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Thursday, September 11, 2014

Mediterranean Sea

Mediterranean Sea

From Wikipedia, the free encyclopedia

Mediterranean Sea
Mediterranean Sea political map-en.svg
Composite satellite image of the Mediterranean Sea
Coordinates 35°N 18°ECoordinates: 35°N 18°E
Type Sea
Primary inflows Atlantic, Sea of Marmara, Nile, Ebro, Rhône, Chelif, Po
Basin countries

Surface area 2,500,000 km2 (970,000 sq mi)
Average depth 1,500 m (4,900 ft)
Max. depth 5,267 m (17,280 ft)
Water volume 3,750,000 km3 (900,000 cu mi)
Residence time 80-100 years[2]

Islands 3300+
Settlements Algiers, Barcelona, Beirut, Athens, Tel Aviv, Alexandria, etc.

The Mediterranean Sea /ˌmɛdɪtəˈreɪniən/ is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Southern Europe and Anatolia, on the south by North Africa, and on the east by the Levant. The sea is sometimes considered a part of the Atlantic Ocean, although it is usually identified as a completely separate body of water.

The name Mediterranean is derived from the Latin mediterraneus, meaning "inland" or "in the middle of the land" (from medius, "middle" and terra, "land"). It covers an approximate area of 2.5 million km² (965,000 sq mi), but its connection to the Atlantic (the Strait of Gibraltar) is only 14 km (8.7 mi) wide. The Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Gibraltar and Spain in Europe from Morocco in Africa. In oceanography, it is sometimes called the Eurafrican Mediterranean Sea or the European Mediterranean Sea to distinguish it from mediterranean seas elsewhere.[3][4]

The Mediterranean Sea has an average depth of 1,500 m (4,900 ft) and the deepest recorded point is 5,267 m (17,280 ft) in the Calypso Deep in the Ionian Sea.

It was an important route for merchants and travellers of ancient times that allowed for trade and cultural exchange between emergent peoples of the region. The history of the Mediterranean region is crucial to understanding the origins and development of many modern societies.

The countries surrounding the Mediterranean Sea are Spain, France, Monaco, Italy, Malta, Slovenia, Croatia, Bosnia-Herzegovina, Montenegro, Albania, Greece, Turkey, Cyprus, Syria, Lebanon, Israel, Palestine, Egypt, Libya, Tunisia, Algeria and Morocco.

Name

The term Mediterranean derives from the Latin word mediterraneus, meaning "in the middle of earth" or "between lands" (medi-; adj. medius, -um -a "middle, between" + terra f., "land, earth"): as it is between the continents of Africa, Asia and Europe. The Greek name Mesogeios (Μεσόγειος), is similarly from μέσο, "middle" + γη, "land, earth").[5]

The Mediterranean Sea has historically had several names. For example the Romans commonly called it Mare Nostrum (Latin, "Our Sea"), and occasionally Mare Internum (Sallust, Jug. 17).
In the Bible, it was primarily known as הים הגדול (HaYam HaGadol), the "Great Sea", (Num. 34:6,7; Josh. 1:4, 9:1, 15:47; Ezek. 47:10,15,20), or simply "The Sea" (1 Kings 5:9; comp. 1 Macc. 14:34, 15:11); however, it has also been called the "Hinder Sea", due to its location on the west coast of the Holy Land, and therefore behind a person facing the east, sometimes translated as "Western Sea", (Deut. 11:24; Joel 2:20). Another name was the "Sea of the Philistines" (Exod. 23:31), from the people occupying a large portion of its shores near the Israelites.

