MACROINVERTEBRATE COMMUNITIES IN RELATION TO SUBMERGED VEGETATION IN 2 CHARA-DOMINATED LAKES

Relationships between macroinvertebrates and the presence of submerged vegetation were studied in two shallow eutrophic lakes in The Netherl ands, Lake Veluwemeer and Lake Wolderwijd. A shift from turbid water w ith sparse macrophyte cover (Potamogeton perfoliatus, Potamogeton pect inatus) towards clear water with a dense cover of submerged vegetation (Chara spp.) has been observed in the lakes over the past 10 years. R elatively large Chara meadows (300-500 ha) have recently developed in both lakes. The composition of macroinvertebrate fauna was determined at sites varying in cover and dominant vegetation type by sampling sed iment and water during 1992 and 1994. Macrophyte biomass, sampling yea r and vegetation type were the major determinants of macroinvertebrate community composition. Valvata piscinalis, Bithynia tentaculata, Gamm arus tigrinus and Chironomus sp. characterized the sites with high cha rophyte biomass, whereas Potamopyrgus antipodarum, Cladotanytarsus sp. , Stictochironomus sp. dominated the samples with low charophyte bioma ss. Chara vegetation was different from Potamogeton sp. by showing low er densities of the midge larvae Einfeldia dissidens and Cricotopus gr . sylvestris. Seasonal variations in densities of the dominant mollusc species (V. piscinalis, P. antipodarum) were closely related to the d evelopment of Chara biomass as well as to periphyton cover on charophy tes. Thus, changes of the light climate in both lakes, which have led to an increase in colonization by submerged vegetation (particular Cha ra meadows), indirectly had a large impact on macroinvertebrate commun ities.