New England Seaweed Culture Handbook
The seaweeds are a diverse group of large marine macroalgae that are as important to our nearshore coastal marine world as land plants are to our terrestrial world. Seaweeds were the evolutionary precursors to land plants, and like land plants they are critical primary producers, forming living links between the inorganic and the organic world, using photosynthesis to convert CO2 and nutrients into living biomass. These primary producers support other marine life through the production of oxygen, their contribution to marine food webs, and by providing structure and habitat for fish and invertebrates.
Seaweeds are also an important resource for humans. Historically, coastal peoples have relied on seaweeds for food, minerals, medicine, insulation, fertilizer, and fodder. Today seaweeds are a multibillion-dollar industry worldwide, providing food, fertilizers, nutritional supplementation, and valuable phycocolloid extracts including agar, carrageenan, and alginate. Although wild harvest supports a significant portion of seaweed to industry, there is an ever-increasing amount of seaweed production from aquaculture, principally in Asia and South America (Chile). Seaweed aquaculture makes up a significant portion of organisms cultured worldwide (~19 million metric tons) with a value of ~US $5.65 billion. Aquaculture production is dominated by kelps (Saccharina japonica and Undaria pinnatifida), tropical red algal species (carrageenophytes species, including Kappaphycus and Eucheuma), nori (including Porphyra and Pyropia species), and the red algal agarophyte species known as Gracilaria. China is the world’s top producer of cultured seaweeds, though other countries in Asia (Japan, Korea, and the Philippines) and in Europe (France, Ireland, Norway, Scotland, and Spain) also grow seaweed. In North America, the seaweed industry comprises small wildharvest cottage operations located along the East and West Coasts of Canada and the United States. Recent development in culture technologies, however, have led the to development of a small sugar kelp industry in the Northeast.
As populations expand, culture of seaweed will be important to supplement the wild resource. Seaweeds can be cultivated in the sea on suspended lines, rafts, or nets, or on land in tank-based culture systems. A sustainable, low-impact process, seaweed culture can provide much-needed employment and independence to rural coastal communities. The development of a seaweed aquaculture industry can also encourage development of other aquacultured species that are higher up in the food chain.
Seaweeds are bioextractive organisms, taking up excess nutrients generated by other species, such as fish or shrimp. The integrated culture of fed aquaculture (fish and shrimp) with extractive aquaculture (seaweed and shellfish) is called "Integrated MultiTrophic Aquaculture," or IMTA. The IMTA concept is an ecologically-based model that couples an inorganic bioextractive organism (seaweed) with an organic bioextractive organism (shellfish) to balance the intensive culture of fed organisms (finfish and shrimp) in order to produce a more sustainable, cleaner, and diversified aquaculture system.
The development of new, ecologically based, sustainable-culture technologies will ensure future employment for coastal communities, healthier coastal ecosystems, and the protection of important wild populations.