In Modern Hebrew, it has been called HaYam HaTikhon (הַיָּם הַתִּיכוֹן), "the Middle Sea", reflecting the Sea's name in ancient Greek (Mesogeios), Latin (Mare internum), German (Mittelmeer), and modern languages in both Europe and the Middle East (Mediterranean, etc.). Similarly, in Modern Arabic, it is known as al-Baḥr [al-Abyaḍ] al-Mutawassiṭ (البحر [الأبيض] المتوسط), "the [White] Middle Sea", while in Islamic and older Arabic literature, it was referenced as Baḥr al-Rūm (بحر الروم), or "the Roman/Byzantine Sea." In Turkish, it is known as Akdeniz,[6] "the White Sea" since among Turks the white color (ak) represents the west.

History

Greek and Phoenician colonies in antiquity
The Battle of Lepanto, 1571, ended in victory for the Venice led Holy League against the Ottoman Turks
The Bombardment of Algiers by the Anglo-Dutch fleet, to support the ultimatum to release European slaves, August 1816

Several ancient civilizations were located around its shores; thus it has had a major influence on those cultures. It provided routes for trade, colonization and war, and provided food (by fishing and the gathering of other seafood) for numerous communities throughout the ages.[7]

The sharing of similar climate, geology and access to a common sea led to numerous historical and cultural connections between the ancient and modern societies around the Mediterranean.

Two of the most notable Mediterranean civilizations in classical antiquity were the Greek city states and the Phoenicians. When[citation needed] Augustus founded the Roman Empire, the Mediterranean Sea began to be called Mare Nostrum (Latin: "Our Sea") by the Romans.

Darius I of Persia, who conquered Ancient Egypt, built a canal linking the Mediterranean to the Red Sea. Darius's canal was wide enough for two triremes to pass each other with oars extended, and required four days to traverse.[8]

The western Roman empire collapsed around AD 476. Temporarily the east was again dominant as the Byzantine Empire formed from the eastern half of the Roman empire. Another power soon arose in the east: Islam. At its greatest extent, the Arab Empire controlled 75% of the Mediterranean region.

Europe was reviving, however, as more organized and centralized states began to form in the later Middle Ages after the Renaissance of the 12th century.

Ottoman power continued to grow, and in 1453, the Byzantine Empire was extinguished with the Conquest of Constantinople. Ottomans gained control of much of the sea in the 16th century and maintained naval bases in southern France, Algeria and Tunisia. Barbarossa, the famous Ottoman captain is a symbol of this domination with the victory of the Battle of Preveza. The Battle of Djerba marked the apex of Ottoman naval domination in the Mediterranean. However, as naval prowess of the European powers grew, they confronted Ottoman expansion in the region when the Battle of Lepanto checked the power of the Ottoman Navy. This was the last naval battle to be fought primarily between galleys.

The Barbary pirates of North Africa preyed on Christian shipping in the western Mediterranean Sea.[9] According to Robert Davis, from the 16th to 19th century, pirates captured 1 million to 1.25 million Europeans as slaves.[10]

The development of oceanic shipping began to affect the entire Mediterranean. Once, all trade from the east had passed through the region, but now the circumnavigation of Africa allowed spices and other goods to be imported through the Atlantic ports of western Europe.[11][12][13] The Malta president described the Mediterranean sea as a "cemetery" due to the large amounts of migrants who drown there.[14]

Following the 2013 Lampedusa migrant shipwreck, the Italian government, has decided to strengthen the national system for the patrolling of the Mediterranean Sea by authorizing "Mare Nostrum", a military and humanitarian mission in order to rescue the migrants and arrest the traffickers of immigrants.[15]

Geography

A satellite image showing the Strait of Gibraltar. Left is the Iberian Peninsula in Europe; on the right, the Maghreb in Africa.
The Dardanelles strait in Turkey. The north side is Europe with the Gelibolu Peninsula in the Thrace region; the south side is Anatolia in Asia.
















The Mediterranean Sea is connected to the Atlantic Ocean by the Strait of Gibraltar in the west and to the Sea of Marmara and the Black Sea, by the Dardanelles and the Bosporus respectively, in the east. The Sea of Marmara is often considered a part of the Mediterranean Sea, whereas the Black Sea is generally not. The 163 km (101 mi) long man-made Suez Canal in the southeast connects the Mediterranean Sea to the Red Sea.

