Ecological Responses to Different Degrees of Hydrologic Connectivity: Assessing Patterns in the Bionomy of Benthic Chironomids in a Large River-Floodplain System

Abstract

Floodplain wetlands of the Middle Parana River, Argentina, are regulated by their hydrologic connectivity to the main channel as well as by their position within the river network. The Chironomids are the most abundant insects that inhabit the benthos of the Parana River floodplain habitats. In order to address whether wetlands with different degrees of connectivity (disconnected, temporarily, and permanently connected) exhibit different abundance patterns and secondary production of benthic chironomids, samples were collected during a year comprising high and low water phases. The disconnected wetland exhibited the highest abundance and secondary production of chironomids. Both attributes were positively correlated to the degree of connectivity for most of the predators among the connected wetlands. Differences in assemblages’ composition and secondary production were found to be in relation to the degree of connectivity, the cover of macrophytes, the detritus at the bottom, the transparency of water, the proportion of clay in bottom sediments and the location of wetlands within the floodplain. The interaction between local environmental factors mediated by lateral connectivity and regional dynamics of metapopulations established diverse patterns in the metrics of chironomids along the Parana River floodplain wetlands. Thus, various degrees of hydrologic connectivity of wetlands should be preserved to maintain a high productivity of different chironomids in the floodplain.