The unpredicted consequences of the life of Monsieur de Lesseps.

 

If you study hard to become a diplomat, you manage to work for one of the strongest countries of your time as a diplomat and you sign a few big accords as a diplomat, you probably want to be remembered as a diplomat. This unfortunately didn’t happen to Ferdinand de Lesseps, whose name is in fact mostly remembered by ecologists and biologists rather than historians. He is also often remembered as an engineer rather than a diplomat. How could this happen?

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.

The migration is already favoured as the sea level at the Red Sea side is on average 1.2 m higher and, therefore, currents usually move towards north, especially during tides. Furthermore, southern winds are prevalent and even when currents are weak they create a northwards movement. The tropicalization of the Mediterranean Eastern Basin has then weakened the barriers against an invasion already favoured by other factors. Right now five to ten species every year enter the Mediterranean through the Suez Canal and hundreds of species including fish, crabs, plankton organisms, algae and worms are now considered resident invasive species in the so called “Lessepsian Region” that extends until Sicily on the west. Most of these species are direct competitors of the native species and in a few cases they are taking over, replacing the original species of the area.

The Lessepsian Migration can be seen as the result of the capacity that humans have to change the environment in different ways, through the construction of manmade structures (the Suez Canal and the Aswan dam) and through their influence on climate with the raise of temperatures. And it is the proof of how carefully the environmental challenges have to be considered when great works as these are planned, especially if they touch communities that for evolutionary reasons are already weak and exposed to decline due to the climate change. The Levantine Basin has an endemic low number of species and this low biodiversity is very susceptible of being perturbed by new highly competitive species as the Red Sea species, adapted to the new “tropical” Mediterranean. This is ecologically called a “low resilient” community, meaning that once disturbed it hardly comes back to the pristine situation. Luckily Ferdinand de Lesseps failed to realise his second dream of building a canal through the isthmus of Panama to connect Atlantic and Pacific Oceans, otherwise we would have had an analogue problems in another part of the world! Oh no, wait a second…

 

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]