Large islands in the Mediterranean include Cyprus, Crete, Euboea, Rhodes, Lesbos, Chios, Kefalonia, Corfu, Limnos, Samos, Naxos and Andros in the eastern Mediterranean; Sardinia, Corsica, Sicily, Cres, Krk, Brač, Hvar, Pag, Korčula and Malta in the central Mediterranean; and Ibiza, Majorca and Minorca (the Balearic Islands) in the western Mediterranean.

The typical Mediterranean climate has hot, dry summers and mild, rainy winters. Crops of the region include olives, grapes, oranges, tangerines, and cork.

Extent

The International Hydrographic Organization defines the limits of the Mediterranean Sea as follows:[16]

Stretching from the Strait of Gibraltar in the West to the entrances to the Dardanelles and the Suez Canal in the East, the Mediterranean Sea is bounded by the coasts of Europe, Africa and Asia, and is divided into two deep basins:
  • Western Basin:
    • On the west: A line joining the extremities of Cape Trafalgar (Spain) and Cape Spartel (Africa).
    • On the northeast: The West Coast of Italy. In the Strait of Messina a line joining the North extreme of Cape Paci (15°42'E) with Cape Peloro, the East extreme of the Island of Sicily. The North Coast of Sicily.
    • On the east: A line joining Cape Lilibeo the Western point of Sicily (37°47′N 12°22′E), through the Adventure Bank to Cape Bon (Tunisia).
  • Eastern Basin:
    • On the west: The Northeastern and Eastern limits of the Western Basin.
    • On the northeast: A line joining Kum Kale (26°11'E) and Cape Helles, the Western entrance to the Dardanelles.
    • On the southeast: The entrance to the Suez Canal.
    • On the east: The coasts of Syria, Israel, Lebanon, and Gaza Strip.

Oceanography

Predominant surface currents for June

Being nearly landlocked affects conditions in the Mediterranean Sea: for instance, tides are very limited as a result of the narrow connection with the Atlantic Ocean. The Mediterranean is characterized and immediately recognised by its deep blue colour.

Evaporation greatly exceeds precipitation and river runoff in the Mediterranean, a fact that is central to the water circulation within the basin.[17] Evaporation is especially high in its eastern half, causing the water level to decrease and salinity to increase eastward.[18] The salinity at 5 m depth is 3.8 %.[19]
The pressure gradient pushes relatively cool, low-salinity water from the Atlantic across the basin; it warms and becomes saltier as it travels east, then sinks in the region of the Levant and circulates westward, to spill over the Strait of Gibraltar.[20] Thus, seawater flow is eastward in the Strait's surface waters, and westward below; once in the Atlantic, this chemically distinct Mediterranean Intermediate Water can persist thousands of kilometres away from its source.[21]

Coastal countries

Map of the Mediterranean Sea
Twenty-two countries have a coastline on the Mediterranean Sea. They are:
Several other territories also border the Mediterranean Sea (from west to east): The British overseas territory of Gibraltar, the Spanish autonomous cities of Ceuta and Melilla and nearby islands, and the Sovereign Base Areas on Cyprus
Barcelona, the largest metropolitan area on the Mediterranean Sea and also the headquarters of the Union for the Mediterranean.
The ancient port of Jaffa in Israel: according to the Bible, where the character Jonah set sail before being swallowed by a whale.[22]
The harbour of Alexandria, one of the largest cities on the Mediterranean
Catania, Sicily, with mount Etna in the background.
İzmir, the third metropolis of Turkey after Istanbul and Ankara.

