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RESEARCH BRIEFINGS
09 August 2023

Local human-derived stressors combine with global ocean warming to threaten coral-reef persistence. Simultaneous reduction of human-derived stressors that originate on land, such as coastal run-off, and sea-based stressors, such as fishing pressure, resulted in greater coral-reef persistence before, during and after severe heat stress than did reduction of either alone. More

Large populations of fish help coral reefs to grow — but can’t protect against heatwaves.Credit: Barry Fackler/Getty

Minimizing land-based and sea-based human impacts at the same time might help reefs to recover from marine heatwaves, a study has found. But researchers warn that, in the absence of aggressive action to limit global warming, addressing impacts such as pollution and overfishing are insufficient to counter the growing threat. The findings — published this week in Nature1 — come as record ocean temperatures scorch reefs off the coast of Florida and scientists fear for the effects of El Niño on Australia’s Great Barrier Reef.Researchers analysed 20 years of reef data from a 200-kilometre stretch of coastline on Hawai’i Island. The data included an unprecedented marine heatwave in 2015, providing the researchers with a unique opportunity to explore how factors such as wastewater run-off and fishing intensity shaped the coral reef’s response. The heatwave was the strongest in 120 years of record-keeping, and saw ocean temperatures rise to 2.2 °C above normal, with a peak at 29.4 °C.A year after the heatwave, nearly one-quarter of the reefs had lost more than 20% of their coral cover. The hardest-hit reef lost close to half of its cover. But for 18% of reefs, coral cover was unaffected or even increased.Local impactsThe team used modelling to determine which factors best explained the differences in coral-cover changes.In the 12 years leading up to the heatwave, reefs with more fish — particularly herbivorous scrapers — and lower levels of wastewater pollution experienced coral growth.Scrapers “literally scrape the reef”, says Jamison Gove, an oceanographer at the Pacific Islands Fisheries Science Center at the US National Oceanic and Atmospheric Administration in Honolulu, Hawaii. “They not only remove fast-growing algae, but they clear space that allows for the settlement of crustose coralline algae, which is a precursor for coral growth,” he says.On the flipside, wastewater pollution from sewage disposal systems and run-off from urban environments damage coral health, says Gove. “It’s not only that you have this soup of virulent bacteria and other things that can cause coral disease,” he says. “You also have whatever everybody’s flushing down or putting down their sink. You have household chemicals, you have pharmaceuticals, so you have all sorts of toxins.”Modest gainsOverall, the researchers estimate that addressing land-based and sea-based human impacts on reefs simultaneously improves their chances of having higher levels of coral cover in the four years after a heatwave by three to six times, compared with addressing them independently. But lower pollution levels and more scrapers — factors that drove increases in coral cover before the heatwave — offered little protection against temperature spikes. Reefs with the lowest levels of urban run-off lost slightly less cover, but the presence of more fish — particularly scrapers — did not have a substantial effect on coral loss or survival.Gove says that the study reveals how human activity, both on land and in the sea, affects coral reefs, but stresses that these local impacts must be addressed in the context of action on climate change.“We can do all the local management you want, but in the decades to come, if we’re not aggressively curbing greenhouse-gas emissions, then climate change and marine heatwaves will most likely overwhelm any of the effects that we’ve identified within our paper,” he said.Terry Hughes, a marine biologist at James Cook University in Townsville, Australia says the study has confirmed that there are three main stressors on coral reefs: overfishing, pollution and climate change. “If you clean up the water quality and rebuild depleted populations of herbivores it does help the reef to recover. But the big, big caveat is provided they have enough time to recover,” he says. “It’s no use improving the recovery rate by managing water quality and fishing if the frequency of these bleaching events continues to increase.”Hughes gives the example of back-to-back bleaching events that struck the Great Barrier Reef in 2016 and 2017, and says that climate modelling suggests that most coral reefs will experience bleaching events every year by 2050 under a business-as-usual emissions scenario.“They don’t discriminate between well-managed reefs, or a polluted and non-polluted reef,” he says. “They all fry if the temperature is high enough.” More

