THE MEDITERRANEAN SEA: CULTURE & BIODIVERSITY

World Oceans Day, Wave for Change

Today is the World Oceans Day and The Grandma and her friends, who are in Malta, have decided to talk about the Mediterranean Sea, source of culture, history and biodiversity. 

The Mediterranean Sea determines the lives of the inhabitants of its coasts and provides them food, resources and culture. Although some lines mark the borders to create countries, share languages or religions, there is something in common in these countries: the Sea and its role as a source of culture, commerce and communications. 

The Mediterranean countries have a special idiosyncrasy and although these countries shares different languages or religions, they have a Mediterranean lifestyle which makes them more similar than they can think.

More information: World Oceans Day

The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin 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. Although the sea is sometimes considered a part of the Atlantic Ocean, it is usually identified as a separate body of water. 

Geological evidence indicates that around 5.9 million years ago, the Mediterranean was cut off from the Atlantic and was partly or completely desiccated over a period of some 600,000 years, the Messinian salinity crisis, before being refilled by the Zanclean flood about 5.3 million years ago.

Posidonia on the Mediterranean seabed

It covers an approximate area of 2.5 million km2, but its connection to the Atlantic, the Strait of Gibraltar, is only 14 km wide. The Mediterranean Sea has an average depth of 1,500 m and the deepest recorded point is 5,267 m in the Calypso Deep in the Ionian Sea. 

The sea is bordered on the north by Europe, the east by Asia, and in the south by Africa. The Mediterranean Sea, including the Sea of Marmara, connected by the Dardanelles to the Aegean Sea, has a surface area of approximately 2,510,000 square km.

The sea 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.

More information: Live Science

The Ancient Greeks called the Mediterranean simply η θάλασσα the Sea or sometimes η μεγάλη θάλασσα the Great Sea, η ημέτερα θάλασσα Our Sea, or η θάλασσα η καθ'εμάς the sea around us. The Romans called it Mare Magnum Great Sea or Mare Internum Internal Sea and, starting with the Roman Empire, Mare Nostrum Our Sea. The term Mare Mediterrāneum appears later: Solinus apparently used it in the 3rd century. It means in the middle of land, inland in Latin, a compound of medius 'middle', terra 'land, earth' and -āneus 'having the nature of'.

The Mediterranean Sea in Rhodes, Greece

Ancient civilizations were located around the Mediterranean shores and were greatly influenced by their proximity to the sea. 

It provided routes for trade, colonization, and war, as well as food, from fishing and the gathering of other seafood, for numerous communities throughout the ages. Due to the shared climate, geology, and access to the sea, cultures centered on the Mediterranean tended to have some extent of intertwined culture and history.

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

More information: Study

The typical Mediterranean climate has hot, humid, and dry summers and mild, rainy winters. Crops of the region include olives, grapes, oranges, tangerines, and cork. 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 characterised and immediately recognised by its deep blue colour.

Dolphins in the Mediterranean Sea

Evaporation greatly exceeds precipitation and river runoff in the Mediterranean, a fact that is central to the water circulation within the basin.  

Evaporation is especially high in its eastern half, causing the water level to decrease and salinity to increase eastward. 

The salinity at 5 m depth is 3.8%. The temperature of the water in the deepest part of the Mediterranean Sea is 13.2 °C.

More information: Educa Poles

The geologic history of the Mediterranean Sea is complex. Underlain by oceanic crust, the sea basin was once thought to be a tectonic remnant of the ancient Tethys Ocean; it is now known to be a structurally younger basin, called the Neotethys, which was first formed by the convergence of the African and Eurasian plates during the Late Triassic and Early Jurassic. 

Because it is a near-landlocked body of water in a normally dry climate, the Mediterranean is subject to intensive evaporation and the precipitation of evaporites. The Messinian salinity crisis started about six million years ago when the Mediterranean became landlocked, and then essentially dried up. 

Gli Faraglioni in Capri, Naples

There are salt deposits accumulated on the bottom of the basin of more than a million cubic kilometres, in some places more than three kilometres thick. 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: the Western Mediterranean, with an area of about 850 thousand km2; and the Eastern Mediterranean, of about 1.65 million km2. A characteristic of the coastal Mediterranean are submarine karst springs or vruljas, which discharge pressurised groundwater into the coastal seawater from below the surface; the discharge water is usually fresh, and sometimes may be thermal.

More information: Mapping Ignorance

During Mesozoic and Cenozoic times, as the northwest corner of Africa converged on Iberia, it lifted the Betic-Rif mountain belts across southern Iberia and northwest Africa. There the development of the intramontane Betic and Rif basins led to creating two roughly-parallel marine gateways between the Atlantic Ocean and the Mediterranean Sea. 

A manta ray in the Mediterranean Sea

Dubbed the Betic and Rifian corridors, they progressively closed during middle and late Miocene times; perhaps several times. 

During late Miocene times the closure of the Betic Corridor triggered the so-called Messinian salinity crisis, when the Mediterranean almost entirely dried out. 

The time of beginning of the Messinian salinity crisis was recently estimated astronomically at 5.96 mya, and it persisted for some 630,000 years until about 5.3 mya.

After the initial drawdown and re-flooding there followed more episodes, the total number is debated, of sea drawdowns and re-floodings for the duration of the Messinian salinity crisis. 

It ended when the Atlantic Ocean last re-flooded the basin, creating the Strait of Gibraltar and causing the Zanclean flood, at the end of the Miocene, 5.33 mya.

