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 tended 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.
"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.
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 square kilometer.
That does not mean that only 10 animals exist in an area of about four-tenths of a square mile (10 square kilometers), it means 10 different kinds of animals.
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 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, sea anemones, corals and jellyfish, flatworms, starfish, sponges and other creatures.