LAUSR

Extensive partial mortality of intertidal corals was observed at the Houtman Abrolhos Islands, Western Australia, associated with extended and recurrent daytime low water levels from September to November 2018. Branching Acropora corals on shallow leeward reef platforms were emersed during the middle of day during the Austral spring due to diurnal tidal influences, seasonal mean sea-level minima associated with the southward flowing Leeuwin Current and interannual variability related to the El Niño–Southern Oscillation. Pre-emersion total live coral cover was estimated to be ~ 35%, dominated by Acropora (~ 24%). Post-emersion, live Acropora cover decreased to 11.1% (± 1.5 SE) and total cover to 21.7% (± 0.8 SE). Mortality of non-acroporid corals which were lower in the water column was not observed. Partial coral mortality associated with seasonal low tides and interannual variability in mean sea level is a universal process and under-reported driver of temporal variability in coral cover on intertidal reef platforms.