The value of oyster and clam aquaculture in terms of their nitrogen removal services has been quantified by a groundbreaking new study.
Researchers used a “transferable replacement cost methodology” to estimate the ecological and economic value of nitrogen reduction that results from oyster and clam aquaculture in Greenwich, Connecticut. The replacement cost method puts a dollar value on ecosystem services by estimating what it would cost for humans to provide those services. In this case, that was the cost of improving wastewater treatment, upgrading septic systems, and better managing stormwater.
The study was conducted by shellfish biologists, economists, and modellers from NOAA Fisheries, NOAA National Centers for Coastal Ocean Science, and Stony Brook University. It was recently published in Environmental Science & Technology.
“When we started discussing this work, I had a long list of ecosystem services in mind—not just nitrogen remediation, but water clarity for swimming and seagrass colonisation, habitat for recreational fish—all leading to improved quality of life in a coastal town,” said Gary Wikfors, chief of the Aquaculture Sustainability Branch at NOAA’s Northeast Fisheries Science Center’s Milford Laboratory in Milford, Connecticut, and a co-author of the study.
“As a biologist, I learned from this study how complex a comprehensive economic valuation is! The economic benefit estimates in this report are just a small fraction of the total—the tip of the iceberg—but still appreciable at the municipal level,” he said.
Greenwich is a community with a thriving shellfish aquaculture industry located on a populous coastline. It serves as an ideal case study for the nutrient-capture benefits of shellfish. About 60 percent of the seafloor off Greenwich is used for shellfish activities, including aquaculture, recreational areas, and seed beds. Particularly in communities with diverse and diffuse nitrogen sources like Greenwich, growing shellfish for food can make a big difference to nutrient management.
Partnerships with two local shellfish growers, Atlantic Clam Farms and Stella Mar Oyster Company, were crucial to this study. The companies provided data on their annual shellfish harvest and local aquaculture practices, which researchers used to model the amount of nitrogen removed.
The owner of Atlantic Clam Farms, Ed Stilwagen, also goes by the moniker “Captain Clam.” He has been growing shellfish in Greenwich waters for more than 20 years and shellfishing since the 1940s. He invented a system for more environmentally-friendly harvesting, and frequently cleans up marine debris while tending to his leases.
“Shellfish are a wonderful food source, and we have perfect conditions to grow them here,” said Stilwagen. “They don’t call me Captain Clam for nothing. I get a lot of interest when I tell people I’m a shellfish farmer—people want to know how many there are and how many I harvest. I hardly ever meet people who don’t like clams, but even if they don’t, they can appreciate that they take care of the environment by filtering the water. Having shellfish in the water improves water quality.”
The approach detailed in this study can be applied to other communities wishing to reduce nutrients to improve water quality. Even without a local shellfish aquaculture industry, decision makers will find the study useful in understanding the environmental benefits of shellfish to their coastal waters.
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