Molluscs


Image above by John Walters


Freshwater pearl mussel Margaritifera margaritifera - Critically endangered and declining

Although this mussel’s stronghold is in Scotland, the conservation of the species across its range is important. It survives in only ten rivers in England. The River Torridge in Devon supports the only sizeable population in southern England. Here about 2,000 individuals live between Hatherleigh and Great Torrington, the last full survey being in 2013 - it is hoped to repeat this in 2020. There is also a very small population (below 100 individuals) on the River Mole. The Devon populations are thought to have the same genetic provenance as those on the Iberian peninsula, unlike those found elsewhere in northern England and Scotland. Freshwater pearl mussels occupy clean, fast flowing streams and rivers. As larvae, they live in the oxygen-rich environment of salmon or trout gills. Individuals can live for over 120 years! However, in Devon in recent years no individuals under 50 years old have been found and they are not thought to have bred successfully since the 1960s. The Freshwater Pearl Mussel Project, led by the Devon Wildlife Trust, has been working with local landowners and others to improve water and habitat quality on the Torridge. The project has also successfully instigated a captive breeding programme with some success; juveniles have been put back into the Torridge, but they won’t be detectable for five years at least. The species is threatened by siltation or other damage to river gravels, by water pollution, and by illegal pearl fishing.
Map to show the Devon distribution of this species



Sandbowl snail Quickella arenaria - Vulnerable and internationally threatened

This small snail is known from only three locations in Great Britain: in Devon in slacks (hollows) between the sand dunes on Braunton Burrows and in Cumbria in base-rich flushes on Orton Gill and Crosby Gill. At Braunton Burrows it remains frequent but is at risk through vegetation succession reflecting a lack of grazing and from dune slacks drying out due to lowering of the water table or climate change. The Dynamic Dunescapes project, planned to start in autumn 2020, led by Plantlife working together with the Christie Estate, will include the scraping or lowering of eight to ten slacks at Braunton Burrows to create favourable conditions for plants like Water Germander (another Devon Special Species). This conservation work is likely to benefit the snail.

Further sources of information:

The Conchological Society of Great Britain and Ireland