Integrated algal farming: A review

Abstract

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 (food). The cultivation of filter-feeders and seaweeds around fish culture cages has been tested for waste recycling. However, success has not been total, 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 systems have been proposed as a technological alternative for integrated aquaculture. The latter type of systems are technically feasible. although, the high investments needed at present, prevent its more general use. In Chile, salmon cultivation is well established, and produces over 200,000 tons yr-1. As a result of the rapid expansion of salmon farming, the concern regarding the environment is rising. Thus we have made experiments to integrate the 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 systems indicate that fish production can reach over 30 kg m-3, with an associated Gracilaria production of 49 kg (wet weight) m-2 y-1. The environmental benefits associated with the development of integrated tank cultivation were assessed by analysing previously published and unpublished data. With these production results, a profitability analysis was made, internalizing the environmental benefits. As the waste discharge is highly reduced by integrating seaweed cultivation into a fish farm, the economic profitability of a commercial project is almost not affected by internalizing the environmental costs as compared to a situation without environmental requirements.