Sea urchins have been successfully raised in tanks and in open-water farms, but the product could become even more valuable if the shellfish could be fattened up before harvested.

That’s where Nick Brown and Steve Eddy come in. Brown is director of the University of Maine’s Center for Cooperative Aquaculture Research and Eddy is one of its biologists. The center has been working on urchin aquaculture for five years.

In 2009, the center spawned over 50,000 sea urchins and raised them to maturity, using both tank farming and what is known as “sea ranching.” 

The project has reached the point where Eddy and his colleagues are exploring developing a better feed by using sugar kelp (saccharina latissima) to bulk up the shellfish. If the sugar kelp proves feasible, they hope it will benefit Maine wild urchin harvesters, urchin processors and seaweed farmers.

A formulated feed imported from Norway has been used, along with Maine farmed and wild harvested sugar kelp. They have discovered that the formulated feed outperforms the kelp in promoting growth in the size of the creature’s body and that it also provides high gonad yields—which raised the value of the product.

But what remains unknown is whether the formulated feed or kelp provides better quality when bulking uni, the edible gonads of the urchins, also referred to as roe or eggs. These are highly valued in Japanese cuisine.

To determine the value of the kelp, trials with four-year-old urchins raised are being conducted in tanks at the center. The urchins, which have been fed formulated feed most of their lives and could be sold for processing now with good quality uni, will be divided into two groups for bulking. One will be fed the formulated diet, which is more expensive; the other will be given seaweed as its finishing diet.

When the urchins are harvested in March, several appraisals of their quality will be conducted by processors, lab technicians and a community taste panel. 

Eddy said the bulking experiment is important because if the urchins fed seaweed have comparable or better quality uni than the formulated feed group, this would not only be more economical, it could provide an additional market for current and potential seaweed farmers in Maine.

Feeding seaweed to urchins could provide a market for seaweed seaweed that is unsuitable for food processing.

“Urchins aren’t picky,” Eddy said. “They thrive on the extra protein.”

If the bulking experiments prove successful with seaweed, not only will seaweed farmers benefit, but so will urchin processors. During the height of the urchin harvests in the 1990s, Eddy says, the uni was often about 15 percent of the urchins’ weight. Now, it is more typically10 percent.

With bulking, it could be as much as 25 percent, giving processors a considerable added value, as uni can sell at auction in Japan for $90 per pound or more.

So far, only sugar kelp has been used, but Eddy believes studies that conclude the ideal bulking diet for highest quality, taste and texture will be a seaweed “salad of red, browns, and greens.”