The oceans around Australia and Japan boast the greatest diversity of sea life on the planet, but the now 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 had been listed as threatened, according to the latest update of the Census of Marine Life, released Monday. Now it seems that the Gulf "is more threatened than we thought it was," said Mark Costello of the Leigh Marine Laboratory at the University of Auckland in New Zealand.
Regions where variety of life is most endangered tended to be the more enclosed seas, such as the Mediterranean, Gulf of Mexico, China's offshore shelves, the Baltic Sea and the Caribbean, according to the newly released study, which was done before the April oil spill.
"The sea today is in trouble," said biologist Nancy Knowlton of the Smithsonian Institution, leader of the Census' coral reef project. "Its citizens have no vote in any national or international body, but they are suffering and need to be heard."
Researcher Ron O'Dor 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."
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.
Gulf ranks among top five habitats
The report disclosed that the Gulf of Mexico, where a battle is under way to clean up a massive oil spill, ranks fifth among 25 regions around the world for diversity of sea life.
The Gulf has 15,374 different species identified so far. That is an average of just over 10 different species per 1,000 square kilometers.
That does not mean that only 10 animals exist in an area of 1,000 square kilometers (about 386 square miles). It means that, on average, 10 different kinds of animals would be found in that area of ocean.
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.
When the area of ocean is taken into consideration, South Korea comes out on top with 32.3 species per 1,000 square kilometers, followed by China, South Africa, the Baltic Sea and the Gulf of Mexico.
On the other end of the scale, Alaska, the Arctic, Antarctica and the Patagonian Shelf have the fewest species per area of ocean. In Antarctic oceans, the diversity count averaged just 0.4 species per 1,000 square kilometers.
Creatures great and small
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 percent. Close behind at 17 percent were mollusks such as squid, octopus, clams, snails and slugs. Fish make 12 percent of ocean species, and it is 10 percent each for protozoa and algae.
Smaller shares go to segmented worms (7 percent); cnidaria such as sea anemones, corals and jellyfish (5 percent); and the groups of sea creatures that include flatworms (3 percent), starfish (3 percent), sponges (3 percent), moss animals (2 percent) and sea squirts (1 percent).
Whales are in the 'other' category
The rest are other invertebrates (5 percent) and other vertebrates (2 percent). The "other vertebrates" include whales, sea lions, seals, sea birds, turtles and walruses. "Thus, some of the best-known marine animals comprise a tiny part of marine biodiversity," the Census of Marine Life said in a statement. That assessment is based purely on the number of species identified, rather than the species' abundance or total biomass.
The most widely found species tend to fall under two broad categories. On the small side of the scale would be microscopic plants and single-celled animals; on the large side of the scale would be seabirds and marine mammals that traverse the world's oceans.
The Census reported that the manylight viperfish (Chauliodus sloani) could be considered the "Everyman of the deep ocean," because sightings of the fish has been recorded in more than a quarter of the world's seas.
Patricia Miloslavich of Venezuela's Universidad Simon Bolivar, a co-senior scientist for the global effort and leader of the regional studies, said the Census would serve as a "baseline" for future research. However, the Smithsonian's Knowlton cautioned that most of the organisms in the world's oceans would "still remain nameless and their numbers unknown" even after the Census is finished.
"This is not an admission of failure," she said. "The ocean is simply so vast that, after 10 years of hard work, we still have only snapshots, though sometimes detailed, of what the sea contains. But it is an important and impressive start."
This report includes information from The Associated Press and msnbc.com. An earlier version of this report mischaracterized the species richness per unit of area, due to a multiplication factor in the research paper that was left out of the calculations.