As described in the Monograph, native thermophilic species, usually restricted to the southern, warmer sectors of the Mediterranean Sea are now moving northwards. This phenomenon (meridionalization) is particularly evident in fish, where over 30 native species have already spread in the northern areas of the Basin. Similarly, climate warming facilitates the establishment and spread of tropical, exotic species that are introduced via the Suez Canal or maritime transport. This process (tropicalization) is fast advancing and more than 500 exotic species have been recorded of late in the Mediterranean Sea .
Experts are worried that if the Mediterranean Sea continues to warm up at the same rate, all the sub-regional biological peculiarities may rapidly disappear, to be replaced by a more homogeneous, tropical ecosystem. Already entire replicas of tropical communities from the Red Sea have been recorded in a few Mediterranean locations, as illustrated in the CIESM Monograph.
Shallow-water species of cold-water affinity that are endemic (i.e. found nowhere else) to the northern, and coldest, areas of the basin such as the North Adriatic and the Gulf of Lyons are facing a serious risk of decline and even extinction, as they are prevented to move further north or deeper in the water column to escape rising sea temperatures. As pointed out by Prof. Ferdinando Boero (Univ. of Salento, Italy) who led the workshop discussions, such risks are real for the already rare species like the hydroids Tricyclusa singularis and Paracoryne huvei whose fate is open to question.
To quote Prof. Frederic Briand, Director General of CIESM, “continuing warming trends, combined with the deepening of the Suez Canal and intense maritime traffic, lead us to think that the question is no longer whether the Mediterranean Sea may turn into a giant tropical aquarium, but how fast?
And will there be a place then for ‘relict’ Mediterranean species representative of today’s ecosystems?”
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 For more information, see the CIESM Atlas of Exotic Species in the Mediterranean
See also CIESM Tropical Signals Programme