Regionalisation of Red Sea coral reefs based on remotely sensed environmental data identifies two distinct regions that align with large-scale climatic forcings

Abstract “Regionalisation” refers to the identification of distinct geographical units relatively homogeneous in their biotic and/or abiotic attributes, with the aims of enhancing the understanding of ecosystem functioning and informing decision-making in conservation planning and research efforts. In the Red Sea, the paucity of in situ data and discipline-specific research interests have hampered quantitative and comprehensive regionalisation, impeding unified conservation policies in a marine biodiversity hotspot. Presented hereby is a robust regionalisation of the Red Sea based on long-term (≥ 24 years) remote-sensing environmental variables deemed important for coral reef ecosystems. Cluster analysis of 2448 sites identified two regions, i.e. the Northern-Central and Southern Red Sea, separated by a transition zone at ca. 18–20°N latitude with some seasonal variability. Sea surface temperature (mean and variability), chlorophyll- α and phosphate mean concentrations contributed most to distinguishing between regions. The regionalisation arising from the analysis concurs with established circulation pathways and ocean processes that combine forcings from evaporation-driven thermohaline circulation, climate oscillations (i.e. the Arabian monsoon, the North Atlantic and El Niño-Southern oscillations) and vertical mixing. Local conditions further confounded the regionalisation with sites subject to nutrient contamination near Jeddah, Saudi Arabia. Overall, this study offers a statistically sound approach for meaningful ecological regionalisation and identification of the underlying mechanisms at play that is applicable to other systems and replicable over different time windows or climate change projections. This robust region delineation opens new opportunities for research and monitoring efforts and constitutes a first, fundamental step to foster effective spatial planning in the Red Sea.