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The mass of water lying above the sea bed, the pelagic domain, is a vast marine environment continually undergoing change, although at first it may seem quite homogeneous. Most of the organisms living in it are small and have a short lifecycle. But changes in the compositions of both animal and vegetal species may be sudden and far-ranging in their effects, and influence other links in the trophic chain.
Changes in the mass of water are the main cause giving rise to the composition of the populations which live in it. Both plankton and nekton, for example, sometimes make considerable vertical migrations up and down the water column. This Habitat volume describes the fascinating domain of “Pelagos”, the Sanctuary for Marine Mammals of the Mediterranean, created thanks to an agreement between France, Italy and the Principality of Monaco. The Sanctuary occupies a large portion of the Corsican, Ligurian and Provençal coastlines, one of the better known areas of the Mare Nostrum, which covers more than 87,000 sq. km.
Due to its peculiar oceanographic and trophic characteristics, this area contains enormous numbers of large pelagic animals - particularly whales, but also cephalopods, tunny, swordfish and sharks, all great attractions for increasing numbers of people. In a system characterised by high biodiversity, the krill of the Ligurian Sea, Meganyctiphanes norvegica, plays a key role.
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