Take a 90-second trip to the underwater world of Maine’s rockweed

By John Boit

The Blue Hill Peninsula Rockweed Forum recently sent The Rising Tide a video showcasing rockweed, the ubiquitous algae that looks like a plant and grows up and down the coast of Maine.

The Rockweed Forum was founded by Allison Snow of Brooksville and David Porter of Brooklin, both retired botany professors. The video includes photos and underwater video shot by Bill Snow, Allison’s Snow’s brother, who is a frequent visitor to Maine, as well as photographs by Richard Leighton of Brooklin.

Rockweed has been used as fertilizer for centuries. Today, rockweed faces pressures from industrial harvesting. The practice raises a host of questions, according to the Rockweed Forum, including how much of the algae can be sustainably harvested, as well as landowner property rights. Rockweed is found in the intertidal zone which, according to centuries of Maine law, belongs to the land-based property owner, although the public may use the area for “fishing, fowling and navigation”--in other words, for activities such as clamming, duck hunting and boating.

That definition has at times been challenged by harvesters, most notably Canadian companies that pay local harvesters to send the algae across the Maine border for processing for the fertilizer, food additives and cosmetics industries. Acadian Seaplants, a large Canadian harvester, halted operations in Maine earlier this year, citing high tariffs and transportation costs.

The local forum says on its website that “at high tide, the floating fronds create an underwater forest where small fish find food and shelter. At low tide, exposed rockweed plants are draped over each other, protecting other marine species from harsh conditions…Consequently, intensive harvesting has the potential to convert a foundational rockweed ‘forest’ into a motley collection of dense ‘shrubs.’”

In a letter to the Island Institute in 2023, the Maine Seaweed Council said that harvesting only affects about one percent of the rockweed in Maine. The letter said that “rockweed regenerates at a rapid rate, fully recovering its biomass within a year of harvest.”

Snow and Porter from the Blue Hill Peninsula Rockweed Forum recently disputed such findings in a letter to The Rising Tide. They cited their own research in a newly published paper that “concluded that key experimental studies of rockweed’s recovery from harvesting often lacked scientific rigor and none have focused on the long-term effects of repeated harvesting.”

More information may be found on the website of the Blue Hill Peninsula Rockweed Forum as well as on the website of the Maine Seaweed Council.

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