Benthic Composition Across Inshore and Offshore Reef Sites Along the Saudi Arabian Red Sea: A Baseline for Coral-Reef Monitoring and Management

Abstract

Coral-reef management requires spatially explicit baselines that describe both living benthic communities and the non living substrates that shape reef habitat and recovery potential. This study assessed benthic composition across ten reef sites along the Saudi Arabian Red Sea, comprising seven inshore sites and three offshore islands. Standardized Reef Check point intercept transects were surveyed at approximately 5 and 10 m depth to quantify hard coral, soft coral, recently killed coral, nutrient-indicator algae, sponge, rock, rubble, sand, silt, and other benthic categories. The study aimed to compare benthic patterns among sites, depth strata, and proximity classes and to identify priorities for long-term monitoring and management. Benthic composition varied markedly among the 20 site-depth transects. Living benthic cover ranged from 13% to 77%, indicating strong site-level heterogeneity. Mean living cover declined from 39.7% at 5 m to 32.5% at 10 m; however, the paired site-level comparison was not statistically significant (t(9) = 1.97, p = 0.080), and depth responses differed among reefs. Offshore reefs showed higher mean living cover than inshore reefs at both depths, but this pattern should be interpreted descriptively because only three offshore sites were surveyed and substantial overlap occurred among individual sites. Yanbu Factory Beach, an inshore site, equalled Baridy Island for the highest living cover at 5 m (77%). Baridy Island supported the highest hard-coral cover (66% at 5 m and 51% at 10 m), whereas Yanbu Factory Beach was distinguished by high soft-coral cover (33% and 40%, respectively). In contrast, Yanbu Plant Beach was strongly rock-dominated, while sand reached 66% at 10 m at El Badei Coast. The results demonstrate that neither depth nor distance from shore alone explains reef condition. Instead, site-specific benthic composition and substrate type provide the most informative basis for monitoring and management. Repeated standardized surveys at the same georeferenced transects, supported by environmental measurements and permanent photographic records, are recommended to distinguish persistent habitat characteristics from ecological change and to guide site-specific management priorities.