Marine resources in many coastal regions are overexploited. Mariculture, the deliberate production of marine plants and animals, may offer one solution to this problem; principles of agriculture can be applied to improve yields of selected marine species.
Marine plant and animal production is controlled by a number of basic chemical and physical constraints. Assuming that the organisms under consideration for coastal mariculture are indigenous, physical factors such as salinity and temperature should not be limiting at normal animal densities. Environmental factors such as wave action and solar energy are also important in planning mariculture activities. Nutrients are essential for all plant or animal production. Some coastal areas are rich in available nutrients; in other regions, strong current flows and wave action can provide large quantities of nutrients for plant production. A critical initial consideration is the cost and availability of nutrients for the specific organisms to be cultured. In some cases, controlled enrichment may be necessary.
If the animal to be cultured is a grazer of phytoplankton or benthic algae, the conditions for sufficient production of these feed sources must be present. Animals feeding higher in the food chain have similar constraints, but the requirements are more complex.
Many underutilized coastal areas have potential as sea farming sites. These activities would not compete with terrestrial farming for space, and many culture techniques are technically unsophisticated and could be implemented by small family units without large investments. This chapter will cover the mariculture potential of species in three major categories: algae, finfish, and crustacea and molluscs.
As with land plants, algae can be cultivated as animal feed, as human food, or as a source of industrial products. In addition, algae may be part of low-cost systems to recycle domestic or agricultural wastes or wastewaters.
Algal Turf Mariculture
Recent research by the Smithsonian Institution's Marine Systems Laboratory (MSL) has shown that mariculture of fine algal turfs, commonly found on highly productive coral reefs and similar hard bottom communities, is biologically feasible. The tropical open ocean is known to be nutrient poor, and its fisheries development potential has long been considered rather limited. Coral reef ecosystems, however, maintain production rates of between 10 and 20 g dry material per m2 per day (10-100 times the productivity of tropical nutrient poor water). They derive nutrients from tropical currents, upwelling of deeper ocean water, and the constant wave action of trade wind seas.
Under proper environmental conditions simulating reef processes, algal turfs may be grown on screens. This production can serve as feed for marine animal grazers that, in turn, could be consumed by humans. Several species: Mithrax spiriosissimus (Caribbean king crab), Cittarium pica (whelk), and Scares (parrotfish) have served as target herbivores for MSL algal turf research. The life cycles of these animals have proved satisfactory for controlled spawning and grow-out. Pilot projects for algal turf mariculture are operating in the Turks and Caicos islands, the Dominican Republic, and Antigua. In all these projects, algal turf, a mixture of red, blue-green, and green algae, is grown on plastic screens and used as feed for the target animals.
Many large marine algae, or seaweeds, are nutritious or provide special flavors and are routinely consumed by Asian peoples. Throughout the world, seaweed extracts are used in a variety of products including foods, biomedical products, cosmetics, and textiles. Agar, a colloidal extract of the red algae Gelidium and Gracilaria, is used as a gelling, stabilizing, and emulsifying agent in ice cream, jelly, candy, and beer. Agar finds its greatest value as the base for microbiological culture media, critical diagnostic tools used in hospitals and research institutes. Other colloids, carrageenans, and algins extracted from a number of red and brown algae, also have wide application in foods, cosmetics, and pharmaceuticals as thickeners, stabilizers, and suspension agents. Calcium alginate fibers derived from Laminaria hyperborea have been used to produce wound dressings that are highly absorbent and hemostatic. Epidemiological studies have indicated lower incidences of some forms of cancer in areas where Laminaria or Porphyra are a regular part of the human diet. Dietary Porphyra is also reported to reduce cholesterol levels in blood. Some marine algae have been evaluated as biomass energy sources through their conversion to alcohol or methane.
Gelidium and Gracilaria, the traditional sources for agar, are harvested worldwide from natural populations. This type of exploitation results in a "boom or bust" industry that might be stabilized by mariculture technology. Considerable research has led to pilot seaweed mariculture in areas of California, Florida, Hawaii, the Caribbean, and China with the proper physical climates for these species. Pilot projects often evaluate enclosures of varying levels of complexity.
Giant kelp (such as Macrocystis and Nereocystis) are also harvested from natural populations off the Pacific coast of North America. Ocean-going harvesters have been developed, and the industry shows a high degree of management including pest control, replanting, and harvesting restrictions.
