Ecology

Zoologist Yolarnie Amepou heard whispers about the fish frenzy when she made her first trip to the Kikori River Delta in the remote reaches of southern Papua New Guinea.It was January 2012, and Amepou was travelling down the delta by dinghy, from village to village, as part of a research project on the vulnerable pig-nosed turtle (Carettochelys insculpta). Amepou heard talk of outsiders appearing across the region offering staggering amounts of cash for swim bladders — an organ cut from some of the delta’s large fish species that helps them to control buoyancy. Consumers in Asia, particularly southern China, know this commodity as fish maw and covet it as a culinary delicacy, a traditional medicine and a symbol of prosperity.The global maw trade has been growing rapidly over the past 25 years1, and market prices now far exceed those of similar dried seafood luxuries such as shark fin and sea cucumber, which are also prized in China. In some low- and middle-income countries where demand for maw is very high, it is sometimes called the cocaine of the seas because it is so lucrative and attracts organized crime interests.Papua New Guinea has become the source of some of the most sought-after maw. In the years since Amepou’s first visit, she’s watched the fish-maw industry in the Kikori delta explode, “like a fisheries gold rush”. Fishers replaced their paddle canoes, lines and hooks with outboard-powered dinghies and commercial nets. The price being offered to delta fishers for dried maw from one prized species — the scaly croaker (Nibea squamosa) — has been recorded at up to US$15,615 per kilogram — potentially the highest price offered to fishers for maw in the world, according to a study by Amepou and her colleagues published earlier this year2.

The Kikori river delta is the source of some of the most highly prized maw in the world.Credit: Minden Pictures/Alamy

Revenue from the maw industry is a lifesaver for many delta communities, with some people using it to move away from the coast to escape rapidly rising seas. “Fish maw has alleviated some quite severe poverty issues,” says Michael Grant, a marine biologist at James Cook University in Townsville, Australia, who researches Papua New Guinea’s sharks and rays in the Kikori delta, one of their last strongholds. Its waterways and mangroves are recognized as a sanctuary of biodiversity and have been nominated for inclusion as a World Heritage Site on the list maintained by the United Nations cultural organization UNESCO.Grant and others fear that the sharp increase in fishing pressure in the Kikori delta and the use of gillnets — which indiscriminately capture many types of fish, dolphin and turtle — could recreate problems that have plagued Mexico, China and parts of Africa, where the maw trade has fished some species into near oblivion. That threat risks damaging the delta’s ecosystems and leaving people worse off, says Grant.The information coming out of Papua New Guinea “is worrying, because it does seem to fit what we’ve seen in other places wherelittle-known species are targeted for the value of their maw”, says Yvonne Sadovy, a Hong Kong fisheries specialist now based in the United Kingdom. Along with Grant and other members of a species-survival commission that is part of the International Union for Conservation of Nature (IUCN), she contributed to a paper sounding the alarm on the increasing maw trade that was submitted by the United States to a meeting of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) in July.“There are very few controls and there is very little knowledge, I think, by the government fishery departments about the value, importance and potential threats of this,” says Sadovy. The consequence is “a sort of cowboy frontier”, whereby high prices push fishers to target species that “we hardly know anything about in terms of the science”.Turtle troublesAmepou wasn’t too concerned when she first heard about the fish-maw trade. In her early years in the Kikori region, she was focused on how hunting and habitat changes were threatening the pig-nosed turtle. The work took her to far-flung villages to monitor nesting sites, survey the consumption of turtle meat and eggs, and build community awareness about the vulnerability of the creatures known as piku.By 2019 she was known locally as mama piku, and was the director of a small conservation organization, the Piku Biodiversity Network, which she still runs. Amid the other changes in the region, the fish-maw trade had become yet another threat to the turtle’s survival because the animals were getting tangled in commercial gillnets that seafood companies were supplying to local fishers.

