The first Census of Marine Life, which has been 10 years in the making, will reveal that almost 250,000 species have now been identified in the world’s oceans, and predicts there may be at least another 750,000 are yet to be discovered.
The report marks the first attempt to provide a definitive record of all the species of plants and animals living in the sea.
During the 10-year project scientists from around the world have identified more than 6,000 new species. Yet despite this great diversity of life, the report will warn 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 will say.
"It will probably take at least another decade of the Census before we can defensibly estimate the total number of marine species.
"The deepsea 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, a blind lobster with a long, spiny, pincer, which was found 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 23cm across in Antarctic seas.
The deepsea 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 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.
Other species on the sea bed, away from vents, feed off the life that falls into the depths from the water above.
The "Squidworm", a new species of worm, was found living in the deep water of the Celebes Sea in South East Asia.
A furry crab, named the Yeti crab (Kiwa hirsute), was also among the discoveries when it was found beside a vent in the deep sea off Easter Island in the south Pacific. Not only was it a new species but part of a new family previously unknown to science.
Recently scientists have discovered a different member of the same family on the ocean floor off Costa Rica where cold fluid enriched with methane has been found seeping through the sea bed, sustaining colonies of animal life.
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.
"The Census provides us with a baseline to measure the effects that humans are having, but it is also opening people's eyes to what are in our oceans. It is showing us that we still have no idea of exactly what we are sharing our planet with."
Genetic testing now allows scientists to work out whether newly-discovered creatures are new species or just differently-coloured or shaped varients of those already known.
One new species of crustacean, which looks like a pale shrimp, was identified in this way. The all-white creature was initially thought to be a variety of Epimeria georgiana, which has orange specks, but turned out to be new when scientists looked at its DNA.
The number of plant and animal species is also dwarfed by the possible number of different types of microbes found in the seas - up to a billion, according to the Census.
Dr Huw Griffiths, a marine scientist at the British Antarctic Survey who has gone on some of the Census expeditions, said: "About 80% of the species in the Antarctic live on the sea floor. It is incredibly rich and varied there.
"They are the sort of creatures that a palaeontologist might be more likely to recognise than a marine biologist because they seem to be communities we normally see in the fossil record than in modern oceans elsewhere."
[Sources: The Sunday Times, Telegraph.co.uk]
