The world's oceans are facing a bleak future, say marine scientists, unless we rebuild its abundance, variety and vitality. David McNew/Getty /file
Tons of dead fish float on the waters of the Rodrigo de Freitas lagoon, beside the Corcovado mountain in Rio de Janeiro, Brazil. Threats from pollution, overfishing and climate change are putting marine life under immense strain. CHRISTOPHE SIMON/AFP/Getty Images
Oceans are home to 90% of the living volume of the planet and contain more than one million species, ranging from the largest animal on the planet -- the blue whale (pictured) -- to one of the weirdest -- the blobfish.
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Upwards of one million sea turtles were estimated to have been killed as bycatch during the period 1990-2008, according to a report published in Conservation Letters in 2010, and many of the species are on the IUCN's list of threatened species.
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"The two worst things in my mind happening to oceans are global warming and ocean acidification," says Ron O'Dor, professor of marine biology at Dalhousie University in Halifax, Canada. "They're going to have terrible effects on coral reefs. Because of acidification essentially, the coral can't grow and it's going to dissolve away."
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Currents estimates suggest 30% of coral reefs will be endangered by 2050, says O'Dor. HASSAN AMMAR/AFP/Getty Images
Los Angeles, June 2012: More than 5,000 children, teachers and volunteers form a massive kid-designed shark and shield on World Oceans Day. This year's event takes place on June 8. Lou DematteisSpectral Q via Getty Images
Overfishing has been going on for decades, say marine scientists. Tens of thousands of bluefin tuna were caught every year in the North Sea in the 1930s and 1940s. Today, they have disappeared across the seas of Northern Europe. Halibut (pictured) has suffered a similar fate, largely vanishing from the North Atlantic in the 19th century.
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"(Bottom trawling is) akin to someone plowing up a wildflower meadow, just because they can," says Callum Roberts, marine biologist at the UK's York University. Others have compared it to the deforestation of tropical rainforests.
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Bottom-trawling's knock-on impacts are best illustrated by the plight of the deep-sea fish, the orange roughy (also known as slimeheads). Populations have been reduced by more than 90%, according to marine scientists.
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