The Mediterranean Sea, an ancient body of water, holds a realm beneath its surface. This unique aquatic environment, cradled between three continents, invites exploration. Its underwater world reveals a tapestry of life and geological formations.
Distinctive Underwater Environment
The Mediterranean Sea has distinct physical and chemical characteristics. Its waters are notably saline, with average values ranging from 36.2 to 39 parts per thousand, increasing from west to east due to higher evaporation rates than precipitation and river runoff. Temperatures are relatively warm, averaging 15-21°C at the surface, which influences the types of marine life that can thrive there. Its semi-enclosed nature, with limited exchange through the narrow 14-kilometer Strait of Gibraltar, results in extended water residence times, approximately 3.8 years for the western basin and 7.7 years for the eastern basin.
It is largely oligotrophic, meaning it is low in nutrients, with concentrations decreasing from west to east. Despite this nutrient-poor nature, oxygen levels remain relatively high, even in deep waters, at around 4.2-4.5 milliliters per liter. These factors create a distinct, somewhat isolated environment, influencing the sea’s unique biodiversity.
Rich Marine Biodiversity
The Mediterranean Sea is a marine biodiversity hotspot, hosting between 10,000 and 12,000 marine species, accounting for 8% to 9% of the world’s total. A significant proportion (20% to 30%) are endemic, found nowhere else on Earth. This rich array of life includes various fish, invertebrates, and marine mammals.
Among unique plant life, Posidonia oceanica seagrass meadows are noteworthy. Often called the “lungs of the Mediterranean,” these endemic seagrass beds oxygenate the water and serve as nurseries, providing shelter and food for juvenile fish and invertebrates. These meadows support a myriad of species, including seahorses, cuttlefish, and numerous fish species like seabreams and gobies. Posidonia oceanica also stabilizes the seabed and prevents erosion.
Submerged Geological Features
The Mediterranean seabed features diverse geological formations. Deep trenches, such as the Hellenic Trench in the eastern Mediterranean, are formed by the convergence and subduction of the African plate beneath the Aegean microplate. The Calypso Deep in the Ionian Sea represents the deepest recorded point in the Mediterranean, reaching 5,109 meters.
Underwater volcanoes are present, including the active Stromboli and the Kolumbo Seamount, part of an inner southern volcanic arc. Seamounts, such as the Eratosthenes Seamount south of Cyprus, are underwater mountains formed by volcanic activity or tectonic processes. The Eratosthenes Canyon, a colossal U-shaped canyon 500 meters deep and 10 kilometers wide near the Eratosthenes Seamount, formed 6 million years ago during the Messinian salinity crisis when the Mediterranean became isolated and dried up.
Threats and Protective Measures
The Mediterranean Sea’s underwater ecosystems face significant threats. Marine pollution is a major concern, with plastic debris, chemical contaminants, and hydrocarbon spills. The Mediterranean is one of the most contaminated seas by hydrocarbons, with over 400,000 tons per year. Overfishing is another widespread problem, with about 75% of its fish populations overexploited. This has led to severe declines in marine mammal populations, which have fallen by 41% since 1950, and puts 53% of its shark species at risk of extinction.
Habitat destruction, caused by unsustainable fishing methods like trawling and coastal development, degrades marine environments. Climate change exacerbates these issues, as the Mediterranean Sea warms approximately 20% faster than the global average, leading to more frequent marine heatwaves and ocean acidification. This warming also facilitates the spread of non-native species, with over 1,000 invasive species documented.
In response, protective measures and conservation initiatives are underway. Marine Protected Areas (MPAs) are a primary tool for safeguarding biodiversity and allowing species to recover. While 6% of the Mediterranean basin is covered by MPAs, only 0.23% are fully or highly protected, falling short of the recommended 30% target for effective conservation. International collaborations, such as the Pew Bertarelli Ocean Legacy Project, work to establish and strengthen networks of highly protected MPAs. Efforts also focus on improving fishing practices, eliminating illegal fishing, and reducing pollution.