Mariculture of red algae as a source of the colloid carrageenan is highly developed. Vegetative propagation of Eucheuma on nets in the Philippines occurs on reefy flats with good water circulation. Monofilament longlines are stocked with fist-sized fragments of highly productive seaweed strains. The cultivated plants are harvested at about 3-month intervals. These family farms are maintained using basic agricultural principles, including weeding, predator control, and selection for vigorous strains. Production is 10-15 dry metric tons per hectare per year.
On the South Tarawa lagoon in Kiribati, family-scale production of Eucheuma is just beginning. Each family has about a quarter-hectare sea garden. Young growth of Eucheuma is tied to lines drawn between mangrove stakes. Trials have shown that a 200 g plant will grow to 2 kg in 8-12 weeks.
Other commercial sources of carrageenan, Chondrus and Iridaea, are harvested from natural populations in cool temperate waters. Net farming of Iridaea in the state of Washington has also been practical.
Mariculture of the edible brown algae Laminaria (kombu) and Undaria (wakamei) is highly developed in cool to warm temperate waters in China and Japan. In China, billions of Laminaria sporelings are produced in large glass houses supplied with seawater. Longlines anchored to the bottom and floated below the surface at proper light levels are transplanted with young plants of selected Laminaria strains. Adult plants can grow to 3-6 m in length and yield about 5 wet tons per longline. Other techniques for Laminaria cultivation include the application of fertilizer in the sea, breeding of new strains, and disease control of sporeling as well as adult plants. Commercial cultivation of Laminaria is being practiced on the entire China coast from Lianoning Province in the north to Fujia Province in the south. About 275,000 dry tons of Laminaria were produced from 18,000 hectares of marine farms in 1974.
When Laminaria is cultivated where herring spawn, the herring lay their eggs on strands of the seaweed. This combination (kazunoku kombu) is harvested and sold as a delicacy in Japan (figure 4.3).
Porphyra, or nori, is the most popular edible seaweed in Japan, the country that dominates the world's production of this crop. In China, Porphyra cultivation has recently become a large mariculture industry. The traditional farming method involved planting bundles of leafless brush or bamboo in shallow water. The floating spores of Porphyra attach to the brush and develop into edible fronds. Modern farming involves growth of spores in indoor tanks with shells of molluscs as substrate and transfer of young plants to synthetic fiber nets for cultivation in intertidal zones (figure 4.4). Crop maintenance includes fertilizing, pest control, and weeding. New developments include floating cultivation in the subtidal zone or shallow sea areas and strain selection and breeding programs.
Algal mariculture has a high potential for development in coastal nations. Initial considerations for such development include evaluation of native and exotic species potentials for different products and cost assessment for the development and implementation of the related industries.
Cage or pen culture is the most promising method for culturing marine fish in coastal environments. Freshwater fish were cultured in cages only several decades ago by the Japanese; perfection of this technique has increased yields of yellowtail (Seriola quineradiata) to more than 280 metric tons per hectare of cage area. Marine fish aquaculture will inevitably become more popular in the future and might be practiced on a small scale by coastal residents.
Floating fish cages make harvesting much simpler and protect fish from predators. Since the fish have a limited space in which to swim, they burn fewer calories, making food conversion more efficient. Cages can also be moved from place to place and clean, oxygenated water is not usually a limiting factor.
Cage cultivation does have drawbacks. The walls of the cages become fouled or covered with algae and must be replaced and cleaned regularly. The high density can lead to disease and parasite problems. Culture is labor-intensive and requires meticulous care. Many fish are extremely sensitive to high levels of pollutants.
The fast-swimming, pelagic yellowtail (Seriola quineradiata) is the marine fish most commonly cultured in Japan. The fry are captured from the sea and stocked in floating nylon net cages, which are between 2 and 50 m2 in area and from 1 to 3 m deep. The cages are set out in parallel rows and a platform may be built so that they can be readily attended. After 4 to 6 weeks of feeding and growth, the fry are stocked in grow-out cages. These larger cages, from 35 to 100 m2 in area and 3 to 6 m deep, may be constructed from nylon or metal. They must be carefully located in protected, accessible areas with good water quality and circulation and appropriate temperature and salinity. Yellowtail are fed fish scraps and less desirable species, so these must be available. The yellowtail are harvested after a 6-month grow-out period.
Dolphin Fish (Mahi mahi)
Recent work on dolphin fish (Coryphaena) in the University of Hawaii's Sea Grant Program has shown them to be extremely fast growers and suitable for cage culture. This species is circumtropical and would be ideal for culture in coral atoll lagoons. More work is needed on hatchery and grow-out techniques, however.
