Ecology

Warm oceans can bleach and kill corals.Credit: Juergen Freund/NPL

The global ocean hit a new record temperature of 21.1 ºC in early April, 0.1 ºC higher than the last record in March 2016. Although striking, the figure (see ‘How the ocean is warming’) is in line with the ocean warming anticipated from climate change. What is remarkable is its occurrence ahead of — rather than during — the El Niño climate event that is expected to bring warmer, wetter weather to the eastern Pacific region later this year.That means warmer-than-average ocean temperatures are likely to persist or even intensify, bringing with them more-extreme weather and marine heatwaves, which spell problems for marine life from corals to whales.“We are probably looking at a string of record highs over the next year or so,” says Josh Willis, an oceanographer at NASA’s Jet Propulsion Laboratory in Pasadena, California. “This coming year is gonna be a wild ride if the El Niño really takes off.”

Source: climatereanalyzer.org; NOAA Optimum Interpolation SST (OISST)

The El Niño Southern Oscillation (ENSO) is a natural, cyclical climate pattern. During the El Niño phase, winds over the Pacific are weakened or reversed, allowing warm waters to slosh eastwards in the Pacific. El Niño tends to coincide with warmer years both in the ocean and on land. The previous record of 21.0 ºC, for example, occurred during a very strong El Niño event.ENSO is currently in a neutral phase, coming out of a rare extended three-year period of La Niña (the opposite phase to El Niño). But El Niño is expected to kick in this year: according to the World Meteorological Organization, there is a 60% chance of it developing between May and July, and an up to 80% chance of it happening by October.Return of ‘the Blob’Andrew Leising, an oceanographer at the Southwest Fisheries Science Center of the US National Oceanographic and Atmospheric Administration (NOAA) in La Jolla, California, expects to see unusually warm waters in the Pacific off the west coast of the United States during the summer and autumn. If the El Niño develops as expected, he adds, “this could create a situation like 2014 to 2015, when we got smacked by the Blob heatwave”, a particularly big and damaging marine heatwave.Marine heatwaves can be devastating for wildlife, and fisheries. Large heatwaves on the US Pacific coast tend to compress the habitable zone for many species into a narrow strip along the coast, Leising says. That can bring whales closer to shore as they chase food, which can increase ship strikes and entanglements in fishing gear. When warm waters butt up against the shore, he adds, they can host harmful algal blooms that close crab and mussel fisheries. But at the moment, Leising says, there is some unusually strong upwelling of cold water occurring along the US west coast, which could protect against some warming this year.In the lead-up to April’s record ocean temperature, some regions in the Southern Hemisphere experienced marine heatwaves, starting in February, says Huang — among them, waters off Peru’s coast and in the Southern Ocean.Unusually warm waters bring particular stress for corals. Almost all coral regions are currently experiencing remarkably high temperatures, says Matthew England, a physical oceanographer at the University of New South Wales in Sydney, Australia. “What we’re seeing now for coral reefs is they’re getting pushed to extreme temps, and they don’t get to regrow because it doesn’t come back to cooler temperatures.”The last record-breaking ocean temperature year of 2016 coincided with an unusual global bleaching event for corals, only the third ever known to have happened. Bleached corals — which have expelled the algae that give them their colour — have poorer health, and many die.“It’s fairly likely that we can expect another global bleaching event this year,” says Christian Voolstra, who studies corals at the University of Konstanz in Germany. Even if an El Niño doesn’t settle in this year, he adds, it will come soon enough. “It’s bad news no matter what.”Heating planetWarm waters are also physically less capable of holding dissolved oxygen, adding to the stress for marine life. “With ocean warming and deoxygenation, the available habitats for many species are decreasing,” says William Cheung, a marine biologist at the University of British Columbia in Vancouver.And high ocean temperatures can trigger extreme weather. The unusually warm waters off Peru this year have helped to feed intense rainfall and Tropical Cyclone Yaku — the first such storm to hit the area in decades.The ocean temperature spike — recorded by NOAA and likely the highest in more than 100,000 years — coincides with other warming trends. For example, in the southern hemisphere, the sea ice extent hit a new all-time low in February 2023. The ocean absorbs about 90% of the extra heat in the climate system resulting from global warming. But because it takes more energy to heat water than air, the surface water temperature is rising more slowly than the surface air temperature is.“This wouldn’t have happened without climate change,” tweeted Jens Terhaar, an ocean biogeochemical modeller at the Woods Hole Oceanographic Institution in Massachusetts, in response to the news of the new temperature record. “We are in a new climate state, extremes are the new normal.” More

Autonomous sensing devices and machine-learning algorithms are being used increasingly to track ecological health and dynamics over large scales with fine resolution. However, nature management and conservation are being compromised by inequitable access to these transformative technologies.
Competing Interests
The authors declare no competing interests. More

