A government move to allow scallop dredging in one of Scotland’s most precious bays will wreck the seabed, damage wildlife and could be illegal, environmental groups have warned.

Scottish ministers have agreed to allow fishing boats to dredge almost a third of Luce Bay on the far southwestern tip of Galloway for four months every year. The bay is legally protected as a conservation area because of its endangered purple-pink maerl beds (a type of coral), brittlestars (a type of starfish) and hundreds of other marine species.

A coalition of seven major conservation groups have joined with an angling network to protest to the government’s Marine Scotland agency over a decision to permit scallop dredging in the Luce Bay and Sands Special Area of Conservation (SAC) on the edge of the Solway Firth.

In a joint letter, they expressed concern that the government’s approach will result in the natural features special to the bay being harmed. “Fisheries management measures for Luce Bay will expose areas of seabed to potential damage by scallop dredging at certain times of year,” they wrote.

They questioned whether the government’s scientific evidence was sufficient to ensure that no damage would occur. There was evidence of an underwater reef – a potentially rich habitat for marine wildlife - to the west of the bay that could be at risk, they said.

The wildlife groups were also worried about the fate of sugar kelp, red seaweeds and sands home to numerous molluscs. Dredging should be totally prohibited in all the conservation area, they argued.

Members of the umbrella group, Scottish Environment Link, raised concerns last year that allowing dredging in part of Luce Bay risked the site failing to meet its conservation aims.

Calum Duncan, the convenor of Link’s marine group, said: “The overall integrity of Luce Bay SAC – the degree to which the complex mosaic of habitats are suitably protected and provide mutual resilience to change – remains at risk, particularly where scallop dredging is still allowed over sensitive habitats.”

The groups signing the joint letter included the Marine Conservation Society, the National Trust for Scotland, the Royal Society for the Protection of Birds in Scotland, the Scottish Wildlife Trust, Whale & Dolphin Conservation and WWF Scotland.

They were backed by the Scottish Sea Angling Conservation Network, which believes that dredging will harm the ecosystem and fail to comply with the European Habitats Directive. “Sea angling, thought to be worth millions to the local economy, is in decline and the government has missed out on an ideal opportunity to help rebuild the fish stocks,” said the network’s trustee, Ian Burrett.

Fishing organisations, however, pointed out that Scottish vessels landed around £30 million worth of scallops every year. “The sector is very important to our fragile coastal communities,” said Bertie Armstrong, chief executive of the Scottish Fishermen’s Federation.

“These management measures in Luce Bay are the agreed end-result of a much discussed and lengthy consultation process involving all stakeholders, including environmentalists. They meet the statutory requirements of protecting valuable marine features whilst at the same time supporting sustainable economic activity.”

The arrangements were a “satisfactory compromise”, Armstrong told the Sunday Herald. “Scottish fishermen support marine protected areas provided they are designated on an evidential basis,” he said.

“Zonal management, as applied in the case of Luce Bay, will ensure both the protection of the marine environment and of fishermen’s livelihoods.”

Steven Girgan, skipper of the scallop vessel, Susan Bird, fishing out of Kirkcudbright, agreed. The reef that wildlife groups talked about had proved “elusive” and was yet to be discovered, he said.

Conservation areas “are not designed to ban sustainable fishing activity needlessly,” he argued. “If managed correctly their conservation objectives can be met whilst allowing for important fishing activity to continue.”

According to the Scottish Government, scallop dredging is permitted in three zones within the Luce Bay SAC during January, February, November and December each year. “The Scottish Government is of the view that the management of Luce Bay maintains the integrity of the site,” said a spokeswoman.