In the last decades, some modifications in stocks, fish species and the marine ecosystems have been recorded as a consequence of climatic changes in the Mediterranean sea. Many authors emphasize more and more frequently a "tropicalization of the Mediterranean sea" (Colloque Scient. Montpellier, 1995). Under a meteorological point of view, this process, shows considerable variability, and is characterized by torrential rains - concentrated in the space and time - followed by periods with high temperature and humidity. At sea, an increase in average temperature has been observed at different levels in the Mediterranean water column (Bethoux et al. 1990).