Agence France-PresseApril 6, 2021 4:56:13 PM IST
Warming waters have pushed thousands of ocean species poleward from the equator, threatening marine ecosystems and the livelihoods of the people who depend on them, researchers reported Monday. Comparing data on nearly 50,000 species over three 20-year periods through 2015 revealed that the exodus from tropical waters is accelerating, they reported in the journal. PNAS. The tropics have long been home to a gargantuan proportion of marine life, but they could see diversity disappear if climate change is not controlled, the authors warned.
“Global warming has been changing life in the ocean for at least 60 years,” said lead author Mark Costello, professor of marine biology at the University of Auckland. AFP.
“Our findings show a drop of around 1,500 species at the equator,” he added. “This will continue throughout the century, but the pace will depend on how we reduce, or not, greenhouse gas emissions.”
The poleward migration was most pronounced north of the equator, where the oceans have warmed more rapidly than in the southern hemisphere.
It was also more prevalent among open-water fish than the so-called benthic species that live on the ocean floor.
“Benthic species can only move during their floating life stage and therefore their movement (towards the poles) is between generations,” Costello explained.
On the contrary, species that live in the high seas “can move with the bodies of water during their life”.
Marine life in tropical waters declines when the annual mean sea temperature rises above 20 to 25 degrees Celsius, depending on the species, the study found.
40 percent drop by mid-century
“‘Missing’ tropical species are likely to continue their thermal habitat as subtropical waters warm,” said co-author David Schoeman, professor of ecology at Nelson Mandela University in Port Elizabeth, South Africa.
Fossil records show the same thing happened 140,000 years ago, the last time global surface temperatures were as high as they are now.
Based on data from the open access Ocean Biodiversity Information System, the statistical study does not analyze how individual species will adapt to new environments.
In general, open-water species are likely to do better, previous research has found.
The impact on commercial fish stocks in the tropics is also not addressed, although it is clear which parts of the world will be the most affected.
“Indonesia and other nations near the equator, such as West Africa, have the most to lose because their stocks can only decrease,” as no new species will replace those that are leaving, Costello said.
Around the world, around 1.3 billion people live in tropical coastal areas, many of whom depend on fishing for food.
A recent review article in Nature estimated that the maximum catch potential of tropical fish stocks in so-called exclusive economic zones, 200 nautical miles (370 kilometers) from the coast, would decline by 40 percent by mid-century if warming global continues unabated.
In most Pacific island nations, the combined catch of skipjack and yellowfin tuna, the two most exported fish, would decline by as much as 40 percent under the same scenario, while locally consumed coral reef fish could still decline. plus.
The study at PNAS began with the PhD thesis of Chhaya Chaudhary from the University of Auckland.