More information: Utrecht University-Netherlands

The present-day Atlantic gateway, the Strait of Gibraltar, originated in the early Pliocene via the Zanclean Flood. The former gateway closed about 6 mya, causing the Messinian salinity crisis; the latter or possibly both gateways closed during the earlier Tortonian times, causing a Tortonian salinity crisis, from 11.6 to 7.2 mya, which occurred well before the Messinian salinity crisis and lasted much longer. 

Catalan Bay, Gibraltar, United Kingdom

Both crises resulted in broad connections of the mainlands of Africa and Europe, which thereby normalised migrations of flora and fauna, especially large mammals including primates, between the two continents. 

The Vallesian crisis indicates a typical extinction and replacement of mammal species in Europe during Tortonian times following climatic upheaval and overland migrations of new species.

The near-completely enclosed configuration of the Mediterranean basin has enabled the oceanic gateways to dominate seawater circulation and the environmental evolution of the sea and basin. Circulation patterns are also affected by several other factors, including climate, bathymetry, and water chemistry and temperature, which are interactive and can induce precipitation of evaporites.

More information: Revolvy

Today, evaporation of surface seawater is more than the supply of fresh water by precipitation and coastal drainage systems, causing the salinity of the Mediterranean to be much higher than that of the Atlantic, so much so that the saltier Mediterranean waters sink below the waters incoming from the Atlantic, causing a two-layer flow across the Gibraltar strait: that is, an outflow submarine current of warm saline Mediterranean water, counterbalanced by an inflow surface current of less saline cold oceanic water from the Atlantic.

A Mediterranean red sea star aka Echinaster sepositus

The end of the Miocene changed the Mediterranean basin. Fossil evidence reveals a humid subtropical climate with rainfall in the summer supporting laurel forests. 

The shift to a Mediterranean climate occurred largely within the last 3 million years, as summer rainfall decreased. 

More information: World Atlas

The subtropical laurel forests retreated; and even as they persisted on the islands of Macaronesia off the Atlantic coast of Iberia and North Africa, the present Mediterranean vegetation evolved, dominated by coniferous trees and sclerophyllous trees and shrubs with small, hard, waxy leaves that prevent moisture loss in the dry summers. Much of these forests and shrublands have been altered beyond recognition by thousands of years of human habitation. There are now very few relatively intact natural areas in what was once a heavily wooded region.

The Mediterranean Sea in Tunisia

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.

More information: Royal Meteorological Society (RMetS)

As a result of the drying of the sea during the Messinian salinity crisis, 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.

Sea urchins on the Mediterranean seabed

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.

The region has a variety of geological hazards which have closely interacted with human activity and land use patterns. Among others, in the eastern Mediterranean, the Thera eruption, dated to the 17th or 16th century BC, caused a large tsunami that some experts hypothesise devastated the Minoan civilisation on the nearby island of Crete, further leading some to believe that this may have been the catastrophe that inspired the Atlantis legend. 

More information: National Geographic

Mount Vesuvius is the only active volcano on the European mainland, while others as Mount Etna and Stromboli are to be found on neighbouring islands. The region around Vesuvius including the Phlegraean Fields Caldera west of Naples are quite active and constitute the most densely populated volcanic region in the world and eruptive event may occur within decades.

Stromboli Volcano in Stromboli Island, Sicily

Vesuvius itself is regarded as quite dangerous due to a tendency towards explosive, Plinian, eruptions. It is best known for its eruption in AD 79 that led to the burying and destruction of the Roman cities of Pompeii and Herculaneum. Unlike the vast multidirectional Ocean currents in open Oceans within their respective Oceanic zones; biodiversity in the Mediterranean Sea is that of a stable one due to the subtle but strong locked nature of currents which affects favorably, even the smallest macroscopic type of Volcanic Life Form. 

More information: Istituto Nazionale di Geofisica e Vulcanologia

The stable Marine ecosystem of the Mediterranean Sea and sea temperature provides a nourishing environment for life in the deep sea to flourish while assuring a balanced Aquatic ecosystem excluded from any external deep oceanic factors.

An octopus on the Mediterranean seabed

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 equalised 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. 

More information: Geographical

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. 

A seahorse in the Mediterranean Sea

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. 

More information: Chris Maser

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, introduced into the Mediterranean through the Suez Canal. 

A whale in the Mediterranean Coast

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.

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.

More information: Geoledgers

By 2100 the overall level of the Mediterranean could rise between 3 to 61 cm as a result of the effects of climate change. This could have adverse effects on populations across the Mediterranean.

Ithaca Island, Ionian/Mediterranean Sea, Greece

Rising sea levels will also mean rising salt water levels in Malta's groundwater supply and reduce the availability of drinking water.

A 30 cm rise in sea level would flood 200 square kilometres of the Nile Delta, displacing over 500,000 Egyptians.

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.

More information: PHYS

Pollution in this region has been extremely high in recent years. 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.

A sea turtle in the Mediterranean Sea

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.

The Mediterranean is also plagued by marine debris. A 1994 study of the seabed using trawl nets around the coasts of Europe 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.

More information: The Telegraph

Fish stock levels in the Mediterranean Sea are alarmingly low. The European Environment Agency says that more than 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.
 

Whale shark aka the rhincodon typus

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.

More information: CRAM (Catalan Version)

A voyage to Europe in the summer of 1921 gave me the first opportunity of observing the wonderful blue opalescence of the Mediterranean Sea. It seemed not unlikely that the phenomenon owed its origin to the scattering of sunlight by the molecules of the water. 

C. V. Raman