Seaweed: it’s trending with foodies as the “new kale” and showing up in soups, salads, and wraps. Eager home gardeners select organic seaweed mulches and potting soils, while farms and livestock producers use seaweed extracts to increase yield. Global seaweed aquaculture has grown 930 percent since 1980, often replacing income from declining wild-caught fisheries.
Is this rapid increase in seaweed use sustainable?
In her 1955 book The Edge of the Sea, Rachel Carson described Maine’s intertidal seaweed beds of rockweed (Ascophyllum nodosum) as an underwater forest. These forests grow between high and low tide levels on the shore and can be 150 years old. Rockweed provides food and shelter for over 100 coastal species, including commercially important lobster and cod, and supports iconic coastal wildlife such as sandpipers, eider ducks, and great blue herons. It protects our shorelines from wave surge and erosion during increasingly common large storms. Even after death, rockweed supplies coastal ecosystems: its decay produces detritus that returns to the ocean and feeds our productive marine bays and estuaries.
Taking 1.4 billion pounds of rockweed annually from the North Atlantic for garden and agricultural products alters habitat for those marine species that depend on rockweed. Annual cutting means that rockweed forests can’t return to their original height. Because rockweed in colder waters recovers slowly from cutting, and because these cold-water ecosystems have high biodiversity, habitat recovery is actually slowest in those areas we want most to protect.
Rockweed is listed as a high-ranking species—higher than salmon and right whales—in the United States and Canada, a high-priority species in Northern Ireland, and a high-sensitivity species in the UK, yet rockweed “take” is increasing. This contradiction makes the rules governing harvest nonsensical. Three state agencies in Maine have an interest in rockweed. The Department of Environmental Protection regulates altering rockweed beds as coastal wetlands through the Natural Resources Protection Act (NRPA), but the NRPA rules are waived for anyone holding a seaweed license from its sister agency, the Department of Marine Resources. The Department of Inland Fisheries and Wildlife has mapped seaweed communities, including rockweed, as significant wildlife habitat, but these ecologically important habitats on the coast are not yet protected in state marine regulations. The National Oceanic and Atmospheric Administration defines Essential Fish Habitat to include rockweed, but there is no limit to the amount of rockweed that can be taken from the vast majority of the Maine coastline, including coastal islands and other areas protected by land trusts, conservation groups, wildlife managers, and local towns.
With ACSF seed funding, I have been studying the impacts of cutting Maine rockweed. It was clear early on that creating a standard for “sustainable” rockweed harvests had to include an ecological definition of sustainability, one that accounts for the multiple species that depend on rockweed, rather than the simpler and more traditional “maximum sustainable yield” definition of sustainability. The latter asks only how much biomass of one species can be harvested in order to leave sufficient biomass for the next harvest. Moving to an ecological approach to seaweed harvest sustainability parallels the current effort in fisheries management to reject a single-species approach and move to ecosystem-based fisheries management. The ecological approach to seaweed harvests also protects coastal jobs that depend on habitat health.
Sustainability of seaweed harvests is in the news, whether it is machine harvests of rockweed, sugar kelp aquaculture and hand-harvest of edible seaweeds in Maine, or global seaweed aquaculture. The annual Maine Seaweed Festival was canceled this year over concerns about sustainable harvest practices. The UN has just published a policy paper warning of ecological consequences if the booming global seaweed aquaculture industry does not take precautions. A legal case that will enable more protection for Maine rockweed is making its way through the courts.
Buying a bag of mulch containing Ascophyllum in Ithaca can impact a coastal ecosystem in Maine. To support recovery of marine ecosystems in trouble, we urgently need to adopt standards for wild seaweed harvests that are ecologically sustainable.
Learn more about efforts to protect rockweed habitat and view underwater films by Robin Hadlock Seeley and David O. Brown at rockweedcoalition.org.