Variable response of Red Sea coral communities to recent disturbance events along a latitudinal gradient

Coral reefs are experiencing a dramatic loss of hard coral abundance and associated habitat structure from a myriad of local and global factors. Here, utilizing U–Th radiometric age-dating of coral death assemblages, we investigated patterns of coral mortality from the eastern margin of the Red Sea along a latitudinal gradient (Yanbu, 24o N; Thuwal, 22o N; Al-Lith, 19o N; Farasan Banks, 18o N) in 2018 and 2019. In all four regions, radiometric ages of in situ dead Acropora and Pocillopora colonies were largely confined to the late twentieth and early twenty-first century. During the early twenty-first century, coral mortality was found to be synchronous with previously documented bleaching events in 2010 and 2015 and, at one site (Farasan Banks), an outbreak of crown-of-thorns starfish (COTS) in 2009. The most northern site, Yanbu, had the highest relative percentage of live coral (42 ± 4%) and of living Acropora, and may serve as a refugium under climate warming scenarios. For the three southern regions (Thuwal, Al-Lith, Farasan Banks) benthic structure was mostly comprised of dead corals. The southernmost survey site, Farasan Banks, underwent a dramatic change in coral benthic structure associated with a COTS outbreak in 2009 and a bleaching event in 2015, and had the lowest relative percentage of live coral (6 ± 2%), comprised mostly of massive Porites, with no live Acropora or Pocillopora. Our results highlight the asynchronous impact of disturbance events on eastern Red Sea coral reefs and emphasize regional differences in recovery and ecosystem state.