Rising sea levels have damaged the remote village of Veraibari.Credit: Jo Chandler

The remoteness and logistical difficulties of working in the Kikori delta — a region with little electrical power, few roads, fragmentary communications and 4–8 metres of rainfall a year — mean that Amepou, Grant and their collaborators are among just a handful of researchers who are active in the area. With support from the Secretariat of the Pacific Regional Environment Programme (SPREP), a multinational organization focused on the region’s natural resources, they collected data on targeted maw species, as well as by-catch. A survey of landings in gillnets reported by fishers from five delta communities over six months to April 2022 found that the hunt for fish maw pulls up huge numbers of non-target fish and mammals3.Elasmobranchs — a subclass of fish that includes sharks and rays — accounted for almost half the catch, whereas target species made up just 22%. Among the other casualties were several species listed as endangered or critically endangered on the IUCN Red List, including three species of hammerhead shark, the giant guitarfish (Glaucostegus typus) and the bottlenose wedgefish (Rhynchobatus australiae), alongside various vulnerable river sharks and critically endangered Indo-Pacific sawfishes (Pristidae)2.Other reports, some unpublished, document declines in two endemic dolphin species that have small local populations and are listed as vulnerable on the IUCN Red List. On one occasion, fishers reported that ten dolphins drowned in a single net, says Amepou. “You’re looking at the very real possibility of a local extinction if nothing is done about the gillnets in the water,” she says.But discussions with local people about curtailing fishing practices for conservation purposes are acutely sensitive given the money flowing into the economically disadvantaged region. “While local fishers acknowledge sustainability concerns, the overarching feeling is everyone is pretty happy for now,” says Grant. “Whether fish-maw money is going back into community and development remains to be seen, and this is our next research focus.”In 2022, the researchers submitted a report to SPREP on the Kikori maw fishery, urging the development of a management plan3. Sources have told Nature that work on a plan has commenced, but Papua New Guinea’s authorities did not respond to questions from Nature on its progress. In 2021, the National Fisheries Authority stopped issuing new fish-maw licences in Gulf Province, where the Kikori delta is located, and in the neighbouring Western Province, owing to increasing illegal, unregulated and unreported activities in the two fisheries.Villages at riskAfter storm surges destroyed many houses in the delta village of Veraibari in 2020, the people formed a relocation committee. They plan to use the windfall maw money to build around 200 homes, a school, a market and churches a short distance inland from the beach where they currently live. The committee estimates that this plan will cost 1,689,000 Papua New Guinean kina (US$431,000). In recent years, waves have damaged and closed the schoolhouse, knocked down freshwater tanks and submerged burial grounds. Abandoned homes decay on their stilts in the shallows alongside the stumps of drowned palm trees.“The land is disappearing, the high land is going down, and then it is very easy for water to enter into the village,” says community and church leader Ara Kouwo. When the big tides come, his family wades into the sea to push away debris that might tip their home off its legs.Kouwo is also the local agent buying maw for one of the six seafood companies, all Asian-led, with licences in Gulf Province. He conducts business at his family table, weighing and trading fish maw, offering 5,000 to 6,000 kina per 100 grams for the finest specimens. He kicked off the relocation fund with his own earnings, urging his neighbours and relatives to provide cash or other contributions. They are lobbying for more government support, but have so far received only sandbags to build a seawall, which soon failed, and some iron roofing, nails and a sawmill to help with the relocation. Money earned from fishing is the only way to save the village, he says, although he recognizes the risks.If there was any other help coming to pay for the new village, “then we would stop these fishing activities”, he says. “We are in fear,” he adds. “When we kill all mothers of the fish, we are in trouble.”

