Production of animal protein is associated with high greenhouse gas (GHG) emissions. Globally, oyster aquaculture is increasing as a way to meet growing demands for protein, yet its associated GHG-emissions are largely unknown. We quantified oyster aquaculture GHG-emissions from the three main constituents of GHG-release associated with terrestrial livestock production: fermentation in the animal gut, manure management, and fodder production. We found that oysters release no methane (CH4) and only negligible amounts of nitrous oxide (0.00012 ± 0.00004 μmol N2O gDW–1 hr–1) and carbon dioxide (3.556 ± 0.471 μmol CO2 gDW–1 hr–1). Further, sediment fluxes of N2O and CH4 were unchanged in the presence of oyster aquaculture, regardless of the length of time it had been in place. Sediment CO2 release was slightly stimulated between 4 and 6 years of aquaculture presence and then returned to baseline levels but was not significantly different between aquaculture and a control site when all ages of culture were pooled. There is no GHG-release from oyster fodder production. Considering the main drivers of GHG-release in terrestrial livestock systems, oyster aquaculture has less than 0.5% of the GHG-cost of beef, small ruminants, pork, and poultry in terms of CO2-equivalents per kg protein, suggesting that shellfish aquaculture may provide a a low GHG alternative for future animal protein production compared to land based sources. We estimate that if 10% of the protein from beef consumption in the United States was replaced with protein from oysters, the GHG savings would be equivalent to 10.8 million fewer cars on the road.
We have demonstrated that oyster aquaculture can provide a low-GHG animal protein source relative to terrestrial livestock production. Further, relative to other aquaculture products that negatively impact local ecosystems or require terrestrial food inputs,11,13 oyster aquaculture presents an opportunity for an ecologically beneficial industry, providing habitat for juveniles of other commercially valuable fish species, protection from storm surges and wave energy, and regulation of nutrients.80 Despite these benefits and the low GHG-cost relative to other animal protein production methods, challenges and questions of the potential of oysters raised in culture to replace terrestrial protein remain. For example, can oyster aquaculture grow to an extent that it can feasibly replace other animal proteins at a significant scale? Will there be a demand for large quantities of oyster meat? What are the ecological consequences of large scale expansion of the oyster aquaculture industry? Will ocean acidification hinder large scale bivalve production? The answers to these questions are the keys in predicting the future of oyster aquaculture and its potential to replace or augment terrestrial livestock production.