Development is planned for St Aubin's harbour in Jersey
A study group has called for the redevelopment of part of St Aubin's Harbour in Jersey to be shelved.
The Société Jersiaise described the plans to extend a harbour wall near the Boat House as "unnecessary".
The group is worried the move would threaten the habitat of two species of rare molluscs which live in the walls.
But Senator Alan Maclean, the economic development minister, said: "Wildlife is an important aspect of developments, the wall however is a safety issue."
An environmental impact assessment drawn up by consultants for Jersey Harbours showed the area was in need of urgent work.
Nick Joualt, from the marine biology section of the Société Jersiaise, said: "They're actually going to remove a very important habitat for two species, and this is of international importance.
"If we lose this habitat we lose the species and it's one of the only places in the UK where we find these two red-listed species together.
"The residents are concerned as well and we've got a week to comment."
Senator Maclean told BBC News: "I fully understand the concerns, and that's the very reason this is going out for consultation.
"We have been monitoring for some time the condition of the north pier.
"We believe the problem is not one of neglect, but dredging work has done some damage to the foundations.
"Technically the wall has failed and there is a risk of severe deterioration should there be, for example, further impact like a vessel going into it or very heavy storms."
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