Maw drying outside in a delta community.Credit: Yolarnie Amepou/Piku Biodiversity Network

Environmental lawyer Watna Mori at Blue Ocean Law, a firm based in Hagåtña, Guam, is part of a team assisting the people of Veraibari to argue a case for funding from the UN for loss and damages due to climate change. She says that the tension between the slow process of structural, systemic change and the community’s urgent need was heartbreakingly stark when she visited Veraibari in 2022.“You see the contrast of these two activities — trying to adapt to climate change, and then you see this act of fishing for this product that causes so much harm to their biodiversity,” says Mori. “What else can they do?”The maw trade generates a boom-and-bust cycle that fisheries researchers and activists have seen before. The most infamous case is that of the totoaba (Totoaba macdonaldi), which is found only in Mexico’s Gulf of California and was hunted for its maw for much of the twentieth century.Although Mexico banned fishing for totoaba in 1975, the species continues to be fished illegally, with trading of totoaba maw increasing on Facebook and the Chinese social media platform WeChat, according to a report released in February by the Environmental Investigation Agency UK, a non-governmental organization in London (see go.nature.com/4ghoiwr). The gillnets used to catch totoaba also entangle the endemic vaquita (Phocoena sinus), the world’s smallest porpoise. It’s estimated that as few as ten individuals remain.The hunt for maw has left a trail of ecological damage elsewhere, too, including in Africa’s Lake Victoria, where there are concerns that the Nile perch (Lates niloticus) might disappear.Hidden dangerFor years, the global scale of fish-maw operations remained mainly under the radar because the volume of the catch was hidden in a broad commodities category of “dried fish”, says Sadovy. She and others urged authorities in Hong Kong, the global trade hub for maw, to introduce a specific code for fish maw separate from other dried fish, which they did in 2015. Data collected using this new code revealed that between 2015 and 2018, 3,144–3,882 tonnes of dried maw, worth $264 million to $394 million, were imported to Hong Kong every year4. These were shockingly high numbers, Sadovy says, “because you might have 3,000 tonnes of maw, but maw is only 5% of the weight of the animal. So that’s tonnes and tonnes of animal, so you begin to think about the scale of those fisheries”.Her team tracked the maw to 110 source countries and territories, but found that, in most of those nations, hardly anything is known about the trade. “A lot of even local scientists had no idea this trade was going on, it’s quite secretive,” she says.

Turtles, marine mammals and non-target fish often get caught in nets used by people fishing for species that supply maw.Credit: Amos Ivei/Piku Biodiversity Network

Her work also exposed the previously unrecognized loss of another species coveted for its maw, the Chinese bahaba (Bahaba taipingensis)5, which can reach 2 metres in length and weigh more than 100 kilograms. Records from the 1930s found specimens in its habitat off the coast of China. Today it is so rare that “it is possible it will become the first marine commercial species to go extinct in recent times in the wild”, Sadovy says.The cycles that have played out with the bahaba, totoaba and Nile perch “illustrate the consequences of escalating prices and lack of management”, including the implications for biodiversity, Sadovy and her colleagues warned in 20194. Concern over the trade has grown in the years since then. In 2021, in response to the high prices being paid for maw in Papua New Guinea, Bangladesh, India and French Guiana, the IUCN adopted a motion urging nations to control and monitor trade in the swim bladders of a group of ray-finned fishes known as big croakers to both protect the target species and reduce by-catch of threatened marine megafauna.“A lot of people are beginning to realize — biologists, fisheries people — that maw is an issue,” says Sadovy. However, she adds that there are also a lot of places where the maw trade operates out of sight. Concerns about the trade are what motivated the drafting of the document submitted by the United States to CITES in July, she says. “It was a first initiative to highlight international maw trade as an issue threatening some species.”
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Sadovy hopes escalating concern will persuade international organizations — in particular, the Food and Agriculture Organization (FAO) of the UN — to become more active in documenting the trade. She wants to see the FAO follow Hong Kong’s lead and introduce a commodity code specifically for maw. “There are opportunities to actually seek better benefits for the fishermen themselves,” says Sadovy. “I see a win–win before some species are really pushed too far down.” But it needs to happen soon.Without action at national and international levels, researchers warn that the risks for both vulnerable marine populations and the people who rely on them for income and food are dire. In the dozen years she has been working in the Kikori delta, Amepou has observed how precarious life is in the villages and how much the people there are exposed to the rapidly changing environment. She hears their stories and tries to answer questions about rising seas, changing weather and vanishing species.Amepou likes to take the conversation back to the creature that drew her to the region: the turtle with the snout of a pig, remarkable enough to etch its way into local lore. When she first arrived, the people of the delta told her they had no concerns for its future, because the pig-nosed turtle was like their mother. It would always provide for them.“And I say ‘your mother will provide for you to a certain point. There’s a time in life when you have to take care of your mother’,” Amepou says. “‘And it’s come to that point, where your mother kind of needs your help.’” More

