Mediterranean Sea Ecosystem
The Mediterranean Sea Ecosystem is a vibrant and diverse marine biome located at the crossroads of Europe, Asia, and Africa, encompassing various smaller seas and connecting to the Atlantic Ocean. This semi-enclosed body of water is renowned for its cultural significance and biodiversity, making it one of the most studied marine environments globally. The ecosystem supports approximately 10,000 to 12,000 marine species, with high levels of endemism, particularly among its flora and fauna. However, the region faces significant threats from human activities, including pollution, overfishing, habitat destruction, and the introduction of invasive species, which have led to the decline of many native species.
The Mediterranean is home to essential marine habitats, such as coral reefs and underwater meadows, which are crucial for various marine life, including cetaceans like dolphins and whales. Environmental changes, exacerbated by global warming, are also altering species distributions and increasing the frequency of marine heatwaves. Despite some conservation efforts, including the establishment of marine protected areas, urgent action is needed to mitigate these threats and preserve the unique biodiversity of the Mediterranean Sea. This ecosystem not only serves as a vital resource for its bordering nations but also plays a crucial role in global marine health.
Subject Terms
Mediterranean Sea Ecosystem
- Category: Marine and Oceanic Biomes
- Geographic Location: Europe
- Summary: Bounded by three continents but connected to the Atlantic Ocean, the Mediterranean boasts a rich cultural history and great biodiversity.
The name Mediterranean originated in Roman times when the sea was referred to as Mediterraneus, meaning “center of the world.” The Mediterranean Sea is subdivided into various smaller lobes, including the Strait of Gibraltar, Alboran Sea, Balearic Sea, Ligurian Sea, Tyrrhenian Sea, Ionian Sea, Adriatic Sea, and the Aegean Sea. Smaller water-body divisions exist throughout in the form of gulfs, bays, straits, and channels.
The Mediterranean Sea is bordered by the three continents of Europe, Asia, and Africa, with twenty-one countries along the coastline. The sea can count among its national borders the countries of Spain, France, Monaco, Italy, Malta, Slovenia, Croatia, Bosnia, Montenegro, Albania, Greece, Turkey, Cyprus, Syria, Lebanon, Israel, Egypt, Libya, Tunisia, Algeria, and Morocco. Water-based boundaries for the Mediterranean include the Atlantic Ocean via the Strait of Gibraltar at the westernmost point, the Sea of Marmara by the Dardanelles, and the Black Sea by the Bosphorus Strait to the east. The Sea of Marmara is often considered to be part of the Mediterranean Sea, whereas the Black Sea generally is not. The 101 mile (163 kilometer) human-made Suez Canal in the southeast connects the Mediterranean to the Red Sea. Because of its central location, the Mediterranean Sea has become one of the most studied water bodies in the world.
Biodiversity
This semi-enclosed sea is rich in islands and underwater beds. It is a critical area for wintering, reproduction, and migration. Although it covers less than 0.8 percent of the world’s ocean area, this biome is one of the major reservoirs of marine and coastal biodiversity on the planet, with a great number of endemic species, as well as seven percent of the world’s marine fauna species and eighteen percent of its marine flora. The Mediterranean is a true crossroads of marine biodiversity.
The marine fauna and flora of the Mediterranean are derived from several biogeographical categories. More than fifty percent of Mediterranean species originate in the Atlantic Ocean. Seventeen percent of these species originate in the Red Sea and four percent are relict species from earlier geologic periods when the Mediterranean was subjected to a tropical climate. Recent estimates of Mediterranean marine species, taken from compilations of former biological studies, show that approximately 10,000 to 12,000 species are present in its waters. The presence of such a large number of distinct species qualifies the region as a biodiversity hot spot. The rate of endemism here is greater in the comparatively small Mediterranean than in the entirety of the Atlantic Ocean. About nineteen percent of endemic Mediterranean species are threatened with extinction, seven percent are considered vulnerable, seven percent are classified as endangered, and five percent are critically endangered.
The marine biota of the Mediterranean Sea is mainly derived from origins in the Atlantic Ocean as a result of a flood more than 5 million years ago that introduced Atlantic biota to the Mediterranean through the Strait of Gibraltar. The marine life introduced to the Mediterranean Sea from the Atlantic Ocean has had to adapt to different climactic conditions. The North Atlantic was then and is now considerably colder and more nutrient-rich than the Mediterranean. Certain species form the foundations of the dense life in this area, and are consequently known as foundation species; they inhabit a multitude of habitats here.
Habitats and Biota
The Mediterranean Sea’s diverse habitats together complete the landscapes and biological ranges of the Mediterranean coastal areas. Submarine meadows of endemic Neptune grass (Posidonia oceanica) and coral beds are prime examples. Many other sensitive habitats are found here, including deep-sea coral communities, underwater caves, dune areas, coastal forests, lagoons, and wetlands.
