After reconnecting with the Atlantic Ocean, the biodiversity of the Mediterranean Sea changed, with the number of species decreasing from west to east, as it is today
Research on the Messinian salinity crisis indicates that only a small fraction of Mediterranean species survived, with biodiversity recovery time exceeding 1.7 million years.
Throughout Earth's history, lithosphere movements have repeatedly isolated regional seas from the global ocean and accumulated vast amounts of salt. "Salt giants" containing thousands of cubic kilometers of salt have been discovered by geologists in Europe, Australia, Siberia, the Middle East and other places. These salt accumulations constitute a valuable natural resource, which has been extracted from salt mines since ancient times, such as the Hallstatt mine in Austria and the Kwara salt mine in Pakistan.
In the early 70s, the "salt giant" of Mediterranean - A kilometer-thick layer of salt under the Mediterranean Sea, which was formed about 5.5 million years ago as a result of separation from the Atlantic Ocean during the Messinian salinity crisis. In a new study published in the journal Science, an international team of researchers - including 29 scientists from 25 institutes across Europe - quantified the loss of biodiversity in the Mediterranean due to the Messinian crisis and the biological recovery that followed.
Long recovery time of marine biodiversity
After decades of careful research on fossils dating from 12 to 3.6 million years, found in the lands of the countries surrounding the Mediterranean and in sediments from the depths of the sea, the team discovered that almost 67% of the marine species in the Mediterranean after the crisis were different from those before it. Only 86 out of 779 endemic species (that lived exclusively in the Mediterranean before the crisis) survived the enormous change in living conditions after the separation from the Atlantic.
The changes in the migration routes of marine organisms, the flow of algae and plankton, and the disruption of key processes in the ecosystem meant that a large part of the Mediterranean's marine inhabitants, such as tropical corals, became extinct. After reconnecting with the Atlantic Ocean, the biodiversity of the Mediterranean Sea changed, with a decrease in the number of species from west to east, as it is today.
Quantifying and understanding biodiversity restoration
As the Mediterranean Sea is an important center of biodiversity, it is highly likely that it has had major effects on the formation of salt throughout geologic history. "Our study now provides the first statistical analysis of an ecological crisis of this magnitude," explains Constantina Agiadi from the University of Vienna, who led the study.
The study also establishes for the first time the timelines for recovery after the marine environmental crisis, which turned out to be longer than expected: "Biodiversity in terms of the number of species recovered only after more than 1.7 million years," said the geologist. The methods used in the study also provide a model linking between Plate tectonics, the formation of the oceans, salt and marine life, which can be applied to other areas of the world.
Research directions and new questions
"The results of the study raise new fascinating questions," says Daniel Garcia-Castellanos from Barcelona, who is the senior author of the study: "How and where did 11% of the species survive the salinity of the Mediterranean? How did previous large salt formations change ecosystems and the Earth system?" These questions are still awaiting research, for example within the new scientific network "SaltAges", which will start in October and will investigate the social, biological and climatic effects of the Salt Ages.
