Planktonic larvae of the invasive bivalves Dreissena spp. and Limnoperna fortunei: review of their effects on freshwater communities

Dreissena polymorpha, Dreissena rostriformis bugensis, and Limnoperna fortunei are considered among the most invasive freshwater mussels. The three species share several biological and ecological traits, resulting in often similar effects on the ecosystems. Their planktonic larvae (“veligers” s.l.) can be a dominant component of the summer zooplankton community. The development from fertilized egg to juvenile normally takes 10–20 days, but only < 1–3% of the fertilized eggs reach the settling stage. Consumption of veligers by invertebrates is likely high, but so far largely unexplored. Predation by larval fishes has been more intensively studied. In Europe and North America, 23 fish species feed on dreissenid veligers, whereas in South America ca. 28 consume L. fortunei veligers. Their importance in fish diets varies widely, but in several cases, veligers represent their main or even only source of food. Further, some species perform significantly better when fed veliger-rich diets, than diets with low veliger densities. Mussel larvae have been reported to feed on particles 1–15 µm in size, as well as on dissolved organic carbon, at clearance rates ~ 10 to > 400 µL/veliger/day. Their competitive impact on other filter-feeding organisms can potentially be significant, but data at hand suggest that usually it is minor.