IMTA, to the uninitiated, is a technique in aquaculture based on the concept that growing species at multiple trophic levels side-by-side is more efficient than a monoculture system.
The classic exemplar of integrated multi-trophic aquaculture (IMTA) is the fin-fish, bivalve, seaweed system. There have been disagreements over the exact wording, but the term IMTA is used for any aquaculture system where the outputs from one species could be used by another species being grown, even indirectly. For example, it could be that bivalves co-cultured with fish only get some additional benefit from being near a fish farm at times of the year when natural food sources are scarce. I know of a seaweed-finfish experiment where the seaweed grew better at a site further away from the fish farm than nearer – there are several such examples in the literature.
The point is that things should be grown where they grow best. The important thing is to grow and sell more food, making best use of the available environmental services. Whether the seaweed was taking up nutrients released from the fish farm or not is irrelevant. What matters in any IMTA system is that additional production is achieved and there are net benefits to the nutrient balance of the water body as well as economic benefits to the enterprise.
The classic fin-fish, bivalve, algae triumvirate is not the only possible setup in IMTA. Across the diverse bio-geographies of Europe, each marine ecosystem will only be able to accommodate a subset of the myriad IMTA species combinations possible. Limitations will be caused by factors such as the trophic status of the water body, the locally available species and, most importantly, what will grow and sell well.
A good example of a non-classical system being studied in IDREEM is the mullet-seabream work going on in Israel. Shellfish and macroalgae of commercial value do not occur naturally in the southern Mediterranean. Haifa University and Suf Fish are exploring a fish-fish system where gilthead seabream are farmed conventionally but the native, high value detritivore grey mullet fills the role of the lower-trophic level species.
In IDREEM we are not using IMTA as limiting concept; rather, what works is best. The goals are a growing, diverse European aquaculture industry, increased food supply and security, and improved environmental performance and efficiency, yielding enhanced social outcomes such as increased employment.
Written by Kenny Black – SAMS