Groupers, Snappers, and Sea Bass
Pilot cage culture projects for groupers and snappers have been implemented in Malaysia and the French West Indies. Floating net cages are being tested to fatten undersized fish of fast-growing marine species, such as mangrove snappers (Lutjanus spp.) and estuarine groupers (Epinephelus spp.). These species are found naturally, are readily accessible, and have a high market value. Juvenile fish weighing 150 g or more are stocked in the cages.
In Malaysia, bamboo rafts (12 x 12 m) are built and floated on discarded oil drums. Four 5-m3 knotless nylon-net cages are suspended from each bamboo raft. The net is removed from the water and cleaned when its openings are about half blocked by fouling organisms. The rafts are anchored with oil drums filled with concrete, sand, and stone. In the French West Indies, 10 x 3 m cylindrical floating nets are used. In Micronesia, rabbitfish (Sigamus spp.), herbivores, are used in floating net cages to consume the fouling organisms and reduce the maintenance of nets.
Milkfish (Chanos chanos)
Milkfish have been reared in brackish waters for centuries. Growth in ponds and pens is very rapid, if adequate algal foods are provided. A recent breakthrough in spawning adults in captivity was achieved at the Oceanic Institute in Hawaii. This should lead to increased availability of juveniles for greater production of this species in Pacific basin countries. The herbivorous nature of this fish would allow the use of low-protein pellet feeds or algae grown either in the culture area or on an appropriate substrate elsewhere. It is a good candidate for polyculture because of its nonpredatory and herbivorous nature.
The culture of mullet from the hatchery to pens is still in the pilot stage. Mullet hatchery production is relatively routine, but economic production of this species has yet to be demonstrated in cages, pens, or ponds. However, the desirability and availability of this species makes it a good candidate for culture in certain areas of the world. In Israel, Taiwan, Indonesia, and the Philippines, mullet are incidental crops in milkfish and shrimp-pond culture.
Tilapia have a long history of culture in freshwater systems and have also been commercially reared in coastal waters. The development of salt-tolerant strains, coupled with the limited availability of fresh water in many areas, may encourage coastal production of tilapia in cages. At low stocking densities, tilapia have growth rates of about one g per day. However, in commercial operations with high density and pelleted feed, growth rates of 22-33 g per day have been reported. There are major technical problems with hatchery production or grow-out with this species. Several new strains have been developed, including a red-colored strain, which make the fish more marketable. Tilapia are also being grown in combination with shrimp and various fish species throughout the world.
Rabbitfish are a popular herbivorous fish of the tropical Pacific. Hatchery operations have produced marketable sizes on a pilot scale, but commercial culture has not yet been successful. Recent development of the algal turf production technology by the Smithsonian Institution's Marine Systems Laboratory could provide a means for producing low-cost food, which would allow the culture of this species in nutrient-poor tropical waters. Rabbitfish can be used in certain cage culture operations to control fouling of nets and screens; in innovative applications, oyster culture strings were cleared by being placed in cages containing rabbitfish.
Pen culture of salmonids is well established in Norway, Scotland, and other northern climates, and several projects are underway for areas of North and South America. Commercial feeds are available, and cage and pen designs have been successful. There are no problems with hatchery rearing before transfer to cages in the marine environment. Specially formulated pelleted foods are provided until market size is reached. New work on manipulating the gene complement of salmon may yield faster growing or sterile fish for certain aquaculture applications.
Ocean ranching, where salmon are produced in the hatchery and then released to the environment, has been successful in Japan and North America and is being tested in Chile. In Chile, only 1 percent of the first generation returned for capture. Their goal is for 5-10 percent of the annual batch to come back to the release point. Salmon return in 2-4 years after release and are then captured. Technologies have been developed in which salmon literally swim directly into the processing plant.
CRUSTACEANS AND MOLLUSCS
Invertebrates now being cultured include crustaceans and molluscs. The culture method of molluscs depends primarily on the organisms" mode of feeding. Bivalves (oysters, mussels, clams, and scallops) are filter feeders. These animals require a substrate that allows them access to large quantities of water for filter feeding. In the culture of oysters, mussels, and scallops, the substrates are typically ropes, stakes, and mud. Off-bottom rope and stake culture is generally more efficient than bottom culture. In recent years, clam production has been improved by tilling and cultivation of natural mud substrates to improve pH and texture.
Gastropods are snails that feed mostly on bottom-dwelling or benthic algae. In this case, an effective growing surface for the algae as well as a protective cage for the snails are the primary requirements for culture.
