Macroinvertebrates on Eichhornia crassipes roots in two lakes of the Parana River floodplain

Changes in the abundance, biomass and in the relative proportions of functional feeding groups of macroinvertebrates were studied for 17 months during low and high water periods in two floodplain lakes with indirect connections to the Parana River. At low water, Eichhornia crassipes root clusters were colonized by comparatively low densities of macroinvertebrates, especially in the lake more distant to the river. Collector-gatherers and predators were the most abundant functional feeding groups, but different taxa of these groups dominated in the two lakes during low water. At high water, macroinvertebrates densities increased as a result of increased flow through the roots. In this period, collector-filterers dominated at both lakes and constituted over 34% of the macroinvertebrates. Four independent variables (conductivity, hydrological periods, dissolved oxygen and site) explain 87% of the variability in macroinvertebrates density expressed as the number of individuals per m(2). No significant relationship were found between macroinvertebrate biomass and any of the independent variables.