Spatial variability in benthic assemblage composition in shallow and upper mesophotic coral ecosystems in the Philippines

Mesophotic coral ecosystems (MCEs) have received increasing attention in recent years in recognition of their unique biodiversity and also their potential importance as refuges from disturbance events. However, knowledge of the composition of MCEs and how they vary in space is lacking in many regions, particularly the Coral Triangle biodiversity hotspot. Here, we compared the benthic components and coral genera composition between shallow-water reefs (SWRs, 8-13 m depth) and upper MCEs (30-40 m) in four locations in the Philippines that are exposed to differing environmental conditions. Coral cover, abundance, and generic diversity were lower in MCEs than SWRs at three of the four locations. Benthic composition and coral generic composition also varied significantly among locations for both shallow and deep sites. Differences in benthic composition among sites was due primarily to variation in hard corals, macroalgae, sand and silt, while variation in coral assemblage was due to differences in abundance of encrusting Porites, branching Acropora, branching Seriatopora. Our results showed that the composition of MCE communities varied significantly from adjacent shallow reefs, but also among MCEs in differing geographic locations. Furthermore, our results suggest disturbances affecting shallow-water reefs, particularly sedimentation, also negatively impact MCEs, and that depth therefore provides no potential refuge from these disturbances. We recommend that conservation of MCEs consider spatial variability in community composition among sites, and urge further research to better understand the spatial variation in the composition of MCE communities in the Philippines.