‘Alien invaders: marine edition’ is the title of a talk to be given by Prof. Patrick Schembri on Wednesday at 7.30pm at St James Cavalier Cinema Room, Valletta, organised by NGO Cafe Scientifique.

The invasion of the Mediterranean Sea by species of animals that are native of other seas started in 1869 with the opening of the Suez Canal, which established a link between the eastern Mediterranean and the Red Sea that had not existed for at least 15 million years. This very soon brought an influx of Red Sea species into the Mediterranean in what was almost exclusively a one-way process.

The phenomenon was called, rather inappropriately, ‘Lessepsian migration’.

The completion of the Aswan High Dam in 1968 accelerated this invasion, but the turning point came in the early 1980s when not only did the influx of Red Sea aliens increase but species which had previously been mostly confined to the eastern Mediterranean started moving westwards at an unprecedented rate, and some crossed over from the eastern to the western basin.

Concurrently, a new phenomenon became evident – the entry of warm-water Atlantic species into the western Mediterranean via the Strait of Gibraltar and their movement eastwards. Other newcomers that joined the fray were species introduced by human activities, mainly shipping, but also through other pathways.

Why did species cross from the Red Sea to the Mediterranean but not vice-versa?

How did construction of the Aswan dam in Egypt, which is nowhere near the Mediterranean, help to speed up this immigration?

What happened in the 1980s to accelerate east to west, and west to east movement of newcomer species?

Why is this trend not only expected to continue, but probably to increase?

And finally, should we be worried by this?

These and other aspects of this phenomenon will be discussed during the talk.

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