MACHIAS, Maine — Opposition to harvesting seaweed continues to grow among owners of Washington County shoreline property from Eastport to Steuben.

At last count the “Rockweed Registry” maintained by the Downeast Coastal Conservancy included 532 oceanfront properties in 12 communities, most fronting Cobscook Bay. Included are parcels whose owners who do not want commercial seaweed harvesters to cut rockweed in tidal areas that front their shorelines. Rockweed harvesting bans also extend to conservation area shorelines and those owned by local, state and federal governmental entities.

Rockweed makes up at least 90 percent of total seaweed landings in Maine. The other 10 percent includes red, green and brown algae, such as dulse; nori; Irish sea moss; sea lettuce and kelp. In 2011, harvesters cut an estimated 8.8 million pounds of rockweed in Maine that was shipped to processors to be dried, ground and sold as a food supplement and as a component of fertilizer and animal feed. Ten years earlier, the rockweed harvest was 4.7 million pounds.

According to the Maine Department of Marine Resources, The 2010 Cobscook Bay rockweed harvest totaled 106,313 pounds out of an estimated baywide biomass of 111 million pounds. While the price paid at the dock is minimal, the DMR notes that only a small fraction of the harvest is sold fresh or raw. The majority of the harvest is processed into wholesale and retail products with a total estimated value of $20 million per year. That makes rockweed, the DMR says, “one of Maine’s most valuable marine resources.”

Until the Rockweed Registry emerged, Washington County’s Cobscook Bay had been the epicenter of commercial harvesting in Maine of rockweed and other species of seaweed that grow along the North Atlantic shoreline in the intertidal zone, the area that is above water at low tide and under water at high tide. Given the jagged continuum of inlets and bays between Calais and Kittery, Maine’s shoreline includes more than 3,000 miles of intertidal zone that is thick with rockweed.

Since 2000 an organized effort has been underway to protect seaweed from commercial harvesters. That cause is now being coordinated by an organization called the Rockweed Coalition. It claims Cobscook Bay has the highest biodiversity of any Eastern Seaboard area in the United States north of the tropics. Included among its long list of concerns about the environmental impact of harvesting rockweed is the extent to which it disturbs lobster nursery habitat in the intertidal zone.

“Rockweed harvesting goes back thousands of years,” says Peter Thayer, a marine resources scientist with the Maine Department of Marine Resources. “The Indians used it for fertilizer. Today, the bulk of the harvest revs up toward the end of summer and fall, and then picks back up in the spring, with most of the harvest trucked to Canada for processing. Among a number of Maine harvesters there is resistance due to a Maine resource being trucked to Canada for processing.”

In 2009, the Maine Legislature approved the Cobscook Bay Rockweed Management Area statute, which requires pre-harvest plans from would-be harvesters and divides the bay into 36 assigned harvest sectors. It also caps the harvest within each sector at 17 percent of the total estimated biomass and establishes a surcharge of $1.50 per wet ton landed. Those funds are used to support seaweed research, management and enforcement.

Conservationists liken the shoreline areas where rockweed thrives to an old-growth “underwater forest” that provides both habitat and sustenance to as many as 150 species of seabirds, shorebirds, ducks, fish and invertebrates, including some species important to commercial fishing. How either hand-harvesting or mechanized cutting of rockweed affects that biosystem remains largely a scientific unknown, given that regrowth after cutting takes years.

Among those studying the issue is Robin Hadlock Seeley, a Rockweed Coalition activist and a marine ecologist who is a senior research associate at New York’s Cornell University. She has been studying the marine ecology of Cobscook Bay for 30 years, doing research during her summer stays at the Shoals Marine Laboratory facility on Maine’s Appledore Island, which is southeast of Kittery.

Seeley says only more research will determine the validity of the claim by harvesters and processors that rockweed is a sustainable source of nutritious biomass.

“To determine whether rockweed cutting is ‘sustainable’ will require data on the long-term and ecosystem-wide impacts of cutting rockweed,” Seeley said in a recent paper published by the New York Academy of Sciences. “Once a sustainable level of cutting is determined, strict regulation by resource managers will be required to protect rockweed habitat. Until sustainable levels of cutting and appropriate regulations are identified, commercial-scale rockweed cutting presents a risk to coastal ecosystems and the human communities that depend on those ecosystems.”

Seeley told the Bangor Daily News in a recent telephone interview that the two overarching questions related to harvesting rockweed — pertaining to its sustainability and legality — have yet to be answered.

The rockweed section of the Maine Department of Marine Resources’ website includes this statement: “In Maine, private property ownership typically extends to the low tide line. By law, people may access a privately-owned intertidal zone only for ‘fishing, fowling and navigation.’ Whether or not rockweed is considered a public resource and harvesting is considered ‘fishing’ from a modern perspective has yet to be determined by the courts.”

Seeley notes that, while the legal right of the public to harvest shellfish, wrinkles and worms from intertidal zones that front private property is well established in Maine law, there is no established right to harvest seaweed.

“Rockweed harvesting just goes on and on and on and on,” Seeley said. “The state is handing out licenses on one hand and on its website reminding people that it may not be legal. I do not understand how you allow habitat that supports 150 species to be disturbed without knowing if it’s sustainable or legal.”

Seeley said her current research is focusing on how machine harvesting compares with hand-rake harvesting in terms of effect on rockweed plants and the habitat in which they thrive.

Alan Brooks, stewardship director for the Machias-based Downeast Coastal Conservancy, said the largest firm harvesting rockweed in Maine — Nova Scotia-based Acadian Seaplants Ltd. — has been responsive to requests to avoid harvesting along shorelines listed on the Rockweed Registry. Whether other, smaller harvesters are following Acadian Seaplants’ lead, he said, remains an unknown.

“A number of other operators have come into Cobscook Bay, using mechanical harvesters,” Brooks said. “That opens areas up to potentially more exploitation if the operators are not self-regulating.

“It’s unclear whether these new operators are respecting the registry or other conservation plans. It’s a different group of actors. Rather than one operation, it’s five different operations. It’s difficult to monitor. With mechanical harvesting they can be in and out before you even know they are there.”

Acadian Seaplants spokesperson Linda Theriault said the company “intends to conduct its sustainable rockweed fishery harvest in Cobscook Bay this year” and will respect the requests of shoreline property owners listed on the Rockweed Registry. She said the company also intends to continue harvesting rockweed in the Jonesport area, as it has for the last 10 years.

Larch Hanson of Steuben has been immersed in rockweed harvesting for 40 years, both as a small-scale harvester and a producer of rockweed byproducts that he sells as animal feed supplements and garden fertilizer. He said Thursday that Acadian Seaplants’ harvesting operations have now extended into Gouldsboro Bay, which fronts his property. He’s not amused.

“They’ve been harvesting in front of my cove, and I’m not happy about it,” he said. “They are not creating any goodwill with people who live on Gouldsboro Bay. Upland owners are concerned about loss of biomass creating beach erosion as it leads to more wind and more waves. These harvesters have no people skills and are perceived as roving pirates of the sea.”

Hanson said he plans to initiate a rockweed registry for Gouldsboro Bay and to organize a coalition of Maine seaweed harvesters. He advocates a three-year apprenticeship for seaweed harvesters.

“The first year they would go out and harvest,” he said. “The second year they would go back and study the impact of their harvest. The third year they would have an opportunity to apply what they’ve learned in the first two years.”