Distribution of benthic invertebrate biomass and secondary production in relation to floodplain connectivity in a large river system (Parana River, Argentina)

An investigation of benthic invertebrates was conducted in the Parana River (Argentina) floodplain to assess patterns of biomass and production in relation to lateral river connectivity. Environmental and invertebrate samples were collected monthly from April 2005 to March 2006 at sites with different lateral surface-connection. The investigated invertebrate assemblages were characterized by high biomass and high production. The key factor determining the benthic assemblages was river connectivity and indirectly, substrate characteristics, water transparency, and depth. With increasing river connectivity, biomass and production of oligochaetes, native bivalves, and dipterans decreased, whereas both variables increased for non-native bivalves, gastropods and ephemeropterans. Benthic assemblages of most of sites had an average similarity in the composition of about 50% along the study period, but the number of taxa contributing to the overall similarity was lower at sites located at long distance from the main channel than at sites located next to it. Potential production was high compared to literature data, which underscores the importance of preserving floodplain areas and maintaining natural lateral connectivity. High habitat patchiness mediated by lateral-surface connectivity appeared to promote benthic resources diversity, which in turn controls productivity of this floodplain-river system.