Data from: Broad-scale patterns of vertical benthic zonation in the mesophotic and deep Red Sea

Abstract Aim: To characterise patterns of mesophotic and deep benthic zonation for the first time in the Red Sea, focusing on depth (from 80 to 600 m) and latitudinal (from 16.56oN to 29.31oN) gradients. Location: The Saudi Arabian Red Sea. Methods: We used high-resolution bathymetry, benthic video transects, and environmental data profiles. Images were extracted from the videos and processed through ReefCloud, using artificial intelligence, to annotate visible benthic organisms and substrate type. The resulting seafloor and macrofauna components were analysed using multivariate statistics to determine patterns of zonation by depth and latitude, and to evaluate relationships with temperature, salinity and slope inclination. Results: With an overall accuracy of 84%, the ReefCloud model delivered high performance in taxonomic identification. Between depths of 80 and 140 m, there was a high coverage of benthic organisms (19-31%), including crustose calcifying red algae (CCRA) and zooxanthellate Scleractinia. There was a community break at 140 m, below which a decrease in light levels correlated with a decline in benthic coverage by these taxa. Species diversity decreased in deeper waters (> 140 m), and the availability of hard substrate, rather than light attenuation, was the primary correlate with biodiversity patterns. The depth distributions of studied taxa in the warm and hypersaline Red Sea were comparable to distributions of similar taxa in other, cooler basins. This similarity highlights the importance of light and substrate composition, versus water temperature, in shaping species zonation. Main conclusions: We identified patterns of zonation along the mesophotic and deep depth gradient throughout the Saudi Arabian Red Sea. Patterns were relatively consistent along the latitudinal gradient, but some fauna were distributed to shallower depths in the more turbid south. These results provide an essential starting point for marine spatial planning in the mesophotic and deep Red Sea. Table of contents Average_slope.csv - Angle of the slope averaged for every 10 m depth range across all survey sites in the Saudi Arabian Red Sea, including standard deviation and standard error. Temp_Sal.csv - Temperature (oC) and salinity averaged for every 10 m depth range across all survey sites in the Saudi Arabian Red Sea, including standard deviation and standard error. ReefCloud_Annotations.csv - All annotations (human and machine) from ReefCloud (before cluster analysis).