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Last summer every sea creature across an area twice the size of Wales was asphyxiated by severely depleted oxygen levels in the Gulf of Mexico. The same phenomenon, the marine equivalent of the ozone hole, happened off South America, China, Japan, south-east Australia, New Zealand, and up to 150 other places.
A United Nations agency warned yesterday that the number of these "dead zones", caused mainly by the run-off of nitrogen fertilisers from intensive farming and sewerage from large cities, had doubled in the past 15 years and was increasing all over the world.
In a new report, the UN environment programme said that 150 sea areas were now regularly starved of oxygen and were becoming major threats to already declining fish stocks, including those in Europe, where areas of the Baltic Sea were lifeless for several months, as were parts of the Irish Sea and the Adriatic.
The Black Sea - the largest and oldest "dead zone" in the world - supported only a few bacteria to a depth of 150 metres.
"Humankind is engaged in a gigantic, global, experiment as a result of the inefficient and often over-use of fertilisers, the discharge of untreated sewage and the ever rising emissions from vehicles and factories," said Klaus Toepfer, the UN environment programme (UNEP) director. "The nitrogen and phosphorous from these sources are being discharged into rivers and the coastal environment or being deposited from the atmosphere, triggering these alarming and sometimes irreversible effects."
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