Invasive mussels induce community changes by increasing habitat complexity

Habitat complexity is among the most important factors affecting the diversity, structure, and density of natural communities. The invasive byssate bivalves zebra mussel (Dreissena polymorpha (Pallas, 1771)) and golden mussel (Limnoperna fortunei (Dunker, 1857)) are sessile suspension feeders that form aggregations (druses), physically changing sediments and increasing habitat complexity, and providing shelter and food for other benthic organisms. In this study, we explored the impact of the change in habitat complexity on benthic community created by druses of L. fortunei and D. polymorpha, formed on various sediments. D. polymorpha was studied in Europe (Naroch Lake, Belarus) and in North America (Glen Lake and Lower Nashotah Lake, USA), and L. fortunei was studied in South America (Rio Tercero Reservoir, Argentina). Druses of D. polymorpha or L. fortunei and samples of bare nearby sediment (without druses of exotic mussels) were collected at each sampling site. We found significant changes in species richness, density, biomass, taxonomic, and trophic structure of communities formed in druses compared to the nearby bare sediments. Community taxonomic richness increased threefold, and density increased sevenfold with increasing complexity of habitat from sand to druse. The feeding functional group approach indicated that the impact of increased complexity was reinforced by an increase in food supply in D. polymorpha and L. fortunei druses. Along with increasing species richness and densities, byssate bivalves homogenized benthic communities.