![Ferdinand de Lesseps (1805-1894) [Source: http://en.wikipedia.org/wiki/Ferdinand_de_Lesseps]](http://scisnack.com/wp-content/uploads/2015/03/Ferdinand_de_Lesseps1.jpg)
Ferdinand de Lesseps (1805-1894) [Source]
A hint could be the adjective “lessepsian” that is used in biology and ecology to name one of the most studied migrations on the planet: the invasion of the Eastern Mediterranean (the Levantine Basin) by species coming from the Red Sea. This Lessepsian Migration has been happening with a worrying magnitude in the last five-six decades. It is named after the French diplomat because simply it couldn’t have happened if monsieur Ferdinand hadn’t reached the greatest goal of his life: the construction of the Suez Canal. This work is so linked to his life that he is sometimes quoted as the engineer that planned the project, while he actually was the man who built up the political network that made the project possible. With his political intelligence, Ferdinand de Lesseps realised his dream to link the Mediterranean and the Red Seas by a continuous waterway, literally cutting a new trading route through the Suez isthmus, but he accidentally triggered one of the most important events in modern ecology.
In fact, although Lesseps opened the Canal in 1869 aiming to facilitate the movements of only one species (ours!), it is also true what Prof. Ian Malcolm says in Jurassic Park: “Life always finds a way!”. And life, in particular marine life, actually found the newly opened way (filled with seawater) and tried to cross the canal. Some species were able to swim, others were transported by currents and a few species properly used the ships to have a “lift” between the two basins either crusted in the fouling or boarded in the ballasting waters. Mediterranean species started to move (or be moved) to the Red Sea and more importantly, as we’ll see, tropical species started to reach the Levantine Basin. There are at this point two important questions. If this migration started soon after the channel was opened, why is the migration happening so strongly only in the last decades? And why does the Lessepsian Migration usually refer to the invasion of the Mediterranean by Red Sea species and not vice versa?
The answer is that the environmental situation has changed and it has changed in such a way that the migration in one direction has been much facilitated. Some of these changes happened within the Canal itself. Two dry salt valleys that used to lie in the isthmus were invaded by water when the manmade waterway reached them and they became the Great and Small Bitter Lakes. These water bodies had a very high salinity (estimated around 68 PSU) coming from the dissolution of the “pavement” of salt that, according to de Lesseps, was 13m thick. This was obviously a physical barrier to the migration, killing both adults and larvae. But over time the salt was totally dissolved and the hypersaline water was diluted, reaching values slightly higher than 40 PSU in 1970’s, not longer a great shock for species from the Red Sea coming from a salinity of 38 PSU. Furthermore, changes happened just outside the Canal, when in 1964 the Aswan dam was built on the Nile, reducing the freshwater inflow at the Mediteranean mouth, increasing the salinity from a range between 34 and 38 PSU to a constant value of 39 PSU. Then with the global warming the temperature of the water increased, elevating the evaporation rate and, again, raising the salinity of the Levantine Basin. The way from the Red Sea to the Mediterranean was then transformed from an obstacle race full of deadly rapid and big changes in salinity (which cause osmotic shocks) to a path with an even and weak gradient that allowed an easier adaptation of the migrating species to the new environment. The increase in temperature due to climate change also has a direct effect, as in the eastern Mediterranean temperatures have changed in particular after 1998 with an increase from +0.8 up to +1.27 °C with respect to the mean temperature in 1985-1997. This means that summer temperatures are now suitable for reproduction of tropical species and winter temperature is not low enough to threaten their survival. These changes go under the name of “tropicalization” and play a fundamental role in the expansion of the geographic distribution of Indo-pacific species in the Levantine Basin.
![Number of Lessepsian species in the different basins within the Mediterranean Sea [Source: Katsanevakis et al., 2014]](http://scisnack.com/wp-content/uploads/2015/03/lessepsian-species.jpg)
Number of Lessepsian species in the different basins within the Mediterranean Sea [Source: Katsanevakis et al., 2014]
![Alien to native species ratio in the Mediterranean Sea. [Source: Katsanevakis et al., 2014]](http://scisnack.com/wp-content/uploads/2015/03/alen-native-ratio.jpg)
Alien to native species ratio in the Mediterranean Sea. [Source: Katsanevakis et al., 2014]
REFERENCES
[Raitsos, D. E., Beaugrand, G., Georgopoulos, D., Zenetos, A., Pancucci Papadopoulou, A. M.,Theocharis, A., Papathanassiou, E. (2010). Global climate change amplifies the entry of tropical species into the eastern Mediterranean Sea. Limnology and Oceanograph 55, 1478-1484.]
[Katsanevakis S., Coll M., Piroddi C., Steenbeek J., Ben R. L. F., Zenetos A., Cardoso A. C. (2014). Invading the Mediterranean Sea: biodiversity patterns shaped by human activities. Frontiers in Marine Science. DOI: 10.3389/fmars.2014.00032]
[Pierre Madl, Marine Biology I, Colloquial Meeting of Marine Biology I, Essay about the phenomenon of Lessepsian Migration. Headed by dr. A. Goldschmid, Salzburg, April 1999 (revised in Nov. 2001). http://biophysics.sbg.ac.at/lm/lesseps.htm]