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The oceans around Australia boast the greatest diversity of sea life on the planet, but the oil-threatened Gulf of Mexico also ranks in the top five regions for variety of species.

Even before last April's oil spill, the Gulf already had been listed as threatened, according to the latest update of the Census of Marine Life, released Monday. Mark Costello of the Leigh Marine Laboratory, University of Auckland, New Zealand, commented that now it seems the Gulf "is more threatened than we thought it was."

Regions where variety of life is most endangered tend to be the more enclosed seas, such as the Mediterranean, Gulf of Mexico, China's offshore shelves, Baltic Sea and Caribbean, the new study, done before the oil spill, concluded.

For every known marine species, such as this sea anemone and clown fish, there are four undiscovered species, marine science professor Paul Snelgrove estimates.For every known marine species, such as this sea anemone and clown fish, there are four undiscovered species, marine science professor Paul Snelgrove estimates. (Associated Press)

"The sea today is in trouble," said biologist Nancy Knowlton of the Smithsonian Institution, leader of the census's coral reef project. "Its citizens have no vote in any national or international body, but they are suffering and need to be heard."

Ron O'Dor, a researcher at Dalhousie University in Halifax, added that "there is a huge amount of diversity under the water. The ocean isn't just this blue sheet of cellophane that spreads out. The oxygen in every second breath we take is produced in the ocean, we ignore what is going on in the ocean at our peril."

Most species undiscovered: Canadian researcher

The Census of Marine Life, a 10-year undertaking involving more than 2,700 scientists worldwide, published an inventory Monday of the distribution of species and their diversity in key areas, a prelude to the Oct. 4 release of its full findings in London.

"We estimate that for every species we know, there's probably another four that we don't know about," said Paul Snelgrove, a professor of marine sciences at Memorial University in Newfoundland and Labrador.

"Pretty much every time you pull something out of the deep ocean, you're very likely to find something new in it."

As if to underline Snelgrove's point, marine scientists on board the Canadian research vessel Hudson returned from 28 days on the Grand Banks off Newfoundland last Wednesday to report some new discoveries. They estimate that of the 500 catalogued samples taken from the ocean, five to 10 were previously unknown, including some corals and sponges.

Philippe Archambault, a marine ecologist with the University of Quebec at Rimouski who is helping provide Canadian input, said the country's climate and size complicates efforts to broaden research.

"We have a snapshot of what's going on in the summer. We don't know what goes on in the winter in most of Canada," he said.

"In addition, Canada has 17 per cent of the world's coastline.… It's a very large area to try and monitor."

-—Canadian Press

The decade-long census is scheduled to release its final report in London in October. The latest update was published Monday in the journal PLoS ONE.

The report disclosed that the Gulf of Mexico, where a battle is underway to clean up a massive oil spill, ranks fifth among 25 regions around the world for diversity of sea life.

Australia, Japan top biodiversity list

The Gulf has 15,374 different species identified so far.

Australian waters had the most species at 32,889, closely followed by Japan with 32,777. Then came China, 22,365, and the Mediterranean, 16,848.

What sort of things have the census researchers found?

Well, Australia has the Dragonfish, a banana-sized creature with a mouth full of sharp teeth, some even on its tongue. It lives deep in the ocean, and since it may be a long time between meals, if it finds something to eat it needs to hang on to it.

In the Gulf of Mexico, queen angelfish have been seen hanging out around oil rigs while the deep regions sport specialized octopuses.

The Caribbean has the bearded fireworm and nocturnal brittle stars, while off South Korea lives the Sargassum fish. It has a trapdoor-like mouth high on the head, and a "fishing lure" formed by the first dorsal spine on the snout.

When it comes to what group of sea creatures have the most different species, it turns out to be crustaceans, such as shrimp, crabs and lobster.

Overall, the report said crustaceans make up nearly one-fifth of the species in the ocean — 19 per cent. Close behind at 17 per cent were mollusks such as squid, octopus, clams, snails and slugs. Fish make 12 per cent of ocean species, and it is 10 per cent each for protozoa and algae.

Smaller shares go to segmented worms, sea anemones, corals and jellyfish, flatworms, starfish, sponges and other creatures.