This year's events, from a port cleanup in 2004 Olympics host city Athens to the launch of an international photographic competition, focus on risks to marine life.

The United Nations Environment Program said the corals, cousins of creatures that build better-known tropical reefs, can live in sunless waters up to 3.5 miles deep and are home to a wide variety of marine life.

They are particularly threatened by 'bottom trawling,' which involves pulling huge weighted nets behind ships. The nets drag along the sea floor scooping up all the marine life in their way - from valuable fish to inedible species and delicate corals.

"Everyone must be aware (that) without intact coral reefs, warm and cold water reefs, you will not be able to restore fish stocks fully," UNEP head Klaus Toepfer said in an interview.

"This is another alarm call to ... change the techniques of fishing, especially bottom trawling which has quite disastrous consequences for these kindergartens of fish," he told Reuters.

Greenpeace also called Friday for an immediate ban on high-seas bottom trawling, saying it can alter the ocean floor in a way that prevents coral growing back.

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Environmentalists trying to persuade governments to cut back on fishing to protect reefs and precarious fish stocks are up against a formidable enemy, however - a voracious international appetite for seafood.

From sushi in Tokyo to fish and chips in London, consumer demand drives a market worth an estimated $75 billion a year and also supports jobs in coastal areas of many countries where other employment options can be limited.

Fishing of more usual commercial species is depleting stocks at an alarming rate, and a target to replenish overfished waters by 2015 is still far off, Toepfer said.

But tumbling numbers of traditional favorites like cod only encourage some fishermen to turn to more exotic deep sea options like orange roughy or blue ling.

The fate of these fish is intimately tied to that of the slow-growing cold-water corals they live in and around, and it can be hard to catch them without damaging or destroying the reefs.

Even if deep sea fishing is scaled back, however, seabed telecommunications cables, waste dumping and fossil fuel prospecting would still threaten the fragile coral beds, which scientists say are more extensive than they originally thought.

Found in seas from Norway to New Zealand, some of those in the east Atlantic have already been destroyed.

And there is little hope of any short-term recovery for the reefs, which Toepfer said could also hold the key to new medicines or industrial products. The cold water corals grow at one-tenth the rate of their tropical cousins.