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Fish Under Threat from Ocean Oxygen Depletion — study

Fish Under Threat from Ocean Oxygen Depletion — study

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The depletion of oxygen in our oceans threatens future fish stocks and risks altering the habitat and behaviour of marine life, scientists have warned, after a new study found oceanic oxygen levels had fallen by 2% in 50 years.

Large fish like marlin will be driven into ever narrower bands of oxygen-rich water near the surface, leading to more competition for food sources. (Photo by: Bill Boyce/Geomar)

Large fish like marlin will be driven into ever narrower bands of oxygen-rich water near the surface, leading to more competition for food sources. (Photo by: Bill Boyce/Geomar)

The study, carried out at Geomar Helmholtz Centre for Ocean Research in Germany, was the most comprehensive of the subject to date. The fall in oxygen levels has been attributed to global warming and the authors warn that if it continues unchecked, the amount of oxygen lost could reach up to 7% by 2100. Very few marine organisms are able to adapt to low levels of oxygen.

The paper contains analysis of wide-ranging data from 1960 to 2010, documenting changes in oxygen distribution in the entire ocean for the first time. “Since large fish in particular avoid or do not survive in areas with low oxygen content, these changes can have far-reaching biological consequences,” said Dr Sunke Schmidtko, the report’s lead author.

Some areas have seen a greater drop than others. The Pacific – the planet’s largest ocean – has suffered the greatest volume of oxygen loss, while the Arctic witnessed the sharpest decline by percentage.

“While the slight decrease of oxygen in the atmosphere is currently considered non-critical, the oxygen losses in the ocean can have far-reaching consequences because of the uneven distribution,” added another of the report’s authors, Lothar Stramma.

It is increasingly clear that the heaviest burden of climate change is falling on the planet’s oceans, which absorb more than 30% of the carbon produced on land. Rising sea levels are taking their toll on many of the world’s poorest places. Warming waters have devastated corals – including the Great Barrier Reef – in bleaching events.

Acidic oceans, caused by a drop in PH levels as carbon is absorbed, threaten creatures’ ability to build their calcium-based shells and other structures. Warming waters have also caused reproductive problems in species such as cod, and triggered their migration to colder climates. Lower oxygen levels in larger parts of the ocean are expected to force animals to seek out ever shrinking patches of habitable water, with significant impacts on the ecosystem and food web.

Callum Roberts, the author of Ocean of Life and a marine conservation biologist at the University of York, is unsurprised by the latest findings. “What we’re seeing is fallout from global warming,” he says. “It’s straightforward physics and chemistry playing out in front of our eyes, entirely in keeping with what we’d expect and yet another nail in coffin of climate change denial.”

(Story and photo courtesy of The Guardian. Read the full article.)

Avatar of Coral Triangle Written by Coral Triangle

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