Influences of suspended inorganic matter on carbon ingestion and incorporation rates of two tropical cladocerans, Diaphanosoma birgei and Moina minuta

Abstract

Bauxite processing in Porto Trombetas, Brazil, generated a fine particulate effluent that was dumped into Lake Batata over a ten-year period, leading to high suspended solids, reduced water transparency and increased turbidity in parts of the lake. The influence of bauxite tailings on cladoceran feeding was studied by measuring carbon ingestion and carbon incorporation rates in Diaphanosoma birgei and Moina minuta. Feeding responses of animals exposed to bauxite tailings concentrations of 10, 20, 50, 100 and 200 mg/l were tested in laboratory experiments at two food levels (0.2 and 2.0 mg C/l) of 14 C-radiolabelled Scenedesmus acutus, and compared to bauxite-free experimental controls. Ingestion rates of both species varied in relation to food level and tailings concentration. Carbon incorporation rates generally declined with increased bauxite tailings levels in both cladoceran species, but precise responses varied between species and for the different combinations of tailings and food. Both carbon ingestion and incorporation rates were less adversely affected by rising bauxite tailings concentrations in M. minuta than D. birgei, indicating a clear differential susceptibility to suspended sediment contamination in these species.