Bauer, S. & Hoye, B. J. Science 344, 1242552 (2014).Article 
PubMed 

Google Scholar 
Twining, C. W. et al. Ecol. Lett. 24, 1709–1731 (2021).Article 
PubMed 

Google Scholar 
Walters, D. M., Fritz, K. M. & Otter, R. R. Ecol. Appl. 18, 1835–1841 (2008).Article 
PubMed 

Google Scholar 
Brandt, J. E. et al. Nature https://doi.org/10.1038/10.1038/s41586-024-07980-2 (2024).Article 

Google Scholar 
Naiman, R. J., Bilby, R. E., Schindler, D. E. & Helfield, J. M. Ecosystems 5, 399–417 (2002).Article 

Google Scholar 
Krümmel, E. M. et al. Nature 425, 255–256 (2003).Article 
PubMed 

Google Scholar 
Razavi, N. R. et al. Sci. Total Environ. 499, 36–46 (2014).Article 
PubMed 

Google Scholar 
Ruggerone, G. T. & Irvine, J. R. Mar. Coast. Fish. 10, 152–168 (2018).Article 

Google Scholar 
Hale, R. & Swearer, S. E. Proc. R. Soc. B 283, 20152647 (2016).Article 
PubMed 

Google Scholar  More

Álvaro Fernández-Llamazares and colleagues document thoroughly how the much-cited claim that 80% of the world’s biodiversity occurs on Indigenous people’s lands is based on a misinterpretation that has cascaded through the scientific literature (Á. Fernández-Llamazares et al. Nature 633, 32–35; 2024). On the basis of their evidence, we agree that the claim should be abandoned, and will encourage our organization to do so.
Competing Interests
The authors declare no competing interests. More

NEWS AND VIEWS
08 October 2024

Lynx numbers ebb and flow as these predators hunt hares across Alaska, but analysis suggests that this population wave is mediated by survival rather than by how lynx disperse. More

Scientists have started swabbing short-tailed Shearwater (Ardenna tenuirostris) for evidence of bird flu. The birds are migrating from the northern hemisphere to Australia.Credit: John Holmes/Alamy