RESEARCH BRIEFINGS
26 April 2023

Biodiversity experiments show that a high diversity of plants increases the accumulation of soil carbon and nitrogen, but whether such conclusions hold in natural ecosystems is debated. An analysis of Canada’s National Forest Inventory provides strong evidence that the build-up of soil carbon and nitrogen on a decadal timescale increased with improved tree diversity in natural forest ecosystems. More

The new United Nations High Seas Treaty (see Nature https://doi.org/j6f3; 2023) provides a path to generating conservation, economic and social-equity gains at global and national scales from a single policy change: close the high seas to fishing. The treaty requires only three-quarters of member countries to vote to establish a marine protected area, making all of these goals politically feasible.
Competing Interests
The author declares no competing interests. More

As a deep-sea researcher at South Africa’s Department of Environmental Affairs, I lead marine research that helps the country to reach its ocean-sustainability goals, especially the establishment of marine-protected areas (MPAs). MPAs are like national parks, but in the ocean.To establish MPAs, we need to know what lives in them. I spend about half my time on the ocean, sampling species. Otherwise, I’m analysing data, planning expeditions and advising the minister on issues such as granting marine oil and gas permits.In this picture, I’m standing on the observer platform of our research vessel, the RV Algoa. As expedition chief scientist, I am responsible for the scientific crew.One area of continuing MPA research is Cape Canyon, off Western Cape. It’s a massive undersea system, up to 3 kilometres deep. We survey marine life there as a guide for where to establish MPAs.Our recent study (Z. Filander et al. Front. Mar. Sci. 9, 1025113; 2022) documented seabed-dwelling animals in Cape Canyon, including marine sponges, deep-water corals, a rare sea urchin (Dermechinus horridus) and an ancient sea star (Brisinga sp.). The canyon head of Cape Canyon has since been made into an MPA.My tribe, the amaBhaca of the Nguni people, has a strong tie with the ocean that began with our most-ancient ancestors. We go to the beach every New Year, but just to stand at the water’s edge. The ocean is a sacred space: we don’t interact with it.Some in my community viewed my work as disrespectful because I had not remained on the shore. I explained my research and why I do it to my community members — who are now excited by my work.As a Black and Indigenous female researcher who advises the government, I strive to ensure that marginalized communities’ perspectives are accurately represented. I address past injustices using ocean sciences as a vehicle for change. More

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Tasmanian devils are susceptible to facial cancers that are spread by biting.Credit: Gapvoy/Shutterstock

For three decades, Tasmanian devils have battled contagious facial cancers that result in debilitating tumours. Now, a comprehensive genetic analysis of these cancers has tracked their evolution, offering clues about how they could spread in future.The study, published on 20 April in Science1, offers some of the first detailed insights into how the diseases emerged, evolved and spread. This lays the groundwork for modelling how they could affect Tasmanian devil populations in future, says Janine Deakin, a genomicist at the University of Canberra. “Looking at the genomics does give us that insight into the past as well as potentially into the future,” says Deakin. “We need to understand the enemy that we’re working with.”Devilish diseasesTasmanian devils (Sarcophilus harrisii) are carnivorous marsupials native to the island of Tasmania in southeast Australia. They are susceptible to two cancers that emerged separately: devil facial tumour 1 (DFT1) and devil facial tumour 2 (DFT2), which are both spread by biting. Cancers that pass from one host to another are rare in nature, but can have devastating effects, says study co-author Rodrigo Hamede, a disease ecologist at the University of Tasmania in Hobart. “In a matter of 10 years, we lost between 60–70% of the overall [devil] population,” he says.Although scientists have been aware of the two cancers for some time, little has been known about their evolution. To investigate, Hamede and his colleagues assembled a Tasmanian devil reference genome and compared it with DNA sequenced from 78 DFT1 and 41 DFT2 tumours. The team then constructed ‘family trees’ of these tumours to track their origin and mapped their mutations to build a picture of how the diseases have evolved.The results show that DFT1 — which has spread across most of Tasmania — emerged in 1986, around a decade before it was first detected in a female devil in the northeast of the island. That individual seems to have been a superspreader, passing its tumour cells on to at least six other devils. This eventually resulted in six major variants of DFT1.The team found that DFT2 didn’t arise until 2011, roughly three years before it was first detected in a male devil in southeast Tasmania. Unlike DFT1, DFT2 is found in only a small region of the island. The cancer is genetically similar to DFT1, but it mutates around three times faster. This could be due to the tumour cells dividing more quickly, providing more opportunity for mutations to occur, says Hamede. “The big question is whether these mutations are selective or not,” he says.In most cases, the facial cancers don’t become contagious until tumours appear, 6–12 months after infection. But the fast-growing DFT2 cancer could shrink this window, leading to more infections that spread faster, says Hamede. This could give the cancer and its variants a competitive edge over less transmissible types. “That will be a long-term evolutionary advantage,” says Hamede.Vulnerable populationsPrevious research2 has shown that Tasmanian devil populations are becoming more resilient, but the relatively recent emergence of DFT2 is concerning, says Hannah Siddle, a geneticist at the University of Queensland in Brisbane, Australia. “It leaves the devil vulnerable in the wild, particularly in those regions where both tumours circulate,” she says. “This could induce local population crashes or as-yet unknown selection on the host population.”Hamede says that more work needs to be done before researchers can predict how the cancers will evolve and spread through remaining Tasmanian devil populations. “This is an ongoing evolutionary process that we have been witnessing in action,” says Hamede. “This second transmissible cancer will make things more complex.” More

