← Back to Nature Notes

Nature Notes: Rockweed

Ed Robinson
March 20, 2017

In Shakespeare’s classic play, Romeo and Juliet, Juliet resists pressure to drop her lover from the hated Montegue family by arguing that “a rose by any other name would smell as sweet.” Her suggestion that names don’t matter would fall flat when we look at many edible marine species, including sea vegetables, since it is pretty important to know what you are eating. The name “rockweed” is commonly applied to a number of seaweeds, but here I am writing about a species known by the scientific name Ascophyllum nodosum (hereinafter abbreviated as AN). To add to the potential confusion, this plant is variously called Norwegian kelp, knotted kelp, knotted wrack, bladder wrack or egg wrack. Is that all clear now?

closeup of rockweed

Rockweed (Weisschr iStock photo)

I first became interested in AN when we moved to our home on Orr’s Island in 2007. Delighted to be living near the ocean, I spent time walking along the coast at low tide. In late summer, the intertidal area was covered in vegetation, including waves of a glossy green and brown plant with large bubbles at the end of its leaves. I had no idea what it was nor its role in the ocean ecosystem. My investigations showed that it is an important plant by any measure.

AN is found along North Atlantic shores, including the coastlines of Greenland, Iceland, and Norway to Portugal. The plant favors quieter, sheltered waters, and AN may dominate the intertidal zone with the right conditions. AN maintains its location thanks to a sturdy foot, known as a holdfast, that attaches to underwater rocks. This seaweed is a slow grower, about 0.5 percent daily, to a height of roughly six feet, with a life span of 10 to 15 years. Many factors affect the success of AN including salinity, nutrient pollution, wave action, temperature, and desiccation (excessive drying at low tide).

The egg-shaped bubbles that caught my eye are, in fact, air bladders and they serve to keep the fronds of the plant erect when submerged, presumably to allow sunlight to reach more of the plant and the seabed. When pinched, they yield with a little “pop.”

AN has long been harvested by people, and I was told that in years past, Harpswellians gathered mounds of the dried plant at the end of summer to use as a compost on their gardens, or to pile against the foundation of their houses for winter insulation. Many seaweeds are rich in nutrients such as nitrogen, calcium, potassium, magnesium, iodine and zinc, along with sugars, fats, vitamins, amino acids and proteins. This opens the door to a wide array of uses. Today you can find extracts of AN in seaweed meal for animal feed, protein snack bars, ice cream and textiles.

Today there is a growing industry for the harvest of AN and various other seaweeds, or sea vegetables as some now refer to them. It won’t surprise you to know that there are differences of opinion about the proper locations and rates of harvest among harvesters, environmentalists, ocean front landowners and government regulators. What some people see as a vital plant for protecting crustaceans and fish, others see as a renewable crop that can bring jobs and badly needed cash to the shores of Maine. Some researchers note that lush stands of AN provide high value habitat for over 100 marine species, including smaller seaweeds, snails, mussels, whelks, and periwinkles, which serve to feed a number of sea and shorebirds. Seaweeds are also effective at sequestering heavy metals that enter the ocean. While scientists know that seaweeds are remarkably adaptable and AN can recover from significant disturbances, no long term studies of harvested AN beds have been completed to date.

According to Maine Sea Grant, AN harvesting in Maine for commercial purposes began in the 1970’s. By the 1990’s, an industry association was formed: the Maine Seaweed Council. By the year 2000, concerns were being expressed about the potential impact of rising harvests, both by hand rake and mechanical cutters, so Maine’s Department of Marine Resources (DMR) mandated landings reporting each year, and limited cutting to at least 16 inches above the holdfast and the lowest lateral branches to promote regrowth. In 2009, the Cobscook Bay Rockweed Management Area was established to regulate harvesting across 36 assigned sectors, capping the AN harvest at 17 percent of each sector’s estimated biomass. A surcharge was established at $1.50 per wet ton landed to support seaweed research, management and enforcement. In 2014, DMR published its Fishery Management Plan for Rockweed. Click here for more information on the rules and management plan.

AN now makes up 95 percent of total seaweed landings in Maine (reported at 15 million pounds in 2015, down from a peak of 19.4 million in 2014). The estimated value of that AN was close to $500,000 in 2015. But when converted to its many commercial uses, the value to Maine’s economy rose to $20 million, close to the value of shellfish harvests in that year ($24 million). Four major seaweed harvest companies are responsible for more than 200 jobs along the coast. Maine Sea Grant estimates that the Gulf of Maine now holds more than 1 million tons of rockweeds, and that as much as 40 percent could be harvested each year while sustaining the species. Current harvest rates are less than one percent of that total.

As more consumers become educated about the foods they eat, the interest in natural and organic foods continues to rise. The “buy local” movement has focused consumers on the trade-offs between imported food products that may be inexpensive, and fresher products from nearby suppliers that may be healthier. It is well documented that sea vegetables such as AN may have anti-inflammatory, anti-tumor, antiviral and immune-enhancing properties if processed carefully before entering the food chain.

It is fair to say that while the harvest of AN is a sizable commercial opportunity, there are still questions about the long term impact of such harvesting. Unlike some marine species that have been studied by many scientists over several decades, research on seaweeds still has far to go. Some groups, such as the Rockweed Coalition, a collection of coastal landowners and interested parties, are limiting AN harvests on private property (in general, down to the mean low tide mark in Maine). They also are suggesting that all AN harvests be suspended until scientific studies can be completed. In 2016 there was press coverage of the impact of harvesting near islands favored by sea birds for nesting sites.

If you like Ed Robinson’s writing, check out his two Nature Notes books! Click here for more information.