Farming Four Feet Under
It sounds like a fame's dream - a crop that "seeds" itself, needs no fertilizer or supplemental nutrients, does not require artificial irrigation, will produce up to three sizeable harvests per year, and sells for around $500 a metric ton (dryweight).
There are, however, a few problems with the dream. The "crop", even at the lowest tide levels is under about four feet of water and needs swift currents to achieve maximum growth. And, at the current state-of-the-art, it must be harvested by hand.
The crop is seaweed, or more specifically, the species kidaes cordata and Gigartina exasperate , which produce a commercially valuable extract called carrageenin. The extract is widely used as a suspension agent in enterprises as diverse as food processing and paintmaking.
And the problems associated with seaweed farming, though looming large at the moment. may be on their way to solution through research sponsored by the Washington Department of Natural Resources (DNR) and the Washington Sea Grant Program.
Dr. Tom Mumford, DNR marine biologist, and Dr. J. Robert Waaland of the Department of Botany at the University of Washington are two researchers who hope to provide the technical base to turn seaweed farming into a commercially viable enterprise. They're looking at all aspects of seaweed culture, from finding the hardiest, highest-yield strains to development of a mechanical harvester.
Dr. David Jamison, formerly employed by DNR and now with the
State Department of Ecology, was the first to
see the commercial potential of
Little was known about the ability of wild populations to re-seed nor was there much knowledge about optimum growing conditions.
But the prospect of enhancing the balanced use of marine lands, one of the operating functions of DNR, and of encouraging the establishment of a new, clean marine resource industry still existed. "The basic research work was
continued by my predecessor at DNR, Cliff Kemp," Dr. Mumford said. "In fact, it was Cliff who discovered you can put a net on a bed of seaweed and spores from the seaweed will set on the net and grow. Cliff did this on a small scale."
To propagate the natural seaweed stocks, nylon nets stretched over plastic pipe frames were placed in wild seaweed beds in early fail. Spores from the mature seaweed settled onto the nets and began to grow. In the spring, the nets were moved to locations where the water, even at low tide, was deep enough to afford the young seaweed blades protection from the sun, and where strong currents existed.
In the summertime, nets are selectively harvested, taking only blades of about one meter approximately 3914 inches). Smaller blades are left on the net to grow. A "hold fast" or small button at the base of the plant fixes it to the net. Generally, a dozen blades will emerge from a single hold fast. Usually only one blade grows to its full length, but smaller blades still are, commercially valuable.
a tiny beginning, the natural seeding experiments have progressed to a full
scale test bed located just off
"The system we're dealing with at
While the natural system
hopefully flourishes, Dr. Mumford and his colleagues
will be carefully measuring a number of factors. Growth rates will be checked
against such variables as sunlight and water movement. Net sizes ranging from
three to six-inch mesh will be monitored to determine which will hold and bring
to maturity the largest number of plants. Similar measurements and evaluations
are being made at smaller test beds in the southern part of Puget Sound and on
Concurrent with the experiments in natural seeding, Dr. Waaland has investigated methods of growing seaweed in laboratory conditions. It was during early attempts at tank culture of seaweed that the importance of moving water to the survival of the plants became apparent.
"In the preliminary experiments in the spring of 1973, we used cylindrical tanks with no provision for agitating the water or the plants," Dr. Waaland said. "There was little or no growth. Within a few weeks the plants had deteriorated."
Since that time, experiments have been conducted using tanks with constant aeration. "We believe the water motion near the plant surface replenishes nutrients in the boundary layer immediately adjacent to the plant surface," Dr. Waaland said. "The addition of aeration almost immediately increased the yield - by about six times - over the net cultured plants, although the rate of yield from net cultures now is catching up to the tank cultured plants."
The use of tanks for growing seaweed offers the possibility for selection of strains with commercially-desirable characteristics, such as rapid growth, Dr. Waaland said. In some cases it may also be possible to increase the plants' carrageenin content by manipulation of the nutrient content of the water. Laboratory or control situations also are used to measure the optimum light, either natural or artificial, necessary for strong plant growth and to test measures for discouraging growth of other naturally present but less desirable species that can rob seaweed of nutrients.
Dr. Mumford and Dr. Waaland agree that solutions to the biological problems involved in seaweed farming are within reach. But there are still technical and socio-economic barriers to be hurdled before seaweed farming can progress from research to commercial venture Chief among these is the problem of harvesting. 'What we're looking for is a sort of sea-going combine," Dr. Mumford explained. The best machine, he noted, would be able to separate the seaweed blades from the nets and then draw them to the surface to a waiting barge.
Both researchers feel that seaweed farming would be a beneficial use of the state’s tidelands resource. "We would be encouraging private industry to come in and use state-owned bedlands for this purpose in exactly the same way sharecroppers use the state's agricultural lands. That's definitely within the charge of responsibility to the Department (of Natural Resources)." Dr. Mumford said. According to Dr. Waaland, the bulk of the tidelands suitable for seaweed farming are not utilized for other marine resource activities, such as clam beds. And because generally shallow waters would be utilized, there would be little or no interferrence with recreational use of the water, such as boating or fishing, Dr. Mumford noted.
"Food production from
seaweeds is only one possibility. The Japanese already consider it an everyday food,"
Dr. Mumford said. He noted that there are at least 30
edible types of seaweed that can be grown in
Seaweed is considered an excellent source of iodine and vitamins. In addition to carbohydrates, fats, and proteins, seaweed contains vitamins A, B-complex, and C, sodium, iodine, and trace elements.
One Step Further
The two graphs which follow were prepared by Tom Mumford and describe some of the results of his studies. Use the two graphs to answer the following questions.
1. When was net 2A harvested? Net 20?
2. Flow large was the net mesh?
3. When was the highest wet weight found on Net 287
4. What accounts for the rapid decreases seen at June 10 and July 20?
5. According to figure 1, when does the period of most active growth occur for Iridaea cordata?
6. For Net 2B when did the optimal (best) time for harvest occur in 1976?
1. Which month (s) had the highest average growth rate?
2. What was the average growth rate during the first half of October?
3. Now can you explain growth rates like those seen from August 15 to November 15?
4. 4. When did the optimal time for harvest occur in 1976 according to figure 2?
5. How does this date agree with your answer for number 6 above?