Major cities (municipalities) with populations larger than 200,000 people bordering the Mediterranean Sea are:

Country Cities
 Albania Durrës
 Algeria Algiers, Annaba, Oran
 Croatia Split, Rijeka
 Egypt Alexandria, Port Said
 France Marseille, Nice
 Greece Athens, Heraklion, Patras, Thessaloniki
 Israel Ashdod, Haifa, Netanya, Tel Aviv
 Italy Bari, Catania, Genoa, Messina, Naples, Palermo, Rome, Taranto, Trieste, Venice
 Lebanon Beirut, Tripoli
 Libya Benghazi, Khoms, Misrata, Tripoli, Zawiya, Zliten
 Morocco Tétouan, Tangier
 Spain Alicante, Badalona, Barcelona, Cartagena, Málaga, Palma, Valencia
 State of Palestine Gaza City
 Syria Latakia
 Tunisia Bizerte, Sfax, Tunis
 Turkey Antalya, Iskenderun, Izmir, Mersin

Subdivisions

Africa (left, on horizon) and Europe (right), as seen from Gibraltar.

According to the International Hydrographic Organization (IHO), the Mediterranean Sea is subdivided into a number of smaller waterbodies, each with their own designation (from west to east):[16]

Other seas

Amalfi viewed from the Tyrrhenian Sea.

Although not recognised by the IHO treaties, there are some other seas whose names have been in common use from the ancient times, or in the present:

Other features

View of the Saint George Bay, and snow-capped Mount Sannine from the Corniche, Beirut
The Port of Marseille seen from L'Estaque

Many of these smaller seas feature in local myth and folklore and derive their names from these associations. In addition to the seas, a number of gulfs and straits are also recognised:

10 Largest islands by area

The two biggest islands of the Mediterranean: Sicily and Sardinia
 
Flag Island Area in km² Population
Italy Sicily Sicily 25,460 5,048,995
Italy Sardinia Sardinia 23,821 1,672,804
Cyprus Cyprus 9,251 1,088,503
France Corsica Corsica 8,680 299,209
Greece Crete 8,336 623,666
Greece Euboea 3,655 218.000
Spain Majorca Majorca 3,640 869,067
Greece Lesbos 1,632 90,643
Greece Rhodes 1,400 117,007
Greece Chios 842 51,936

Climate

The climate map of the areas surrounding the Mediterranean Sea, according to Köppen climate classification.

Sea temperature

Mean sea temperature (°C)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Marseille[23] 13 13 13 14 16 18 21 22 21 18 16 14 16.6
Gibraltar[24] 16 15 16 16 17 20 22 22 22 20 18 17 18.4
Málaga[25] 16 15 15 16 17 20 22 23 22 20 18 16 18.3
Athens[26] 16 15 15 16 18 21 24 24 24 21 19 18 19.3
Barcelona[27] 13 13 13 14 17 20 23 25 23 20 17 15 17.8
Heraklion[28] 16 15 15 16 19 22 24 25 24 22 20 18 19.7
Venice[29] 11 10 11 13 18 22 25 26 23 20 16 14 17.4
Valencia[30] 14 13 14 15 17 21 24 26 24 21 18 15 18.5
Malta[31] 16 16 15 16 18 21 24 26 25 23 21 18 19.9
Alexandria[32] 18 17 17 18 20 23 25 26 26 25 22 20 21.4
Naples[33] 15 14 14 15 18 22 25 27 25 22 19 16 19.3
Larnaca[34] 18 17 17 18 20 24 26 27 27 25 22 19 21.7
Limassol[35] 18 17 17 18 20 24 26 27 27 25 22 19 21.7
Antalya 17 17 17 18 21 24 27 28 27 25 22 19 21.8
Tel Aviv[36] 18 17 17 18 21 24 26 28 27 26 23 20 22.1

Geology

A submarine karst spring, called vrulja, observed through sea surface rippling near Omiš
Messinian salinity crisis, 5.96 to 5.33 mya, before the Zanclean flood
Messinian salinity crisis animation

The geologic history of the Mediterranean is complex. It was involved in the tectonic break-up and then collision of the African and Eurasian plates. The Messinian salinity crisis occurred in the late Miocene (12 million years ago to 5 million years ago) when the Mediterranean dried up. Geologically the Mediterranean is underlain by oceanic crust.

