- Researchers have found that the restoration of eastern oyster (Crassostrea virginica) reefs in the U.S. have been largely successful, improving oyster production, enhancing habitat, and increasing nitrogen cycling.
- They also found that oyster restoration was more successful in deeper, saltier parts of coastal waters and that it generally took at least eight years for restored reefs to yield long-term benefits.
- But since the 1800s, more than 85% of global reefs have disappeared due to overfishing, disease and other anthropogenic pressures.
- Researchers say their findings can help restoration managers identify which ecosystem services can benefit from their work, how long those benefits might take to accrue, where to construct oyster reefs.
Research has shown that oyster restoration projects in the U.S. have been largely successful, but ecosystem benefits may take decades to fully emerge.
In a study published in Conservation Biology, scientists synthesized data on the restoration of eastern oyster (Crassostrea virginica) reefs in the U.S. They found that such projects improved the local ecosystem by increasing oyster production by a multiple of 21. Restored oyster reefs also enhanced habitat for fish and shellfish by 34-97% and increased nitrogen cycling by 54-95%, which helps improve water quality.
A second study in Ecological Applications, published by two of the same authors, noted that eastern oyster restoration was the most successful in deeper, saltier parts of coastal waters that generate more tidal exchange. It also found that the number and diversity of oysters, fish and shellfish on restoration sites increased over time and that these reefs generally took at least eight years to yield long-term benefits.
Oyster restoration refers explicitly to creating new oyster habitat by adding substrate from materials like shell, concrete, limestone or rock — or simply adding live oysters — to generate reefs in intertidal or subtidal coastal areas.
“Both of these studies show that oyster restoration is by and large successful, even if it’s more successful in certain places,” Max Castorani, a co-author of both studies and a marine ecologist at the University of Virginia, told Mongabay. “So that’s a really good thing, and that’s evidence that conservation practitioners can point to.
“The studies also show the expectations managers should have about which ecosystem services should be benefited by their restoration projects, and how long those benefits might take to accrue [and] it provides guidance on where to construct oyster reefs,” Castorani added.
Oyster reef habitats are considered critical ecosystems that create habitat and food sources for various species, improve water quality, protect coastlines from storms, and support fisheries. But since the 1800s, more than 85% of global reefs have disappeared due to overfishing, disease, and other anthropogenic pressures. In response, oyster restoration has gained traction worldwide, especially in the past two decades.
The researchers drew data from hundreds of oyster restoration sites, degraded oyster reefs and pristine oyster reefs, over a 3,500-kilometer (2,200-mile) stretch of the U.S. Gulf of Mexico and Atlantic coastlines.
Rachel Smith, also of the University of Virginia and lead author of both studies, said the studies helped identify several knowledge gaps around oyster restoration. For instance, the studies showed that little is actually known about how oyster restoration can help protect coasts, store carbon or clarify water, even though conservation practitioners often tout these benefits of oyster reefs, she said.
“We really need more studies of [oysters] in a restoration context where we have comparisons and real controls that allow you to show the effect of restoration,” Smith told Mongabay. “It points out areas for more work and where we should focus restoration efforts in the future.”
Melanie Bishop, a coastal ecologist at the Macquarie University Marine Research Centre in Sydney, Australia, who was not involved in the research, said the studies showed the “considerable environmental benefits” of oyster restoration over time.
“As oyster reef restoration scales up across Europe, Asia, and Oceania, it is useful to reflect on the decades of oyster reef restoration that has been undertaken in the USA and the key drivers of success for those projects,” Bishop told Mongabay in an email. “Though there is always a tendency for failed projects to be under-represented in the literature, the analyses nevertheless highlight the considerable environmental benefits that can be gained from appropriately designed oyster reef restoration projects and highlight that these benefits may occur across a broad spectrum of the environmental settings in which oyster reefs are found.
“Oyster reefs are critically important ecosystems,” she added. “Although the studies suggest that considerable environmental benefits can be incurred through oyster reef restoration, they also suggest that these take time to accrue and that some components of the ecosystem may not recover, at least within the time frame of studies. This is an important reminder that alongside oyster reef restoration, there is [a] need to conserve remnant oyster reefs.”
Banner image: Eastern oyster (Crassostrea virginica) reefs in the U.S. Image by Bo Lusk / Nature Conservancy.
Elizabeth Claire Alberts is a senior staff writer for Mongabay. Follow her on Twitter @ECAlberts.
Smith, R. S., Cheng, S. L., & Castorani, M. C. N. (2022). Meta‐analysis of ecosystem services associated with oyster restoration. Conservation Biology, 37(1). doi:10.1111/cobi.13966
Smith, R. S., & Castorani, M. C. N. (2023). Meta‐analysis reveals drivers of restoration success for oysters and reef community. Ecological Applications. doi:10.1002/eap.2865
Beck, M. W., Brumbaugh, R. D., Airoldi, L., Carranza, A., Coen, L. D., Crawford, C., … Guo, X. (2011). Oyster reefs at risk and recommendations for conservation, restoration, and management. Bioscience, 61(2), 107-116. doi:10.1525/bio.2011.61.2.5