Like most babies, tiny shellfish have voracious appetites that can keep those who are tending them on the run.
If you put about 1,000 fingernail-size oysters into a container and then add about 6 billion cells of algae, the oysters will make short work of this nutritious food. “When you first add the algae,” says Scott Feindel, shellfish hatchery manager at The Darling Marine Center in Walpole, “the water will look like chocolate milk, but after three or four hours, it will be as clear as pool water.”
At the Darling hatchery, Feindel, Christopher Davis of the Maine Aquaculture Innovation Center and Paul Rawson of University of Maine School of Marine Sciences, with support from a $94,000 grant from the Maine Technology Institute (MTI) Marine Research Fund, have developed a way to refine the job that all shellfish hatcheries face: how to produce enough algae to feed their hungry babies.
To grow algae, most hatcheries use a process known as the batch method. The Darling hatchery used it before the installation of the new Seasalter Continuous Algal Production System (SeaCAPS) in a greenhouse built last winter by Davis and Feindel with help from Mainely Carpentry and Granite Hill Electric of Bristol.
The batch method, Feindel explains, begins with filling a disinfected 200-liter tank with pasteurized, filtered sea water and inoculating it with a one-to-20 or one-to-50 ratio of a species of algae to water.
The Darling Center, Feindel explains as he gives a tour of the hatchery, keeps 12 strains of algae, which differ in fat, protein and carbohydrate content. Having different strains makes it possible to supply the shellfish seed with a balanced and varied diet. (These strains are made available to commercial hatcheries in the state if they lose a particular strain due to contamination or a crash in their system.)
After algae is added to the tank, it is fed a mix of nitrates, vitamins and minerals, kept warm and given plenty of light, and the plants begin to multiply rapidly. In eight to ten days, Feindel says the batch becomes so dense, light can no longer penetrate, and the algae is ready to be fed to the baby shellfish. Then, the entire process has to be started over again.
The Seasalter Continuous system has the great advantage of being exactly what it is called: it can provide a continuous supply of algae for an entire season (the heaviest demand is from January to June) without time out to re-clean bags and introduce new culture. In this method, shellfish are grown in sterile 400-liter bags that are set into containers formed with lobster trap wire.
To start up a new bag, Feindel plugs in an air line and starts water dripping in through a tube at the top (glass and silicone tubing, which can easily be steam cleaned, are used in the system). When the bag is filled about one-quarter or one-fifth of the way, he adds a two-liter flask of algae through another tube. The algae, stimulated by warmth, light and nutrients, immediately begins to divide, and gradually keeps up with additional water that is filling the bag to capacity. As it grows, carbon dioxide is added to the tank to support faster growth and balance PH. The culture reaches feeding density by the time the bag is full, about four to five days.
Feindel sets up a drip from the bag to send algae through tubes to the shellfish tanks in the hatchery. Meanwhile, he monitors the amount of heat and light in the greenhouse. He adjusts the flow of water into the top of the bag and the amount of algae dripping out so that the algae mix remains at the optimum density for shellfish needs at that particular time. Generally, he says, there is a 20 to 25 percent exchange each day.
“Optimum density,” he explains, “is a much debated topic. In dense cultures, the cells tend to have more lipids (fats) or to be high in carbohydrates, depending on the species. Light, or less dense cultures tend to be more protein rich.
Some people think it is best for larvae to have a high protein diet, so they would up the flow in the continuous system to produce less dense cultures. Alternatively, some think that a diet rich in lipids is best for juvenile animals and egg production.” That, he adds, is one of the advantages of the system: it can be adjusted easily to adapt to the needs of researchers who experiment with ways to fine-tune shellfish diets.
Almost all of the algae grown at the Darling Center is used to supply various ongoing shellfish research projects such as the Maine Oyster Broodstock Program at the hatchery, a collaboration between shellfish growers and the University of Maine since the 1980s. This program seeks to provide growers in the state with different strains of oyster that show the most growth and disease resistance for each of the particular conditions at each grower’s site.
However, some of the hatchery algae will be available for The Little Pearl, a company that has rented a space in the Aquaculture Incubator facilty to conduct research with saltwater caviar-producing fish. Development of this low-rent space at the Darling Center was part of the MTI grant, a way of providing support for start-up businesses that are doing aquaculture research.
“These days, this is the model of most businesses conducting aquaculture research,” Davis says – “a university connection gives them access to the technical expertise of faculty who are conducting research.”
Although the Darling facility is used exclusively to raise algae for hatchery research, Feindel says they have received numerous inquiries about the continuous system’s operation and its implications for raising algae as a source of biofuel. This promising way to obtain fuel has already taken off in other areas of the country; a member of the Darling hatchery’s staff recently left to work at a large-scale algae production facility in Hawaii. Davis also notes that exploring algae as a source for biofuel has been designated a future high priority by the Maine Office of Innovation.
Considerable research is also being conducted on the pharmaceutical and nutraceutical uses of algae, which Feindel says can contain as much as 60 percent DHA (Omega 3s). “That’s more than fish, and without the mercury,” he says.