Depth diagnostic mesophotic assemblages in the Northern Red Sea (Saudi Arabia) as analog to the Cenozoic fossil record

While mesophotic assemblages in the Gulf of Aqaba have been described in some detail, in the Red Sea proper, data are rare. Here we present a first report on a detached carbonate platform fragment from the Northern Red Sea off Al Wajh that stretches over a water depth range of 25 to 130 m. The assemblages observed comprise depth-typical large benthic foraminifers, crustose coralline algae, and mesophotic scleractinian corals (e.g., Leptoseris spp.). Encrusting bryozoans and foraminifers are abundant. A soft sediment cover in the deeper areas indicates the absence of strong currents. Radiocarbon ages confirm that this community is currently thriving. This example resembles the previously known occurrences of mesophotic reefs in the Gulf of Aqaba with respect to assemblage despite different oceanographic conditions. At the same time, it reminds of Cenozoic, in particular pre-Upper Miocene (i.e., before 8.5 million years ago), coral-associated assemblages, when coral bioherms preferentially occurred in mesophotic rather than euphotic settings. The present study thus contributes to improving the interpretation of those fossil bioherms with respect to their ecosystem dynamics and environmental significance.