In the past few decades there has been a dramatic mass extinction in the eastern Mediterranean, researchers report. According to an analysis, the number of species of domestic snails, mussels and other invertebrates belonging to the mollusc group has decreased by up to 95 percent in some regions.
The team led by Paolo Albano from the Institute of Paleontology at the University of Vienna has reconstructed the occurrence of the species along the Israeli coast in the past decades using empty shells in the sediment and compared it with today’s diversity of species.
The diversity in shallow depths has decreased particularly sharply: “For anyone who is used to snorkeling or diving in the Mediterranean, the underwater scenario in Israel is unrecognizable,” Albano explained. While the native species have largely disappeared, tropical species are now romping off the coast and migrating via the Suez Canal.
Poor growth of native species
The newer species in the region are thriving, according to the researchers. Among the native species that were found alive, however, 60 percent did not even make it to reproductive maturity, but died beforehand. Albano sees this as a sign that the decline in biodiversity in the region will continue.
The researchers cannot say in which period exactly the previous species loss occurred. “Mussels remain in superficial marine sediments for decades to millennia,” they write in the specialist journal “Proceedings of the Royal Society B”. The result could theoretically have been falsified, but the examined mussels, which lived in hard ground, were on average only between 26 and 56 years old.
The study thus suggests that most of the loss has occurred in the past few decades, which correlates with the changes due to climate change.
Warmer water, fewer mussels and snails
The waters off the coast of Israel are among the warmest in the Mediterranean and warmed by around three degrees between 1980 and 2013. In summer the water now reaches temperatures of 32 degrees Celsius.
Now it becomes clear that most of the native species have long been at the tolerance limit for the water temperature. For many it has now been exceeded. The researchers fear that the regionally documented extinction is far from everything.
Similar effects could already have occurred unnoticed in other regions of the Mediterranean. Further increases in water temperatures could also mean that areas in the western and northern Mediterranean will also be affected by the decline in the future, according to the team.
Native species that live in the tidal range, i.e. are sometimes covered by water due to the ebb and flow of the tide and are sometimes illuminated by the sun, as well as those in deeper and therefore cooler areas of the sea, the experts do not see in danger so far.
“But the future is bleak if we don’t act immediately to reduce our carbon emissions,” said Albano. “The changes that have already occurred in the warmest areas of the Mediterranean may not be reversible, but we could save large parts of the rest of the sea basin.”