, our studyreveals that minor deformities have not been reduced to the same degree except atsome localities. This is likely to be a result of exposure to various environmentalpollutants deposited in the sediments.