A shade under R300-trillion will get you the ocean and all that sails on it and lives in it. But the ocean is a depreciating asset thanks to over-fishing, pollution and climate change.The World Wildlife Fund, with the Global Change Institute at the University of Queensland and the Boston Consulting Group, has crunched some numbers and come up with a value for the world's oceans. That figure is $24-trillion.But the wildlife fund says collapsing fisheries, mangrove deforestation and disappearing corals and sea-grass are threatening marine ecosystems and the livelihoods of millions.Its report titled "Reviving the Ocean Economy" indicates that oceans are changing more rapidly today than at any other point in millions of years.The statistics are alarming - some 90% of global fish stocks are already over-exploited or fully exploited, and marine species declined by 39% between 1970 and 2010.Global warming could prove to be a death sentence for delicate coral reefs, containing some of the most diverse ecosystems on the planet.Already half of all coral reefs have vanished, and they are all expected to be gone by 2050 if temperatures continue to rise at the prevailing rate, the report says."The ocean rivals the wealth of the richest countries, but it is being allowed to sink to the depths of a failed economy," said Marco Lambertini, director-general of World Wildlife Fund International.Researchers came up with a value for the world's oceans by evaluating seven assets associated with the seas: fisheries, mangrove forests, coral reefs, sea-grass, shipping lanes, productive coastlines and carbon dioxide absorption.The report says that more than two-thirds of the annual value of the ocean relies on healthy conditions to maintain its annual economic output.The annual value of goods and services (such as shipping and fisheries) generated by the oceans, the report adds, was evaluated at $2.5-trillion.If compared with the world's top 10 economies, the ocean would sit at number seven.The sea off South Africa faced over-fishing, the invasion of alien species and the depletion of coral , said John Duncan, senior manager for the wildlife fund's marine programme.Some fish species, he said, had fallen to 10% of pre-fished stock levels.South Africa had, however, established 24 marine protected areas, which, Duncan said, was a positive move Additional reporting by AFP..