How many species live in the sea?
By Catherine Brahic How many species are there in the sea? Some 230,000 recorded so far, all of which will soon be available to anyone at the click of a mouse. The World Register of Marine Species is launched today by the Census of Marine Life. Once complete, it will provide the first definitive list of all known species in the world’s oceans. The Register is freely accessible online and includes descriptions of the species and photos. It will allow both the public and scientists to identify species they come across and easily recognise entirely new species. Until now censuses have been incomplete, focussing on single species or regions, making proper assessment of the impact of humans on oceans difficult. “Convincing warnings about declining populations of fish and other marine species must rest on a valid census,” says Mark Costello of the University of Auckland, co-founder of the World Register. Jesse Ausubel of the Sloane Foundation, which funds the Census of Marine Life, says he was first struck by the need to catalogue marine species in 2000, when he realised the UN Environment Programme‘s Global Biodiversity Assessment had little information on what lived in the sea. Ausubel asked the author of the report’s only chapter on marine life, Frederick Grassle of Rutgers University, US, how many species there were in the sea. He was told that the best estimate was between 1 and 10 million. “I asked him if he could at least give me a list of the species that were known at the time,” says Ausubel. Grassle was embarrassed to admit he could not. “How could there not be a list in the year 2000 of what we knew to live in the oceans?” marvels Ausubel. Since then, the Census of Marine Life has worked to establish such a list. With the help of experts worldwide, they are painstakingly reviewing and compiling published records of marine species. Much of the work has focussed on identifying species given different names that are in fact the same. The sperm whale, for instance, has been found to have 4 different Latin names, and one sponge species, the breadcrumb sponge, has 56. So far, the catalogue contains 122,000 species, about half the estimated 230,000 known species. It should be complete by 2010. But there are still millions more ocean species to be discovered. Meeting in Belgium on 20-21 June, marine taxonomists discussed Grassle’s estimate of between 1 and 10 million total marine species. “We think that a million is reasonable,” says Ausubel, adding that experts have little idea what the upper limit could be. The group hope to be able to make a more informed guess once they have finished cataloguing those that have already been described. Mysteries of the Deep Sea – The deep sea is one of the harshest habitats on Earth, but is home to many remarkable creatures. Learn more in our comprehensive special report. Endangered species – Learn more about the conservation battle in our comprehensive special report. More on these topics: