A "roll call" of marine species has identified Australian and Japanese waters as the most biodiverse on Earth with each ocean zone containing an estimated 33,000 known forms of life, ranging from algae and single-celled protozoa to whales and sea birds.
The Mediterranean was also listed as a hotspot for different kinds of species by Census of Marine Life (CoML) scientists who surveyed 25 key marine regions.
On average, the number of known species per region totalled 10,750, ranging from 2,600 to 33,000. But for every marine species of all kinds known to science, experts estimate that at least four are yet to be discovered.
Waters around popular holiday resorts in southern Europe were in the top five of the biodiversity league table, along with oceans off China and the Gulf of Mexico.
However, the Mediterranean was also one of the areas where biodiversity was most threatened, along with other "enclosed" sea areas, such as the Gulf of Mexico, Baltic and the Caribbean.
The main historic threats to marine life were listed as overfishing, lost habitat, invasive species and pollution. Emerging threats included rising water temperature, acidification and oxygen depletion.
The Mediterranean was ranked fourth in the biodiversity league table, after Australia, Japan, and China, with a total of 16,848 recorded species.
Almost 400 scientists from more than 80 nations are involved in the project, which aims to provide the most accurate assessment possible of the diversity, distribution and abundance of life in the oceans.