Oyster farming is one of the oldest forms of mariculture. Transfer of excess young oysters from reproduction areas to grow-out areas has been practiced for centuries. New off-bottom culture techniques produce far higher yields than do natural bottom areas. Environmental degradation of estuarine ecosystems, where oysters reproduce and grow, endangers oyster cultivation in many areas. Even if the oyster grounds are not destroyed, pollutants, which the oysters concentrate in their tissues, can make them unfit for consumption.
Oyster species extend over a broad geographic range, both in tropic and temperate zones, and require areas of reduced salinity. They fall into two groups: flat (Ostrea) and cup-shaped (Crassostrea). These sedentary molluscs spawn whenever the water temperature remains above a species' specific minimum. Tropical species may spawn year-round, whereas temperate species have limited spawning periods. Depending on species environment and availability of food, they take from 6 months to 5 years to reach marketable size. Bottom cultivation of oysters is used in many areas because of its ease, but it has the disadvantages of low productivity and lack of protection from predators. Farmers prepare the bottom for cultivation by spreading dead oyster shells or gravel over the bottom or by stirring shell-covered bottoms; this provides clean surfaces to which the spat can attach. These preparations occur as close to spawning time as possible. Production can be moderately increased by cultivating the oysters, or by breaking up clusters, removing fouling organisms, and returning the individuals to the substrate. The oyster area can also be fenced off to protect it against predators.
In the Philippines and Thailand, bottom cultivation is called the broadcast (sabog) system. Where the bottom is firm, oyster shells or stones are scattered to provide surfaces for oyster larvae attachment. The oysters are simply left on the collectors until harvesting.
Off-bottom cultivation offers the potential for higher productivity and protection against such predators as starfish and oyster drills. In many areas, oysters are grown on sticks in the intertidal or uppermost subtidal zone. Philippine oyster farmers impale tin cans and oyster shells with bamboo stakes (tulos) to collect the spat, and then drive the stakes into estuarine sediments and
tidal mud flats. The clean stakes, which are 5-10 cm in diameter, are placed just before the oyster larvae are expected to attach. Some farmers increase the surface area available for attachment by adding horizontal bars of bamboo. Harvesting simply involves lifting the stake out of the water and removing the attached oysters. The soft bottom of southeast Manila Bay is literally a forest of bamboo poles used in this type of culture.
Longline cultivation is also productive and economical. Ropes, wires, or branches are hung from a horizontal wire, suspended by buoys or posts; the spat attach themselves to these underwater surfaces. When the oysters are ready for harvesting, the lines or branches are lifted from the water. In the Philippines, the hanging method (bin) uses old oyster shells or coconut husks as collectors.
In Japan and the Philippines, longline methods have been responsible for recent increases in natural oyster production. Longlines, 45-75 m long, consist of a pair of ropes strung between pairs of floats, arranged in a row. The floats may be metal, wood, or styrofoam, and are spaced at intervals from 3 to 7.5 m. Three oyster lines, usually 7.5-10 m long, are suspended from each float and are never permitted to touch the bottom. The two end floats are anchored. These longlines allow oysters to be grown in deep water, exposed to the conditions of the open ocean. This system is not easily damaged by waves, winds, or currents.
The mangrove oyster, associated with mangrove roots, has traditionally been collected in Cuba. The introduction of a variant of longline cultivation, in estuaries where oyster spawning occurs, has resulted in a large increase in oyster production. Typically, mangrove or concrete stakes are driven into the mud, at 3-m intervals, to form two parallel rows about 3 m apart and 30 m long. Wooden crossbeams are then attached to the top of each stake above the high-tide levels. Mangrove poles are placed to extend from crossbar to crossbar, forming two parallel lines that extend the length of the structure. Mangrove branches are cut and hung from the poles into the water, serving as a surface for oyster spat attachment. About 150 branches or collectors may be hung from each unit.
An artificial collector has recently been introduced to replace the mangrove branches. The innovation, which simulates a mangrove branch, is made of aluminum wire and has 24 branches. Before it is hung, the artificial collector is given a cement bath, creating an improved surface for spat attachment.
Cuba's largest oyster farm (at Jujuru, Holguin) has a total of 105,000 mangrove branch collectors, each producing about 6 kg of oyster meat annually.
One of the world's largest mariculture activities, pearl culture, is no longer the sole province of Japan. The culture of pearl oysters is being developed in China and French Polynesia.
Mussels are widely distributed throughout the world. They are cultured in Western Europe, North America, and Southeast Asia. About 90 percent of the green mussels consumed in the Philippines are cultured. Mussels are easily harvested and their culture is very productive.
