Engineering by the invasive Asian clam Corbicula fluminea: Effects on macrozoobenthic assemblages
The Asian clam Corbicula fluminea is one of the most invasive species in aquatic ecosystems. Given the usual high density and large spatial distribution, this species can significantly alter ecosystem structure and functioning through several mechanisms, including ecosystem engineering. In this study, the engineering effects of C. fluminea were evaluated using three different experiments in a highly invaded ecosystem (River Minho, Portugal). The first study assesses the possible effects of different C. fluminea densities on macrozoobenthic assemblages subjected to brackish and freshwater conditions. A second complementary study used 5 different treatments (control bare sediment, live shells, empty open dead shells, closed dead shells and inanimate materials) to evaluate the main mechanisms responsible for the results obtained in the previous work. Finally, a last experiment assessed possible differences in the colonization by macroinvertebrates between invasive and native bivalve empty shells to assess possible differences prior and after the invasion of C. fluminea. In this context, this work aimed to evaluate the importance of ecosystem engineering activities mediated by an invasive species and how this situation can change the biodiversity in a highly invaded area.
Our comparisons indicated that the two macrozoobenthic assemblages’ surveyed (brackish and freshwater) respond positively to the increasing density of C. fluminea in terms of density, biomass and diversity being Crustacea, Insecta and Gastropoda the faunal groups most positively affected. Interestingly, in the second experiment the higher density, biomass and diversity values were obtained in treatments with live and empty open shells. Two mechanisms may explain these results: i) excretion by live shells can enhance organic matter in the sediments and several species (mainly polychaetes) respond positively to this resource enhancement and ii) the physical structure provided by shells can enhance the refugee area and several species (mainly crustaceans) respond positively to this situation. Finally, when using just empty native and invasive bivalve shells as a physical substratum for colonization our results indicated that the macrozoobenthic assemblage did not vary among treatments, with the exception of species richness that was higher in the treatments containing native species. Overall, our results were able to demonstrate that an invasive ecosystem engineer can change the macrozoobenthic assemblages’ characteristics in terms of density, biomass and diversity.