The short version
Oysters, clams and mussels eat microscopic algae that grow on excess nitrogen. When farmed shellfish are harvested, the nitrogen in their meat and shells leaves the water with them. Scientists call this “nutrient bioextraction.” In this short policy paper, three NOAA scientists and the director of EPA’s Long Island Sound Office argue that shellfish farming deserves a formal place in nitrogen cleanup programs. They also explain why it can’t replace sewers and other controls that keep nitrogen out of the water in the first place.
What the researchers did
This is a “feature” article, a review and argument rather than a new experiment. Julie Rose, Suzanne Bricker, Mark Tedesco and Gary Wikfors drew on research and management experience, much of it from Long Island Sound, to make the case.
- They reviewed the limits of traditional nitrogen controls, including the rising cost of upgrading sewage treatment plants and the difficulty of controlling scattered “nonpoint” sources.
- They summarized studies that measured or modeled how much nitrogen shellfish remove, including work in Massachusetts estuaries.
- They laid out the main barriers to using shellfish at a large scale and suggested ways around them.
What they found
- Treatment plants get expensive at the margin. In the Connecticut River basin, nitrogen removal at treatment plants was estimated to cost about $12 per pound at 8 mg/L of nitrogen in effluent, $14 at 5 mg/L, and $37 at 3 mg/L.
- Shellfish compare well with other nonpoint fixes. In a Chesapeake Bay comparison, the high-end cost for shellfish aquaculture was about $150 per pound of nitrogen removed, versus $366 to $2,215 at the high end for urban stormwater practices.
- Nitrogen removal is easy to verify. It can be measured directly in shellfish tissue and shell. One Chesapeake study found oyster nitrogen content was closely tied to shell length, so harvest counts can be converted into nitrogen removed.
- The Massachusetts estimate is modest but real. A study of four Massachusetts estuaries predicted that farming oysters on 0.5–1% of the estuary bottom could offset 1–15% of the total nitrogen load.
- Barriers are mostly social and practical. The biggest limit on growth in the US is public acceptance of shellfish farms and conflicts with other users of the water, not space or food for the shellfish. The most nitrogen-polluted waters are often closed to shellfishing because of bacteria, so new markets would be needed for shellfish that can’t be eaten.
What it means for Waquoit Bay today
The authors are clear that shellfish farming functions most effectively as a complement, not a replacement
(Rose et al., 2014) for controlling nitrogen at its source. Shellfish only remove nitrogen that has already reached the bay and fueled algae, while septic upgrades and sewers stop it before it gets there. They also note shellfish fit best in suburban places where scattered sources dominate. That describes Waquoit Bay’s watershed, where most nitrogen comes from septic systems rather than a single treatment plant.
The paper is also a useful checklist for any town hoping to lean on shellfish: competing uses of the water, public acceptance of farms, and waters closed to shellfishing because of bacteria all limit how far aquaculture can grow. The authors suggest paying growers for the nitrogen they remove, or including them in nutrient trading programs, to help the industry expand. For measurements of how much nitrogen Cape Cod shellfish hold, see our summary of the Cape Cod shellfish study.
Read the paper
Rose, J. M., Bricker, S. B., Tedesco, M. A., & Wikfors, G. H. (2014). A Role for Shellfish Aquaculture in Coastal Nitrogen Management. Environmental Science & Technology, 48(5), 2519–2525. https://doi.org/10.1021/es4041336
License: © 2014 American Chemical Society. The article is not openly licensed, so we link to the publisher’s page rather than hosting a copy. All four authors were NOAA or EPA scientists.
Drafted with AI assistance from the linked source.
