Invasive Asian clam distribution pattern reveals minimal constraints to downstream dispersal and imperceptible ecological impacts

Abstract

The Asian clam Corbicula fluminea is an invasive freshwater species that can cause adverse ecological and economic impacts. Information on its dispersal abilities, ecological preferences and impacts may contribute towards the improvement of management strategies, including those relating to regulatory demands such as the European Water Framework Directive (WFD). Both the above perspectives were addressed through inspection of environmental constraints to C. fluminea dispersal and impacts in a semi-natural drainage catchment (interconnected system of ditches). Forty sites were surveyed in 2014 to describe the species distribution and to characterize benthic macroinvertebrate communities, water column and sediment physico-chemistry, as well as the hydromorphological conditions. Clams were unevenly distributed in the study area and artificial barriers (dikes) did not prevent downstream dispersal of juveniles. Large variation in clam density (0–3077 clams m−2) could not be explained by physico-chemical or hydromorphological gradients. Although typical clam preference ranges reported in the literature were often exceeded, dense populations were nevertheless observed. Macroinvertebrate community structure suggested associations between the Asian clam and some functional feeding groups. However, the impacts of clams on macroinvertebrate assemblages and ecological quality were negligible, suggesting that contemporary methods designed to comply with the WFD bioassessment scheme may fail to detect important drivers of ecological change in freshwater ecosystems. This study demonstrated the reduced ecological impacts and broad ecological competence of the Asian clam, but also that its spread depends on human vectors. These findings highlight the need to rethink prediction tools supporting preventive measures against the introduction and spread of this invasive bivalve.