What is the most common fish in the world and what kinds of creatures lurk in the depths of the Mediterranean? These are just some of the questions that scientists around the world are able to answer, now that the first findings of the "World Ocean Census: A Global Survey of Marine Life" have been released. The scientists involved in the census, which was published on Monday, admit however that beyond the riches of 230,000 marine species, they are still groping in the dark as close to 80 per cent of marine life forms have yet to be identified.

The marine census results appeared in the U.S.-based online Public Library of Science (PLoS ) as part of its "What lives in the sea?" project, whose participants include the National Geographic magazine and Israeli scientist Prof. Bella Galil of the Israel Oceanographic and Limnological Research Institute. Complete findings will be published over the next three months.

The researchers said that in light of climate change, pollution and the destruction of natural habitats, there is great concern that many species will become extinct before they are discovered. One of the most troubled sites from this point of view is the Mediterranean Sea, described as the most threatened by invasive species.

One of the most destructive of these invaders is a creature called a "comb jelly" (ctenophore ) - similar but not identical to jellyfish; it was first sighted in Israeli waters two years ago and by last year had spread in the direction of Spain. This species, whose origin is American, consumes fish larvae, disturbing the marine food chain.

The work of identifying species is continuous, with about 100 new fish discovered each year. In addition, the scientists collect information about which species may be found in 25 different marine areas around the world. The Mediterranean is one of five areas containing the most varied number of species: 17,000, according to the census to date. Nonetheless, as in other oceans, there is a great amount of marine life still unknown to science. According to estimates, about three quarters of the species in the Mediterranean's deep waters have yet to be identified.

The species termed the most cosmopolitan are seaweed and single-celled organisms found in the greatest number of marine sites. In addition, the most common fish - manylight viperfish - is also to be found in Israel, and even has a Hebrew name, "tsfaon hama'amakim," documented in more than a quarter of the marine sites surveyed.