Freshwater Mussel Ecology and Conservation

Scientists in the Department of Zoology here at the University of Cambridge are investigating the life-cycles, ecology and conservation of freshwater mussels.

Aquatic Ecology Research Group webpage

Glochidia larvae
SEM images of glochidial larvae, open (top) and clasped to a fish scale (bottom).

Freshwater mussel lifecycle
Freshwater mussels belonging to the order Unionoida (also called naiads) are large bivalves which live in the sediment of lakes and rivers around the world. The lifecycle of freshwater mussels is unique among bivalves: larvae (called glochidia) are released into the water where they attach to the gills and fins of fish. The glochidia remain attached to the fish for between one week and several months, developing into juvenile mussels before detaching from the fish host and dropping off into the sediment to grow. In this way the mussels can be
transported upstream by the host fish.

Some mussels in North America have evolved elaborate modifications of the mantle tissue that protrude from the shell and act as a lure to attract host fish and increase the likelihood of successful mussel attachment.

Epioblasma haysiana, University Museum of Zoology, Cambridge
Acornshell, Epioblasma haysiana , presumed extinct.

Freshwater Mussel conservation
Freshwater mussels are some of the most threatened animals in the world. Over half of the 300 mussel species in North America are classified as threatened with extinction and a further 37 species are already presumed extinct, including the Coosa elktoe ( Alasmidonta mccordi ), Sugarspoon ( Epioblasma arcaeformis ), Acornshell ( Epioblasma haysiana ).

British freshwater mussels, University Museum of Zoology, Cambridge
Threatened British freshwater mussels. Left: Depressed River Mussel ( Pseudanodonta complanata ). Right: Freshwater Pearl Mussel ( Margaritifera margaritifera ).

The UK is home to 6 species of freshwater mussel of which two, the depressed river mussel ( Pseudanodonta complanata ) and the pearl mussel ( Margaritifera margaritifera ), have experienced significant declines during the 20th century. Both are now included on a list of the most threatened UK species drawn up as part of the Government’s Biodiversity Action Plan.

Pearl mussels have been exploited for centuries for their natural ability to produce pearls. This, plus their sensitivity to water pollution, dam construction, dredging of river beds and declines in host fish (salmon and trout), threatens their survival. Globally there are thought to be only 150 rivers containing breeding populations of freshwater pearl mussels, and approximately half of those rivers are in Scotland. These globally important strongholds for freshwater pearl mussels are protected by law under the Wildlife and Countryside Act.

Filter feeding bivalves
Bivalves take up particles, such as algae and bacteria, from the water and help maintain clean water in aquatic habitats around the world. It has been calculated that one adult mussel can filter as much as 40L of water per day. In addition, the shells of bivalves help stabilise sediment at the bottom of lakes and rivers and provide shelter for small animals living in these habitats. Researchers in the Zoology Department are looking at ways of using this natural filtration by bivalves to help clean water in Chinese lakes and UK reservoirs, and are working to highlight the importance of bivalves by calculating a value for the services they provide to humans.

Invasive bivalves
Invasive species are animals and plants which are living outside their natural habitat and causing problems for native wildlife.

Zebra mussels, University Museum of Zoology, Cambridge
Zebra mussels, Dreissena polymorpha

Zebra mussels ( Dreissena polymorpha ) are freshwater bivalves that were introduced to the UK in about 1824. Unlike native freshwater mussels, which live partly buried into the sediment at the bottom of rivers and lakes, zebra mussels attach to hard surfaces using their byssus. The shells of native freshwater mussels make an ideal surface for zebra mussels to attach themselves to, and in doing so they can restrict the extent to which the native bivalves are able to filter feed.

Zebra mussels can also cause problems for humans by attaching to the inside of pipes at water treatment works and inside the cooling systems of power stations. In the United States, where they have also been introduced, the lost revenue from zebra mussel infestations has been estimated to cost as much as $2-3 billion per year.

The traditional strategy for controlling zebra mussels has been to add chlorine to the water where they are living. However, the mussels are able to detect chlorine in the water and close their shells, so the dosing must be continued for up to 3 weeks when they will be forced to open their shells and resume filter feeding. Regular addition of large amounts of chlorine to the water is undesirable as it can harm other animals living there.

Researchers at Cambridge University have developed a method to help overcome this problem: by coating a zebra mussel toxin (potassium chloride) in a fatty, nutritious layer to form microscopic “BioBullets”. The zebra mussels are tricked by the harmless coating to take the BioBullets up from the water as they filter feed. As this layer dissolves inside the mussel they are killed by the toxin contained inside the BioBullet. By encapsulating the toxin in this way, much lower dosages are needed to remove zebra mussels and the amount of chlorine entering the water can be reduced.

Last updated: 29 March 2011