Some aspects of the ecological niche of chironomids associated with submersed aquatic macrophytes in a tailwater

High values of chironomids' production were recorded and analysed in the tailwater of a dam reservoir located on a large river. The values resulted from submersed aquatic macrophytes (SAM) patches that appear on the bottom in summer, as an effect of a specific discharge pattern through the dam. Abundant and taxonomically rich chironomid assemblages develop there, but their populations display different spatial and trophic preferences, which are the main topic of our interest here. We focused on dominant taxa of Orthocladius/Cricotopus spp., Chironomus riparius Meigen and Glyptotendipes cauliginellus (Kieffer), whose abundance and biomass exceeded 90% of all chironomids inhabiting the SAMs. The developmental time of their aquatic stages (cohort production interval − CPI) and thus production, and production to biomass ratio (P:B) differed considerably. A P:B ratio of 13.8 was estimated for the first taxon, a mid-body size scraper living on stems and leaves of SAMs. In contrast, P:B ratios of 5.2-7.7 were assessed for the second and third taxa, rather large body size benthic gathering collectors inhabiting the roots of SAMs. The main food categories of gathering collectors were particulate organic matter trapped by the roots, while scrapers fed on algae developing on leaves and stems.