Oyster fishermen in Cornwall say their industry is under threat from another shellfish.
Slipper limpets have thrived in the warm summer weather
The slipper limpet competes with oysters for space and food and is now breeding in the Fal estuary in huge numbers.
Fal fishermen say they are dredging four times more slipper limpets than oysters.
They are now trying to find ways of clearing the limpets from the valuable oyster beds.
The warm summer weather has helped the oysters to grow to good sizes, but the limpets have also thrived.
Oyster fisherman Colin Frost said: "We have got a problem with slipper limpets. There are thousands of them.
"They grow on the back of each other and they can increase 10-fold in a year. They are a real pest."
Dr Clive Askew, a marine biologist with the Shellfish Association of Great Britain, said slipper limpets liked to settle on similar surfaces to oysters.
Fishermen are three weeks into the annual oyster season
"They will settle on top of oysters. The problem is they settle earlier in the year than native oysters do," he said.
"By the time oyster larvae come to settle down, much of the settlement surface has already been taken by slipper limpets."
In France, oyster fisheries have been closed down by the limpets, whose Latin name is Crepidula fornicata.
The industry in the Fal estuary is attempting to get Objective One funding to create a market for slipper limpet meat.
The idea is to give the fast-breeding invaders a landing value to encourage fishermen to bring them ashore and so clear the oyster beds.