Limpets lunch on chalk cliffs

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Sussex loses more land to the sea each year than it gains. Every year, millions of pounds are spent on sea defences in an attempt to prevent flooding and coastal erosion: in 1999 the government announced a £30 million project to safeguard the cliffs at Beachy Head after large chunks of chalk fell into the English Channel.

Storms and rising sea levels (which are believed to be caused by global warming) are commonly held to be responsible. But research by Claire Andrews, a DPhil student in CPES, points the finger at gastropods such as piddocks and polydora worms - and, in particular, at tiny but hungry limpets (Patella vulgata), who are nibbling away the soft chalk rocks at Cuckmere Haven, Birling Gap and Saltdean. As the limpets graze the rocks eating algae, they also eat the chalk and hollow out places to rest between tides.

Claire was following up on the work of an obscure Victorian scientist, Hawkshore, who calculated that limpets were reducing the height of the foreshore at Dover by up to 1.5 mm a year. Nobody believed him, but more than a century later he seems to have been vindicated by Claire's findings.

Over three years, she measured the amount of calcium carbonate (i.e. chalk) excreted by limpets at three research sites in Sussex, where they live in colonies on the shore platforms that extend from the base of the cliffs. Claire then calculated that up to 30 per cent of the natural erosion of the cliffs (1.3 mm a year in an area of dense limpet population) is caused not by wind and weather but by the limpets.

Dr Rendell Williams of CPES presented Claire's findings to the annual conference of the Royal Geographical Society and the Institute of British Geographers, which Sussex hosted last week on campus.

He said of Claire's work: "It was a very successful pioneer study. One always thinks it is waves, wind and storms which cause the greatest damage. However, where these limpets are found in large quantities they can be really destructive, moving across the chalk like mini-cows grazing away the green film on the rock."

The findings have potential implications for government strategies on coastal defences. Engineers have previously assumed that chalk provided sure foundations for concrete defences, but Brighton & Hove Council warned only last month that it needs millions of pounds to rebuild the sea wall between the Marina and Ovingdean, which is crumbling despite being only 10 years old. "The engineering assumptions about the durability of soft rocks as foundations for sea defences will have to be revised", said Rendell. "With other destructive chalk borers like piddocks and polydora worms, the limpets are making a significant difference. "

A spokeswoman from the Environment Agency said that although the research was unlikely to change sea-defence strategy, the Agency would be looking at Claire's findings in more detail.