The Census has been 10 years in the making, and during the ambitious project scientists from around the world have identified more than 250,000 new species. The report, which marks the first attempt to provide a definitive record of all the species of plants and animals living in the sea, has also predicted that there may be at least 750,000 more species still waiting to be discovered in the ocean depths, the Telegraph reported.
Yet despite this great diversity of life, the report warned that humans are having a devastating impact on the numbers of many species through fishing and pollution.
"Marine scientists are at present unable to provide good estimates of the total number of species that flourish in the ocean," it said.
"It will probably take at least another decade of the Census before we can defensibly estimate the total number of marine species.
"The deep-sea floor is no longer considered a desert, characterised by a paltry diversity of species.
"Over exploitation, habitat loss and pollution have depleted many fisheries that previously provided food and employment."
More than 2,700 scientists have helped to compile the Census, with more than 540 expeditions to visit all of the world's oceans. Among the new species discovered are Dinochelus ausubeli, the blind lobster with a long, spiny, pincer, which was found 330 yards (300 metres) below the surface in the Philippine Sea.
British scientists have made huge numbers of finds in the cold and inhospitable ocean around Antarctica. In these conditions, marine life grows larger than anywhere else in the world. Sea spiders, a family of eight-legged creatures which rarely grow bigger than a fingernail in UK waters, have been discovered up to nine inches (23cm) across in Antarctic seas.
The deep sea floor, previously thought to be an almost lifeless desert due to the huge pressure, pitch black conditions and cold water found at depths greater than 6,000 feet (1.8km), has provided some of the biggest surprises.
Researchers have discovered huge communities of different species scattered across the ocean floor, living at the mouth of thermal vents and rifts that seep nutrients into the ocean. Dr Maria Baker, a researcher at the National Oceanography Centre in Southampton and a project manager on the Census, said: "Life is much more widespread on the ocean floor than was thought.
"We still don't know how it spreads from vent to vent, but there could be stepping stones all over the place provided by food that falls from the water above."