PERIPHYTON PATCH PREFERENCE IN GRAZING CHIRONOMID LARVAE

We determined the feeding preference of chironomid larvae (Paratanytarsus dubius) by observing dispersal of larvae among patches differing in periphyton composition. Nutrient-diffusing substrates were used to generate four algal patch types, which differed in the abundance of several diatom species and the green alga Stigeoclonium. Patch preference of larvae was negatively correlated with abundance of Stigeoclonium, chlorophyll a concentration, and algal biovolume. Preference was positively correlated only with algal diversity. At a density of 0.66 individual/cm2 on preferred patches, larvae did not significantly reduce the chlorophyll a content of patches. Chironomid grazing had no effect on taxon diversity of periphyton assemblages. Data on the relationship between periphyton preference and grazer growth and reproduction are necessary to assess the importance of periphyton patch preference in natural populations.