Reef and coral communities of Oman, with a description of a new coral species (Order Scleractinia, genusAcanthastrea)

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Abstract
The coastline of Oman extends 2000 km from 16.5°N to 26.5°N in the north-west Indian Ocean. Most of it is long, exposed sandy beach or mixed sand and shallow rocky areas subject to severe scour, and there is a seasonal, cold-water upwelling whose influence increases towards the equator. Three areas of the mainland support corals, separated by long stretches of shallow sandy or muddy sublittoral. Three categories of coral or reef development are recognized: (A) coral reefs develop with characteristic profiles of reef flat and reef slope; (B) corals provide framework but there is no reef growth and no characteristic reef profile; and (C) no true reef development occurs, but mixed coral/phaeophyte communities are attached directly on to old, often non-limestone substrate. A and B are common in the north and central regions but are rare in the south. Type C is found in the centre and especially the south where the poor reef development is more typical of marginal, high-latitude coral areas. Ninety-one coral species from 47 genera were recorded (77 species from 37 genera being zooxanthellate), although diversity declines towards the equator. Regional comparisons show the Oman fauna to be fairly similar (up to 63% similariy) to that of the Arabian Gulf, but relatively dissimilar to faunas of the Gulf of Kutch (20%) and Lakshadweep (35%), the only other areas known to have significant amounts of corals in the Arabian Sea. A new species of Acanthanstrea with calices 5–8 cm wide is described.