European shellfish aquaculture can help reduce negative water quality impacts of excess nutrients (nitrogen and phosphorus) in coastal communities, according to a recent study funded by the European Union’s Horizon 2020 programme. The study, conducted by a multi-national team during the GAIN project (Green Aquaculture Intensification in Europe http://www.unive.it/gainh2020_eu) examined the potential for including aquaculture of mussels, oysters, and clams in watershed-scale nutrient management policies.

Nutrient discharges to coastal waterbodies can stimulate excessive growth of algae leading to water quality degradation with consequences such as low oxygen, dead fish, and/or harmful algal blooms. These nutrient-related impacts have been reported for many EU estuaries.

Nutrient pollution, or eutrophication, is typically controlled by  preventing nutrient discharges to coastal waters through management measures including wastewater treatment and careful use of agriculture fertilizer. Wastewater treatment has been very successful in reducing direct loads, but reductions that require major changes in agriculture, livestock, and community management are economically costly and may have severe social consequences.

Growing bivalve shellfish provides direct economic benefits to a community by supporting jobs and making local seafood available to consumers. It also provides ecosystem services—benefits that nature provides to people—including reductions of algae, which are eaten by the clams, oysters and mussels. The shellfish absorb nutrients into their tissue and shell and remove algae and nutrients from the waterbody, contributing to the environmental sustainability of estuaries, bays, and coastal zones.

The removal of algae by filter-feeding bivalve shellfish is an important and economically valuable ecosystem service—in the USA, compensation to shellfish farmers for the water clearance service they provide is at an advanced stage of debate; in the Chesapeake Bay, growers have been paid for services provided by oyster aquaculture.

Results of this study will provide the basis for strategic guidelines to develop a nutrient credit trading programme in Europe. Our study shows that EU annual production of over half a million metric tons of bivalves removes between 5 and 13 thousand tons of nitrogen per year. The annual cost of removing the same amount of nutrients using other measures would be between 18 and 48 billion €.

“Our hope is that our approach will be useful throughout the EU, and that our positive results will help inform discussions about the value of shellfish aquaculture to water quality, in addition to seafood provision,” said Prof. Roberto Pastres, coordinator of the GAIN project.

Prof. Pastres added “We recommend the inclusion of bivalves within comprehensive nutrient management plans. Shellfish farming, with its reduced ecological footprint, net removal of organic material, and low food-web nutritional requirements, is perhaps the best example of nature-based intensification for blue growth.”