Mary Seddon is the Chair of the IUCN SSC Mollusc Specialist Group. Mary is one of the contributors of the European Red List of Freshwater Molluscs.
The assessment to which you contributed revealed that freshwater molluscs are the most threatened group, among those considered, in Europe. Why are molluscs in such a bad conservation status?
Freshwater molluscs in Europe have very high levels of endemism, as the Mediterranean region is one of the top 15 hotspots in the world for this group of organisms. Many of the very range restricted species are found in small freshwater springs or the groundwater systems that feed these springs. However these sources of water are also under increasing pressure from exploitation for domestic supplies as well as irrigation to support agriculture and take-off for industrial processes. As such the changes in flow regime, pollution and alteration of the habitats impact the species that are only found in these water sources, leading to loss of the springs and depletion of the groundwater sources, hence populations of these small freshwater snails are lost. In contrast the larger freshwater mussels are found in our big river systems, and these species are threatened by pollution of the rivers, often impacting the juveniles more than the adults, and the decline of the fish that are vital to the continued life-cycle have also lead to a decline on the populations of these long-lived species.
The Freshwater Pearl Mussel (Margaritifera margaritifera) is probably the most long-lived species of freshwater molluscs, as individuals of over 150 years are known in some populations in Scandinavia. There are many populations in Europe where there has been nil recruitment for over 30 years, and this is due to the high pollution levels, increased sediment and algal content on the riverbeds and decline in the fish-hosts. Hence the EU27 and European assessments of this species as Critically Endangered, whereas the Global assessment (including populations in Russia, USA and Canada) remains as Endangered.
Like any other species, molluscs play their fundamental role for the functioning of their ecosystem and hence of the whole natural world! What is exactly their function and why is it so important to conserve them?
Freshwater molluscs provide the breakdown of nutrients in the ecosystem. Freshwater bivalves are filter-feeders and provide the vital water cleaning services in our rivers. A high number of mussels on the river-bed are considered beneficial to water quality. In contrast, small freshwater gastropods are detrivores, feeding on algae and vegetation, and are often part of the food-chain, being taken by other animals such as fish, birds, mammals.
What would you suggest as a solution to try and improve the status of these little creatures?
The implementation of the EU Water Framework Directive should provide some benefits to the fauna, in that levels of pollution have been reducing within Europe, although more recently the biggest problems lie in the level of use of fertilisers, leading to high nitrate and phosphate levels in our local water sources. The implementation of "improvements" to off-take points for water supplies in southern Europe, especially in the Mediterranean zone, has led to a marked decline to spring-snail populations which often live in the marginal vegetation on the banks of these springs and pools, and these zones are replaced by 'concrete tanks', and these can be minimised through better communication about the presence of the species in these water sources, which is one outcome of this project, as many of these species have been mapped.
Continued expansion of the Natura 2000 reserves and inclusion on full water catchment management practices would also benefit the freshwater molluscs.
Spengler’s Freshwater Mussel (Margaritifera auricularia), once widespread, is now restricted to France and Spain. Currently listed as Critically Endangered, it was considered to be nearly extinct in the 1980s and its status is improving. What measures have been taken which could apply also to other species in this group?
There are many successful conservation breeding programmes for various large freshwater mussels operating in Europe. However, it takes time to reestablish favourable river conditions, in our freshwater ecosystems, as these species are long-lived, and as such recovery of these species requires knowledge of suitable fish hosts, assistance during the reproduction phase and establishing small areas are suitable for juvenile survival after re-introduction with river beds that remain undisturbed by any sort of activity (e.g. animals, heavy plant machine, dredging). This has been successfully implemented in various LIFE projects, and further work is continuing to ensure the long term health of our river systems.
Smaller projects aimed at rehabilitating freshwater springs are in their trial phase in Andalucia, Spain and these methods offer an interesting potential solution across the Mediterranean zone.