During exploration of the narrow Western shelf in the Gulf of Aqaba by means of the research submersible 'GEO’, bioherms formed by the stony coral Madracis interjecta were discovered between 120 m and at least 200 m depth. The growth of the bioherms is supposed to be linked to the particularly warm-temperature regime of the Gulf of Aqaba, whereas distribution depends probably on current patterns (providing nutrients), submarine topography and availability of hard substrate. The absence of symbiotic algae below the euphoric zone does not hamper the building of bioherms by stony corals. The Madracis-bioherms are true reefs in the definition of the term by the Earth Science in as much as the bioherms are surrounded by selected detritic facies types similar to ordinary, sheltered patch reefs in the photic zones.