Monitoring of coastline to be stepped up for limpet shellfish

Scientists are stepping up their monitoring of the Irish coastline for a limpet shellfish which can be a menacing presence along shorelines. Its spread throughout northern Europe is causing growing concern.

The slipper limpet, a small shellfish which frequently forms a chain that looks something like a clenched fist, came to Europe from Long Island Sound attached to oysters more than 100 years ago. It often appears where there are oyster beds. They move from place to place on the hulls of ships, as indicated by their occurrence in the vicinity of ports.

Shells from the slipper limpet (crepidula fornicata) have been found along the west coast, and there may have been a population at one time in Clew Bay, possibly as a result of being imported with oysters from France. They have also been found in Tralee Bay, Kilmakilloge harbour and Dublin Bay over the past 50 years.

Cold frosts during the Irish winters of 1962 and 1963 may have started their decline in those years. There is evidence, however, that they may be on the increase again. Despite their fascinating lifestyle, there is no suitable use for them and they do not taste particularly nice. They attach, one above the other, to form a chain.

These chains provide each individual with the opportunity of having sex, firstly as a male and then as a female. Females have males that climb on to their backs and remain there. These males in time become females and a male may then climb on its back, and so the chain is formed. But they can radically change sea-bottom sediments, smothering many sea animals and stealing the food of oysters, clams and mussels.

In northern France it is estimated that the population may exceed one million tonnes. Their shells in some areas are so dense that they completely cover the sea bed.

Should you find slipper limpets, please contact: Dr Dan Minchin, Marine Institute, Fisheries Research Centre, Abbotstown, Dublin 15. Tel: (01) 821-0111. Email: dminchin@frc.ie