The Eastern Mediterranean Sea is a marine environment of scientific interest. It is a semi-enclosed basin with ecological characteristics that set it apart from the wider Mediterranean. Its unique oceanography, biodiversity, and the rapid ecological shifts it is undergoing are defined by the region’s specific physical, chemical, and biological dynamics.
Defining the Eastern Mediterranean: Borders and Basins
The Eastern Mediterranean Sea is defined by a complex underwater landscape and the coastlines of several countries, with the island of Cyprus situated centrally. It is bordered by:
- Greece and Turkey to the north
- Syria, Lebanon, and Israel to the east
- Egypt and Libya to the south
This expanse is not a uniform body of water but is composed of several interconnected basins. The primary basins are the Ionian Sea to the west, the Aegean Sea to the north, and the large Levantine Basin in the southeastern portion.
The region’s seafloor, or bathymetry, is highly varied, featuring deep trenches, abyssal plains, and seamounts. The Hellenic Trench, south of Greece, is the deepest part of the Mediterranean Sea and results from the African tectonic plate subducting beneath the Eurasian plate.
Further east, the Eratosthenes Seamount is a large underwater mountain in the Levantine Basin that influences local currents and provides a deep-sea habitat.
Unique Oceanographic Conditions
The Eastern Mediterranean’s waters have some of the highest salinity and temperature measurements in the Mediterranean. This is a consequence of high evaporation rates driven by the hot, dry climate and limited freshwater input, which concentrates sea salts over time.
A key feature is the formation of Levantine Intermediate Water (LIW). In winter, surface waters in the Levantine Basin become cooler and saltier, increasing their density and causing them to sink to depths of 200 to 600 meters. This dense water then spreads westward, influencing the hydrography of the entire Mediterranean Sea.
The Eastern Mediterranean is also an ultra-oligotrophic system, meaning its surface waters are extremely low in nutrients like nitrates and phosphates. This scarcity limits phytoplankton growth, which forms the base of the marine food web, making the region one of the least productive in the world’s oceans. This “marine desert” condition shapes the structure of its ecosystems.
A Sea of Contrasts: Biodiversity and Endemic Life
Despite its nutrient-poor waters, the Eastern Mediterranean hosts a diversity of marine life, including many endemic species found nowhere else. Its habitats range from sunlit shallows to the dark abyss, each supporting a different community of organisms. Important coastal habitats include extensive meadows of Posidonia oceanica, a seagrass that forms vital nursery grounds for fish and helps stabilize the seabed. Deeper down, coralligenous outcrops, which are hard, biogenic concretions, create complex structures that shelter a wide array of invertebrates.
The deep-sea ecosystems, particularly around the Hellenic Trench and seamounts, harbor unique fauna adapted to high pressure and darkness.
A defining feature of the region’s biodiversity is Lessepsian migration. The opening of the Suez Canal in 1869 created a corridor for marine species to travel from the Red Sea into the Mediterranean. Hundreds of Indo-Pacific species have since established populations in the Eastern Mediterranean, altering the biological landscape. Examples include the venomous lionfish (Pterois miles) and various species of rabbitfish (Siganus).
Human-Induced Stresses and Ecological Shifts
The Eastern Mediterranean ecosystem is under pressure from human activities, leading to rapid ecological changes. Climate change is a driver of these shifts, with sea surface temperatures in the region rising faster than the global average. This warming contributes to more frequent marine heatwaves, which can cause mass mortality events in native species and favor the expansion of heat-tolerant invasive species.
Pollution from various sources also threatens marine health. Plastic debris is a concern, with high concentrations found on the seafloor and in submarine canyons. Chemical runoff from agricultural and urban areas introduces contaminants, while heavy maritime traffic creates a risk of oil spills.
Overfishing further disrupts the ecological balance by depleting stocks of many commercially valuable fish species. The removal of top predators and other species alters marine food webs and ecosystem structure. Compounding these issues is the impact of invasive species, especially Lessepsian migrants. These newcomers often outcompete native organisms for food and habitat, leading to declines in local populations and transforming marine communities.