Warming waters have driven thousands of ocean species poleward from the equator, threatening marine ecosystems and the livelihoods of people who depend on them, researchers reported Monday. Comparison of data on nearly 50,000 species over three 20-year periods up to 2015 revealed that the exodus from tropical waters is accelerating, they reported in the journal PNAS. The tropics have long harboured an outsized proportion of marine life, but could see that diversity disappear if climate change is not brought to heel, the authors warned.
“Global warming has been changing life in the ocean for at least 60 years,” senior author Mark Costello, a professor of marine biology at the University of Auckland, told AFP. “Our findings show a drop of about 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 ‘missing’ tropical species are likely following their thermal habitat as subtropical waters warm,” noted co-author David Schoeman, a professor of ecology at Nelson Mandela University in Port Elizabeth, South Africa.
Fossil records show that the same thing happened 140,000 years ago, the last time global surface temperatures were as hot as they are now. Based on data in the open-access Ocean Biodiversity Information System, the statistical study does not look at how individual species will adapt to new environments. The impact on commercial fish stocks in the tropics is not addressed either, though it is clear which parts of the world will be hit the hardest. “Indonesia and other nations near the equator, such as in West Africa, have the most to lose because their stocks can only decrease,” as no new species will replace those leaving, Costello said.