The common mussel, Mytilus edulis, is cultured in Western Europe and North America, while the most important species in Southeast Asia is the green mussel, Perna viridis. Mussels spawn with rising temperatures in spring and summer. Spawning can also be induced by reducing salinity. The free-swimming larval stage lasts for 10-15 days before the larvae settle onto fibrous substances, stones, or shellfish. They are found in estuaries but seem to prefer intertidal zones. Bottom, stake, and line culture are all successfully employed.
Bottom culture of mussels is practiced primarily in Holland, the United States, and Thailand. Fishermen seed designated culture areas with young mussels collected from public grounds. During the grow-out stage, the mussels may be thinned and transferred to deeper grounds.
The stake method is common in France and the Philippines. In Brittany, the seed is collected on long woven ropes suspended in intertidal regions near natural beds. These ropes are then wrapped around 4-m poles embedded into estuarine sediments. The bottoms of the poles are sheathed in plastic to exclude predators. In the Philippines, bamboo poles are driven into the soft mud in water 2-4 m deep shortly before the mussel-setting periods. The stakes are often set in a circle, slanted toward the center, with the top ends fastened or tied by horizontal crossbars. Mussels are usually harvested after 6-10 months of growth.
Productivity is also high in raft-line culture, a method perfected in Spain and also practiced in the Philippines, Western Samoa, and North America. In this method, mussel grow-out
lines of nylon, polypropylene, or of local grass are suspended from rafts or lines of floats. These lines should not touch the bottom, since this allows access to crab predators. Anchored rafts are built of wooden timbers or bamboo supported by cubical floats made of wood, fiberglass, or discarded oil drums, and a cross-lattice of sticks is constructed on the platform of the raft. In the longline approach, floats can be drums or large fishing buoys. Hundreds of ropes may be suspended from each raft. A rope-web culture method developed in Sapian Bay, Panay, the Philippines, increased annual production to 300 tons per hectare, over five times the production of stake methods. Culture trials of green mussels attached to ropes suspended from bamboo rafts, have been performed at Asau Bay in Western Samoa. Production has ranged from 7 to 15 kg of mussels per m of rope.
Clam fisheries are important sources of seafood throughout the world. Natural populations may be found in both estuarine areas and in more oceanic conditions. Stocks in deeper areas are often exploited by larger vessels. Clam mariculture uses bottom and off-bottom culture methods, similar to oyster and mussel culture. In bottom culture, wild and hatchery-produced seed is planted in managed plots. Bottom culture is generally unsophisticated and is only moderately productive.
Off-bottom culture utilizes trays or cages that contain soil. Hatchery-produced seed of Mercenaria may be planted in raised, low-profile rectangular cages. These are arranged in rows in subtidal areas in depths between 2 and 3 m. The containers, measuring 1 x 2 x 0.15 m, have plastic screening on the top and bottom, allowing for water and nutrient circulation. The sides are constructed of treated wood. Seed clams are placed into the 8-10 cm of sediment contained in each cage. Periodic thinning of stock and the removal of fouling organisms add to the labor-intensive aspect of this culture method.
Giant clams are excellent candidates for broader use in shallow-water ocean farms. They are fast growing and, as adults, sedentary, predator resistant, ecologically innocuous, and commercially valuable.
At the Micronesia Mariculture Demonstration Center in the Republic of Palau, methods for the mass culture of giant clams have been developed. Through careful observation of spawning behavior, larvae were captured and reared in tanks and raceways. Once young clams reached shell lengths of 5-10 mm, mortality rates dropped dramatically, and clams larger than 30-40 mm had a high survival rate in the laboratory. In nature, 10-20 mm clams suffered total mortality from predation within a few days of unprotected release on a reef near the mariculture center. In protective cages, clams of this size survived well, and clams released at a shell size of 130 mm required no protection for high survival rates.
Preliminary estimates of potential biomass production capacity in giant clam culture indicate that 16 tons of edible clam meat per hectare per year could be produced. This compares well with mussel culture and exceeds most fish-based aquaculture yields.
The Palau mariculture center has also developed packing techniques that allow juveniles to be shipped throughout the world with minimum losses.
In recent years, methods of culturing scallops that are similar to those for oysters, mussels, and clams have been attempted. Because they are mobile, these bivalves must be caged at relatively low densities. Research is now underway in the United States at the University of South Carolina and the University of Georgia sea grant programs to test the use of suspended lantern nets and polyculture of scallops with fish in ponds. This is a promising area that is likely to be of increasing significance.
The culture of snails is likely to become a major area of development in mariculture. In most cases, these animals feed on small algae (see discussion above under algal turf mariculture), and the basic requirements are those of providing an algal growth surface and sometimes a protective cage. Wild young have not been a major source of juveniles for these organisms, and the basic limitation to developing marine snail mariculture has been that of the hatchery process. Major advances have been made in spawning, hatching, and grow-out processes, but culture has not progressed past the pilot stage. Cage culture for abalone also seems promising, and several organizations in Caribbean countries have been testing larger scale operations. The transition period from the hatchery to grow-out conditions seems to be especially critical, and more work is needed on nursery systems to reduce high juvenile mortality.
Extensive efforts over many decades have been made to hatch crabs, shrimp, and lobsters of various genera and species. The larval development process has often proved complex, difficult, and expensive, and is probably not of near-term interest to artisanal fisheries. Marine shrimp hatchery technology is now routine, but crabs and lobsters have yet to be produced under commercial hatchery conditions. However, recent work with the grazing Caribbean king crab (Mithrax spinosissimus) has shown promise.
Mithrax crab eggs are obtained from gravid females caught in the wild or grown in captivity. When the female is about to release her eggs, she is placed in a juvenile cage, where she spawns. The larval crabs grow undisturbed without the mother for 60 days. During this period, the small crabs feed on algae growing on the screen of the box. Between 60 and 100 days after hatching, screens covered with algal turf are introduced into the cages to provide food to the juvenile crabs.
The juvenile crab cage is a wooden frame box, covered with fine mesh (375 micrometers) screen. During the crabs' first 100 days, the cage is anchored about 3 m below the surface in a shallow area with moderate wave action.
After 100 days, the crabs are about 15 mm in diameter and are transferred to grow-out cages fitted with the plastic algal screens for grazing. The growth rate of the crabs depends on adequate feeding and replenishing of the algal screens. Stocking densities must be decreased as the crabs grow and increase their consumption of algae.
Four hundred days after hatching, the crabs will have grown to about 1 kg in weight, 100 mm in length, and will need about one-third of a screen of turf algae per day.
Marine shrimp culture is expanding rapidly in ponds adjacent to estuaries. Pond culture will not be covered in this report, but the enhancement of natural areas with juvenile shrimp has had some success in Italy and Japan. This ocean ranching, where juveniles are raised in the hatchery and allowed to grow out in a natural environment, may be appropriate for certain tropical areas where stocks have been depleted because of overfishing. In this method' it is best to grow the shrimp in transition ponds to bring them to a larger size before release.
INTEGRATED SEA FARMING
Integrated sea farming has been suggested as a possibility for inhabitants of the South Pacific who live by reef foraging. Several precedents exist for this type of activity. The Seruti people in Irian Jaya, Indonesia, live in wooden houses on stilts over the water and raise fish in floating cages. Farmhouses are often built in the Eucheuma farm areas, raised on bamboo stilts over the reef flats on which the farms are located. A reef flat is the ideal location for such an integrated farm. The water is shallow, protected, and productive.
Polyculture is a technique developed by the Chinese for the culture of several aquatic species in the same body of water. The Chinese obtain very high production with several species of carp that feed at different trophic levels in freshwater ponds.
Polyculture in the marine environment has been practiced in Southeast Asia with shrimp and milkfish, and Israel has experimented with mullet and shrimp. Work is currently being done in Hawaii with a combination of oysters, tilapia, and shrimp. The South Carolina Sea Grant Program is working on a combination of clams or scallops with striped bass. Many other combinations are possible and should be considered in any new development project.
The life cycles of many marine species are not well understood. Without this basic knowledge, modern culture techniques are impossible. An increased number of marine animals and plants will inevitably be farmed once husbandry techniques have been developed. Special attention needs to be given to the cage culture of marine fish, a technique that is still in its infancy.
Increased productivity of cultured marine species must be a basic research goal. The environmental conditions for optimal production, as well as the constraints, must be identified and then considered in choosing the most appropriate species and cultivation sites.
Much has been learned in recent research on the control of reproduction and growth of molluscs. In many species of molluscs, spawning is induced by the enzymatic synthesis of prostaglandins. This production of prostaglandin hormones can be initiated by a low concentration of hydrogen peroxide in the seawater surrounding these organisms.
After development to the larval stage, the organism must attach to some suitable surface and undergo metamorphosis. This transformation is also biochemically controlled. Specific chemicals extracted from red algae, for example, will induce abalone larvae to settle and continue their growth to adulthood.
For the oyster Crassostrea virginica, bacterial by-products have been demonstrated to induce metamorphosis. Oyster larvae have a preference for surfaces coated with specific bacteria.
