The scale of the problem facing oyster reefs provides the backdrop for the new valuation. Worldwide, an estimated 85 percent of oyster reefs have been lost over the past century, with the steepest declines concentrated in estuaries and river deltas, the very environments where these reef-building bivalves thrive. Like all coastal ecosystems, oyster reefs are under growing stress from overexploitation, pollution, and climate change. The United Nations’ Sustainable Development Goal on life below water calls for the conservation and sustainable use of coastal and marine resources to safeguard human wellbeing, yet the habitats that could deliver many of those benefits continue to disappear. The new study was designed to quantify exactly what is being lost, and what could be regained, if restoration were pursued at scale.

To build their global picture, the researchers, led by corresponding author Dr Matteo Convertino, an associate professor at Tsinghua University, began by assessing where suitable habitat for oyster reefs exists today and where reefs could spontaneously form given the right protection and restoration interventions. They imported thousands of geotagged records of oyster reefs from two public databases and then applied a well-established machine learning algorithm to predict geographic distributions and habitat suitability around the world, flagging potential new locations where reefs might be established. The suitability model weighed a suite of environmental variables, including local water temperature, salinity, light availability, nutrient richness, and oxygenation. Any location scoring 65 percent or greater on habitat suitability was classified as suitable for reef formation.

The team then went a step further, combining each area’s suitability score with a measure of the ecosystem services a reef there could provide to calculate what they call the ecopotential of every location. The higher the ecopotential, the greater the potential benefit of restoring or protecting a reef at that site. This portfolio of services extends far beyond oysters for human consumption. Oyster reefs filter enormous volumes of water, protect shorelines from erosion and storm damage, recycle nutrients through the food web, and sequester carbon. They also provide food, shelter, and nursery grounds for a plethora of fish and invertebrates, functioning as foundational habitat that supports entire coastal food webs. Capturing the full value of this portfolio is what pushes the estimated GEP into the trillions.

The modeling results identified ten hotspot nations where predicted ecopotential is greatest: the United States, Australia, Chile, China, Japan, South Korea, Argentina, France, Germany, and Italy. Across these countries, approximately 295,000 square kilometers, or about 6 percent of their coastal zones, were deemed suitable for oyster reefs. Yet reefs are currently known to occupy only 10 percent of that suitable area, mainly in lagoons and bays, estuaries, and river deltas. The gap between what exists and what could exist points to enormous room for expansion. Perhaps more striking is the finding that only 23 percent of the suitable area currently falls under any form of marine protection, meaning the vast majority of remaining and potential reef habitat remains exposed to the pressures that have already erased most of the world’s oyster reefs.

The quantified benefits of full restoration are vivid when expressed in raw ecological terms. If every area with positive ecopotential were occupied by reefs, the authors calculate that these ecosystems could filter prodigious volumes of water: 77.58 quadrillion liters in the United States, 69.92 quadrillion liters in Australia, and 46.58 quadrillion liters in Chile. Water filtration by dense aggregations of filter-feeding oysters improves clarity, removes excess nutrients, and can help suppress harmful algal blooms, cascading through coastal ecosystems in ways that benefit seagrasses, fish populations, and human users alike. The same fully realized reef network could sequester as much as 12.3 million metric tons of carbon per year, adding a meaningful climate mitigation component to the reefs’ portfolio of services.

For a single country, the monetary value of just a subset of these services is already substantial. In the United States alone, the combined potential value of nitrogen removal, carbon sequestration, and water purification by oyster reefs was estimated at 25.1 billion dollars a year. Nitrogen removal matters because coastal eutrophication, driven by agricultural and urban runoff, is one of the most damaging forces in estuarine systems worldwide, and oysters incorporate and process nitrogen as they filter and grow. Carbon sequestration reflects the burial of organic material in reef structures and surrounding sediments. Water purification, meanwhile, underpins fisheries, tourism, and coastal water quality. These three services represent only part of the total portfolio, which is why the global GEP estimate reaches into the trillions when all services and all suitable nations are considered.

The authors are careful to frame these figures as estimates rather than guarantees. The calculations infer ecosystem services from global averages of key parameters, and the actual values could shift with changes in oyster populations over time or with the advancing climate crisis. Significant work on habitat restoration and protection would also be required before any of the potential could be unlocked. We estimated that 90 percent of sites suitable for oyster reefs require restoration, while 80 percent need protection through conservation efforts, Convertino said. In other words, the current oyster situation is very suboptimal, but there is a huge opportunity, considering the benefits. The statement captures the central tension of the study: the ecological and economic potential is enormous, but realizing it demands investment and policy action on a comparable scale.

Climate change adds a further layer of complexity to the outlook. Because global warming generally decreases the habitat quality of oyster reefs, the researchers expect the global GEP to decline from the current potential value of twelve trillion dollars as conditions shift. Yet the picture is not uniformly negative. Some countries may see an expansion of reefs due to more favorable conditions for the growth and dispersal of oysters. The study singles out Australia, Indonesia, South Korea, Japan, and France as places where reef extent could grow under warming conditions, a reminder that the biogeography of coastal ecosystems will be reshuffled rather than simply diminished. For policymakers, the implication is that restoration priorities may need to be dynamic, tracking shifting habitat suitability over decades.

What the study ultimately offers is a new way of seeing an ecosystem that most people encounter only on a dinner plate. By translating the ecological work of oyster reefs into the language of gross ecosystem product, the researchers make a case that resonates in ministries of finance as much as in marine biology laboratories. A reef that filters quadrillions of liters of water, sequesters millions of tons of carbon, buffers shorelines, and nurseries commercial fish stocks is not a luxury but infrastructure, and infrastructure that has been allowed to collapse by 85 percent in a single century. The twelve trillion dollar figure is not a promise but a ceiling, one that depends on restoring nine tenths of suitable sites and protecting four fifths of them. Whether the world’s nations choose to make that investment will determine whether oyster reefs remain a remnant of past coastlines or become a cornerstone of future planetary health.

Subject of Research: Global valuation of the gross ecosystem product of oyster reefs

Article Title: The world’s oyster reefs could add $12 trillion to planetary health each year – if they were better managed

Article References: The world’s oyster reefs could add $12 trillion to planetary health each year – if they were better managed. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: oyster reefs, ecosystem services, gross ecosystem product, marine restoration, coastal ecosystems, water filtration, carbon sequestration, habitat suitability, machine learning, climate change, marine conservation, Frontiers in Marine Science