The Irish moss harvest is at about five per cent of what it was 10 years ago. (CBC)

There is no single reason for a devastating crash in P.E.I.'s Irish moss harvest, says a marine biologist.

Irish moss, a source of carrageenan, a thickening agent used in food, was not long ago a major player in the economy of western P.E.I.  But it has been in steady decline over the last decade, and this year the harvest is at about five per cent of what it was 10 years ago.

One processor of the moss has blamed the practice of raking it off the sea bottom. Traditionally moss harvesters gather what has broken off and floated to shore. Marine biologist Irene Novaczek said raking is a factor, but it is not the only one.

"The primary reason for the long term decline in the Irish moss beds is damage done by raking, but more recently there has been a doubling in our rates of coastal erosion," said Novaczek.

"What gets clawed off the shore, all that dirt has to go somewhere, and whole areas of bottom that used to be moss beds or kelp beds are now covered in this dirt."

Colin MacIsaac, area chief of resource management for the Department of Fisheries and Oceans, said he has heard the concern over raking, but there is not a clear request from the industry to research it.

"If there's an interest in revisiting science questions with the respect to the harvest of Irish moss, we'd be more than happy to entertain ideas to look into that," said MacIsaac.

"We'll work with the industry and all stakeholders involved to try to accommodate a request."

The industry is not united behind the concern over raking. While one processor is expressing concern and refuses to purchase raked moss, another believes raking simply collects moss that might otherwise drift out to sea.  He believes erosion is the main factor in the dwindling harvest.