Proposals to close down scallop beds that generate £4m in income a year are being fought by local fishermen.
English Nature has asked the government to shut 60 square miles of beds off the shore, between Beer Head in Devon and West Bay in Dorset.
About 70 fishermen from Dorset, Devon and Cornwall have formed the Southwest Inshore Scallopers Association (Swisa) to fight any closure plans.
English Nature claims damage is being done to a site of national importance.
The beds are home to protected pink sea fans, ross corals and sunset corals.
English Nature said there had been a 200% increase in fishing on the beds.
Chris Davis, a maritime conservation officer, said the damage caused by scalloping to the low lying, mudstone reefs could take the ecosystem up to 10 years to recover from.
Jim Portus, Swisa's secretary, said the body had been formed by the fishermen because of the "shock news" that English Nature had asked Fisheries Minister Ben Bradshaw to apply his emergency powers to close the beds.
Mr Portus said he had already written to the government expressing the concerns of the fishermen.
"What is most interesting is that scallop fishing has been conducted sometimes very heavily in this area since the end of the Second World War, and yet the marine biodiversity of the seabed puts it today in the top five sites around the UK," said Mr Portus.
"The fishermen argue that their activity evidently does more good than harm.
"It is clear that despite all the human and natural action on the seabed in this area the density and variety of marine life remains relatively constant and healthy.
"The fishermen are determined to fight for the continuation of their livelihoods."
Mr Davis said "all scientific evidence" contradicted the fishermen's claim that their activities did more good than harm.
He added: "The reefs in Lyme Bay are a fraction of the quality and area that they used to be.
"There is evidence that scallop-dredging has resulted in destruction, for example the disappearance of a reef off Exmouth over the past 15 years.
"The request for a stop order is a position that we have been forced into."