Despite its ecological importance, the photosynthetic deep reef below 40 m around the world is understudied and poorly understood. Most coral reef science is performed within the depth limits of recreational SCUBA diving. However, zooxanthellate scleractinian corals occur far below these depths in clear oceanic waters (Fricke and Meischner 1985; Reed 1985; Fricke et al. 1987). In Hawaii, extensive deep reef habitat is associated with insular shelves which surround most islands, and which extend laterally several km offshore to depths of 110-120 m where they are typically bordered by steep fossil carbonate slopes created during periods of low Pleistocene sea level (Jones 1993; Fletcher and Sherman 1995). Vaughan (1907) described deepwater corals from Hawaii, including four species of the zooxanthellate genus Leptoseris. Dredge hauls were made to depths of 312 fathom; but the exact depth of each collection and original in situ development cannot be discerned. The deepest in situ record for a zooxanthellate scleractinian coral in the Pacific is Leptoseris hawaiiensis at 165 m in Johnston Atoll (Maragos and Jokiel 1986). In Hawaii Leptoseris sp. has been recorded at 153 m (Hawaii Undersea Research Laboratory M288) and in the Red Sea, Leptoseris fragilis at 145 m (Fricke et al. 1987). The deepest record in the Caribbean is Agaricia grahamaeat 119 m in the. Bahamas (Reed 1985) In 2001-2004, deep-water surveys of Maui, Lanai, and Kauai using submersibles, showed Leptoseris spp. to be dominant on hard substrata below 60 m with benthic cover exceeding 90% in some areas (unpublished). Specimens were collected at depths of 70- 120 m. The three dominant scleractinian species wereL. hawaiiensis, Leptoseris yabei (previously unknown to Hawaii), and an undescribed congeneric species. These findings highlight the need for additional research to better understand the deep reef communities in Hawaii. The relative clarity of the Central Pacific oligotrophic waters (Kirk 1994) likely plays a role in these exceptional depths and provides a natural laboratory for studying the extreme depth limits to which zooxanthellate scleractinian corals can thrive.