Marine sediments containing numerous fossils dating from the Late Miocene, approximately 8 to 7 million years ago. Fish otoliths, bivalve and gastropod shells, bryozoans and microscopic shells attest to the presence of numerous organisms in this area, which were analyzed in this study. Credit: Konstantina Agiadi
A new study paves the way for a better understanding of biotic recovery after an ecological crisis in the Mediterranean about 5.5 million years ago. An international team led by Konstantina Agiadi from the University of Vienna has now been able to quantify the impact of Mediterranean salinization on marine biota: only 11% of endemic species survived the crisis, and biodiversity did not recover until at least 1.7 million years later.
Lithospheric movements throughout Earth’s history have repeatedly led to the isolation of regional seas from the World Ocean and to massive salt accumulations. Salt giants of several thousand cubic kilometres have been discovered by geologists in Europe, Australia, Siberia, the Middle East and elsewhere. These salt accumulations represent valuable natural resources and have been exploited from antiquity to the present day in mines around the world (e.g. at the Hallstatt mine in Austria or the Khewra salt mine in Pakistan).
The Mediterranean Salt Giant is a kilometer-thick layer of salt beneath the Mediterranean Sea, first discovered in the early 1970s. It formed about 5.5 million years ago due to the disconnection of the Atlantic during the Messinian Salinity Crisis.
In a study published in the journal ScienceAn international team of researchers, consisting of 29 scientists from 25 institutes across Europe, led by Konstantina Agiadi from the University of Vienna, has now been able to quantify the loss of biodiversity in the Mediterranean Sea due to the Messinian crisis and the subsequent biotic recovery.
A huge impact on marine biodiversity
After several decades of painstaking research on fossils dated 12 to 3.6 million years old found on land in peri-Mediterranean countries and in deep-sea sediment cores, the team discovered that nearly 67% of marine species present in the Mediterranean Sea after the crisis were different from those before the crisis.
Only 86 of the 779 endemic species (which lived exclusively in the Mediterranean before the crisis) survived the enormous change in living conditions after the separation from the Atlantic. The change in the configuration of the gateways, which led to the formation of the salt giant itself, caused abrupt fluctuations in salinity and temperature, but also changed the migration routes of marine organisms, the flow of larvae and plankton and disrupted central ecosystem processes.
As a result of these changes, many of the Mediterranean’s inhabitants at the time, such as tropical reef-building corals, disappeared. After the reconnection to the Atlantic and the invasion of new species such as the great white shark and oceanic dolphins, Mediterranean marine biodiversity showed a new pattern, with the number of species decreasing from west to east, as is the case today.
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Reconstruction of a Lower Pliocene (5.1-4.5 million years old) seascape off the coast of Tuscany (central Italy) showing the monodontid Casatia thermophila and the sirenian Metaxytherium subapenninum – two of the many species that were only discovered in the Mediterranean Sea after the Atlantic Gateway reopened. Credit: Alberto Gennari
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The end of the Messinian Salinity Crisis, about 5.3 million years ago, was marked by a distinct change in the sediments deposited on the Mediterranean Sea floor, as seen here in the Pissouri area of Cyprus. Credit: Konstantina Agiadi
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Konstantina Agiadi on the coast of Laganas, Zakynthos, Greece, where the end of the Messinian salinity crisis can be seen. Credit: Konstantina Agiadi
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Cast of a bivalve shell preserved in a 6.5 million-year-old sediment in Crete, Greece. Scientists analyzed the presence of organisms such as this one to complete their in-depth analysis. Credit: Konstantina Agiadi
Recovery took longer than expected
Because peripheral seas like the Mediterranean are important biodiversity hotspots, it was very likely that the formation of salt giants throughout geological history had a large impact, but this had not been quantified until now.
“Our study provides the first statistical analysis of an ecological crisis of this magnitude,” says Konstantina Agiadi from the Department of Geology. It also quantifies for the first time the recovery times after a marine environmental crisis, which are in reality much longer than expected.
“Biodiversity in terms of number of species only recovered after more than 1.7 million years,” the geoscientist explains. The methods used in the study also provide a model linking plate tectonics, the birth and death of oceans, salt and marine life that could be applied to other regions of the world.
“These results raise many exciting questions,” says Daniel García-Castellanos of Geosciences Barcelona (CSIC), lead author of the study. “How and where did 11% of species survive the salinization of the Mediterranean? How did earlier, larger salt formations change ecosystems and the Earth system?”
These questions remain to be explored. For example, in the new SaltAges Cost Action Network, which will begin in October and will invite researchers to study the social, biological and climatic impacts of salt ages.
More information:
Konstantina Agiadi, The impact of the late Miocene Mediterranean salinity crisis on marine biodiversity, Science (2024). DOI: 10.1126/science.adp3703. www.science.org/doi/10.1126/science.adp3703
Provided by the University of Vienna
Quote: How a Salt Giant Radically Reshaped Mediterranean Marine Biodiversity (2024, August 29) retrieved August 29, 2024 from
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