Integrated algal farming: a review

Integrated aquaculture has been proposed as an environmentally friendly way of recycling wastes, especially those produced through the cultivation of high trophic level species, which require the supply of exogenous energy (f ood). The cultivation of filter-feeders and seaweeds around fish culture ca ges has been tested for waste recycling. However, success has not been tota l, partly because the amount of filter-feeders and seaweed needed to remove a significant proportion of the wastes produced from intensive large scale cultivation systems is very large. Thus, semi-closed and land-based system s have been proposed as a technological alternative for integrated aquacult ure. The latter type of systems are technically feasible, although, the hig h investments needed at present, prevent its more general use. In Chile, sa lmon cultivation is well established, and produces over 200,000 tons yr(-1) . As a result of the rapid expansion of salmon farming, the concern regardi ng the environment is rising. Thus we have made experiments to integrate th e cultivation of the agarophyte Gracilaria, with salmon farms. Our results indicate that this alga is capable of removing a significant proportion of the ammonium excreted by fish. Studies in land-based integrated culture sys tems indicate that fish production can reach over 30 kg m(-3), with an asso ciated Gracilaria production of 49 kg (wet weight) m(-2) y(-1). The environ mental benefits associated with the development of integrated tank cultivat ion were assessed by analysing previously published and unpublished data. W ith these production results, a profitability analysis was made, internaliz ing the environmental benefits. As the waste discharge is highly reduced by integrating seaweed cultivation into a fish farm, the economic profitabili ty of a commercial project is almost not affected by internalizing the envi ronmental costs as compared to a situation without environmental requiremen ts.