The Red Sea: Israel

The mesophotic coral ecosystems (MCEs) of Eilat, in the Northern Red Sea, are among the best-studied worldwide, as demonstrated by the high number of publications from the region. Nonetheless, Eilat’s MCEs remain relatively unexplored compared to its shallow reefs. Its MCEs host diverse benthic communities that are potentially linked ecologically to shallow reefs. Here, we summarize the history of MCE research and compare the shallow and mesophotic reefs using long-term biotic and abiotic data. Eilat’s MCEs exhibit lower fluctuations in temperature, light, sedimentation, and a decreased frequency of shore-related disturbances than adjacent shallow reefs, supporting the hypothesis that key environmental parameters become more stable with increasing depth. However, nutrient concentrations are more variable in MCEs than nearby shallow reefs. We provide a novel definition of the upper (30–80 m) and lower (80–160 m) mesophotic zone boundaries in Eilat, based on the degree of light penetration, as well as the relative abundance of major fauna and flora. Scleractinian coral diversity increases with depth, as well as the abundance of specialist taxa. Corals (93 spp.) comprise the major organisms contributing to living benthic cover. A mass coral-bleaching event took place in 2015 that exclusively affected MCEs, and we discuss the event’s potential mechanisms and consequences for shallow vs. mesophotic coral assemblages. Protection and regulations of MCEs are needed to maintain and support these unique ecosystems.