Black corals (Antipatharia) of the northern Red Sea: ancient predators of the mesophotic reef

Black corals (Antipatharia) are among the most common and diverse taxa in mesophotic and aphotic rocky habitats. Studies of their ecology and biology are limited mostly because of the technical challenges involved in deep-water work. Here, we describe taxonomic traits, habitat, and nutrition of 2 species from the upper mesophotic zone of the northern Red Sea, Gulf of Aqaba, Israel. Our study describes a broader distribution of the branched Antipathes griggi, which to date has been primarily found in the Hawaiian Archipelago. Additionally, a new record is reported regarding the coiled Stichopathes spp. discovered at the upper mesophotic zone. The branched A. griggi were more abundant than the coiled Stichopathes spp. in all explored sites, and differences in light and water flow conditions significantly affected their distribution. Both species lacked symbiotic algae (Symbiodiniaceae). Analysis of the amino acid compound-specific stable isotope signature (AA-CSIA) revealed that both antipatharian species show a high trophic position relative to known mixotrophic and heterotrophic corals. Although both species inhabit the same area and are planktivorous, their carbon signature suggests they have different carbon sources. Our findings imply that antipatharians have a vital role in the trophic dynamics of mesophotic coral ecosystems, a unique habitat whose ecology remains largely unexplored.