The first Census of Marine Life (CoML) hopes to act as a baseline of how human activity is affecting previously unexplored marine ecosystems.
The international project involved more than 2,700 researchers from 80 nations, who spent a total of 9,000 days at sea during at least 540 expeditions.
It has been described as the most comprehensive study of its kind.
“This co-operative international 21st Century voyage has systematically defined for the first time both the known and the vast unknown, unexplored ocean,” said Ian Poiner, chairman of the Census Steering Committee, speaking before a conference that is being held in Central London to mark the “decade of discovery”.
“All surface life depends on life inside and beneath the oceans,” he added.
“Sea life provides half of our oxygen, a lot of our food and regulates the climate. While much remains unknown, including at least 750,000 undiscovered species and their roles, we are better acquainted now with our fellow travellers and their vast habitat.”
The $650m (