Macroalgae and Mariculture

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Macroscopic marine algae (seaweeds or sea vegetables) form an important living resource of the near shore environment. For millennia, people have collected sea weeds for food, fodder for animals, as well as fertilizers and soil enhancers. More recently, seaweeds have become important sources of various biochemicals, such as phycocolloids, and are important in medicine and bio technology. We all use seaweed products in our daily life in some way or other. For example, some seaweed poly saccharides (sometimes referred to as phycocolloids) are used in toothpaste, soaps, shampoo, cosmetics, milk, ice cream, processed meats and other foods, air fresheners, and many other items. In many Asian countries such as Japan, China, and Korea, they are dietary staples.

Table 1 Production (metric tons) and value (thousand of US dollars) of the five most important seaweed genus produced by aquaculture

Genus

Production (mt)

Value (103 USD)

Three main producers

Laminaria

Undaria

Porphyra

Eucheuma and Kappaphycus Gracilaria

4075 415 2 519905 1 397 660 1 309344 948282

2 505474.9 1 015040.5 1 338994.7 133325.2 385 793.7

China (98.3%), Japan (1.2%), and South Korea (0.5%) China (87.1%), South Korea (10.4%), and Japan (2.5%) China (58%), Japan (25.6%), and South Korea (16.4%) Philippines (92%), China (7.5%), and Tanzania (0.5%) China (93.7%), Vietnam (3.2%), and Chile (2.1%)

Total

10250606

5 378629

Modified from Aquaculture production 2004 (2006) FAO Yearbook, Fishery Statistics, vol. 98/2. Rome: FAO.

Modified from Aquaculture production 2004 (2006) FAO Yearbook, Fishery Statistics, vol. 98/2. Rome: FAO.

Seaweeds have also been gaining momentum as new experimental systems for biological research and are now being promoted in polyculture systems as an integral part of integrated multi trophic aquaculture (IMTA).

Traditionally, seaweeds were collected from natural stocks or wild populations. However, these resources were being depleted by overharvesting, so cultivation techniques have been developed. Today, seaweed cultivation techni ques are standardized, routine, and economical. Several factors may account for the success of large scale seaweed cultivation including the unravelling of complex life his tories, regenerative capacity of the thalli, prolific spore production, and the understanding of environmental inter actions. Different taxa require different farming methods. Although some seaweeds need one step farming through vegetative propagation, others need multistep farming pro cesses. The latter must be propagated from spores and cannot survive if propagated vegetatively. Eucheuma, Kappaphycus, and Gracilaria are propagated vegetatively (one step), whereas Porphyra, Ulva, Laminaria, and Undaria are started from spores.

Although large scale open water cultivation of some species has been carried out in many Asian countries, other species are cultivated in tanks and ponds. For example, Chondrus crispus Stackhouse has been mainly cultivated in tanks in Canada. Gracilaria is being culti vated in tanks and raceways in Israel and in man made ponds in China, Taiwan, and Thailand. Tank cultivation of some Eucheuma spp. was tried in Florida and other parts of the world; however, it was economically unsuccessful. Epiphytes, fouling, and critical nutrient requirements caused serious problems. The major scientific challenges for successful tank cultivation are: (1) site selection; (2) tank design and construction; (3) knowledge of the reproductive biology of the species; (4) selection of the best strains; (5) control of the environmental variables including temperature, pH or CO2 availability, light and salinity; (6) plant agitation to remove boundaries for nutrient uptake; (7) seawater exchange/nutritional requirements; and (8) stocking density. A critical review of these factors may be found in the works of Craigie and

Shacklock (see the 'Further reading' section) which focus on the cultivation of Chondrus crispus, the most success fully cultured seaweed species in tank culture.

During the last 50 years, approximately 100 seaweed taxa have been tested in field farms, but only a dozen are being commercially cultivated today. Table 1 provides production data for the top five taxa as of 2004. A brief introduction to life cycles and cultivation techniques of these species is presented in subsequent sections.

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