Economic Value of Oyster Reefs

Anne Smiley collects sediment samples as part of her study on nitrogen burial rates in restored oyster reefs.
Photo Credit: Johnny Andrews/UNC-Chapel Hill

Scientific Frontline: Extended "At a Glance" Summary: Economic and Ecological Value of Oyster Reefs

The Core Concept: Oysters continuously filter coastal waters and deposit excess nitrogen into the ocean floor sediment, a natural process known as nitrogen burial. A recent study demonstrates that this ecosystem service has an economic value 42% higher than previously estimated.

Key Distinction/Mechanism: While all oysters filter water, the efficiency of nitrogen sequestration relies heavily on the reef's architecture and spatial location. Taller, denser reefs situated on open flats and exposed at low tide bury nitrogen at significantly higher and faster rates than submerged, shorter, or less dense reefs.

Major Frameworks/Components:

• Biogeochemical Cycling (Nitrogen Burial): The ecological process by which bivalves filter nitrogen-rich organic matter and sequester it into benthic sediments.
• Ecosystem Services Valuation: An economic framework used to assign monetary value to natural environmental functions, specifically supporting nutrient credit trading programs across the US.
• Structural Reef Dynamics: The assessment of physical reef traits, primarily height and density, as the main drivers of environmental filtration efficiency.
• Tidal and Spatial Variability: The comparative environmental analysis of intertidal versus subtidal reefs and their placement near salt marshes versus open flats.

Branch of Science: Marine Ecology, Biogeochemistry, Environmental Economics, and Coastal Management.

Future Application: These findings will directly guide the physical design, engineering, and placement of future oyster reef restoration projects to maximize nitrogen removal, increase return on investment, and inform water quality policies.

Why It Matters: Excess nitrogen in aquatic ecosystems causes toxic algal blooms and low-oxygen dead zones that destroy marine life. Recognizing and maximizing the true economic and environmental value of oyster reefs provides a robust, natural solution for purifying coastal waters while simultaneously stabilizing shorelines.

Researchers sampling sediments adjacent to an oyster reef in coastal North Carolina.
Photo Credit: Johanna Rosman/UNC-Chapel Hill

A UNC Institute for the Environment study shows the environmental and economic benefits of oyster reefs.

A new finding by researchers at the University of North Carolina at Chapel Hill shows that oysters’ ability to bury nitrogen may have an economic value 42 percent higher than previous estimates.

These findings, published in PLOS One, have important implications for oyster reef design to improve water quality, as well as for developing a more comprehensive understanding of the environmental and economic benefits of oyster reefs.

Carolina is a global leader in oyster reef research. UNC-Chapel Hill ranked second in the world for oyster reef research, according to a study in Water.

“Oysters provide tremendous value to society in many ways, including regulating water quality,” said Anne Smiley ’24 (PhD), a postdoctoral researcher at the UNC Institute for the Environment and lead author of the study.

“Nitrogen removal, specifically, is a valuable ecosystem service that has been used to develop nutrient credit trading programs across the US,” Smiley said. “Factoring in how oysters bury nitrogen in sediments would more accurately capture their value, support stronger water quality policies, and increase returns on investment for restoration projects.”

Mike Piehler, the institute’s director, is an author of the paper. “Anne’s new manuscript is an important contribution to our understanding of the role of oyster reefs in both coastal ecosystems and economies,” he said. “Carolina is a longtime leader in oyster reef research, and this study is a great addition to that body of work.”

A diagram depicting intertidal oyster reefs on open flats (center) buried more nitrogen than intertidal reefs next to salt marshes (left) and subtidal reefs (right).
Image Credit: Courtesy of University of North Carolina at Chapel Hill

Improving Water Quality

A single oyster can filter several gallons of water per day. Oysters filter nitrogen and deposit it on the ocean floor, where it gets buried in sediment. Too much nitrogen in the water can cause algal blooms and low-oxygen dead zones where marine life cannot survive, creating conditions that are unsafe for humans. Oysters not only play a key role in maintaining water quality, but they also stabilize the shoreline and provide a harvestable source of shellfish for human consumption.

For this study, researchers measured nitrogen burial in restored oyster reefs in Back Sound, North Carolina, located in Carteret County near Morehead City. They accounted for different environmental settings, such as oyster reefs that remain submerged, reefs that are exposed at low tide, and reefs that are on open flats or salt marshes. They found that nitrogen burial rates were strongly linked to reef structure, and that taller, denser reefs buried nitrogen at higher and faster rates than shorter, less dense reefs.

“We found that reefs located on open flats and exposed at low tide buried nitrogen at faster rates,” Smiley said. “If improving water quality through nitrogen removal is the goal, restoration efforts should prioritize this reef design.”

Oyster reef restoration is a costly undertaking, and measuring the return on investment involves numerous variables. Having these new measurements of nitrogen burial helps provide a more complete assessment of the value of oyster restoration projects. Future oyster restoration initiatives can benefit from these findings to ensure effective coastal management.

“This research improves our understanding of how oysters maintain water quality, supports a more complete account of the economic value they provide to society, and informs reef restoration to maximize environmental and economic benefits,” Smiley said.

Published in journal: PLOS One

Title: Habitat context affects sediment nitrogen burial by restored Eastern Oyster reefs

Authors: Anne Margaret H. Smiley, F. Joel Fodrie, Jonathan H. Grabowski, Antonio B. Rodriguez, Suzanne P. Thompson, and Michael F. Piehler

Source/Credit: University of North Carolina at Chapel Hill | Emily Williams

Edited by: Scientific Frontline

Reference Number: eco052426_01

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