Life cycles, microdistribution and production dynamics of six species of net‐spinning caddisflies in a large southeastern (U.S.A.) river

Abstract

Hydropsyche incommoda. H. rossi, Cheumalopsyche pasella, Mocronema Carolina. Chimarra moslyi, and Neureclipsis crepuscularis were studied on woody substrates (snags) in the lower Savannah River. Distribution of most species biomass was positively correlated with attached macrophytes on snags at medium (25–50 cm s‐1) current velocities. All species were bivoltine at the study site with the exception of M. Carolina which was univoltine. Annual and cohort production estimates (Hynes and removal‐summation methods) were obtained for each species at three velocity ranges. Total annual caddisfly production calculated by the Hynes method was 12.6, 41.4, and 22.7 g (ash free dry wt m‐2 of snag surface area at low, medium and high velocities, respectively; 9.6, 34.4, and 19.9 g with removal‐summation; and, 11.5, 36.1 and 21.1 g when the Hynes method was applied to discrete cohorts. Higher cohort production was attained by the overwintering generation because of higher terminal instar body weights. Dissolved organic carbon comprised most of the total organic load transported by the river; however, abundant paniculate organic food was also apparently available for filler feeders. Organic and inorganic seston concentrations were highest in winter months and lowest in autumn. Over 90 percent of the seston (by weight) was <105 μm. It is suggested that the variation in catchnet mesh size, coupled with spatial heterogeneity of the snag habitat, allows the caddisflies to partition space, which is apparently the limited resource.