Located at the crossroads of several major biogeographic provinces connected by major seasonal currents and upwellings, Socotra’s marine biodiversity is rich and is characterized by a unique mixture of species from the following regions - the western Indian Ocean, the Red Sea, Arabia, East Africa and the wider Indo-Pacific. It is among the richest in the Western Indian Ocean, rivaling other much larger coastal areas
The numbers of species of hard corals and fish are comparable to those of the Red Sea, despite the small size of the archipelago. There is a high degree of faunal similarity and biogeographic affinity between Socotra and the Southern Arabian region across most groups, although there is also a strong Indo-Pacific influence at Socotra. Different taxa show different affinities to the regions.
For the corals, most occur across much of the Indo-west Pacific region, others are more widespread in the Western Indian Ocean, but some 20% were not previously known from Arabian seas, and a few were previously known only from the Red Sea or Arabian Gulf.
The Archipelago may provide the crucial "link" for some marine species in maintaining their distribution governed by the duration of their planktonic larval stages.
Coastal and Marine Habitats
There is a wealth of habitat diversity around the islands – coastal cliffs, rocky coves, cobble and sandy beaches, mudflats, lagoons and coral reefs. Some of the coastal cliffs continue underwater, their sheer sides occasionally poked by caves. Others fall away to a flat limestone plain fronted by ancient coral reef, some of which now lies above sea level.
In places more sheltered from the monsoon winds, waves and currents; small patches of tropical coral reef, tranquil shallow lagoons and mudflats occur. Further offshore, the open sea is influenced by the seasonal onset of eddies and gyres, with major effects on productivity, dispersal and community structure.
Beaches range from small sand or cobble patches scattered among the boulders, fossil reefs and cliffs, to long expanses kilometres in length. The longest continuous sandy beach is located on the north coast at Ghubbah, where it extends over 20 km and providing the main local nesting site for Loggerhead Turtles Caretta caretta. Cobble beaches occur along parts of the Noged Plain on the south coast, on the north coast near Hadiboh, Qadheb, Ras Qadama and south of Qalansiyah and Shu’ub in the west.
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