Oceans contain the largest living volume of the "blue" planet, inhabited by approximately 235-250,000 described species, all groups included. They only represent some 13% of the known species on the Earth, but the marine biomasses are really huge. Marine phytoplankton alone represents half the production of organic matter on Earth while marine bacteria represent more than 10%. Life first appeared in the oceans more than 3.8 billion years ago and several determining events took place that changed the course of life, ranging from the development of the cell nucleus to sexual reproduction going through multi-cellular organisms and the capture of organelles. Of the 31 animal phyla currently listed, 12 are exclusively marine phyla and have never left the ocean. An interesting question is to try to understand why there are so few marine species versus land species? This pattern of distribution seems pretty recent in the course of Evolution. From an exclusively marine world, since the beginning until 440 million years ago, land number of species much increased 110 million years ago. Specific diversity and ancestral roles, in addition to organizational models and original behaviors, have made marine organisms excellent reservoirs for identifying and extracting molecules (>15,000 today) with pharmacological potential. They also make particularly relevant models for both fundamental and applied research. Some marine models have been the source of essential discoveries in life sciences. From this diversity, the ocean provides humankind with renewable resources, which are highly threatened today and need more adequate management to preserve ocean habitats, stocks and biodiversity. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
