Bionomy and Secondary Production of Midges Inhabiting Wood: Unravelling Linkages at a Large River System

In the near pristine free-flowing section of the Parana River the biomass, organic matter, annual and cohort production and turnover ratios of midges inhabiting LWD were estimated. Richness and frequency of occurrence of the stages, genera and functional feeding groups of midges were calculated. Generalized linear mixed effect models were performed to evaluate whether environmental and woods characteristics predicted the biomass of midges. Eggs, larvae, pupae and imagoes of 32 taxa and functional groups were collected. Biomass was of 44.79 mg/m2 and AFDW was of 28.1 mg/m2, on average, with the maximum values obtained for collectors and shredders. Water transparency was the only one significant predictor of midge stocks. Annual production ranged between 190 and 858 g/m2 year and P/B between 31 and 224. The natural free-flowing conditions and high food availability, provide woody substrates that favour a high production and overlap in resource utilization, thus supporting a high diversity of midges.