The effects of the invasive mussel, Limnoperna fortunei, on associated fauna in South American freshwaters: importance of physical structure and food supply

We examined the importance of the introduced Asian golden mussel (Limnoperna fortunet) in structuring invertebrate communities in South American freshwaters. An experiment using artificial substrata (i.e., concrete tiles with either a layer of living mussels, a layer of intact empty shells that mimicked living mussels, or blank tiles) showed that, when considered in bulk, invertebrates (density and biomass) are enhanced significantly in the presence of live mussels (as compared with shells only and blank tiles). On a taxon-by-taxon basis, however, significantly higher densities and biomass on live mussel tiles than on blank and/or shells-only tiles were found only for Oligochaeta, which would especially benefit from the feces and pseudofeces produced by the living mussel beds. At the end of the experiment, the amount of accumulated sediment on the tiles differed greatly among treatments, with values up to three times higher on shells-only tiles than on live-mussel and blank tiles. Dead mussels act as a sediment trap, whereas the activity of live mussels helps keep the tiles less clogged with sediments. On the other hand, proportions of organic matter were two times higher in the presence of live mussels than in the other two treatments. Although the physical structure created by mussel shells plays a significant role, we conclude that the activity of living mussels is of major importance for controlling invertebrate numbers, biomass and diversity.