Philippa Kaur

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Sea urchins enable complex reef ecosystems to thrive by eating algae that would otherwise smother corals. But that delicate natural balance is under threat in the Red Sea and Western Indian Ocean.

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doi: https://doi.org/10.1038/d41586-024-01400-1

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Conservation biology More

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A tank of captive-bred Chinese sturgeons about to be released to the Yangtze River.Credit: Xiao Yijiu/Xinhua via Alamy

Five fish species, including the iconic Chinese sturgeon, have gone extinct, or will soon be extinct, because of dams on the Yangtze River in China, according to a paper released on 10 May in Science Advances1. The findings have reignited a long-running debate among Chinese scientists about the best way to rescue the species in the Yangtze, with some saying that the analysis is flawed.The Yangtze River is a mighty 6,300-kilometre-long waterway and a global biodiversity hotspot that runs through 11 Chinese provinces. But over the past 50 years, six major hydropower dams and more than 24,000 smaller hydropower stations have been built in the river’s main stream and branches — with even more on the drawing board.The dams were built to help generate electricity, provide flood protection and make the river easier to navigate. But dams can block migratory fishes and damage their habitat. To mitigate the effects of the dams, fish-rescue programmes have been in place in various forms since 1982, when the first dam was being constructed.Huang Zhenli, the deputy engineer-in-chief at the China Institute of Water Resources and Hydropower Research in Beijing, and his colleague Li Haiying developed an analytical tool that models the impact of the Yangtze River dams on its fish populations.They focused on five iconic species: the Chinese sturgeon (Acipenser sinensis), the Yangtze sturgeon (Acipenser dabryanus), the Chinese paddlefish (Psephurus gladius), the Chinese sucker (Myxocyprinus asiaticus) and the largemouth bronze gudgeon (Coreius guichenoti).By the time of the analysis, the paddlefish was already extinct. The Yangtze sturgeons are being kept alive only through captive-breeding programmes. The Chinese sturgeon is critically endangered. The International Union for Conservation of Nature lists the sucker as vulnerable, and the gudgeon as endangered.The researchers’ modelling found that all five species will be entirely extinct or extinct in the wild by 2030.David Dudgeon, a retired freshwater ecologist at the University of Hong Kong, says that the study is helpful in identifying the effect of the dams on the five species, particularly the understudied Chinese sucker. “There is nothing much that surprises me about the conclusions of the study,” he says. “It is good to see a well-integrated investigation of these five species.”However, not all researchers are convinced by the study. Wei Qiwei, a conservation researcher at the Yangtze River Fisheries Research Institute, Chinese Academy of Fishery Sciences, in Wuhan, says that the authors’ work “deserves to be encouraged”, but disagrees with their conclusions.Wei — who co-authored a 2020 paper2 that declared the Chinese paddlefish extinct — says the predictions that all species will be extinct or near extinct in by 2030 can’t be relied on because the parameters in the analysis are uncertain and difficult to quantify.Xie Ping, a freshwater ecologist at the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences in Wuhan, agrees that it might be too soon to draw definitive conclusions from the models’ findings. “More needs to be done to cover more fish species in more geographic regions, so as to validate the effectiveness of the models and to optimize their parameters,” Xie says.‘Six misjudgements’The authors blame the dams, and the lack of specialized passageways for migratory fish to bypass the dams — known as fish-ladders — for the five species’ collapse.“To prevent more migratory fishes from going extinct in China, [its] dam-related fish-rescue programmes must undergo fundamental changes,” Huang says.As fish numbers continued to decline from the 1980s onwards, China stepped up its efforts to safeguard the ecology and environment of the Yangtze.In 2021, it commenced a ten-year fishing ban and increased its restocking of the river with young, captive-bred fish.

The Wudongde Hydropower Station on the Jinsha River, an upper stretch of the Yangtze, became operational in 2020 — after the Chinese paddlefish was declared extinct.Credit: CFOTO/Future Publishing via Getty

