In a new report, the conservation group said oceans each year generate goods and services worth at least USD 2.5 trillion, while their overall value as an asset is worth 10 times that.
If oceans were a nation, they would constitute the world's seventh largest economy, ranking just after Britain but ahead of the likes of Brazil, Russia and India, WWF said.
Their estimated asset value of USD 24 trillion would meanwhile dwarf the world's largest sovereign wealth fund, in Norway, which holds just USD 893 billion, it said.
"The ocean rivals the wealth of the world's richest countries, but it is being allowed to sink to the depths of a failed economy," WWF chief Marco Lambertini warned in a statement.
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Today's report, produced in cooperation with Queensland University's Global Change Institute and the Boston Consulting Group, indicated that oceans are changing more rapidly today than at any other point in millions of years.
A full two thirds of the economic value generated by oceans depends on healthy ocean conditions, the report said.
But unfortunately oceans are "showing serious signs of failing health," it said.
The statistics are frightening -- some 90 percent of global fish stocks are already over-exploited or fully exploited, and marine species declined by 39 percent between 1970 and 2010, it said.
Global warming could meanwhile prove to be a death sentence for delicate coral reefs, containing some of the most diverse ecosystems on the planet.
Mangroves, considered vital to coral reefs and fisheries, and which serve as important buffers for coastal cities against rising sea levels and storm surges, are meanwhile facing deforestation rates three to five times higher than the average global forest loss, it said.