Australia and the rest of Oceania are the last regions free of the highly pathogenic strain of bird flu that has caused mass mortality in birds across the world and a massive outbreak in dairy cattle in the United States. Why animals in the southern region have so far escaped infection is a mystery, but scientists have several theories.For one, Australia is geographically isolated and doesn’t import live poultry, says Frank Wong, a virologist at the CSIRO Australian Centre for Disease Preparedness in Geelong. Many of the countries’ birds are endemic and do not migrate to regions where the virus is spreading.But the virus’s arrival in Australia is “a matter of when, not if”, says Michelle Wille, a virologist at the Centre for Pathogen Genomics at the University of Melbourne, Australia.Bird surveyWille thinks that long-distance migratory shorebirds and seabirds that come from Siberia and Alaska through southeast Asia to Australia are most likely to carry the virus into the country.This week, Australian scientists, including Wille, started swabbing the first of nearly 1,000 migratory birds for the virus. Over the coming weeks, the team will capture wedge-tailed shearwaters (Ardenna pacifica) and short-tailed shearwaters (Ardenna tenuirostris) as they migrate from the northern autumn to the southern spring. At night, shearwaters sleep in burrows and are relatively easy to grab. The researchers will swab the birds for the virus, and take blood to test for antibodies that will reveal previous exposure. They will be testing for the H5N1 clade 2.3.4.4b in particular, which has caused mass mortality in birds and some mammals.To swab the birds, the researchers will travel to seven locations across Australia, as far apart as Broome in the northwest, Lord Howe Island in the east and Phillip Island in the south.Deadly ducks?Wille says another possible route for the virus is through ducks. Scientists think migrating ducks and geese in other parts of the world can spread the disease without succumbing to it.That’s because ducks’ epithelial cells have a sensor, known as RIG-I, that detects an invading influenza virus and triggers an immune response that usually fends it off. Kirsty Short, a virologist at the University of Queensland in Brisbane, says ducks might have evolved such defences in Asia from repeated infections with many less-pathogenic forms of the virus, giving them pre-existing immunity. Although they don’t get sick from H5N1, they can still pass it on, and ducks congregate in lakes and ponds with other birds, increasing the chances of disease spread.Isolated ecosystemsAnother reason that Oceania is currently free of the virus is that the region’s ducks are endemic and they don’t tend to migrate overseas.This isolation is partly explained by a biogeographical division called the Wallace Line, first described by naturalist Alfred Russel Wallace in 1859, which runs through Indonesia. Many animal species tend to stay on one side of the line or the other, and because of this isolation, the fauna on each side are distinct. Michael Andersen, an evolutionary biologist at the University of New Mexico in Albuquerque describes this phenomenon as “one of the great mysteries” of the world.The sharp division might also mean that the virus is not adapted to animals east of the Wallace Line, says Wong. “Avian influenza viruses, including this high-pathogenicity avian influenza virus, are particularly well-adapted to certain species,” he says. Birds in Australia could have a genetic make-up that circumvents the usual infection route for the virus, but no one has yet tested this hypothesis.Although many duck species are short-distance migratory birds and tend not to cross the Wallace Line, some species — including Pacific black duck (Anas superciliosa) and spotted whistling duck (Dendrocygna guttata) — do, and Wille thinks they could introduce H5N1 to the region.If the virus is detected, government veterinarians will immediately move in to cull the affected population, which happened when H7N3 and H7N9 strains of the flu were detected in Victoria in May.Short says that, when it happens, the effect on Australia’s birds, mammals and ecosystems is unknown, but many species are probably susceptible. “It’s a big research gap,” she says. More

Hummocks of moss cover Ardley Island off the tip of the Antarctic Peninsula.Credit: Dan Charman

A fast-warming region of Antarctica is getting greener with shocking speed. Satellite imagery of the region reveals that the area covered by plants increased by almost 14 times over 35 years — a trend that will spur rapid change of Antarctic ecosystems.“It’s the beginning of dramatic transformation,” says Olly Bartlett, a remote-sensing specialist at the University of Hertfordshire in Hatfield, UK, and an author of the study1, published today in Nature Geoscience, that reports these results.From white to greenBartlett and his colleagues analysed images taken between 1986 and 2021 of the Antarctic Peninsula — a part of the continent that juts north towards the tip of South America. The pictures were taken by the Landsat satellites operated by NASA and the US Geological Survey in March, which is the end of the growing season for vegetation in the Antarctic.To assess how much of the land was covered with vegetation, the researchers took advantage of the properties of growing plants: healthy plants absorb a lot of red light and reflect a lot of near-infrared light. Scientists can use satellite measurements of light at these wavelengths to determine whether a piece of land is covered by thriving plants.The team found that the area of the peninsula swathed in plants grew from less than one square kilometre in 1986 to nearly 12 square kilometres in 2021 (see ‘An icy land goes green’). The rate of expansion was roughly 33% higher between 2016 and 2021 compared with the four-decade study period as a whole.

