Hard coral diversity and species distribution in Yemen are thought to be principally controlled by hydrology and hydrodynamic factors acting in the Arabian region. In particular, a strong seasonal upwelling linked to the SW summer monsoon is typically described as a major forcing function prevailing in the Gulf of Aden and Socotra. The diversity of the hitherto little known scleractinian coral fauna of Yemen was investigated through surveys extending from the Kamaran Island area, in the southern Red Sea, to Socotra in the Arabian Sea, and including Aden, Balhaf, Bir Ali, Burum, and Al Mukallah in the Gulf of Aden. Results showed that the scleractinian fauna of the Gulf of Aden is notably different from that of the Yemen Red Sea and from the Socotra Archipelago. More unexpectedly, striking patterns of species and genera distribution and relative frequency were observed along a relatively short stretch of coastline. It is hypothesized that, at the local scale, the synergistic effects of the seasonal upwelling, of fresh water input from major wadi estuaries, and of westward moving eddies in the Gulf of Aden could play a role as for the observed striking coral species distribution patterns
