Macroinvertebrate communities in relation to submerged vegetation in two Chara-dominated lakes

Relationships between macroinvertebrates and the presence of submerged vegetation were studied in two shallow eutrophic lakes in The Netherlands, Lake Veluwemeer and Lake Wolderwijd. A shift from turbid water with sparse macrophyte cover (Potamogeton perfoliatus, Potamogeton pectinatus) towards clear water with a dense cover of submerged vegetation (Chara spp.) has been observed in the lakes over the past 10 years. Relatively 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 sediment and water during 1992 and 1994. Macrophyte biomass, sampling year and vegetation type were the major determinants of macroinvertebrate community composition. Valvata piscinalis, Bithynia tentaculata, Gammarus tigrinus and Chironomus sp. characterized the sites with high charophyte biomass, whereas Potamopyrgus antipodarum, Cladotanytarsus sp., Stictochironomus sp. dominated the samples with low charophyte biomass. Chara vegetation was different from Potamogeton sp. by showing lower 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 development of Chara biomass as well as to periphyton cover on charophytes. Thus, changes of the light climate in both lakes, which have led to an increase in colonization by submerged vegetation (particular Chara meadows), indirectly had a large impact on macroinvertebrate communities.