Are snails the "canaries" of biodiversity change in streams?
Science Centres: Aquatic Biodiversity and Biosecurity
An unnamed hydrobiid species collected from a stream near Waitomo (photo: M. Haase).
Mollusca make up about 7% of all living fauna and flora and are the second largest phylum in the animal kingdom. In freshwater ecosystems there are two classes of molluscs – bivalves and gastropods. The Hydrobiidae from the gastropod group are especially diverse with more than 1000 species currently recognised. Recent overseas research has uncovered a remarkable biodiversity and level of endemicity in Hydrobiidae, particularly in association with spring and headwater seepage habitats.
In New Zealand there are 17 described species of Hydrobiidae. The most common species is the ubiquitous Potamopyrgus antipodarum, which has successfully invaded a wide range of habitats in Europe, North America, and Australia. However, the undescribed hydrobiid fauna of New Zealand is believed to be much richer and may comprise more than 50 species.
NIWA has recently begun to unravel the biosystematics of freshwater Hydrobiidae, with particular emphasis on spring and seepage habitats in northern New Zealand, as part of its freshwater biodiversity research. Identifying the range of endemic hydrobiid species present is important to our understanding of the ecological requirements of the different species and identifying important areas and habitats for their conservation. This research is being carried out by NIWA scientist Dr Martin Haase, a post-doctoral fellow with international experience in hydrobiid taxonomy, in collaboration with the Australian Museum, Landcare Research, and Te Papa.
Despite the hardy nature of some species (e.g., Potamopyrgus), molluscs are very sensitive to environmental change and are therefore prone to extinction. More than one-third of all known animal extinctions have been in this phylum, and 10% of these extinctions have occurred in fresh waters, mostly in rural and urban settings. Changes in water quality and habitat degradation (including siltation, the removal of shade, and flow regulation or cessation) can lead to changes in the composition of species in snail communities, and to the loss of biodiversity. Seepage habitats are particularly sensitive to land-use changes because of their susceptibility to desiccation and degradation. By increasing our understanding of the biodiversity of the hydrobiid fauna, and the ecological requirements of different species, we should be able to help provide early warnings of adverse environmental changes to freshwater habitats. With better taxonomic knowledge, snails may prove to be the “canaries” of biodiversity change in downstream ecosystems.