"Scientists are discovering and describing an astonishing new world of marine microbial diversity and abundance."
The ICoMM was one of four of the Census's projects that focused on "hard to see" marine organisms.
The team, involving researchers from the Netherlands and the US, collected samples from more than 1,200 locations, which resulted in the compilation of a dataset containing in excess of 18 million DNA sequences.
CoML researchers suggested that the total number of marine microbes, based on molecular characterisation, could be in the region of one billion species.
They added that the micro-organisms were vital for sustaining life on Earth, as they are responsible for about 95% of respiration in the oceans.
"They play a really critical role in keeping the oceans working," said Paul Snelgrove, leader of CoML's Synthesis Group.
"Certainly, life in the oceans - and then life on Earth - would collapse very quickly without the microbes."
In the 1950s, scientists estimated that about 100,000 microbial cells inhabited in one litre of seawater. However, with the aid of modern technological advances, researchers now suggest that the figure is closer to one billion micro-organisms.
They have also calculated that the estimated total mass of marine microbes is equivalent to 240 billion African elephants.
'Microbial mat' found off S America
As part of the CoML, Chile-based researchers found a "microbial mat" off the south-west coast of South America that covered a vast area, equivalent to the size of Greece.
The mats were found at a depth where "oxygen minimum layers" (OML) occurred. These are regions where there is very little oxygen, or none at all.
However, the researchers found that the communities of microbes thrived on hydrogen sulphide, which is toxic to most lifeforms, and is the product of the breakdown of organic material in an environment where there is no oxygen.
The team - led by Victor Gallardo, vice-chairman of the Census Scientific Steering Committee - said the mats resembled an ecosystem that existed between 2.5bn and 650m years ago.
As well as microbes, scientists working on Census projects also assessed the diversity of zooplankton species; collected samples from abyssal plains, and hydrothermal vents and seeps.
Decade of discovery
Professor Snelgrove said it was thanks to recent technological advances that it was now possible for scientists to study "hard to see" organisms.
The diversity and abundance of "hard to see" species surprised scientists
"In the case of microbes, we could not tell them apart because they were so small and all looked the same," he told BBC News.
"Now we know that things that look identical do very different things in the oceans.
"It is really only in the last decade that we have had the technology that allowed us to start asking who was out there and what exactly were they doing."
He explained that information collected by the various projects will be listed on a open-access database called the Ocean Biogeographic Information System (Obis).
"Everyone who has participated in the Census has agreed to deposit their data into this database," he said.
Currently, Obis - which is accessible via the world wide web - has more than 27 million records covering in excess of 110,000 species.
It contains a wide range of information, including details of a species; where it was recorded, and at what depth.
"This has led to the building up of this global ocean biodiversity dataset," Professor Snelgrove observed.
"This is already allowing people to test predictions about where life is in the oceans, where are the biodiversity hotspots and lowspots?
"I think it is going to be an extremely rich dataset to mine well into the future."
A final synthesis report will be published at the beginning of October to mark the end of the decade-long project involving in excess of 2,000 scientists from more than 80 nations.
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