Oceans losing oxygen at unprecedented rate, experts warn
Sharks, tuna, marlin and other large fish at risk from spread of ‘dead zones’, say scientists
Sharks, tuna, marlin and other large fish at risk from spread of ‘dead zones’, say scientists
Oxygen in the oceans is being lost at an unprecedented rate, with “dead zones” proliferating and hundreds more areas showing oxygen dangerously depleted, as a result of the climate emergency and intensive farming, experts have warned.
Sharks, tuna, marlin and other large fish species were at particular risk, scientists said, with many vital ecosystems in danger of collapse. Dead zones – where oxygen is effectively absent – have quadrupled in extent in the last half-century,
and there are also at least 700 areas where oxygen is at dangerously low levels, up from 45 when research was undertaken in the 1960s.
The International Union for the Conservation of Nature presented the findings on Saturday at the UN climate conference in Madrid, where governments are halfway through tense negotiations aimed at tackling the climate crisis.
Grethel Aguilar, the acting director general of the IUCN, said the health of the oceans should be a key consideration for the talks. “As the warming ocean loses oxygen, the delicate balance of marine life is thrown into disarray,” she said.
“The potentially dire effects on fisheries and vulnerable coastal communities mean that the decisions made at the conference are even more crucial.”All fish need dissolved oxygen, but the biggest species are particularly vulnerable to depleted oxygen levels
because they need much more to survive. Evidence shows that depleted levels are forcing them to move towards the surface and to shallow areas of sea, where they are more vulnerable to fishing.The world’s oceans are already being overfished, and assailed by a rising
tide of plastic waste, as well as other pollutants. Seas are about 26% more acidic than in pre-industrial times because of absorbing the excess carbon dioxide in the atmosphere, according to the Intergovernmental Panel on Climate Change, with damaging impacts on shellfish
Low oxygen levels are also associated with global heating, because the warmer water holds less oxygen and the heating causes stratification, so there is less of the vital mixing of oxygen-rich and oxygen-poor layers.
Intensive farming also plays a major role. When excess artificial fertiliser from crops, or manure from the meat industry, runs off the land and into rivers and seas, it feeds algae which bloom and then cause oxygen depletion as they decompose.
The problem of dead zones has been known about for decades, but little has been done to tackle it.
This year’s UN climate conference, known as COP25, was originally billed as the “Blue COP”, with a spotlight on the oceans for the first time in the history of the negotiations. The focus was chosen because of the original location in Chile,
a country with more than 4,000km of coastline and a strong reliance on the marine economy.
Protecting marine life could help the oceans to function better, soaking up more carbon and providing barriers against sea level rises and storm surges, in the form of coral reefs and mangrove swamps.
Ending overfishing is a quick, deliverable action which will restore fish populations, create more resilient ocean ecosystems, decrease CO2 pollution and increase carbon capture, and deliver more profitable fisheries and thriving coastal communities.”