In these and other instances, metamorphosis-inducing biochemicals have been shown to originate from some feature of the preferred adult environment. These features can include individuals of the same species, algal or bacterial films, or other plant species that may serve as nutrients for the adult organism.
In addition to biochemical control of spawning, larval settlement, and metamorphosis, research is also in progress on growth enhancement. The use of growth-regulating hormones isolated from mammals has accelerated early growth in abalone, giving increases of about 25 percent over the mean growth rate in the first few days after metamorphosis.
Thus, various biochemicals already present or readily introduced to the environment can serve to benefit marine aquaculture. Research is needed on the identification of more of these materials and methods for their use.
The major drawback to the expansion of mariculture is the need to collect larvae in the wild for stocking many sea-farming systems. Better hatchery techniques for more species are needed. Mariculture systems that are generally located in protected near-shore areas will be threatened by pollutants and siltation unless proper conservation methods are followed. Another consideration is the possible damage or destruction of culture systems by storms or waves.
Control of a coastal area will be necessary for many mariculture systems. Therefore, cooperation with governmental regulating agencies and local fishing communities must be considered.
Fishermen working as sea farmers may require a change in life style that may involve social and cultural difficulties.
Socioeconomic considerations will determine the ultimate success or failure of any sea-farming venture. Fluctuating prices for marine products complicate planning and economic assessment.
The materials required for the construction and maintenance of culture systems may not be available at remote sites.
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Mann, R. 1978. Exotic Species in Mariculture. MIT Press, Cambridge, Massachusetts, USA
McVey, J. P. 1984. CRC Handbook of Mariculture Vol. I. Crustacean Aquaculture. CRC Press, Boca Raton, Florida, USA.
Morse, D. E. 1984. Biochemical and genetic engineering for improved production of abalones and other valuable molluscs. Aquaculture 39:263-282.
Morse, D. E., and K. K. Chew. 1984 Recent Innovations in Cultivation of Pacific Mollusks. Elsevier, London, U.K.
Rabanal, H. R., U. Pangsuwara, and W. Poochareon. 1977. Shellfisheries of Thailand: Background and Proposal for Development. Report SCS/77/WP/61 of the South China Sea Fisheries Development and Coordinating Programme, Manila, Philippines.
Ubeda, L. 1984. Cuando de ostion se trata. Mar y Pesca (Cuba) 226:20-23.
Agriculture and Fisheries Department, Hong Kong, and Division of Fisheries, Malaysia. 1978. Cage Culture of Marine Fish in East Coast Peninsular Malaysia. Report SCS/78/WP/69 of the South China Sea Fisheries Development and Coordinating Programme, Manila, Philippines
Cho, C. Y., C. B. Cowey, and T. Watanabe. 1985. Finfish Nutrition in Asia: Methodological Approaches to Research and Development. IDRC, Ottawa, Canada.
Neff, G. N., and P. C. Barrett. 1979. Profitable Cage Culture. Report by the Inqua Corp., Dobbs Ferry, New York, USA.
Dixon, B. 1986. Seaweed for wound dressing: BIO/TECHNOLOGY 4:604.
Doty, M. S. 1986. Biotechnological and economic approaches to industrial development based on marine algae in Indonesia. Pp. 31-43 in Workshop on Marine Algae Biotechnology: Summary Report. National Academy Press., Washington, D.C., USA.
Edwards, P. 1979. Seaweeds: an underexploited resource in developing countries. Appropriate Technology 6(1):252-27.
Evans, L. V. 1986. Seaweed bioproducts. Science progress. 70(279):287-303.
Fei, X.G. 1983. Macroalgal culture in California and China. Pp. 301-308 in Raft and Farm Design in the United States and China. L. McKay (ed.). New York Sea Grant Institute, New York, USA.
Hansen, J. E. 1985. Strain selection and physiology in the development of Gracilaria mariculture. Hydrobiologia 116/117:89-94.
Hansen, J. E., J. E. Packard, and W. T. Doyle. 1981. Mariculture of Red Seaweeds. Report T-CSGCP-002. California, Sea Grant College Program Publication. University of California, La Jolla, California, USA.
Harger, B.W.W., and M. Neushul. 1983. Test-farming of the giant kelp. Macrocystis as a marine biomass producer. Journal of the World Mariculture Society 14:392-403.
Jacobs, R. S., P. Culver, R. Langdon, T. O'Brien, and S. White. 1985. Some pharmacological observations on marine natural products. Tetrahedron 41:981-984.
