Some Irish moss on P.E.I. is still harvested with horses. (Tignish Irish Moss Festival)

This year's Irish moss harvest on P.E.I. has been abysmal, with about five per cent of what was harvested a decade ago being raked up.

The seaweed is a source of carrageenan, a thickening agent used in food processing. Ronnie Costain, one of three seaweed buyers in western P.E.I., said 10 years ago rakers would have harvested a couple of millions of pounds of Irish moss on the west coast by now. This year, Costain says it's been 100,000 pounds (40,000 kg).

Costain said if things don't improve he'll have to close early. He used to employ up to 12 workers for four months. This year, Costain worries it'll only be 5 weeks.

"It's having quite an impact," he said.

"Especially now when mackerel and herring, there's been none of them for a couple of years. So really all the fishermen have to fall back on is lobsters, where they used to make maybe a third of their income from Irish moss."

One of the Island's three buyers has not opened yet, and is waiting to see if the harvest will improve.

Costain says the problem is an invasive seaweed, called fucellaria, which is choking out the Irish moss beds. There is a market for fucellaria as well, but it goes for just six cents a pound where Irish moss is worth twice that.