Aquaculture production systems and environmental interactions

A variety of frameworks currently define the standards for human activities in the European Union. This includes food production systems, and, as stipulated in the Marine Strategy Framework Directive, EU aquaculture must comply not only with human health and consumer protection standards but must also include environmental sustainability issues.

The Blue Growth Strategy emphasizes European concern for sustainable jobs and industrial development and specifies aquaculture, with a lower carbon footprint than most conventional protein production systems, as a means to achieve this. An additional challenge is social acceptability, and, if the aquaculture sector can operate sustainably, this too can be overcome.

One of the key features of organic aquaculture is the “water quality” as the sector relies on good water quality and must not pollute the environment it operates within. The most common aquaculture production systems are classified as “flow through” (FT) where water quality (water temperature, pH, alkalinity, dissolved oxygen, turbidity, ammonia, etc.) is maintained by a continuous flow of new water via these systems.

There is a wide variety of such systems which include land-based tanks and ponds and net-cage structures that may be situated in lakes, rivers and the sea. An alternative approach to maintain good water quality in aquaculture systems and to avoid pollution of receiving waters is the use of recirculating aquaculture systems (RAS).

Such systems enable the cultivation of a large number of commercial species practically anywhere due to the fact that they are often hyperintensive, rely on external energy sources, involve high stocking densities and are not connected to the natural aquatic environment. These features of RAS, however, clash with some of the basic principles of organic aquaculture.

Integrated multi-trophic aquaculture (IMTA) employs macroalgae and shellfish to consume particulate and dissolved compounds from aquaculture effluents, enabling the production of several commercial species while reducing the waste stream to the surrounding environment. Such “win-win” systems enable farmers to comply with regulations regarding waste effluents and to “reuse” the expensive feed offered to the “fed” species, i.e. there are environmental, regulatory and economic incentives in employing IMTA.