The Mediterranean Sea

Let's start talking about the Mare Nostrum, it will help us to better understand marine organisms and their environment.

@Jessica

Published in

Aquarium

· 19 Aug 2018

The Mediterranean Sea is formed by two basins: the western basin and the eastern basin, that communicate through the Strait of Sicily and the Strait of Messina.

The Mediterranean Sea is formed by two basins: the western basin and the eastern basin, that communicate through the Strait of Sicily and the Strait of Messina. The Black Sea, the Aegean, the Adriatic Sea and the Ionian Sea are part of the eastern basin. The Tyrrhenian Sea, with the Ligurian Sea, is part of the western basin.
In each of these basins are specific physical characteristics that affect all the present organisms; the eastern basin is warmer and saltier (up to 39% near Cyprus) and reaches its maximum depth in the Ionian Sea (5020 meters).
In the Strait of Gibraltar flows a superficial water current directed from the Atlantic ocean to the Mediterranean sea, below which a water current moves in the opposite direction. The thermal conditions of the Mediterranean sea affect the living organisms: the deep waters maintain a constant temperature of about 13 °C, up to the abyssal zone. Therefore the Mediterranean sea lacks almost all the typical organisms of the deep waters that are present in the Atlantic oceac, where the temperature is always much lower than 13 °C.

To outline the physiognomy of the Mediterranean fauna it is important to provide some historical information. During the Tertiary period (Eocene and Oligocene: about 65 million years ago), Mediterranean was a tropical sea with a notable development of coral reefs rich in fish that gave rise to numerous fossil remains, currently present only in other warmer seas. During this time frame, the Mediterranean sea did not have the actual aspect and it communicated with other seas, both to the west and to the east side. In the following period, called Miocene (23 to 5.3 million years ago), the plate corresponding to the current Arabian peninsula moved, which closed to the east side the communication with the sea corresponding to the current Indian Ocean. Moreover, for some time the western opening was also closed. The Mediterranean sea, having become a closed basin, partly dried up and therefore many paleomediterranean organisms became extinct.

The Mediterranean sea almost dried after complete disconnection from the Atlantic ocean.

During the Pliocene (5.3 to 2.6 million years ago) the western basin communicated again with the Atlantic ocean through the Strait of Gibraltar. This allowed the penetration of surface and intermediate water species coming from the ocean: the current fauna was formed, which has typically Atlantic characteristics with, especially among fish (about 18% of species), many endemisms (species that are present only in the Mediterranean). Other organisms, however, are present everywhere in the oceans; among these live forms are, for example, different sharks, tuna and the moon fish. The Mediterranean fauna is definitely not uniform, even if characterised by many fish and invertebrates widespread in every place. The southern Mediterranean, having a subtropical physiognomy (with medium superficial isotermes of 20 °C), hosts species that are normally found on other warmer seas, such as some species of Groupers and other Perciforms. In general, compared to other European seas, the Mediterranean sea is still to be considered a warm sea, dependent on the Atlantic ocean for the most substantial water supplies necessary to counterbalance the strong evaporation.