Ecology of Mediterranean Sea

As a result of the drying of the sea during the Messinian Salinity Crisis, the marine biota of the Mediterranean are derived primarily from the Atlantic Ocean. The North Atlantic is considerably colder and more nutrient-rich than the Mediterranean, and the marine life of the Mediterranean has had to adapt to its differing conditions in the five million years since the basin was reflooded.

The opening of the Suez Canal in 1869 created the first salt-water passage between the Mediterranean and Red seas. The Red Sea is higher than the Eastern Mediterranean, so the canal serves as a salt-water river that pours Red Sea water into the Mediterranean.

The Bitter Lakes, which are hypersaline natural lakes that form part of the canal, blocked the migration of Red Sea species into the Mediterranean for many decades, but as the salinity of the lakes gradually equalized with that of the Red Sea, the barrier to migration was removed, and plants and animals from the Red Sea have begun to colonize the eastern Mediterranean.

The Red Sea is generally saltier and more nutrient-poor than the Atlantic, so the Red Sea species have advantages over Atlantic species in the salty and nutrient-poor Eastern Mediterranean. The construction of the Aswan High Dam across the Nile River in the 1960s reduced the inflow of freshwater and nutrient-rich silt from the Nile into the eastern Mediterranean, which has made conditions there even more like the Red Sea. This species exchange is known as the Lessepsian Migration, after Ferdinand de Lesseps, the engineer who oversaw the canal’s construction.