PERIPHYTON PATCH PREFERENCE IN GRAZING CHIRONOMID LARVAE

We determined the feeding preference of chironomid larvae (Paratanytar sus dubius) by observing dispersal of larvae among patches differing i n periphyton composition. Nutrient-diffusing substrates were used to g enerate four algal patch types, which differed in the abundance of sev eral 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 posit ively correlated only with algal diversity. At a density of 0.66 indiv idual/cm2 on preferred patches, larvae did not significantly reduce th e chlorophyll a content of patches. Chironomid grazing had no effect o n taxon diversity of periphyton assemblages. Data on the relationship between periphyton preference and grazer growth and reproduction are n ecessary to assess the importance of periphyton patch preference in na tural populations.