China’s large coastal animals are poorly served by biodiversity protections, a nation-wide assessment has revealed. The study1, published in Science Advances, suggests that there’s a need for improved conservation measures along China’s coasts.Study co-author Qiang He, a coastal ecologist at Fudan University in Shanghai, says that larger coastal animals are often overlooked. “You can see a lot of news about the giant panda and terrestrial biodiversity conservation, but you don’t see a lot of news about megafauna in coastal areas in China,” he says.To gauge how coastal animals are faring, He and his colleagues collated data on fish, mammals, birds, reptiles and cephalopods — including octopuses, squid and cuttlefish — with an adult body mass of at least 10 kilograms that live in China’s coastal habitats. They identified more than 200 species across ecosystems including salt marshes, mangrove forests, seagrass beds, coral reefs and deeper waters.They then looked at whether those species were identified as being threatened on the International Union for Conservation of Nature (IUCN) Red List — a global inventory of species’ conservation status — and what level of protection exists in China.Almost half of the species identified (44%) are classed as critically endangered, endangered or vulnerable on the IUCN Red List. Yet 78% of the species have not been assessed for local extinction risk, and so don’t appear on China’s own Red List, or are listed as data deficient. “Even if they’re critically endangered or endangered on a global level, they are still not assessed in China,” He says. And almost three-quarters are not protected by any of China’s wildlife-protection laws.Regulation gapsThe researchers also assessed species’ importance using a measure called the FUSE index — standing for functionally unique, specialized and endangered — which scores endangered species on the basis of the importance of their roles in their ecosystems. Of the top 50 large coastal animals ranked by their FUSE score, only 17 are currently protected in China.This is a problem, says co-author Xincheng Li, an ecologist at Fudan University. Populations have declined for species including the red-crowned crane (Grus japonensis) and the critically endangered Chinese sturgeon (Acipenser sinensis). And Li says that the precise mixture of threats to most of the species the team looked at is poorly understood. Large marine species are often inadvertently killed as by-catch in fishing. But these and other creatures are also threatened by pollution, competition from invasive species and depletion of prey species owing to over-fishing.“These results point out the existing gaps in the current management system of China’s coastal protected areas,” says Baoshan Cui, a wetland ecologist at Beijing Normal University. And he says that other countries, especially those that with rapidly expanding economies, probably have similar conservation gaps.Nicholas Murray, a conservation ecologist at James Cook University in Townsville, Australia, says the lack of protection for larger species “suggests that most coastal species in China — the small ones as well — are being similarly impacted”.The study lays important groundwork that will help conservation in these coastal zones, says Murray. “They did a lot of work to build a new database,” he says, and the more such data sets become available for analysis, the better countries such as China will be able to manage their coastal ecosystems.Better protectionsChina has made progress towards reducing overfishing in its domestic waters, says Songlin Wang, president of the Qingdao Marine Conservation Society. In 2017, the agriculture ministry adopted a ‘negative growth’ policy for its domestic fishing harvest in an attempt to reduce catch levels each year. And in June, China formally signed on to the World Trade Organization’s international agreement to end harmful fisheries subsidies. But Wang says that the slow decline in small-scale fishing won’t be enough to protect its coastal ecosystems.As a first step, He says, “the Chinese government needs to include many more of those coastal megafauna species in the nation’s register” of protected species.Wang says that this could be difficult. Although marine mammals such as whales, dolphins, porpoises and marine turtles have legal protections in China, few species of fish are protected, because of their commercial value as seafood.The Chinese Ministry of Agriculture and Rural Affairs did not immediately respond to a request for comment.Protected areas can help, says He, but they need to be properly enforced. China has more than 200 marine protected areas, he adds, but these are poorly regulated: “There’s so many marine protected areas, but there’s no boundary information available to the public,” so there’s no way for fishers to know whether they are in a protected area.Furthermore, protected areas are often small and unconnected, says ecologist Zhonghua Ning at Beijing Normal University. This compromises their effectiveness as refuges, he says.But Wang says that marine protected areas alone are inadequate to protect large marine species — he says that better enforcement of laws requiring fishers to use gear that doesn’t trap large animals such as turtles, dolphins and sharks as by-catch would do more to protect those species. Wang says that despite regulations, fishers often modify their gear or use illegally small mesh to maximize their harvest. More

