This water brought with it living organisms. The Gibraltar straits, until the opening of the Suez canal, formed the Mediterranean's only link with the other oceans. Through it entered many species of fish and other marine animals. Evaporation exceeded, as it does now, the fresh water in flow into the Mediterranean maintaining a steady current from the surface Atlantic into the Mediterranean.

Today's Mediterranean is characterized, as a result of its morphology and hydrography, by a rather low productivity. It is a relatively deep sea, reaching abour 4.500 metres at its deepest with a generally narrow continental shelf.

The productivity of any sea is

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Satellite Image of The Mediterranean Sea.

based mainly on the concentration of the various nutrients salts that are in circulation in the water. These are basically the phosphates and the nitrates, though lack of oxygen can also, under certain circumstances, limit productivity. This is the case in the deeper layers in the East Mediterranean. Silicates also play a role as some planktonic organisms, such as diatoms, have a cell wall that is based on silica.

The Mediterranean gets most of its nutrients salts from surface layers of the Central Altantic which are not very rich either. The Atlantic Water that enters the Mediterranean through the Gibraltar straits follows the North Coast of Africa, with various branches on the way, and reaches the East Mediterranean. Here water travels mainly in an anticlockwise rotation around Cyprus. On the way to the east Mediterranean the nutrients enter into various life cycles and are either landed as fish or sink, ultimately, to the lower layers of the sea; as a result the East Mediterranean gets what is left over. This has its merits as it results in the East Mediterranean being one of the bluest seas in the world.

On its way here the sea water gets not only poorer but also warmer and very salty, hence denser. In the area south west of Cyprus, in winter,

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Peacock Wrasse with Blue Damsel Fish - Papadies ( Chromis chromis) in shallow waters

this water (which is known as Mediterranean Water), sinks to the deeper layers and moves west. Ultimately it gets out of the Mediterranean and into the Atlantic through the lower strata of the straits of Gibraltar. With it, it takes any nutrients that have dropped into it as organic debris. A complete change of the Mediterranean water takes over 100 years.

Within this general pattern we can now look at the sea around Cyprus. Its productivity is about the same as the productivity of the rest of the East Mediterranean. Its temperature rang- es from about 16C in winter to about 28C in summer in all the areas around the island, with one exception, the area around Petra-tou- Romiou, where in summer the water is cooler by several degrees. This is the result of the prevailing currents causing water from deeper layers to come to the surface. In most areas a strong thermocline is formed in summer at a depth ranging from 20 to 30 metres. The temperature just below the thermocline is about 18C. The presence of this thermocline has significant effects on the vertical distribution of the marine iife of the island. The richer areas, both in quantity and variety of life, are below the depth which the thermocline reaches, in summer at least. The salinity in the area is about 39% and is among the highest in the world.