The invasive bivalve Limnoperna fortunei enhances benthic invertebrate densities in South American floodplain rivers

Abstract

We assessed the effects of the introduced bivalve L. fortunei on the abundance and biomass of associated benthic invertebrates in South American large floodplain rivers. The survey was based on comparisons of L. fortunei-covered and L. fortunei-barren areas in five artificial cages from where large predators were excluded, exposed to colonization by the mussel for a total of 17 months in the lower Parana river delta. Accompanying invertebrates were dominated by Oligochaeta, Nematoda, Rotifera, Copepoda, Gastropoda, Hirudinea, Chironomidae and nauplii. Also present in minor numbers were Tardigrada, Turbellaria, Cladocera, Ostracoda, Insecta, Hydracarina and Decapoda. Dominant invertebrates were 27–100% more numerous (and hosted 43–100% more biomass) in areas with L. fortunei than in areas barren of the mussel. In areas with L. fortunei, total invertebrate biomass (excluding the bivalve) was positively correlated with mussel biomass, and increased with time of exposure under water. No such trend was observed in areas barren of L. fortunei. It is suggested that higher invertebrate growth is associated with enhanced substrate complexity and, probably, the transfer of organic matter from the plankton to the sediments due to the mussels’ feces and pseudofeces. Some of the adverse ecosystem-wide effects of filter-feeding invasive mussels observed in European and North American water bodies may be offset in the Parana by the extremely high loads of organic matter in these turbid waters.