The Mediterranean Sea has an average depth of 1,500 m (4,900 ft) and the deepest recorded point is 5,267 m (17,280 ft) in the Calypso Deep in the Ionian Sea. The coastline extends for 46,000 km (29,000 mi). A shallow submarine ridge (the Strait of Sicily) between the island of Sicily and the coast of Tunisia divides the sea in two main subregions (which in turn are divided into subdivisions), the Western Mediterranean and the Eastern Mediterranean. The Western Mediterranean covers an area of about 0.85 million km² (0.33 million mi²) and the Eastern Mediterranean about 1.65 million km² (0.64 million mi²). A characteristic of the Mediterranean Sea are submarine karst springs or vruljas, which mainly occur in shallow waters[37] and may also be thermal.[38]

Tectonic evolution

The geodynamic evolution of the Mediterranean Sea was provided by the convergence of European and African plates and several smaller microplates. This process was driven by the differential seafloor spreading along the Mid-Atlantic Ridge, which led to the closure of the Tethys Ocean and eventually to the Alpine orogenesis. However, the Mediterranean also hosts wide extensional basins and migrating tectonic arcs, in response to its land-locked configuration.

According to a report published by Nature in 2009, some scientists think that the Mediterranean Sea was mostly filled during a time period of less than two years, in a major flood (the Zanclean flood) that happened approximately 5.33 million years ago, in which water poured in from the Atlantic Ocean and through the Strait of Gibraltar, at a rate three orders of magnitude larger than the current flow of the Amazon River.[39] However, the sea basins had been filled for many millions of years before the prior closure of the Strait of Gibraltar.

Eastern Mediterranean

In middle Miocene times, the collision between the Arabian microplate and Eurasia led to the separation between the Tethys and the Indian oceans. This process resulted in profound changes in the oceanic circulation patterns, which shifted global climates towards colder conditions. The Hellenic arc, which has a land-locked configuration, underwent a widespread extension for the last 20 Ma due to a slab roll-back process. In addition, the Hellenic Arc experienced a rapid rotation phase during the Pleistocene, with a counterclockwise component in its eastern portion and a clockwise trend in the western segment.

Central Mediterranean

The opening of small oceanic basins of the central Mediterranean follows a trench migration and back-arc opening process that occurred during the last 30 Myr. This phase was characterised by the anticlockwise rotation of the Corsica–Sardinia block, which lasted until the Langhian (ca.16 Ma), and was in turn followed by a slab detachment along the northern African margin. Subsequently, a shift of this active extensional deformation led to the opening of the Tyrrenian basin.

Western Mediterranean

The Betic-Rif mountain belts developed during Mesozoic and Cenozoic times, as Africa and Iberia converged. Tectonic models for its evolution include: rapid motion of Alboran Domain, subduction zone and radial extensional collapse caused by convective removal of lithospheric mantle. The development of these intramontane Betic and Rif basins led to the onset of two marine gateways which were progressively closed during the late Miocene by an interplay of tectonic and glacio-eustatic processes.

Paleoenvironmental analysis

Its semi-enclosed configuration makes the oceanic gateways critical in controlling circulation and environmental evolution in the Mediterranean Sea. Water circulation patterns are driven by a number of interactive factors, such as climate and bathymetry, which can lead to precipitation of evaporites.
During late Miocene times, a so-called "Messinian salinity crisis" (MSC hereafter) occurred, where the Mediterranean entirely or almost entirely dried out, which was triggered by the closure of the Atlantic gateway. Evaporites accumulated in the Red Sea Basin (late Miocene), in the Carpatian foredeep (middle Miocene) and in the whole Mediterranean area (Messinian). An accurate age estimate of the MSC—5.96 Ma—has recently been astronomically achieved; furthermore, this event seems to have occurred synchronously. The beginning of the MSC is supposed to have been of tectonic origin; however, an astronomical control (eccentricity) might also have been involved. In the Mediterranean basin, diatomites are regularly found underneath the evaporite deposits, thus suggesting (albeit not clearly so far) a connection between their geneses.

