Corbicula fluminea impact in Lake Maggiore (Italy): feeding plasticity and dietary overlap with native mussels

Feeding plasticity of Corbicula fluminea is possibly of major importance for successfully competing indigenous bivalves in Lake Maggiore (Italy), thus promoting overdomination of the alien species in the area. After its first detection in 2010, our studies on spatial and temporal dynamics of abundance, biomass and population structure revealed that the newcomer spreads to over 1/3 of the lake littoral, reaching.103ind.m-2 in three years. A comparison with historical data evidenced a strong decline of the most abundant native mussel species (Unio mancus), whose actual density is reduced of about 75% after Corbicula establishment. Although native mussel depletion cannot be unequivocally attributed to the impact of Corbicula, change in bivalve species dominance is expected to impact ecosystem structure and functioning. Understanding the ecological role of invasive/native species is essential for predicting how the ecosystem might be altered after the invasion. To this aim, we compared daily filtration rates and food spectra of the two competitors- U. mancus and C. fluminea. Filtration rates were measured by the clearance method under different experimental conditions and over the whole diurnal cycle. Dietary sources and trophic niche overlap were determined by C, N stable isotope analyses of soft tissues of organisms collected along the season and at different developmental stages. Preliminary results suggest that success of Corbicula is also related to its ability to shift diet preferences along the seasons. Corbicula seems to stand already as a keystone littoral species in Lake Maggiore, likely being a strong competitor for space and food to native mussels (i.e. Unio mancus).