| Abstrakt: |
The population age structure, microhabitats and individual morphology of the Cheumatopsyche lepida and Hydropsyche pellucidula larvae living in the river Kymijoki, Finland, were studied. This river is currently recovering from gross pollution by industrial and municipial effluents. Unusually young instars of both species dominated the winter and spring populations. Canonical correspondence analysis demonstrated that the species and different instars occupied relatively similar microhabitats. However, there were significant small-scale differences in the distribution of the instars and species. The smaller C. lepida larvae inhabited significantly larger stones with greater amounts of organic matter than the larger larvae. The final instar larvae of the H. pellucidula occupied significantly higher current velocities than the smaller instars. Abnormal nodule formation, malformation, darkening and reduction of the tracheal gills were observed in the older larvae of both species. The highest incidences of abnormalities, over 25 %, were observed in September. A significant positive correlation was established between the incidence of abnormalities and the amount of mosses on the stone. It is suggested that the population age structure and gill abnormality patterns of the Cheumatopsyche lepida and Hydropsyche pellucidula larvae reflect the cumulative effect of pollutants in the food chains of the river Kymijoki. |