However, the authors say that it was not enough. They describe “six misjudgements” of these fish-conservation campaigns, including that overfishing is the primary cause of the population declines; and that restocking is a “viable strategy” for mitigating the effects of the dams.Wei and his team lead the scientific research behind the current conservation plan. He says that the dams’ impacts on fishes exist, but “one cannot ignore other factors”, such as overfishing.“I believe if the 10-year fishing ban had been introduced to the Yangtze River 30 years earlier, the Chinese paddlefish would not be extinct. Nor would the Chinese sturgeon, the Yangtze sturgeon and the Chinese sucker get so close to extinction,” Wei notes.As for restocking from captive-bred populations, he describes it as “the most important protection and restoration task” for the Chinese sturgeon and Yangtze sturgeon.A 2023 study led by IHB researchers3 found that a 2017 pilot fishing ban introduced to the Chishui River — an upstream tributary of the Yangtze — was “an effective measure to facilitate fish resources recovery”.Steven Cooke, a biologist specializing in fish ecology and conservation at the Carleton University in Ottawa, says that science-based restocking can work “quite well” in cases such as the white sturgeon (Acipenser transmontanus) in North America. “But if the habitat is degraded and fish can’t complete their life cycles, then stocked fish may not survive,” Cooke says.Dudgeon, meanwhile, regards the paper’s criticism of restocking of the Yangtze as being “well-founded”.“There is absolutely no evidence that sturgeon restocking has enhanced wild populations, despite the release of millions of cultured juveniles … [and] the fact that the practice has continued for many years,” he says.Fishway or highwayXie highlights that, for large and long-lived species such as sturgeons, conservation work is “very hard”.Chinese sturgeons feed and grow near the sea when they are young and migrate more than 3,200 kilometres up the Yangtze to reproduce. “They spent at least 10 to 20 million years adapting to such a cycle,” Xie says, “They cannot adapt to the huge changes caused by humans within these few decades.”Xie says that fish ladders might not be enough to save the sturgeons. “Fish passages in Europe and North America are mainly designed for relatively small-sized fishes, such as salmon. But sturgeons are mostly large and need a lot of space to swim in rivers,” Xie says. “Less than 2% of sturgeons are able to successfully navigate through the fish passages in dams,” he says.Dudgeon says that, even when fish ladders work, the stillness of the water in the dam might not provide adequate cues to guide the fish upstream to complete their migration.On the downstream journey, both adult and juvenile fish have to find a way to navigate the dam, locate the fish ladder and make a safe descent, he adds.
Dam removals: Rivers on the run
Some countries, such as the United States, France and the United Kingdom, have started to dismantle dams to re-establish migration corridors. When removal is not feasible, or fish ladders are ineffective, Xie and his colleagues suggested in a 2023 paper4 that building river-like side channels around hydropower dams is “the best way” to restore sturgeon migration routes and provide alternative habitats. Successful such cases have been observed in Russia, Canada and the United States, they noted.Dudgeon says that, with so many complications, improving the situation for fishes in the Yangtze “will be challenging”. More

“It’s dirty, hot work picking up blue crabs (Callinectes sapidus). They like murky water, and you need special clothing and equipment to wade through the swampy lagoon here in the Palud – Palù ornithological reserve in Pula, Croatia. It was the end of a long day in September last year when this photo was taken, and I was hot and sweaty under that special clothing. And once you find a crab, you have to be careful not to injure yourself picking it up: either on its sharp lateral spine, or from its very strong claws.I catch the crabs because they are an invasive species, and because it’s my job: as well as working as a biotechnologist, I’m a fisher. Blue crabs are native to Chesapeake Bay in the eastern United States, and they probably made their way here on a ship in the early twentieth century.There has been a large population in the Po river estuary for many years — but a combination of factors, including global warming, has seen them spread down the Adriatic coast since 2022.The crabs are a problem because they eat the bivalves, fish and other crabs that make up the diets of many of the endangered seabirds here at the nature reserve — without that vital source of food, these birds will be even more threatened and we’ll face a serious loss of biodiversity.My colleagues and I at the Juraj Dobrila University of Pula are encouraging local people to eat the crabs, which are sold at the markets. We’ve held awareness activities since long before 2022, in anticipation of the explosion of the invasive population. I know more and more people who collect blue crabs for food.We’re losing the battle against climate change: the changes are too fast and we are far too slow to adapt to them. But I hope by better understanding the biological capital we have available here, we can build a better relationship with nature.” More

Jorge Lengua and his son (also Jorge) do not need to cut down trees to harvest Brazil nuts in the Bolivian Amazon.Credit: Martin Silva/AFP/Getty

