The peculiarity of the Mediterranean Sea are the following:

- it is a half-closed river basin communicating with the Atlantic Ocean through the strait of Gibilterra (wide 10 km and deep 320 mt).

- it is formed from three river basins with characteristics various (western deep to maximum 3000 mt; deep oriental to maximum 5100 mt; Mar Nero deep to maximum 2000 mt).

- it is in continuous narrowing because of the drift of the continents (the continent African presses on the euro-asiatic compressing those that remains of the mythical sea of Tetide - the existing superocean when 240 million years ago all the emerged lands constituted an only block, the so-called Pangea -).

- the water of the Mediterranean Sea constantly is exchanged with the Atlantic thanks to currents that in surface bring in the river basin, while in depth they bring back it in the ocean 

- insufficient production of biomass from part of the organisms vegetables for deficiency of upward movements of the water (except in the western From Liguria Sea, where it is a lot abundant). 

- strongly seasonal thermal excursion in superficial waters.