The Mediterranean Sea also has a vast array of deep-sea habitats, including hydrothermal vents, seamounts, and deep-sea coral reefs. Underwater canyons are of major importance for many species as places for reproduction and feeding for fish and marine mammals such as Risso’s dolphin (Grampus griseus) and the sperm whale (Physeter macrocephalus). Such habitats also represent a remarkable reservoir of endemism among jellyfish and annelid worms. Chemosynthetic communities harboring essential microorganisms—hydrothermal vents, deep hypersaline habitats, and cold-water corals—are of great ecological value, but are threatened by deep-sea trawling by humans and by the direct seawater temperature-elevating effects of global warming.
The flora of the Mediterranean Sea has a high incidence of aquatic plant endemism, ranging as high as about 20 percent of the aquatic plants. More than 1,000 species of flora exist in the Mediterranean in all.
The Alboran Sea region of the Mediterranean is the most important feeding grounds in Europe for loggerhead sea turtles. In addition, the Alboran Sea hosts important commercial fisheries, including those for sardines and swordfish.
The most commonly seen marine mammals here include the fin whale (Balaenoptera physalus), sperm whale, striped dolphin (Stenella coeruleoalba), Risso’s dolphin, long-finned pilot whale (Globicephala melas), bottlenose dolphin (Tursiops truncates), common dolphin (Delphinus delphis), and Cuvier’s beaked whale (Ziphius cavirostris). Other, less-prevalent cetaceans here include: the minke whale (Balaenoptera acutorostrata), killer whale (Orcinus orca), false killer whale (Pseudorca crassidens), rough-toothed dolphin (Steno bredanesis), and humpback whale (Megaptera novaeanglia). There is also a small population of harbor porpoises (Phocoena phocoena) that range into the Black Sea.
The Mediterranean monk seal (Monachus monachus) is the only pinniped to be found within the Mediterranean Sea. It is now very rare and listed as an endangered species, with the only known colonies in the Alboran Basin and the Aegean Sea. The Alboran Sea, with the largest population of bottlenose dolphins in the western Mediterranean, is also home to the last population of the harbor porpoise in the Mediterranean.
Environmental Threats
Some of the greatest ecological concerns for the marine biodiversity of this area are human population growth that has come in tandem with habitat destruction, increased pollution, invasive species, and climate change. The Mediterranean Sea is one of the most polluted bodies of water, mainly by plastic, which is ingested by marine creatures. Overfishing is a significant threat to native fish species. According to the United Nations, 87 percent of fish species in the sea are overfished and at risk of being depleted. The coasts are under constant and growing human pressure caused by the activities of 150 million residents and the arrival of 200 million tourists every year, the consequences of which have for decades been nearly uncontrollable.
Unchecked urbanization and the overexploitation of resources, combined with the introduction of nonnative species; increased maritime transport; and increased runoff of sediments, nutrients, and heavy toxics have created devastating environmental consequences. Degradation of essential biodiversity, scarcity of the most sensitive species, and destruction of unique and irreplaceable coastal habitats, such as Port-Cros National Park and the Zembra Archipelago, are just a few of the most blatant effects of human activity across the region.
Studies from 2020-2024 show the Mediterranean Sea was warming at a rate twenty percent faster than the global average, making it one of the world's most rapidly changing seas. This warming has led to more frequent marine heatwaves, causing mass die-offs of marine species and the northward migration of tropical species. Rising temperatures have also accelerated the spread of non-native species through the Suez Canal, with over 1,000 invasive species now documented in the Mediterranean. Moreover, the sea faces new challenges from intense coastal development, with mega-projects like artificial islands and expanded ports threatening critical marine habitats. Despite these pressures, there have been some conservation successes, including the expansion of marine protected areas and international efforts to reduce plastic pollution, though scientists stress that more urgent action is needed to protect this unique ecosystem.
Worldwide, nonnative introduced species are of great ecological concern to regional habitats. Invasive species have become a major problem for the Mediterranean ecosystem in particular, and have endangered many local and endemic species. Analyzed populations of exotic species present in the Mediterranean Sea show that more than seventy percent of the nonindigenous decapods and about sixty-three percent of the exotic fish occurring in the Mediterranean are of Indo-Pacific origin, introduced into the Mediterranean through the Suez Canal. This pathway through the Red Sea is complicated by the differing salinity, nutrient, and climate regimes between the two—which has often allowed the somewhat hardier and more adaptable Red Sea species to colonize the Eastern Mediterranean basins, crowding out native taxa.
When the Suez Canal was initially constructed, the natural hypersaline condition of the Red Sea at first acted as a barrier, blocking the migration of Red Sea species into the Mediterranean for decades. Over time, however, the salinity in the channel roughly equalized with that of the Red Sea, opening the doors to invasion and colonization of the eastern area of the Mediterranean by species adapted to the lower-nutrient, higher-salinity, warmer-temperature conditions of the Red Sea, Arabian Sea, and Indian Ocean.
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