The present-day Atlantic gateway, i.e. the Strait of Gibraltar, finds its origin in the early Pliocene. However, two other connections between the Atlantic Ocean and the Mediterranean Sea existed in the past: the Betic corridor (southern Spain) and the Rifian Corridor (northern Morocco). The former closed during Tortonian times, thus providing a "Tortonian salinity crisis" well before the MSC; the latter closed about 6 Ma, allowing exchanges in the mammal fauna between Africa and Europe. Nowadays, evaporation is more relevant than the water yield supplied by riverine water and precipitation, so that salinity in the Mediterranean is higher than in the Atlantic. These conditions result in the outflow of warm saline Mediterranean deep water across Gibraltar, which is in turn counterbalanced by an inflow of a less saline surface current of cold oceanic water.

The Mediterranean was once thought to be the remnant of the Tethys Ocean. It is now known to be a structurally younger ocean basin known as Neotethys. The Neotethys formed during the Late Triassic and Early Jurassic rifting of the African and Eurasian plates.

Paleoclimate

Because of its latitudinal position and its land-locked configuration, the Mediterranean is especially sensitive to astronomically induced climatic variations, which are well documented in its sedimentary record. Since the Mediterranean is involved in the deposition of eolian dust from the Sahara during dry periods, whereas riverine detrital input prevails during wet ones, the Mediterranean marine sapropel-bearing sequences provide high-resolution climatic information. These data have been employed in reconstructing astronomically calibrated time scales for the last 9 Ma of the Earth's history, helping to constrain the time of past Geomagnetic Reversals.[40] Furthermore, the exceptional accuracy of these paleoclimatic records have improved our knowledge of the Earth's orbital variations in the past.

Ecology and biota

As a result of the drying of the sea during the Messinian salinity crisis,[41] the marine biota of the Mediterranean are derived primarily from the Atlantic Ocean. The North Atlantic is considerably colder and more nutrient-rich than the Mediterranean, and the marine life of the Mediterranean has had to adapt to its differing conditions in the five million years since the basin was reflooded.

The Alboran Sea is a transition zone between the two seas, containing a mix of Mediterranean and Atlantic species. The Alboran Sea has the largest population of Bottlenose Dolphins in the western Mediterranean, is home to the last population of harbour porpoises in the Mediterranean, and is the most important feeding grounds for Loggerhead Sea Turtles in Europe. The Alboran sea also hosts important commercial fisheries, including sardines and swordfish. The Mediterranean monk seals live in the Aegean Sea in Greece. In 2003, the World Wildlife Fund raised concerns about the widespread drift net fishing endangering populations of dolphins, turtles, and other marine animals.

Environmental threats

Biodiversity

Invasive species

The Reticulate whipray is one of the species that colonised the eastern Mediterranean through the Suez Canal.

The opening of the Suez Canal in 1869 created the first salt-water passage between the Mediterranean and Red Sea. The Red Sea is higher than the Eastern Mediterranean, so the canal serves as a tidal strait that pours Red Sea water into the Mediterranean. The Bitter Lakes, which are hyper-saline natural lakes that form part of the canal, blocked the migration of Red Sea species into the Mediterranean for many decades, but as the salinity of the lakes gradually equalized with that of the Red Sea, the barrier to migration was removed, and plants and animals from the Red Sea have begun to colonise the Eastern Mediterranean. The Red Sea is generally saltier and more nutrient-poor than the Atlantic, so the Red Sea species have advantages over Atlantic species in the salty and nutrient-poor Eastern Mediterranean. Accordingly, Red Sea species invade the Mediterranean biota, and not vice versa; this phenomenon is known as the Lessepsian migration (after Ferdinand de Lesseps, the French engineer) or Erythrean invasion. The construction of the Aswan High Dam across the Nile River in the 1960s reduced the inflow of freshwater and nutrient-rich silt from the Nile into the Eastern Mediterranean, making conditions there even more like the Red Sea and worsening the impact of the invasive species.

