Could Seaweed Help Turn Cape Cod's Nitrogen Problem From Lemons Into Lemonade?

The first results of an edible seaweed experiment in Waquoit Bay are in, and it looks promising.

Scientists say the seaweed is both a source of crunchy salad greens and a way to remove nitrogen from the bay. However, anyone who farms it as a cash crop will need to take precautions to keep other species from taking over and wait for state regulations to be written.

In June, researchers from the Marine Biological Laboratory (MBL) in Woods Hole arranged two 100-meter ropes a foot or two underwater festooned with the edible seaweed Gracilaria tikvahiae. On the surface, the structure looks like a buoyed swimming lane to nowhere in particular. The scientists placed one of the strings in the Seapit River and the other north of Washburn Island. After four months and many harvests, they finally pulled the ropes out of the water just before Super Storm Sandy hit in late October.

“We have a lot of seaweed proliferating in the bay already,” Scott R. Lindell, director of the Scientific Aquaculture Program at MBL, said in a talk at the Waquoit Bay National Estuarine Research Reserve last week. “The question is, can we turn lemons into lemonade?”

Gracilaria is not your run-of-the-mill slimy stuff that grows out of control in the region’s nitrogen-rich estuaries. It is, however, a native plant. At its best, Gracilaria has a dark red color and a nutty and salty taste with hints of mushroom, Mr. Lindell said.

“It’s crunchy like salad. You can eat it cooked. It’s great for thickening chowders and I like to add it to fried greens,” he said.

The audience at WBNERR wanted to know how long it stays fresh in the refrigerator (at least one week), how well it grows in cloudy weather (not sure, but the scientists can track that), and how late in the season the seaweed grows (it was still growing in October).

Like other seaweed, Gracilaria gobbles up nitrogen to grow, doubling its size every two weeks. It can be part of the solution to Cape Cod’s billion-dollar wastewater problem, Mr. Lindell said.

“Not any one solution is going to answer it,” he said. “Seaweed farming will help.”

Based on the results of this summer’s experiment, Mr. Lindell estimates that a seaweed farmer could remove about 3 kilograms of nitrogen over a four-month period using the same length of rope, 200 meters. By way of comparison, the nearby shellfish cultivators, Atlantic Oysters, grow 75,000 oysters in the same cove, which removes about 20 kilograms of nitrogen each year. The owner of Atlantic Oysters allowed Mr. Lindell to share his shellfishing area and assisted with deploying and retrieving the lines.

Both oysters and seaweed may be helpful in reducing nitrogen in Waquoit Bay, but Mr. Lindell points out that between 12,000 and 21,000 kilograms of nitrogen must be removed from the bay each year to return it to health.

“To remove 50 percent of the nitrogen load in Waquoit Bay we would need to cover 70 percent of the bay with seaweed,” he said, adding that the lines would be spaced 10 feet apart. “That’s probably not going to happen.”

During the experiment, the scientists ran into a thorny, or rather, slimy, problem. Sea squirts and fine, hair-like seaweed began to smother the Gracilaria. Anyone who has cleaned the bottom of a boat or pulled an old rope out of a harbor is familiar with the tunicates and epiphytes that the scientists found.

“Fouling is a potential spoiler,” Mr. Lindell said. “And the longer the cultivation, the more fouling.”

For example, the seaweed that was allowed to grow for four weeks had more hitchhikers than the seaweed that was only allowed to grow for two weeks before harvesting.

To solve the problem, Mr. Lindell and his team unhitched each meter-long length of rope from its mooring and dunked it in a freshwater bath for 15 minutes. The process would take a seaweed farmer about one hour once a week, he said.

The solution worked. The Gracilaria survived, but the colonizers could not get a foothold.

Very few farmers are currently marketing Gracilaria in the United States and it is not yet legal to cultivate seaweed in Massachusetts for commercial sale. Mr. Lindell hopes that will change soon, and has heard from state regulators that they may have rules drafted by this time next year. In the meantime, he will plan to put in the next experimental crop of Gracilaria in early June next year.

“It is another important ingredient for our local food,” he said. “Another yummy dish.”


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