Source: Ref. 1

“These numbers shocked us,” says Thomas Roland, a study co-author and an environmental scientist at the University of Exeter, UK. “It’s simply that rate of change in an extremely isolated, extremely vulnerable area that causes the alarm.”The research is “really important”, says Jasmine Lee, a conservation scientist at the British Antarctic Survey in Cambridge, UK. Other studies2,3 have found evidence that vegetation on the peninsula is changing in response to climate change, “but this is the first study that’s taken a huge-scale approach to look at the entire region”, she says.Previous visits by the authors to the peninsula lead the authors to think that most of the vegetation is moss. As mosses spread to previously ice-covered landscapes, they will build up a layer of soil, offering a habitat for other plant life, Roland says. “There’s a huge potential here to see a further increase in the amount of non-native, potentially invasive species,” he says.

Moss covers rocks on Norsel Point, an arm of an island off the Antarctic Peninsula.Credit: Dan Charman

This is a concern because Antarctica’s native flora are adapted to extreme conditions, and they might not be able to compete with an influx of other species, Lee says.The researchers point to climate change as the driver of the landscape’s shift from white to green. Temperatures on the peninsula have risen by almost 3°C since 1950, which is a much bigger increase than observed across most parts of the planet. The “phenomenal” rate of expansion of greenery, Roland says, highlights the unprecedented changes that humans are imposing on Earth’s climate. More

“I’ve always felt a connection with the ocean. I completed my PhD, on seabirds’ movement decisions, at the University of Milan in 2022. The following year, I joined the Institute for Environmental Protection and Research (ISPRA) at Ozzano dell’Emilia, Italy, as a researcher. In this photograph, taken in 2021, I was on an expedition that forms part of a collaborative project between ISPRA and the University of Milan. Its aim is to track the sea movements of European storm petrels (Hydrobates pelagicus).My colleagues and I had travelled to the caves on Foradada Island off the northwestern coast of Sardinia, which is a popular nesting site for the birds. It’s hard to get there: you arrive on a small boat, before climbing through the cave in the picture to reach the main chamber. Here, field assistant Danilo Pisu (on the right) and I are fitting petrels with tiny GPS loggers before returning them to their eggs. The birds have a distinctive smell, which everyone describes differently. To me, they have the slightly dusty scent of an old book.For thousands of years, humans have lived around the coastline of the Mediterranean Sea, and because of this it’s heavily polluted. We wanted to find out where the storm petrels range over the sea, and why, so that we could protect them better in this area.We found that the birds are attracted to parts of the sea where the water churns from currents meeting far below the waves. This creates a phenomenon that brings plankton up to the surface.Out of all the birds I have studied, these are the most interesting. They have a history of myth and mystery. In nineteenth-century folklore, seafarers believed them to be the spirits of dead sailors, who brought storms to ships. In reality, the birds were seeking shelter near the boats in bad weather. Having a deeper understanding of them makes them even more special.” More

Workers for the Billion Oyster Project prepare to place juvenile oysters in a waterway running through New York City.Credit: Diana Cervantes/Redux/eyevine