Invasive species have become a major component of the Mediterranean ecosystem and have serious impacts on the Mediterranean ecology, endangering many local and endemic Mediterranean species. A first look at some groups of exotic species show that more than 70% of the non-indigenous decapods and about 63% of the exotic fishes occurring in the Mediterranean are of Indo Pacific origin,[42] introduced into the Mediterranean through the Suez Canal. This makes the Canal as the first pathway of arrival of "alien" species into the Mediterranean. The impacts of some lessepsian species have proven to be considerable mainly in the Levantine basin of the Mediterranean, where they are replacing native species and becoming a "familiar sight".

According to the International Union for Conservation of Nature definition, as well as Convention on Biological Diversity (CBD) and Ramsar Convention terminologies, they are alien species, as they are non-native (non-indigenous) to the Mediterranean Sea, and they are outside their normal area of distribution which is the Indo-Pacific region. When these species succeed in establishing populations in the Mediterranean sea, compete with and begin to replace native species they are "Alien Invasive Species", as they are an agent of change and a threat to the native biodiversity. In the context of CBD, "introduction" refers to the movement by human agency, indirect or direct, of an alien species outside of its natural range (past or present). The Suez Canal, being an artificial (man made) canal, is a human agency. Lessepsian migrants are therefore "introduced" species (indirect, and unintentional). Whatever wording is chosen, they represent a threat to the native Mediterranean biodiversity, because they are non-indigenous to this sea. In recent years, the Egyptian government's announcement of its intentions to deepen and widen the canal have raised concerns from marine biologists, fearing that such an act will only worsen the invasion of Red Sea species into the Mediterranean, facilitating the crossing of the canal for yet additional species.[43]

Arrival of new tropical Atlantic species

In recent decades, the arrival of exotic species from the tropical Atlantic has become a noticeable feature. Whether this reflects an expansion of the natural area of these species that now enter the Mediterranean through the Gibraltar strait, because of a warming trend of the water caused by global warming; or an extension of the maritime traffic; or is simply the result of a more intense scientific investigation, is still an open question. While not as intense as the "lessepsian" movement, the process may be scientific interest and may therefore warrant increased levels of monitoring.[citation needed]

Sea-level rise

By 2100, the overall level of the Mediterranean could rise between 3 to 61 cm (1.2 to 24.0 in) as a result of the effects of climate change.[44] This could have adverse effects on populations across the Mediterranean:
  • Rising sea levels will submerge parts of Malta. Rising sea levels will also mean rising salt water levels in Malta's groundwater supply and reduce the availability of drinking water.[45]
  • A 30 cm (12 in) rise in sea level would flood 200 square kilometres (77 sq mi) of the Nile Delta, displacing over 500,000 Egyptians.[46]
Coastal ecosystems also appear to be threatened by sea level rise, especially enclosed seas such as the Baltic, the Mediterranean and the Black Sea. These seas have only small and primarily east-west movement corridors, which may restrict northward displacement of organisms in these areas.[47] Sea level rise for the next century (2100) could be between 30 cm (12 in) and 100 cm (39 in) and temperature shifts of a mere 0.05-0.1°C in the deep sea are sufficient to induce significant changes in species richness and functional diversity.[48]

Pollution

Pollution in this region has been extremely high in recent years.[when?] The United Nations Environment Programme has estimated that 650,000,000 t (720,000,000 short tons) of sewage, 129,000 t (142,000 short tons) of mineral oil, 60,000 t (66,000 short tons) of mercury, 3,800 t (4,200 short tons) of lead and 36,000 t (40,000 short tons) of phosphates are dumped into the Mediterranean each year.[49] The Barcelona Convention aims to 'reduce pollution in the Mediterranean Sea and protect and improve the marine environment in the area, thereby contributing to its sustainable development.'[50] Many marine species have been almost wiped out because of the sea's pollution. One of them is the Mediterranean Monk Seal which is considered to be among the world's most endangered marine mammals.[51]

