As global warming intensifies, the Mediterranean are feeling the heat. Some mollusk populations in the eastern areas of the sea are buckling the waters they call home have become too hot to survive in, new research shows.

The waters around the coast of Israel are some of the hottest in the whole Mediterranean. But they’re rapidly becoming even hotter, as average temperatures have risen here by 3° Celsius over the last four decades. Today, water temperatures here regularly exceed 30°C (86°F) which, alongside invasive species coming through the Suez Canal from the Red Sea, are putting local mollusk populations under a lot of pressure.

Wipe-out

“My expectation was to find a Mediterranean ecosystem with these ‘newcomers’,” said Paolo Albano from the University of Vienna’s Department of Paleontology, lead author of the paper, for the AFP.

“However, after the first dive, I immediately realised that the problem was another one: the lack of the native Mediterranean species, even the most common ones that you would find everywhere in the Mediterranean.”

Albano initially set out to study the differences between native and non-native populations along the Israeli shelf in the eastern Mediterranean but was stuck by the dearth of local species in the area.

The team gathered over 100 samples from the seafloor, using these to gauge the characteristics of local mollusc populations, such as which species were present, their numbers, and so forth. These were then compared to historical data on the same topic. Only around 12% of the shallow-sediment molluscs noted in the historical records were still present today, the paper reports. In rocky reef environments, that figure dropped as low as 5%.

Furthermore, the researchers estimate that 60% of the remaining local mollusc populations are below their reproductive size, meaning they’re shrinking over time.

Albano says that there are many factors contributing to this collapse, most notably pollution and the pressures from invasive species. But warming waters are playing the main part in driving local mollusk populations into the ground.

“Tolerance to temperature is what really matters here and most of the native Mediterranean species are in the easternmost Mediterranean Sea at the limits of their tolerance to temperature,” said Albano.

Populations of invasive species, however, are thriving in the area. In effect, these changes are setting the stage for a “novel ecosystem“, the team explains, as species moving in from the Red Sea stand poised to effectively replace local ones. Albano says the Eastern Mediterranean is “paradigmatic of what is happening in marine ecosystems due to global warming: species respond to warming by shifting their ranges and in some areas, this means local eradication of species.”

The paper “Native biodiversity collapse in the eastern Mediterranean” has been published in the journal Proceedings of the Royal Society B.