Philippa Kaur

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

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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

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

A kelp forest off the coast of California.Credit: Douglas Klug/Getty

The vast swathes of kelp forest growing along the world’s coastlines are estimated to generate US$500 billion a year on average, making them considerably more valuable than previous studies have suggested, according to an analysis that assessed economic contributions made by six types of the seaweed.The study, published on 18 April in Nature Communications1, estimates that kelp forests provide services worth between $465 billion and $562 billion a year worldwide, mainly by providing a habitat for valuable fish and seafood species, and by removing nitrogen from contaminated seawater. The results suggest that each type of kelp forest (see ‘Seaweed services’) generates up to $147,100 per hectare annually, a figure that’s more than three times higher than previous estimates.“Until now, most kelp-forest evaluations were regional,” says Cristina Piñeiro-Corbeira, a marine ecologist at the University of A Coruña in Spain who was not involved in the project. “This study is a step forward in understanding kelp forests and their importance for human well-being on a global scale.”

Source: Ref. 1

Kelp forests are widespread in temperate and polar regions, with some 740 million people thought to live within 50 kilometres of one of these tracts of brown seaweed. They provide habitat for more than one thousand species, draw carbon dioxide from the atmosphere and help to remove nutrient pollution, such as nitrogen and phosphorus, from the ocean. “Outside of the tropics, kelp forests are really the dominant [coastal] habitat,” says study co-author Aaron Eger, a marine scientist at the University of New South Wales in Sydney, Australia. “These are the essential threads to marine ecosystems.”Despite this, few studies have attempted to quantify the economic value of kelp forests on a global scale. To address this gap, Eger and his colleagues assessed the value of common types of kelp forest by considering their contributions to fisheries, nutrient cycling and atmospheric CO2 removal. They collated kelp-distribution estimates, data from biodiversity surveys and current seafood prices from different regions.
World leaders are waking up to the ocean’s role in a healthy planet
The team’s estimates suggest that kelp forests provide an average harvest for fisheries of more than 900 kilograms per hectare a year, worth about $30,000. In many locations, lobsters and abalone accounted for more than one-quarter of a kelp site’s fisheries value. Pollack, giant seabass, South American morwongs and lingcod were the most valuable fish across the sites surveyed.Each hectare of kelp forest also removes an average of 657 kilograms of excess nitrogen — which flows into the ocean in waste water and agricultural runoff — from seawater, a service worth almost $74,000 per hectare per year. And together, kelp forests absorb almost five megatonnes of atmospheric CO2 each year, putting them on a par with other prominent carbon sinks, such as mangrove forests and terrestrial woodland. The economic value of this carbon removal is only $163 a year per hectare of kelp, however, owing to the low market price of carbon and its widespread presence in the ocean, says Eger. “The impacts of nitrogen are quite localized, so there is a higher demand to address the problem,” he says. “Carbon is diffuse and hard to attach to damages in any one location.”Kelp conservationPiñeiro-Corbeira says the findings could provide a push for kelp forests to be included more prominently in climate-change policies and could also encourage better ways of managing and conserving them. But she adds that because the study focuses on only three ecosystem services, it could still underestimate the value of kelp forests.The inclusion of other services — such as coastal protection, tourism and recreation — in the models is likely to further boost kelp forests’ estimated value, says Eger. The value might also increase as more areas are mapped and researchers gain a better understanding of how much kelp is in the ocean. “It has a strong potential to go up,” he says. More