New York CityAs the Sun dropped behind the Statue of Liberty on Saturday, a staff member for a conservation group unlocked a gate on a nearby island to reveal the ingredients for a potential oyster renaissance: stacks of ‘reef balls’, large domes made of oyster shells and concrete. They will soon be placed in tanks filled with free-swimming oyster larvae. Once the larvae latch onto the balls and mature, the structures will be submerged in the murky waters off New York City in an effort to revive a lost ecosystem.Coastlines around the globe were once protected by oyster reefs, expansive masses of oysters that had fused to rocks and each other. Overharvesting and habitat loss have demolished about 85% of Earth’s oyster reefs in the past two centuries. But bringing them back could help coastlines to become more resilient to the effects of climate change, including intense storms and erosion, scientists say.
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The Billion Oyster Project, a non-profit organization in New York City, is leveraging the bivalve’s engineering skills to slowly build a living breakwater. After a decade of refining the process, the project is generating know-how for other efforts that it has inspired elsewhere.“The foundations are there to rebuild these ecosystems, and there are considerable environmental and social benefits of doing this,” says Melanie Bishop, a marine ecologist at Macquarie University in Sydney, Australia. But it is still unknown1 whether restored reefs can grow large enough to buffer coastlines, and oyster-restoration proponents acknowledge that it will take an untold number of transplanted oysters and many years before reefs can provide a bulwark against rising seas.Mass of molluscsCenturies ago, New York Harbor, which lies between the five boroughs of the city — Manhattan, Staten Island, Brooklyn, the Bronx and Queens — and parts of New Jersey, was home to a massive conglomeration of eastern oysters (Crassostrea virginica) spanning nearly 900 square kilometres. Demand for the succulent molluscs skyrocketed as the city’s population boomed; at the same time, pollution in the harbour escalated, and by 1927, the oyster-reef ecosystem had collapsed.The Billion Oyster Project seeds oyster beds at 18 sites around New York City. Its goal: to initiate the reef-building process. If the oysters can consistently reproduce on their own, they could one day form a structure that buffers against hurricanes and extreme storms while protecting the shoreline from eroding into the rising sea, says Asly Ventura, a public-outreach coordinator for the project. Studies have found that oyster reefs boost biodiversity2 and can improve water quality3, which could create safe havens for other species as ocean conditions change.The larval molluscs need to settle onto hard, stable surfaces to grow. To provide a home for them, the project staff and volunteers mix crushed oyster shells, donated by restaurants, with recycled concrete, and use the slurry to make hollow, domed structures pocked with holes that are roughly one metre in diameter. Staff drop several of these domes at the project’s reef sites each summer, with the goal of forming vast shoals of oysters at each site.

Domed structures called reef balls are stored in New York City. They will be lowered into the nearby waters to provide a home for young oysters.Credit: Alix Soliman/Nature

The campaign has had mixed success. Of the 122 million oysters that were transplanted into the harbour by the end of last year, about half have died. “We do expect a large amount of die-off,” Ventura says. Oysters produce a lot of young because so many larvae die, she says. In 2022, the organization reported that oysters were naturally reproducing at about half of the installations.Pollution could partially explain why the molluscs aren’t multiplying on their own at every site. After it rains, a combination of raw sewage and stormwater is piped into the harbour. Lingering industrial waste contributes to poor water quality. Noise pollution could also be interfering with the larvae’s ability to find a suitable place to settle, because they use auditory clues to locate existing reefs, Ventura says.Ray Grizzle, a marine biologist at the University of New Hampshire in Durham, who has done scientific assessments for the project, says that juvenile oysters mostly settle within 400 metres of their parent reef. As a result, oysters might not self-seed readily at sites far from existing reefs.Grizzle’s greatest concern is how pathogens, such as the parasites Haplosporidium nelsoni and Perkinsus marinus, might affect oysters over the long term. “They’re down to about a 3- to 5-year lifespan now, when historically it was probably 10 to 20,” he says. When the lifespan is reduced, so is the population’s ability to form lasting vertical reef structures, he says. All the same, the project is “moving in a good direction”, Grizzle says.Reef resurgenceOther restoration projects are taking off around the world. In Australia, biologists attracted oysters simply by dropping limestone boulders onto a sandy sea bed. Larval flat oysters (Ostrea angasi) naturally settled on the rocks in densities that far exceeded expectations2, suggesting the larvae are travelling from unknown remnant reefs or oyster farms.“We didn’t know we were going to get any natural recruitment when we started,” says study co-author Dominic McAfee, a marine biologist at the University of Adelaide in Australia. The effort is meant to sustain the seafood industry and has increased the biodiversity of invertebrates at the site.In the North Sea, researchers are placing oyster larvae on the granite boulders at the base of wind turbines in an effort to fortify the structures and increase biodiversity.Bishop says that for oyster-reef projects to be successful, they need to be located in areas where the issues that led to their demise are no longer present, constructed to withstand predicted changes to the ecosystem and monitored for much longer than two to three years. Although there is a long way to go, “there is a lot of hope”, she says. More