Integrated aquaculture: rationale, evolution and state of the art emphasizing seaweed biofiltration in modem mariculture

Rising global demand for seafood and declining catches have resulted in the volume of mariculture doubling each decade, a growth expected by the FAO to persist in the decades to come. This growth should use technologies with economical and environmental sustainability. Feed accounts for about half the cost in current high-volume fed mono-species aquaculture, mainly fish net pens or shrimp/fish ponds, yet most of this feed becomes waste. The resulting environmental impact and rising feed costs therefore hamper further growth of such farms. As in certain traditional polyculture schemes, plants can drastically reduce feed use and environmental impact of industrialized mariculture and at the same time add to its income. These nutrient-assimilating photoautotrophic plants use solar energy to turn nutrient-rich effluents into profitable resources. Plants counteract the environmental effects of the heterotrophic fed fish and shrimp and restore waterquality. Today's integrated intensive aquaculture approaches, developed from traditional extensive polyculture, integrate the culture of fish or shrimp with vegetables, microalgae, shellfish and/or seaweeds. Integrated mariculture can take place in coastal waters or in ponds and can be highly intensified. Today's technologies are well studied and documented. They are generic, modular and adaptable for several culture combinations of fish, shrimp, shellfish, abalone, sea urchin and several species of commercially important seaweeds and vegetables. A I-ha land-based integrated seabream-shellfish-seaweed farm can produce 25 tons of fish, 50 tons of bivalves and 30 tons fresh weight of seaweeds annually. Another farm model can produce in I ha 55 tons of seabream or 92 tons of salmon, with 385 or 500 fresh weight of seaweed, respectively, without pollution. Preliminary calculations show a potential for high profitability with large integrated farms. Several freshwater integrated fish-vegetable farms and a couple of modem fish-algae-shellfish/abalone integrated mariculture farms exist today, and several additional farms are planned. Three major international R&D projects promise to soon expand the horizons of the technology further. Therefore, modem integrated systems in general, and seaweed-based systems in particular, are bound to play a major role in the sustainable expansion of world aquaculture. (C) 2004 Elsevier B.V. All rights reserved.