The Nagoya Protocol on Access and Benefit-sharing (ABS), adopted in 2010, ensures that the advantages arising from the use of genetic resources are distributed fairly (www.cbd.int/abs/). Ethiopia established a similar treaty four years earlier, in part to protect its rich and unique biodiversity against biopiracy. Contrary to the suggestion by ThankGod Ebenezer and his colleagues (Nature 603, 388–392; 2022), this ‘Access to Genetic Resources and Community Knowledge, and Community Rights law’ welcomes applications from non-parties to the Nagoya Protocol, as well as from parties to it (go.nature.com/3oxztad).
Competing Interests
The authors declare no competing interests. More

For her master’s degree, Anaëlle Durfort calculated levels of carbon sequestered by whale carcasses that had fallen to the ocean floor in the Southern Hemisphere.Credit: Raphael Seguin

Anaëlle Durfort quantifies carbon sequestered in marine fauna for her PhD in ecology at the University of Montpellier, France, to highlight the links between biodiversity and climate change.Why are you investigating carbon sequestration in animals?The way in which carbon moves into the ocean through whales demonstrates the complex links between biodiversity and climate. Climate change affects living organisms, which themselves affect greenhouse-gas emissions.One striking example comes from my master’s degree, also at Montpellier, which focused on quantifying the carbon sequestered in the Southern Hemisphere since 1890 by the carcasses of five species of whale. Because they’re so huge, whales hold a lot of carbon in their tissues and, after dying, they trap that carbon on the ocean floor for more than a century. But the effectiveness of these animals as a carbon ‘pump’, moving carbon from the atmosphere, and eventually to the bottom of the ocean, varies according to the size of cetacean populations.Before they were exploited on an industrial scale, whales were abundant in the Antarctic, and a team that I worked with during my master’s estimated that they sequestered a total of 400,000 tonnes of carbon per year1. We calculated that this figure had dropped to 60,000 tonnes by 1972, because of the impact of centuries of commercial whaling. Since whaling was banned temporarily through an international agreement in 1986, populations have been slowly recovering.
The ancient whale from my Egyptian home town
But the projected restoration of whale populations depends on the extent of climate change (as well as on factors such as the incidence of collisions between whales and ships). Looking at two scenarios, we estimated what the biomass of whale carcasses on the sea floor would be by 2100. Under the worst-case scenario proposed by the Intergovernmental Panel on Climate Change (in which global warming ranges from 3.3 °C to 5.4 °C by 2100), the sequestration would reach 170,000 tonnes per year. Without climate change, recovered whale populations would be able to sequester nearly twice as much carbon.Whales won’t save the climate — global carbon emissions reached 10 gigatonnes (10 × 109 tonnes) in 2021 (ref. 2) — but my work shows how human activities are affecting the carbon sink that these animals provide, and might stop its recovery.Your research now focuses on krill. Why?Yes, I’ve moved down the food chain. My research focuses on assessing the biomass of Antarctic krill (Euphausia superba), small crustaceans that are essential to the Antarctic food web — and especially to whale diets.Looking at carbon sequestration mediated by exploited species such as whales and krill, the team I work with highlights the links between biodiversity, human activities and climate. Krill catching on an industrial scale, often for pet food or aquaculture supplements, has an impact on the entire marine food chain, as well as on biogeochemical cycles.More generally, the practice raises questions about using krill as a resource: are the benefits worth the environmental and climate damages? All of us should consider our activities with these questions in mind.

