Spatial variability in coral assemblages in the northeastern and central Red Sea

Variability in coral cover, community composition and population size structure results from a wide range of biological and environmental processes that operate at different spatial scales. Coral reefs in the Red Sea span latitudinal and environmental gradients in temperature and salinity, which may facilitate the formation of distinct coral assemblages in different regions. This study assessed spatial differences in benthic coral cover, taxonomic composition, juvenile abundance and size structure of three common coral genera (Acropora, massive Porites and Pocillopora) at each of two reef habitat types (reef crest and slope) in two regions of the Saudi Arabian Red Sea (northern and central regions). Average coral cover on the northern Red Sea coral reef sites was 42.6 % higher than comparable reefs in the central Red Sea. Spatial differences in coral colony size structure by region and habitat were strongly genera specific. Massive Porites colonies were larger in diameter on the reef crest in the northern sites compared to the central ones, with a significant region and habitat interaction, while acroporids did not vary in size between regions but were larger on the reef crest than the slope. Although Pocillopora did not vary notably in size across study sites, it was less abundant in the central Red Sea. The number of juvenile corals also varied spatially, with higher densities on the reef slope at northern sites. Observed differences in coral assemblages by region were likely driven by the known environmental and latitudinal gradient from north to south in the Red Sea, which also corresponds with different historical exposure to thermal stress (e.g., recent bleaching event that affected the central coast) between the two regions. The spatial differences in coral cover and demographic structure described here suggest that conservation strategies in the Red Sea should be tailored to specific reef habitats and regions.