Chronicle of a change foretold

(Illegal immigrants, n.0)

by Massimo Boyer and Francesca Scoccia

With this article I open a series of files dedicated to the new species that have recently settled in the Mediterranean, which I have decided to call "illegal“, referring to the fact that they migrate to an environment different from the one where they should be, mostly frowned upon and opposed.

These are species arriving from other environments, of tropical origin, which have settled in the Mediterranean following climate change and tropicalization. In biology, these species are often referred to as alien, with reference to their origin from elsewhere.

The purpose of these factsheets is to help divers recognize new species they might encounter while diving, understand who they are, where they come from, what they do, and why they're there. I preface the factsheets with an introductory article.

Dimensions of the phenomenon:

In 1869, with the opening of the Suez Canal, an artificial connection was established: to date, in just over 130 years, over 650 marine animal and plant species have used it to reach the Mediterranean from the Red Sea, compared to a dozen or so that have taken the reverse route, which is more difficult both due to the canal's prevailing currents (to the north) and increased competition in the Red Sea. And the invasion continues.

The entry of these species, called Lessepsian Named after the architect De Lesseps, who designed the canal, this is just one aspect of the change. Other species from the tropical Atlantic Ocean have settled here, entering through Gibraltar, taking advantage of the favorable climate and higher temperatures of recent years. Still others have been transported by humans, jumping from even distant parts of the globe.

Limiting the discussion to fish, currently around 120 exotic species have been recorded by biologists, that is, 19% of the fish in the Mediterranean are of alien origin!

Introduction routes:

Obviously, a natural canal (Gibraltar) or an artificial one (Suez) allows direct passage. But humans often transport organisms to distant areas, for example, attached to the hulls of ships (gorgonians, sponges, bryozoans), or in the ballast water of merchant ships (which often use seawater to fill special compartments and become heavier). There are also known cases of organisms introduced following release from aquariums.

Keep in mind that the vast majority of marine species migrate as larvae, tiny plankton organisms. Don't think of an adult fish packing its bags from the Red Sea and embarking on a journey through the Suez Canal. Adult fish are sedentary creatures, and in most cases they move very little. They can be moved by a current, it's true, but all marine organisms, from fish to corals to algae, have a life stage where they are transported by currents (as eggs, larvae, or spores in the case of algae), and it is during this stage that they are much more likely to take unusual routes and colonize new territories.

Consequences:

The first consequence, obvious to everyone, is an increase in Mediterranean species and diversity: a positive effect? ​​At first glance, it might seem so. But experience teaches us that when non-native species have established themselves in distant areas over long periods of time, they have caused damage, such as the extinction of resident species and ecosystem changes.

Regarding the new species arriving from the Red Sea, it must be said that so far few have competed with the local ones. Many have colonized unoccupied ecological niches and appear to coexist peacefully, perhaps also taking advantage of the low diversity of the eastern Mediterranean, their beachhead, which is much less diverse than the western Mediterranean.

Let's also consider that the climate is changing, and we can't assume that ecosystems remain fixed and immutable. The Mediterranean has a tropical past, and has undergone dramatic changes in relatively recent times, through the glaciations. It is a sea in constant evolution, and the current invasions can be seen as an aspect of this evolution. This is an aspect that must be carefully considered, certainly, but without hysteria, catastrophism, or crusades.

Everyone's contribution:

The topic of illegal immigrants is timely, important, and often overlooked. I'd like to open a roundtable discussion here where everyone can participate, to increase awareness of the phenomenon. If you'd like to comment on my articles, point out some "strange" species you've seen while diving, or show us a photo, please do so: we'll welcome all comments. If you have the photo on Facebook or your own website, please include the link. We'll all be making our own small contribution, branded Scubazone, to raising awareness of a change that has been announced but no less momentous.

Please report your sightings to us, especially if they involve species we've never seen before or are "out of the area."

In the next article: the rabbit fish Siganus luridus.

To learn more:

In the book Atlas of Reef Flora and Fauna, by Massimo Boyer, you will find a chapter dedicated to the migrations of species and one on the movements of larvae.

Available on Scubashop 

On the next issue of Scubazone (23) my article will be dedicated to biogeography.

Massimo Boyer

Marine biologist, underwater photographer, writer, tour operator, instructor, and guide. Excellent knowledge of the Indonesian seabed. Author of four books: Underwater Nature Photography: Technique, Art, and Science, Scylla. Story of a Great White Shark, The Underwater Photographer's Diary. Become an Underwater Photographer in 12 Months, Atlas of Reef Flora and Fauna, and over 500 articles on diving. He teaches Underwater Photography at the University of Genoa and collaborates with the Polytechnic University of Marche and the University of Milan-Bicocca. https://rubrica.unige.it/personale/UkJFXVpo