The Red Sea and the Arabian Gulf are the most saline seas that are linked directly to oceans, because of high evaporation and low volumes of freshwater input. The Arabian Gulf is shallow with a constricted entrance at the Straits of Hormuz. In the Red Sea, salinity averages 36 ppt near the Indian Ocean, to more than 40 ppt in the north. Few coral species can live in areas of very high salinity. The Gulf emptied during the last ice age, about 12,000 years ago, so species that occur there recruited through the narrow Straits of Hormuz.
Coral reefs grow in offshore, clear waters near Kuwait and Saudi Arabia in the Gulf.
Some fringing reefs have developed at a few sites near the shore, but are generally not well developed due to extreme variations in temperature and light. The rest of the area consists of mud or sand, with some dense seagrass beds. Much of the coastline of the Gulf of Aden, Arabian Sea, and Gulf of Oman is sandy or rocky. Coral communities often develop on rocks, but are limited by cold intense seasonal upwellings. There are few major natural stresses on these reefs as tropical storms do not penetrate into the enclosed waterways, and runoff from the land is minimal.