The skeletal remains of a whale fall at the bottom of the Andaman Sea, off the coast of Thailand.Credit: Getty

What do you think of putting a carbon price on whales?Looking at how much carbon whales can lock in, some economists and non-governmental organizations put a carbon price on the animals, betting that having this in place will encourage carbon offsetting and protect the animals. The idea is that companies, by paying the price in funding whale protection, can claim carbon credits for every whale they save.But this commodification of nature in the name of conservation seems problematic to me. These solutions are part of the same economic and societal framework that put us in the ecological and social crisis we are facing. This is not in line with the transformative changes that we need. What needs to change is our relationship with nature.You attended COP15, the United Nations biodiversity conference held in Montreal, Canada, in December 2022. What was it like?I was part of the Global Youth Biodiversity Network (GYBN), with more than 100 young representatives from all continents. This was a great experience for me, both as a scientist and as an environmental activist.
France’s research minister has a plan to shake up science
The conference was also an opportunity to get to know more about international biodiversity-conservation policies, to see the underlying mechanisms. What struck me most was the complexity of the negotiations — groups of all sorts were attending, including states and observers, such as non-profit entities, businesses, Indigenous people — and the technical nature of the debates. A lot is going on apart from the main negotiations between states’ representatives, with many interests represented at networking sessions and lobbying during the side events.At the GYBN, we had some victories, including Target 22 of the new Global Biodiversity Framework, which guarantees the participation of Indigenous peoples and local communities in decision-making on biodiversity-conservation policies.Have you ever seen a whaleUnfortunately, no. My work is in front of a computer, making models to look at how carbon-sequestration dynamics evolve under global warming and in response to commercial fishing. This work requires a lot of scientific collaboration, to access models of ocean change and population dynamics. I do a lot of cooperation, but no fieldwork. More

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Botos use clicks and whistles to communicate with each other and to find prey.Credit: Sylvain Cordier/Gamma-Rapho via Getty

Researchers have used artificial intelligence (AI) to map the movements of two endangered species of dolphin in the Amazon River by training a neural network to recognize the animals’ unique clicks and whistles.The findings, published in Scientific Reports on 27 July1, could lead to better conservation strategies by helping researchers to build an accurate picture of the dolphins’ movements across a vast area of rainforest that becomes submerged each year after the rainy season.Using sound is much less invasive than conventional tracking techniques, such as the use of GPS tags, boats or aerial drones.
Saving the Amazon: how science is helping Indigenous people protect their homelands
“Sound is probably the only sense that we know of that we all share on Earth,” says co-author Michel André, a bioacoustician at the Technical University of Catalonia in Barcelona, Spain.André and his colleagues wanted to explore the activity of two species, the boto (Inia geoffrensis) — also known as the pink river dolphin — and the tucuxi (Sotalia fluviatilis) across the floodplains of the Mamirauá reserve in northern Brazil. The researchers placed underwater microphones at several sites to eavesdrop on the animals’ whereabouts.To distinguish the dolphin sounds from the noisy soundscape of the Amazon, they turned to AI, feeding the recordings into a deep-learning neural network capable of categorizing sounds in real time, “exactly as we do with our own brain”, says André.Using this technology, researchers can analyse volumes of information “that would otherwise be almost impossible”, says Federico Mosquera-Guerra, who studies Amazonian dolphins at the National University of Colombia in Bogotá.The AI was trained to identify three types of sound: dolphin, rainfall and boat engines. Both dolphin species use echolocation clicks almost constantly to sense their environment, and they communicate to others by whistling. Detecting these clicks and whistles enabled the researchers to map the animals’ movements. Botos and tucuxis have distinct whistles, so the neural network could distinguish between the species.Conservation effortsThe study is a part of a collaboration between the Technical University of Catalonia and the Mamirauá Institute of Sustainable Development in Tefé, Brazil, which aims to use this technology for monitoring the Amazon’s biodiversity and threats to it.
AI empowers conservation biology
Both dolphin species are endangered: estimates suggest that the boto population is declining by 50% every ten years, and the tucuxi population every nine years2. Monitoring when and where the animals move will allow researchers to help protect their populations and come up with measures to help “Indigenous communities to cohabitate with the presence of dolphins”, says André. Dolphins can disrupt fisheries across the floodplains, for example, by competing for fish or becoming tangled in nets.Mosquera-Guerra says that collecting such information is “fundamental” to inform decisions on conservation across the Amazon region.In future, the team wants to train the neural network to detect other aquatic species, and to deploy the system over a wider area. The same approach could also be used in the ocean. André’s previous work using this system has shown the effects of human-made noise pollution on sperm whales, and has enabled the development of a warning system for ships to help avoid the animals3. More