Lessepsian migrant

Lessepsian migration (also called Erythrean invasion) is the ongoing migration of marine species across the Suez Canal, usually from the Red Sea to the Mediterranean Sea, more rarely in the opposite direction. It is named after Ferdinand de Lesseps, the French diplomat in charge of the canal's construction.

In a wider context, the term "Lessepsian migration" is used to describe any animal migration over man-made structures, i.e. that which would not have occurred had it not been for the presence of an artificial structure.

The opening of the Suez Canal in 1869 created the first salt-water passage between the Mediterranean and Red Seas. The Red Sea is slightly higher than the Eastern Mediterranean, so the canal serves as a tidal strait 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 less salty and nutrient-rich Eastern Mediterranean. Accordingly, most invasions are of Red Sea species into the Mediterranean, and only few in the opposite direction. 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, making conditions in the eastern Mediterranean even more like the Red Sea thus increasing the impact of the invasions and facilitating the occurrence of new ones.

Invasive species originating from the Red Sea and introduced into the Mediterranean by the construction of the canal have become a major component of the Mediterranean ecosystem, and have had serious impacts on the Mediterranean ecology, endangering many local and endemic Mediterranean species. To this day, about 300 species native to the Red Sea have been identified in the Mediterranean Sea, and probably others are as yet unidentified. In recent years, the Egyptian government's announcement of its intentions to deepen and widen the canal have raised concerns from marine biologists, fearing this will worsen the invasion of Red Sea species into the Mediterranean, facilitating the crossing of the canal for additional species.

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