The world’s forests are vital to its future. In terms of climate change, they are increasingly seen as key to both mitigation — in their role as carbon sinks — and adaptation, through sustainable management of forests. Tied in with both is the funding provided by those looking to offset carbon dioxide emissions by planting trees, a source of much-needed climate finance.It is, therefore, unsurprising that ‘climate change’ and ‘climate finance’ are terms that dominate studies in forestry policy, according to a review of the literature published last week (see go.nature.com/4decszc). That, in itself, need not be a problem. But one stark conclusion from the report is that too few studies focus on the people who live in, or who make a living from, forests.
Swathes of Earth are turning into desert — but the degradation can be stopped
This finding should be taken on board by science funding agencies and the United Nations-affiliated research networks for biodiversity and climate change. And it should be taken into account when research priorities are set and collaborations are formed. Quite aside from the ethical case for more community-focused forestry policy, forest conservation is unlikely to succeed without the involvement of those most closely associated with forests.The review is published by the International Union of Forest Research Organizations (IUFRO), a global body representing more than 600 institutions across over 100 countries. It assesses mostly English-language social-science literature published between 2011 and 2022 — covering the period since the last such review, in 2010. The authors find that the literature is dominated by the climate-mitigation interests of governments in high-income countries. They dub this the ‘financialization’ and ‘climatization’ of the literature surrounding forest policy.This trend can be explained partly by the fact that forests are increasingly being incorporated into climate policies at all levels of governance — not least because of legally binding targets set by the 2015 Paris climate agreement. Forests are seen as providing the path of least resistance to achieving these targets, because their involvement requires little in the way of behaviour change from high-income countries. This has led to an expanding array of forest-related climate agreements at both regional and global levels. The largest of these is REDD+, through which low- and middle-income countries are paid (by companies and governments in high-income countries) to protect their forests. In return, contributors benefit from associated carbon credits. By the end of 2023, projects covered by REDD+ encompassed more than 60% of the forested area of developing countries. The scheme is not without controversy, with studies showing that carbon offsets can be overstated1 and have little impact on the economic well-being of forest communities2.
Biodiversity thrives in Ethiopia’s church forests
Forest agreements rely on the research community for support. Take REDD+ again. Some scientists are looking at ways to measure how carbon is stored in different forests; others are working on verifying that countries comply with climate commitments. Researchers also sit on scientific advisory committees.But there’s more to the study of forest governance than climate. For example, there’s the matter of how Indigenous and local knowledge contribute to biodiversity conservation today. And there are studies of the various ecotourism schemes being set up. But these subjects are less well-represented in the literature.Researchers in such fields do advise on forest-related international agreements not linked directly to climate change. These include the UN Convention on Biological Diversity and the UN Forum on Forests (UNFF), a global body dedicated to discussing a wide range of forest-related issues. But the UNFF is a voluntary arrangement; unlike the UN conventions on biodiversity and climate change, its decisions have no legal force.
We must get a grip on forest science — before it’s too late
The UN biodiversity convention, whose member states have agreed to conserve 30% of Earth’s land, waters and coasts by 2030, draws on a wider set of research disciplines — not least through its scientific advisory body, IPBES, which incorporates studies in Indigenous and local knowledge into its work3. The convention also contains an explicit mandate to provide benefits for the people who rely on biodiversity for their livelihoods. However, the IUFRO review’s authors found that there is little coordination between the biodiversity convention and the UN’s climate convention — or between the researchers who advise these two bodies.The review is far from the first to highlight that research that should aim to benefit all stakeholders instead focuses on areas that are priorities for the governments of high-income countries. This is an important and timely reminder. It should not be difficult for the researchers involved in the world’s largest scientific networks — the IPCC for climate and IPBES for biodiversity — to create a shared agenda for the study of forests that extends beyond climate change and climate finance. And, given the need for such action, funders should respond positively to such a proposal.Earth’s forests have the potential to benefit people everywhere. Researchers, policymakers and funders must ensure that everyone’s needs are taken into account. More

“Many Nigerians consider bats to be pests or bad omens of some kind. But I see them as cute and amazingly diverse. Bats provide ecosystem services that many people don’t know about. For example, they eat the insects that destroy crops.I spend a lot of time mapping bat populations and tracking their health. This picture was taken earlier this year at the Oban Forest Reserve in Cross River State in southern Nigeria. The reserve, which isn’t in great shape ecologically, lies on the border of Cross River National Park, one of the country’s last undisturbed forests.We catch the bats using traps and release them as soon as we can. In the photo, I’m looking at the wings of a bat to identify its age. Juvenile bats have cartilage growth plates in their joints; these plates are visible through the skin as light and dark bands.The bat pictured belongs to a common species. But my team and I found a small population of the much rarer short-tailed roundleaf bat (Hipposideros curtus) in the nearby Afi mountains. It was only the third population of the species to be discovered in Nigeria. These bats are so rare that it took us nine years working in this region before we finally captured one last year.The main threats to bat populations here are wildfire, deforestation, logging and agriculture. The southeast, where the Oban reserve is located, is of interest to mining companies. And meat from fruit bats is a popular source of protein in Nigeria; bats are sometimes hunted in their cave roosts, and might abandon a cave after they’ve been disturbed in such a way.An important part of what I do is to educate the public about the ecological roles that bats have and to dispel myths about them. In the United States, there’s been a turnaround from people fearing bats to thinking they are cute and deserving protection. We need that energy here.” More

