Bivalves at Work: Quantifying Nutrient Removal Services in UK Coastal Waters

Nutrient loading from agriculture, urban discharge, and industrial effluents contributes to eutrophication, a critical environmental challenge impacting water quality. This research evaluated the role of bivalves in nutrient removal as a bioremediation tool under aquaculture practices in the UK, focusing on current key commercial species: blue mussels Mytilus edulis, Pacific oysters Magallana gigas, (formerly Crassostrea gigas), native oysters Ostrea edulis, and Manila clams Ruditapes philippinarum. The removal of nutrients by bivalve aquaculture was estimated based on the Nitrogen (N) and Carbon (C) fixed in their tissue and shell at the point of harvest using two complementary methods: (i) proximate analysis based on nutrient content in shellfish tissue and shell (for N and C), and (ii) using the FARM model (N only). The monetary value of these services was estimated through comparison to costs of alternative mitigation methods. The results show that the UK bivalve aquaculture sector contributed to the removal of an estimated ca. 127 to 286 tonnes of N in 2019. The harvested bivalves also fixed an estimated ca. 1763 tonnes of C in their tissue and shell. Mussels accounted for the majority of N removed, ca. 116.7 to ca. 264.5 tonnes, due to higher yields. Together, oysters and clams potentially removed an estimated ca. 9.9 to ca. 21.9 tonnes of N. The potential annual value of N removal from the UK bivalve aquaculture sector ranged from £33,000 to over £314 million, depending on estimated harvest and type of alternative removal measure. The results of this work highlight that the expansion of UK bivalve aquaculture could deliver water quality improvements, enhance ecosystem services gains, provide economic benefits and strengthen its role as part of holistic nutrient management strategies.