Eating more oysters could reduce greenhouse gas emissions

If Americans replaced 10% of their meat consumption with oysters, the greenhouse gas savings would be the equivalent of keeping nearly 11 million cars off of the road, according to a new study by Sea Grant-funded researchers. That’s roughly 20 times the number of cars registered in Rhode Island.

Their findings were recently published in the journal of Environmental Science & Technology by the American Chemical Society and comes at a time when meat consumption is at an all-time high in the U.S.

According to the U.S. Department of Agriculture (USDA), Americans were estimated to consume an average of 222 pounds of red meat and poultry in 2018 – that’s almost double the 5 to 6.5 ounces recommended for daily consumption. To meet that demand, farms were estimated to ramp up livestock production in the same year by nearly 66%, or 103 billion pounds.

Land-based animal production is linked in a variety of ways to greenhouse gas emissions from land-clearing and fuel usage to waste production and methane release from the animals–all of which account for 15% of annual global emissions associated with increasing global temperatures.

This highlights that there is a critical need for alternative sources of protein due to this contribution to greenhouse gas emissions and limited land availability to increase production to meet demand. Shellfish aquaculture, however, requires a fraction of the space and is growing rapidly with the potential to meet this protein demand by consumers, yet little is known about greenhouse gas emissions from these types of operations.

To compare land-based meat production with oyster cultivation, Dr. Robinson Fulweiler and her team from Boston University looked at the three main greenhouse gases: carbon dioxide, methane, and nitrous oxide, and the main drivers of greenhouse gas release in livestock: land-use change, gas formation in the animal digestive tract, and manure management and feed production–excluding greenhouse gas production from transportation, refrigeration, etc.

“We wanted to be comparing apples to apples…what’s the greenhouse gas footprint for growing a cow in terms of how much they’re producing from their gut, their manure, and how much is produced from feeding?” explained Fulweiler during a Coastal State Discussion presentation earlier this spring about research led by Ph.D. candidate Nick Ray, and conducted with Dr. Tim Maguire, a former Ph.D. student and now a postdoctoral researcher at the University of Windsor, Ph.D. student Alia Al-Haj, and undergraduate researcher Maria Henning.

They made direct measurements of methane and nitrous oxide, and estimated carbon dioxide fluxes via oxygen consumption rates, from feed production, gut fermentation, and manure management associated with the Eastern oyster. They noted that there is no greenhouse gas release from growing or transporting feed for oysters as they filter their food directly from the water. Any greenhouse gas release would be from the oysters themselves via shell formation, respiration, or microbial processes in their guts, or by bacteria in the sediment metabolizing oyster waster, or “manure.” Any carbon dioxide produced from respiration was omitted from their overall estimate to match methods used for estimating livestock greenhouse gas production. Carbon dioxide release from shell formation was also not included as knowledge of the future use of the oyster shell is needed for accurate assessment of carbon release or sequestration.

“Oysters are a friendly alternative if you want to eat protein and not contribute to the greenhouse gas footprint.”

Oysters were collected for lab incubations and sediments were sampled from a farm using rack and bag aquaculture in Ninigret Pond, one of 9 coastal salt ponds in Rhode Island. In addition to a control site, three sites were selected for sediment samples based on the age of the site used within the farm from 2, 4, and 6 years, in the first season of sampling.

“We are thankful for Jim Arnoux, owner of the oyster farm East Beach Blondes, who allowed and enabled them to sample on his farm,” said Fulweiler.

Their study demonstrated oyster aquaculture didn’t release any methane and only negligible amounts of nitrous oxide and carbon dioxide, with all greenhouse gas release coming directly from the oyster itself. There was no difference in greenhouse gas release from microbial communities in the sediments beneath oyster aquaculture compared to bare sediments. They did, however, observe increases of carbon dioxide production from sediments when an aquaculture site was in place for more than three years, but the carbon dioxide release returned to baseline levels after six years.

Ultimately, the study suggests oyster aquaculture appears to be a good alternative for protein production as it has less than 0.5% of the greenhouse gas-cost of beef, small ruminants, pork, and poultry in terms of carbon dioxide equivalents per kilogram of protein.

“Oysters are a friendly alternative if you want to eat protein and not contribute to the greenhouse gas footprint,” said Fulweiler.

More work needs to be done, noted Fulweiler, to better understand the potential oysters pose as protein alternatives with regard to the impacts of culture methods and farm locations, as well as long-term impacts of ocean acidification, ecological consequences of large-scale operations, and consumer demands for oyster meat.