By Rebecca Morelle
Source: BBC News 
During a two-week dive researchers discovered scores more species of fish than previously known in the region and vast beds of "seaweed cities".
But the team says the biodiversity hotspot is in danger: oil tankers in the area threaten the fragile reefs.
The researchers are hoping to get the area protected by the International Maritime Organization (IMO).
The find was made in the Saba Bank Atoll, a coral-crowned seamount, 250km south-east of Puerto Rico in the Netherlands Antilles.
It is ranked as the third largest atoll in the world and has an enormous active reef.
The dives took place during the first two weeks of January, and involved a scientific team of 12 from Conservation International, the Netherlands Antilles government and the Smithsonian Institution's Museum of Natural History, as well as local fisherman.
Scientists chose to explore the area because although it was predicted to have high concentrations of marine life, only a small number of species had been reported.
During the dives, the researchers counted a total of 200 species of fish, over 150 more than previously known.
Among their find were two new species of fish, both gobies, which have the distinctive feature of fused pelvic fins on the underside of their body which forms a sucker.
"Many [gobies] live in the canals inside sponges, so we take samples out of sponges, and open the canals up to search for the small fish that can be in there," explained Dr Smith, a scientist on the expedition from Conservation International.
"When we did that, we found quite an extraordinary one. It's still known from a single specimen, and it is so very very distinctive that it is probably a new genus."
The sighting of vast and luxurious seaweed beds were also astonishing, with at least 12 new species of algae discovered.
Dr Mark Littler, a marine botanist at the Smithsonian Institution's Museum of Natural History and a diver on the expedition, declared the Saba Bank the richest area for seaweeds in the Caribbean.
Seaweeds form the base of the food chain in coral reefs, from which the rest of biodiversity depends.
"When we add everything together - the species of new fish, the dozen new species of algae - that means during the time we were there we discovered a new species every day. That's pretty exciting," said Dr Smith.
However, the biodiversity hotspot could be under threat. A petroleum trans-shipment depot on the nearby island of St Eustatius causes a significant amount of marine traffic.
The big tankers, in order to avoid mooring fees at St Eustatius are said to anchor on the bank, causing significant damage to the reef.
"The anchor for a supertanker is as big as my office, and the links in the chain are as big as my desk. They sweep around and just crush all of the coral. They are enormously destructive," explained Dr Smith.
To stop the damage and protect the atoll, the researchers are attempting to get the Saba Bank designated a Particularly Sensitive Sea Area (PSSA) by the IMO.
The 1,500 strong community on Saba Island are responsible for the Bank, and derive about 10% of their economy from it, making the atoll a major source of their livelihood.
Leroy Peterson, a Saba fisherman, called the expedition crucial for protecting Saba Bank's unique marine life.
"Some of the scientists actually found new species not located anywhere else," Peterson said.
"There should be no-anchor zones. For things to survive there must be stricter controls."
Alison Shaw, a marine biologist from the Zoological Society London, added: "By gaining this greater understanding of what lives in the atoll, we can implement better management systems that will provide protection of this resource both for the local community and for the wildlife too."
Dr Smith said that Saba Bank's unique location makes it a prime candidate for conservation.
"It's in an interesting position because many of the Caribbean reefs are close to shore and have damage that is of a land based source," he said.
"But Saba is free of all of that, so potentially it can be the keystone for protecting biodiversity in the Caribbean."