Senegal is one of the countries most actively involved in the Great Green Wall initiative.Credit: Hemis/Alamy

‘Not just another summit.’This is how the Élysée Palace, the office of France’s President Emmanuel Macron described last month’s high-level One Forest Summit, co-led by France and Gabon. The focus of this year’s event was on protecting forests and biodiversity in the face of climate change. It was hosted by Gabon, most of which is forested, and was held in Libreville. The event did garner some eye-catching headlines. France announced that it will contribute half of the funds for a €100-million (US$110 million) project to pay communities to protect forests and ecosystems. Under a scheme called the One Forest Vision, scientists will have the task of mapping carbon (including carbon sequestration) and biodiversity in the world’s tropical forests in the next five years. And business leaders have promised to create 10 million jobs related to the sustainable management of forests by 2030.These initiatives are part of what is called the Libreville Plan. The world needs it to succeed to have even a fighting chance of limiting global warming to within 1.5 °C of pre-industrial levels and turning the corner on the decline in species and ecosystems. But more than a month after the event, no further detail has been published to explain how these initiatives will be achieved — whether through existing institutional mechanisms or by creating new ones. The organizers must remedy that quickly. At the same time, they should explain how their new project fits in with continuing priorities from previous summits.
Get Africa’s Great Green Wall back on track
For example, what about unfinished business from the last summit, which took place in Paris in 2021? The One Planet Summit for Biodiversity ended with delegates recommitting to the Africa-led Great Green Wall initiative, one of the world’s most ambitious ecological-restoration schemes.The Sahel–Sahara region is home to many of the world’s poorest people, who live in some of the driest conditions and are among the most vulnerable to climate change. The green-wall project was formally adopted by the African Union in 2007, five years after the union’s creation. It was championed by two powerful heads of government: Nigeria’s Olusegun Obasanjo and Senegal’s Abdoulaye Wade. The aim is to restore 100 million hectares of degraded land in 11 countries straddling the Sahel south of the Sahara, from Senegal in the west to Djibouti in the east — all by 2030. Originally conceived as a 7,000-kilometre wall of trees, it has evolved into a more complex set of activities, including not only planting new trees but also improving soils, setting up community gardens and protecting existing forests.The project also aims to create 10 million jobs and to sequester 250 million tonnes of carbon dioxide. International donors promised to provide most of the project’s budget. But as Nature and others have pointed out, the pace of financing is too slow to achieve this target.
How to make Africa’s ‘Great Green Wall’ a success
As of 2020, one-fifth of degraded land (20 million hectares) had been restored and 350,000 of the promised 10 million jobs had been created. That is mainly, although not solely, because just US$2.5 billion of a required $30 billion has been spent since the project began.A United Nations representative told Nature that donors have committed $15 billion to a pipeline of 150 projects. But a UN report published in February acknowledges that it’s not clear how much of this is grants, how much is loans and how much is existing funding relabelled as Great Green Wall money (see go.nature.com/3uhwtae). Moreover, coordination between Great Green Wall countries and donors is weak.The report suggests that trust between the African Union and international donors is in short supply. Donor nations seem to be picking and choosing which countries to invest in, with a preference for those in relatively stable regions. So Ethiopia, Eritrea, Niger and Senegal are among the most active participants (see ‘Off-target’). The less-involved countries — Chad, Mali, Burkina Faso and Sudan, for example — also happen to be the ones that are ruled by their armed forces, with instability, insurgencies and high rates of internal displacement, lost livelihoods and poverty as people flee fighting. The situation in Sudan has become particularly precarious, because military and paramilitary forces are now in open conflict. Conservation and economic-development projects are challenging to achieve in such conditions. The tragedy is that international donors seem to be pulling away (or moving only slowly) just when the people of these countries need their help the most.

Source: United Nations Convention to Combat Desertification; go.nature.com/3uhwtae

The project has also found it hard to excite Africa’s top leaders in the way it did Obasanjo and Wade, both of whom saw it as something the continent could unite over in the early days of the African Union. Now, the continent’s Great Green Wall is at risk of becoming its Great Green Walled Garden — a network of isolated activities in a relatively small number of countries. It is also in danger of seemingly abandoning the people most in need of it. There are lessons here for the Libreville Plan. In embracing a new project, donors don’t want to give the impression that they are done with the Green Wall and ready to move on.International summits are not difficult to organize if you have the money, and pledges are easily made. But unkept promises fuel anger and mistrust, at the same time worsening both poverty and the environment. While we await details of the new forest conservation plan, it’s essential that the original vision of Africa’s Great Green Wall is not filed away in the ‘too difficult’ box. More