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The Dahlak islands, politically part of Eritrea, and can be found in the southern part of the Red Sea. This sea, relatively small, is considered by geologists a real Ocean in training, because of separation of African plate from the Arabica one, a process similar to the one that have formed the Atlantic Ocean. The strong sunshine due to the tropical position and the low cloud cover make the sea of Dahlak one of the hottest in the world, with a temperature ranging between 26°C of the winter period and the 32°C of July and August. Also the salinity (38 per thousand) at the Dahlak is high, as a result of strong sunshine, the relative isolation from the Indian Ocean
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and the lack of permanent rivers. The waters of the Dahlak are biologically richest and more productive than those far more popular in the northern Red Sea, because the Dahlak emerge from a low shelf and the local winds and currents can shift from the bottom the necessary salts for the development of plankton. Moreover, for many months a year, a constant current leak from the Indian Ocean bringing richer waters. One consequence of the abundance of plankton, however, is that the waters are often murky. Only during the summer the visibility improves, because then prevailing winds from the north who are pushing the clearer water |
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of the Sudan towards the Dahlak. Great is the biodiversity of the Red Sea and the waters of Dahlak are a demonstration. High is also the degree of endemism, to be more precise the percentage of animal and plants species in a restricted geographical area. Many of these living only in the Red Sea and in the Gulf of Aden where they have evolved in partial isolation condition from the rest Indian Ocean, due to the presence of cold water along the coasts of Southern Yemen and Oman. Other species are found only in the Red Sea and have managed to survive the salinity crisis of the last ice age, when the level of the oceans was
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lowered to 130-150 meters compared with the present, slowing the entry of water in the Red Sea that was transformed into a hypersaline lake, unsuited to the life of the normal tropical marine fauna and flora. In some points but, as in the estuaries of the rivers or southern entrance of the Red Sea, the salinity was less high and these species survived. Then at the end of the Ice Age, the level of the oceans start again to rise and 11000 years ago, the salinity of the Red Sea was at normal levels, so that all the tropical species that in the meantime had survived in the near Aden Gulf, repopulate the Red Sea. |
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