Molluscs form one of the largest groups within the animal kingdom at around 93,000 species, of which 5,000 are found in freshwater. As part of the SRLI project, we are currently finalizing the assessment process for 1,500 species of freshwater molluscs, in collaboration with the IUCN SSC Mollusc Specialist Group.
Freshwater molluscs fall into the classes Bivalvia (mussels and clams), which are suspension feeders, and Gastropoda (snails), which are generally surface grazers. As such, freshwater molluscs provide a variety of important services to freshwater systems, such as assistance in nutrient cycling, decomposition, and water filtration. They often comprise a large portion of the biomass within freshwater ecosystems, and hence feature prominently in aquatic food webs.
Preliminary results suggest that worldwide, an estimated 29% of freshwater mollusc species are threatened with extinction. This would mean that freshwater molluscs are among the more threatened species groups within our SRLI assessments. Threat levels are likely to be highly variable amongst regions, with threat levels expected to be particularly high in Europe and North America, corroborating the findings of a recent assessment of all European freshwater molluscs ( 44% of species threatened ). Damming and modification of rivers, sedimentation, pollution and invasive species all contribute towards these alarming levels of threat. Full results will be available in 2013.