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Abstract
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.
Highlights
Worldwide, both terrestrial and marine ecosystems are experiencing heightened stress and rapid degradation (Canadell and Jackson 2021)
20.0°N; b 2 regions separated at 19.0°N; c 2 regions separated at 17.5°N–19.0°N; d 2 regions separated along the approximate middle of the basin; e 3 regions separated at 21.0–22.0°N and 16.5–18.0°N; f 3 regions separated at 20.0
The present study focused on Red Sea coral reefs and the abiotic conditions associated with their geographic locations
Summary
Both terrestrial and marine ecosystems are experiencing heightened stress and rapid degradation (Canadell and Jackson 2021). While some zonations were approximated, regionalisation of the Red Sea was either inferred from expert knowledge (e.g. Spalding et al 2007) or statistical analyses with restricted spatial and temporal coverage (e.g. Ormond et al 1984; Sheppard and Sheppard 1991), or were limited to one set of parameters (e.g. Shaltout 2019; Kheireddine et al 2021; Wang et al 2022) These regionalisations provided a practical foundation for other studies (e.g. Riegl et al 2012; Krumhansl et al 2016), their limited reproducibility or discipline-specific nature impeded their universal applications and led to a lack of consensus regarding the number of regions that compose the Red Sea, their borders and spatial extents. A comprehensive regionalisation of the Red Sea coral reefs remains to be statistically established
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