Global hindcasts and future projections of coastal nitrogen and phosphorus loads due to shellfish and seaweed aquaculture

Abstract

A model was developed to estimate nitrogen and phosphorus budgets for aquaculture production of crustaceans, bivalves, gastropods, and seaweed, using country production data for the 1970–2006 period from the Food and Agriculture Organization and scenarios based on the Millenium Assessment for 2006–2050. Global production of crustaceans (18% yr−1), molluscs (7.4%), and seaweed (8%) increased rapidly during the 1970–2006 period. Scenarios indicate that annual nutrient release from all shellfish (crustaceans, bivalves, and gastropods) aquaculture will rapidly grow from 0.4 to up to 1.7 million tonnes of nitrogen and from 0.01 to 0.3 million tonnes of phosphorus between 2006 and 2050. The nitrogen and phosphorus releases from global freshwater shellfish aquaculture will increase from 1% of river export in 2006 to up to 6% in 2050. Marine shellfish production is an important contributor to nutrient loading of coastal seas, particularly in Eastern Asia. Nitrogen (7% of marine aquaculture + river export in 2006 and up to 19% in 2050) and phosphorus (12% in 2006 and up to 30% in 2050) releases from Chinese marine shellfish aquaculture are important and growing contributors to total nutrient inputs to coastal seas. Production of crustaceans and bivalves causes changes in nutrient stoichiometry and increasing reduced and organic nitrogen forms, which are of concern because of their preferential use by some harmful algae. Nutrient withdrawal by seaweed is projected to increase rapidly over the coming decades. To overcome effects of increasing nutrient release from shellfish production, integrated systems that include seaweed may play an important role in reducing this nutrient load.