Khan, A. 1986. Seaweed farming shows bright promise. Agricultural Information Development Bulletin 8(3):4-5.
Lim, J. R. 1982. Farming the Ocean (The Genu Story). R. P. Garcia Publishing Co., Manila, Philippines.
Mottel, M. G. 1982. Enhancement of the Marine Environment for Fisheries and Aquaculture in Japan. Technical Report No. 69, Department of Fisheries, Olympia, Washington, USA.
Neushul, M. and B. W. W. Harper. 1985. Studies of biomass yield from a near-shore macroalgal test farm. Journal of Solar Energy Engineering 107:93-96.
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Tseng, C. K. J. 1981. Commercial cultivation. Pp. 680-725 in The Biology of Seaweeds C. S. Lobban and M. J. Wynne (eds.). Blackwell Scientific Publications, London, U.K.
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Wong, J. L. 1986. Cancer and chemicals...and vegetables. CHEMTECH 16(7):436-443.
Aquaculture Development Program of the State of Hawaii, 335 Merchant St., Room 359, Honolulu, Hawaii 96813, USA (John S. Corbin).
Asian Institute of Technology, P.O. Box 2754, Bangkok, Thailand (S. Boromthanarat).
FGAPP/UNDP Network of Aquaculture Centers, c/o SEAFDEC Aquaculture Department, P.O. Box 22256, Iloilo, Philippines (T. E. Chua).
International Center for Living Aquatic Resources Management, P. O. Box 1501, M.C.C., Makati, Metro Manila, Philippines.
National Sea Grant College Program, 6010 Executive Blvd., Room 804, Rockville, Maryland 20852, USA (J. McVey).
National Institute of Oceanography, Dona Paula, Goa 401 004, India (S. Z. Qasim).
South China Sea Fisheries Development and Coordinating Programme, P.O. Box 1184, M.C.C., Makati, Metro Manila, Philippines.
Marine Systems Laboratory, Smithsonian Institution, Washington, D.C. 20560, USA (W. Adey).
Aquaculture Department, Southeast Asian Fisheries Development Center, Tigbauan, Iloilo, Philippines (W. G. Yap).
Binangonan Research Station, Aquaculture Department, Southeast Asian Fisheries Development Center, Binangonan, Rizal, Philippines (M. Tabbu).
Council of Agriculture, Taipei, Taiwan 107 (J. C. Lee).
Fisheries Division, P. O. Box 206, Apia, Western Samoa (L. Bell).
Foundation for Pride, 7600 S.W. 87 Ave., Miami, Florida 33173, USA (C. Hesse).
Granja Ostricola de Jururu-Bariay, Holguin, Cuba (F. Orestes).
Institute of Zoology, Academia Sinica, 7 Nan Hai Road, Taipei, Taiwan 115 (K. H. Chang).
International Center for Living Aquatic Resources Management' South Pacific Office, P.O. Box 1531, Townsville, Queensland 4810, Australia (J. L. Munro).
Marine Advisory Service, University of Connecticut, Avery Point, Groton, Connecticut 06340, USA (T. Visel).
Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA (C. Berg).
Micronesian Mariculture Demonstration Center, Marine Resources Division, P.O. Box 359, Koror, Palm, Western Carolina Islands 96940, USA (G. A. Heslinga).
Motupore Island Research Centre, University of Papua New Guinea, University P.O., Port Moresby, Papua New Guinea.
Cage Culture of Marine Fish
Binangonan Research Station, Aquaculture Department, Southeast Asian Fisheries Development Center, Binangonan, Rizal, Philippines.
Council for Agricultural Planning and Development, 37 Nanttai Road, Taipei, Taiwan 107 (J. C. Lee).
Inqua Corp., P.O. Box 86, Dobbs Ferry, New York 10522, USA.
Institute of Zoology, Academia Sinica, Taipei, Taiwan 115 (K. H. Chang).
International Center for Aquaculture, Auburn University, Auburn, Alabama 36849-4201, USA (E. W. Shell).
Department of Botany, University of Hawaii, 3190 Maile Way, Honolulu, Hawaii 96822, USA (M. S. Doty).
Harbor Branch Foundation Inc., Fort Pierce, Florida 33450, USA (J. H. Ryther).
Institute of Oceanology, Academia Sinica, Qingdao, People's Republic of China (X. G. Fei).
Neushul Mariculture Inc., 5755 Thornwood Dr., Goleta, California 93117 USA (B. W. W. Harger, M. Neushul).
Plant Sciences, Inc., 514 Calabassas Road., Watsonville, California 95076 USA (J. E. Hansen).