February 9, 2017. Water / Oceans
The Mediterranean Sea (“the sea in the middle of the Earth”) is a microcosm of the world’s ocean. Twenty-two countries surround its 2.5 million square kilometers, and throughout history its waters have suffered the strongest human pressure of all the world’s oceans
Cristina G. Mittermeier, Gregory S. Stone, Russell A. Mittermeier, Octavio Aburto-Oropeza, Claudio Campagna, Kent E. Carpenter, Laurence P. Madin, David Obura, Enric Sala, Sebastian Troëng, Peter A. Seligman & Stefan Gutermuth
The Mediterranean Sea is connected to the Atlantic through the Gibraltar Strait on the west, and to the Black Sea and the Sea of Marmara through the Dardanelles Strait on the northeast. The average depth of the Mediterranean is 1,500 m, and its deepest point is the Calypso Deep in the Ionian Sea at 5,267 m. Compared to the global oceanic average depth of 4,000 m, the Mediterranean is relatively shallow, although it is the deepest enclosed sea on the planet.
Because of its virtually enclosed nature, the Mediterranean is evaporating faster than it is being replaced by the water cycle. The Mediterranean loses three times more water from evaporation than it receives from the discharge of rivers and from rainfall. Without the water flowing in from the Atlantic Ocean, the Mediterranean would dry up. It has already happened once. Six million years ago, the European and African continental plates collided and closed the Strait of Gibraltar, separating the Mediterranean from the Atlantic Ocean. After becoming a closed sea, all the Mediterranean evaporated in less than 2,000 years. Given these “dead sea” conditions, most marine life in the Mediterranean disappeared. Then, some 5.3 million years ago, an earthquake caused the collapse of the Gibraltar threshold, releasing a massive cascade of Atlantic seawater into the empty Mediterranean basin and it was refilled within two years.
Twenty percent of the known marine species (other than microbes) are found only in the Mediterranean; among some groups, such as sponges, these endemics account for a remarkable 48% of the total number of species. Mediterranean has a rich diversity of habitats, including salt marshes, coastal lagoons, sandy beaches, rocky reefs, sandy bottoms, muddy bottoms, seamounts, deep canyons, hydrothermal vents, cold seeps, and open waters.
The Mediterranean is currently under siege. While the human threats to the biome are serious, there are some small success stories that, if scaled up, could reverse the trend of degradation. No-take areas—marine reserves where fishing is prohibited—are the best example. After a decade, fish biomass in these reserves can be more than five times larger than in unprotected sites nearby. Wonderful success stories of marine reserves include the Tavolara Marine Reserve in Sardinia and the Medes Islands Marine Reserve in Catalonia.
This is an excerpt from the CEMEX Conservation Series Book OCEANS: HEART OF OUR BLUE PLANET (2011)