Original paper

Algal foraging by a rheophilic chironomid (Eukiefferiella claripennis Lundbeck) extensively encountered in high nutrient enriched streams

Maasri, Alain; Fayolle, Stéphanie; Franquet, Evelyne


Water enrichment has been described to have major impact on the freshwater food-webs structure. We investigated the structure of the epilithic algal assemblage and the gut contents of a rheophilic orthoclad in situ in a nutrient enriched stream. 4-th instar larvae of Eukiefferiella claripennis, a widespread orthoclad in the Palearctic ecozone and abundant in nutrient-enriched streams, were chosen to be studied due to their great densities in such environment. The taxonomic composition of the epilithic algal assemblage, the gut contents and the ingested algalcell biovolumes were used to establish the foraging behavior of this chironomid, and to explain its success under such environmental conditions. A CoInertia analysis, and a Two Way INdicator SPecies ANalysis were uses to compare the co-structure of algae assemblages in the epilithon and the guts. Then Strauss's linear food selection index was used to assess the electivity of each algae taxon. Cell biovolumes and distribution were also compared and tested for significant differences between the epilithic algal assemblage and the gut contents. Biovolumes of cells in the epilithon were tested for significant differences from the mean biovolume value of the ingested cells. Eukiefferiella claripennis larvae seem to feed preferentially on Chlorophyceae and Cyanophyceae; Diatomophyceae were randomly grazed without preference while Rhodophyceae were avoided. Cell biovolumes were significantly different between the epilithon and the gut contents, and the larvae preferentially consumed a narrow range of cell biovolumes compared to the wide range of cell biovolumes encountered in the environment. Stigeoclonium and Oscillatoria were the key taxa of the algal assemblage foraged by the larvae. Two complementary approaches seem to drive the foraging behavior of this orthoclad, 1) taxa-type preference and 2) cell-bivolume preference. In nutrient enriched streams, an algal assemblage consisting of cells of Chlorophyceae and Cyanophyceae averaging 1702 μm3 offers the best diet to this chironomid.


chironomidaegrazinggut contentepilithic algaeselective foragingoscillatoria