Wednesday, November 3, 2021

Far-reaching ecological change in the eastern Mediterranean

Tropical wing snail (Conomurex persicus),
an Indo-Pacific species, off the Israeli coast (© Jan Steger)
Different ecological niches: Tropical species are profoundly changing the way ecosystems in the eastern Mediterranean - with hardly any consequences

Communities of introduced tropical species differ significantly in their biological properties from the native wildlife in the eastern Mediterranean, as an international team of researchers led by Jan Steger from the Institute of Paleontology found. As a result - and due to the progressive collapse of Mediterranean species - the shallow water ecosystems in the region are changing particularly profoundly. The study was published in the journal Global Ecology and Biogeography.

The eastern Mediterranean is undergoing dramatic ecological change - while native species are disappearing more and more, tropical organisms introduced through the Suez Canal, called Lesseps’s species, thrive splendidly as a result of ever warmer water temperatures. However, they do not directly displace the native species, but rather occupy "free niches", according to a study that has now been published in the Journal Global Ecology and Biogeography.

"To understand how the increase in tropical species affects the native fauna and the function of the ecosystems, one has to compare their biological properties - such as lifestyle or nutrition - with those of the native fauna," says Jan Steger, doctoral student and first author of the new one Study.

In order for introduced organisms to establish themselves successfully, they not only have to cope with local environmental conditions, but also with any competition from native species. The latter can succeed, for example, if they use resources such as living space or food more efficiently, which can ultimately lead to the displacement of native species with similar ecological roles; however, the functioning of the ecosystem itself does not change much in such processes. "This has long been a common hypothesis. However, recent studies on fish from the eastern Mediterranean suggested the opposite, namely that Lesseps species are successful only when their biological properties differ greatly from those of the native fauna, i.e. they take 'free' niches in the ecosystem and thereby avoid competition ", explains Steger.

Unknown invasion story

So far, however, the long history of the invasion has been a great unknown when interpreting observed patterns: While tropical species invaded the Mediterranean shortly after the Suez Canal opened in 1869, systematic data on the composition of native fauna have only recently become available . "Today we see the result of decades of massive ecological transformation, but we didn't know how it came about," said Paolo Albano, head of the FWF project, as part of which the study was carried out. "We may only observe functional differences between the indigenous and tropical components of the communities because existing Mediterranean species with similar ecological roles have been displaced in the past without us knowing about them. Finding out if that is so is crucial to understand the effects of the Lesseps invasion."

Shellfish and snail shells as natural archives

This is exactly where the new study started. In order to close the critical data gap, the scientists concentrated on the examination of mollusks (mollusks), i.e. the group of animals that includes mussels and snails. "Shells and snails have species-specific limestone shells that are often preserved on the seabed for decades to millennia after their death. They form so-called dead communities, natural archives that can be dated to age, and a reconstruction of the species composition before the Suez Canal opens or. allow from early phases of the invasion, "says Steger.

The researchers took samples along the Mediterranean coast of Israel, one of the regions with the most introduced species, by research ship and with divers, and analyzed both the mollusk communities living there and the shell remains deposited on the seabed. "We have been able to demonstrate that the functional differences between indigenous and tropical species have actually existed since the invasion began. This suggests that the progressive disappearance of indigenous species is probably not primarily due to direct biological competition. On the other hand, it also means that today's communities dominated by tropical species are functionally very different from those of the past, "explains Steger.

The Lesseps components of the mollusk communities show, for example, significant differences in body size distributions and diet, which can affect material flows and food webs. How and whether socially relevant services of ecosystems could be influenced is still unknown. Research in this area has only just begun. However, it is clear that the change in fauna due to the warming of the sea and the further expansion of the Suez Canal will become more and more extensive regionally, and could also cover other sectors of the Mediterranean in the future. "It is therefore absolutely essential to prevent further changes in the Mediterranean fauna as best it can. This can only be achieved through consistent climate protection, because it is above all the progressive warming that is doomed to the native species, while at the same time promoting the spread of tropical species, "warns Paolo Albano.

Source/Credit: University of Vienna

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