Growing kelp above mussels

Aquaculture, growing worldwide, finds a beachhead in Chilmark.

Stanley Larsen grabs a handful of wild mussels for a customer at the Menemsha Fish Market. — Stacey Rupolo

On a five-acre site one mile offshore and four miles east from Menemsha Harbor, there are five 300-foot ropes hanging in 70 to 100 feet of water. This is the first Martha’s Vineyard mussel farm. Started by fisherman Al Gale six years ago, it has been worked by Stanley Larsen of Menemsha for the past year in a grant leased to him by the state.

The heavy lines hang tightly in the swift tidal currents of the area. Held up by buoys, both at the surface and submerged, the head rope stretches horizontally through the water, and the mussels grow on “droppers,” lines that hang down at intervals from the head rope. “Originally [the droppers] were hanging in loops,” Mr. Larsen said, “but the state had us change them to straight up and down to avoid entangling turtles and whales.”

It is important to keep the lines from dragging on the bottom, where oyster crabs and starfish make quick work of the bivalves. But most mussel mortality takes place between the time they become swimming larvae and when they settle down to begin their attached, sedentary existence as shelled invertebrates. In mussels, Mr. Larsen said, this motile period lasts about two weeks. Once they become attached and start to grow their shells, it takes them about a year to reach a harvestable size.

Scott Lindell is a researcher at the Woods Hole Oceanographic Institution (WHOI) who has just finished planting sugar kelp above Mr. Larsen’s mussels. “We got a grant from the USDA [U.S. Department of Agriculture] to work with shellfish farmers to do some double cropping,” Mr. Lindell said. “Diversification is a good thing.”

The kelp is attached to lines that hang above the mussel lines; the marine algae need to be in the sunlit portion of the water column. Unlike terrestrial vegetables, kelp is a winter crop, Lindell said. You plant it in November and December, and harvest it in April and May. “If you don’t harvest it by then,” Mr. Lindell said, “the blades [leaves of the algae] get things — we call them epiphytes — growing on them. That is not too attractive as food.” The kelp begins to die back as the water warms through the summer.

In addition to collaborating with a kelp farmer, the mussel farmer practices sustainable farming; he makes sure there are always enough mussels for self-seeding to keep the population on the ropes growing. “I just take the bigger ones off,” Mr. Larsen said. “There isn’t really a legal size. A lot of people like the smaller ones because they’re sweeter and more tender, and they cook more quickly.” Other people, he said, like the bigger ones. Mr. Larsen, who also runs the Menemsha Fish Market, is quick to recommend ways to prepare mussels; he suggests marinades (tomato-based or Italian salad dressing), cooked salsas, pasta sauce, or simply in lemon and butter.

He gets out to the mussel farm at least every two weeks, and more often when he can find the time. At this point in the evolution of his business, he only harvests enough to sell locally. Farm-raised mussel shells are a bit less encrusted than the wild ones that grow on the rocks along shore, but they still come up dotted with barnacles and quarterdecks (also known as sweetmeats or slipper shells) that Mr. Larsen has to remove.

The market for kelp is more complex than is the one for mussels. “It is most attractive as a fresh, seasonal product, like kale,” said Mr. Lindell. “But it can also be blanched and frozen.” Mr. Lindell admitted that the rich green color is lost after it is blanched, but when thawed, the kelp retains “a nice umami flavor” and a texture comparable to fresh seaweed.

Kelp aquaculture is in its infancy in the U.S., but has been thriving in Asia for decades. “There is a small horizontal industry in Maine,” said Mr. Lindell, referring to a market in which every customer uses a product for one purpose. “They sell it fresh. They don’t dry it and try to compete with the Asian industry.”

“Seaweed is by far the biggest biomass grown and sold in the world,” Mr. Lindell said. This is due to the vertical aspects of the market: Products derived from seaweeds are used for many purposes, as stabilizers, emulsifiers, and to produce other effects in the pharmaceutical, cosmetics, and (human and pet) food industries. “For example, they put it in lipsticks to make it ‘wet looking,’” he said.

Most of the supply is still marine algae collected “in the wild,” but, Mr. Lindell said, as the demand grows, aquaculture will play a growing role.

When he is asked about the market for Vineyard kelp, Mr. Lindell returns to the subject of fresh seaweed, and cites Bren Smith’s GreenWave in Connecticut as a model. Smith is a protégé of Charlie Yarish, a University of Connecticut researcher whom Mr. Lindell calls “the godfather of Northeastern kelp.” GreenWave is inaugurating a line of foods that relies on cultivated kelp, and has already developed a market that supplies high-end New York City restaurants with “sea greens.”

There are many species of seaweed. Why grow kelp? “It grows really quickly,” Mr. Lindell said, “and sugar kelp, as the name implies, is sweet and crunchy.” There are also established cuisines in Asia that require kelp. Mr. Lindell described a Korean-made machine that cuts kelp into long, noodle-like strips so it can be used as a pasta substitute. The boutique popularity of kelp in the U.S. and mass appeal in Asia means there is an existing market demand.

How much kelp does Mr. Lindell expect to harvest off Chilmark? “In the Long Island Sound,” he said of GreenWave’s farm off Branford, Conn., “they can get 10 to 15 kilograms per meter on a 100-meter line, so that’s about 3,000 pounds of kelp.” There are five lines off Chilmark. Mr. Lindell said the investment required to add kelp lines to the existing mussel array was “negligible”: $20 worth of nylon line; four or five buoys for about $150, and the cost of the “seed string” from the kelp “hatcheries.”

The double-cropping of kelp and mussels is achieved by attaching a line to the vertical rope that leads up from the head rope to a corner buoy that allows Mr. Larsen to locate the array from his 50-foot boat. Mr. Lindell said that the vertical rope is knotted, and a nylon rope is tied above it about 10 feet below the ocean surface; his kelp are attached to this line.

The arrangement of lines and buoys for a mussel (and kelp) farm varies according to the location. In calm, protected waters like those off Prince Edward Island, Canada, most of the buoys are at the surface. Because the weather is rougher a mile from shore at the grant leased from the state to Mr. Larsen, most of the buoys are submerged and keep the mussel-bearing lines suspended at a depth below 30 feet and above the seafloor.

Why aren’t mussels grown in protected inshore waters at Martha’s Vineyard as they are in Maritime Canada? The water in places like Lake Tashmoo and Lagoon Pond, said Mr. Lindell, is not deep enough, and too warm for the cultivation of mussels.

For the present and the foreseeable future, Mr. Larsen is working largely alone at his mussel operation — although people do volunteer to go out with him — and both the harvesting and the cleaning require special equipment. There is nothing, however, very fancy about his mussels. When asked if he is cultivating specialized local varieties like oyster farmers are doing now, Mr. Larsen laughed: “Ha. No. These are just wild and crazy farm mussels.”