Credit: Evelyn Hockstein/Polaris/eyevine

Diana Wall was a true ecology and climate pioneer. Biodiversity in soil is often overlooked — a case of out of sight, out of mind — but Wall understood its importance for a sustainable future. The soil is home to more than half of all species, which are crucial for Earth’s terrestrial ecosystems. Wall spent her entire career exploring how soil-dwelling organisms regulate carbon and nutrient cycling, and how they respond to climate change. She focused on a little-studied but ubiquitous group of soil organisms — nematodes (roundworms) — across ecosystems. She also unflaggingly championed the importance of soil biodiversity for society. She has died aged 80.From 2011, as founding chair of the Global Soil Biodiversity Initiative, Wall brought together soil ecologists to inform policy, education and the public. She was at her best when she travelled around the world for research, to connect with soil ecologists — including many from marginalized communities — and to advocate for soil biodiversity to be at the heart of sustainability discussions. She also orchestrated the 2016 Global Soil Biodiversity Atlas, which mapped the organisms that live under our feet and the threats they face.Born in Durham, North Carolina, Wall first became interested in nematodes during her undergraduate studies at the University of Kentucky in Lexington. There, she launched her career in soil ecology by investigating nematodes that fed on the roots of red clover (Trifolium pratense), earning a PhD in 1971. As a postdoc in the Department of Nematology at the University of California, Riverside, Wall focused initially on nematode communities in North American desert soils. During the late 1980s, she became interested in the unexplored soil biodiversity of the McMurdo Dry Valleys in Antarctica — one of the coldest, driest regions on Earth, and a place at the environmental limits of what underground life can tolerate.
Secrets of life in the soil
She spent more than 25 consecutive years visiting the valleys, investigating the survival and functioning of soil organisms as well as their response to climate change. Only a handful of animals live in these dry, cold soils. Wall and her colleagues discovered that — by feeding on its microbial prey — one nematode species, Scottnema lindsayae, was crucial for the carbon cycle there. The team also showed that climate change has caused big shifts in Antarctic soil food webs over time. The decreasing abundance of S. lindsayae and increasing prevalence of other animal species has had large knock-on effects on the turnover of soil carbon, revealing that this often-ignored but crucial component of biodiversity can have widespread impacts on the region’s ecosystem.In 1993, Wall moved to Colorado State University in Fort Collins, where she remained for the rest of her career. She had a huge influence on students and colleagues alike, through her science and her leadership roles. She was the director of the university’s Natural Resource Ecology Laboratory until 2005, and the inaugural director of its School of Global Environmental Sustainability — a post she held from 2008 until her death.Although Antarctic soil ecology remained Wall’s passion throughout her career, her scientific contributions didn’t end there: they encompassed the world. Wall had a remarkable gift for bringing people together to tackle scientific questions that could not be addressed in any other way. For example, she recruited an international team to conduct a global-scale decomposition experiment, which showed that the role of soil animals in regulating the decomposition of biological matter — a key process in the global carbon cycle — varies between ecosystems and depends on the region’s climate. Together with researchers worldwide, she also investigated the distribution of soil animals across biomes and found that high above-ground plant diversity doesn’t always coincide with high below-ground animal diversity at a global level.
Current conservation policies risk accelerating biodiversity loss
Wall also regularly convened, or joined, global groups of soil ecologists to synthesize a growing body of knowledge on the importance of underground biodiversity for ecosystems and society — for instance, through its role in regulating food production, suppressing soil-borne pathogens and providing clean air and water. This led to influential articles on sustaining soil biodiversity for ecosystem services and the need for global monitoring and conservation of soil-dwelling organisms. She spearheaded what is now a vibrant, inclusive community, promoting and communicating soil biodiversity research on a global stage. Wall received many honours for her contributions to the field, including the Tyler Prize — an award sometimes considered equivalent to a Nobel for environmental scientists. Her national and international leadership roles included the presidencies of the American Institute of Biological Sciences and the Ecological Society of America.I first met Diana at a conference she had organized in Colorado in 1995. I was an early-career scientist, starting out on my own journey into soil ecology. It was clear then that she was special. I was struck by her enthusiasm, openness and boundless energy — characteristics that remained constant throughout her career. Diana was also humble, often playing down her own achievements while celebrating those of others. She always cared about other scientists, and was eager to learn about their research and their lives outside work. She has supported many people in their careers or during difficult times. Rarely do people touch as many lives as Diana did. She will be sorely missed, as a colleague, friend and mentor, and the field of soil ecology is at a loss without her. She will be remembered fondly as the global ambassador for soil biodiversity. More

RESEARCH BRIEFINGS
08 May 2024

By using volunteers to map roads in forests across Borneo, Sumatra and New Guinea, an innovative study shows that existing maps of the Asia-Pacific region are rife with errors. It also reveals that unmapped roads are extremely common — up to seven times more abundant than mapped ones. Such ‘ghost roads’ are promoting illegal logging, mining, wildlife poaching and deforestation in some of the world’s biologically richest ecosystems. More