The Mediterranean is also plagued by marine debris. A 1994 study of the seabed using trawl nets around the coasts of Spain, France and Italy reported a particularly high mean concentration of debris; an average of 1,935 items per km². Plastic debris accounted for 76%, of which 94% was plastic bags.[52]

Shipping

The port of Piraeus is the busiest passenger port in Europe and the Mediterranean.[53]

Some of the world's busiest shipping routes are in the Mediterranean Sea. It is estimated that approximately 220,000 merchant vessels of more than 100 tonnes cross the Mediterranean Sea each year—about one third of the world's total merchant shipping. These ships often carry hazardous cargo, which if lost would result in severe damage to the marine environment.

The discharge of chemical tank washings and oily wastes also represent a significant source of marine pollution. The Mediterranean Sea constitutes 0.7% of the global water surface and yet receives seventeen percent of global marine oil pollution. It is estimated that every year between 100,000 t (98,000 long tons) and 150,000 t (150,000 long tons) of crude oil are deliberately released into the sea from shipping activities.

Approximately 370,000,000 t (360,000,000 long tons) of oil are transported annually in the Mediterranean Sea (more than 20% of the world total), with around 250-300 oil tankers crossing the Sea every day. Accidental oil spills happen frequently with an average of 10 spills per year. A major oil spill could occur at any time in any part of the Mediterranean.[48]

Tourism

Antalya on the Turkish Riviera (Turquoise Coast) is the third most visited city in the world with 10.5 million tourists.

With a unique combination of pleasant climate, beautiful coastline, rich history and diverse culture the Mediterranean region is the most popular tourist destination in the world—attracting approximately one third of the world's international tourists.

Tourism is one of the most important sources of income for many Mediterranean countries. It also supports small communities in coastal areas and islands by providing alternative sources of income far from urban centres. However, tourism has also played major role in the degradation of the coastal and marine environment. Rapid development has been encouraged by Mediterranean governments to support the large numbers of tourists visiting the region each year. But this has caused serious disturbance to marine habitats such as erosion and pollution in many places along the Mediterranean coasts.

Tourism often concentrates in areas of high natural wealth, causing a serious threat to the habitats of endangered Mediterranean species such as sea turtles and monk seals. Reductions in natural wealth may reduce incentives for tourists to visit.[48]

Overfishing

Fish stock levels in the Mediterranean Sea are alarmingly low. The European Environment Agency says that over 65% of all fish stocks in the region are outside safe biological limits and the United Nations Food and Agriculture Organisation, that some of the most important fisheries—such as albacore and bluefin tuna, hake, marlin, swordfish, red mullet and sea bream—are threatened.[date missing]

There are clear indications that catch size and quality have declined, often dramatically, and in many areas larger and longer-lived species have disappeared entirely from commercial catches.

Large open water fish like tuna have been a shared fisheries resource for thousands of years but the stocks are now dangerously low. In 1999, Greenpeace published a report revealing that the amount of bluefin tuna in the Mediterranean had decreased by over 80% in the previous 20 years and government scientists warn that without immediate action the stock will collapse.

Aquaculture

Aquaculture in western Greece

Aquaculture is expanding rapidly—often without proper environmental assessment—and currently accounts for 30% of the fish protein consumed worldwide. The industry claims that farmed seafood lessens the pressure on wild fish stocks, yet many of the farmed species are carnivorous, consuming up to five times their weight in wild fish.

Mediterranean coastal areas are already over exposed to human influence, with pristine areas becoming ever scarcer. The aquaculture sector adds to this pressure, requiring areas of high water quality to set up farms. The installation of fish farms close to vulnerable and important habitats such as seagrass meadows is particularly concerning.

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