Extreme differences: Oceanographic conditions control upward growth of reefs through El Niño low mean sea level in Palau

The extremes of the 2015-2016 El Niño in Palau produced large scale coral mortality from low mean sea levels (shallow) and cold water bleaching at reef lower depth limits. La Niña-like conditions in summer 2016 initiated a warm water coral bleaching event, which reversed quickly with a switch in western Pacific oceanographic conditions. Aerial exposure of corals due to El Niño low mean sea level (MSL) caused mortality to very shallow corals which had grown upward since previous low MSL periods. The tidal threshold of coral mortality was quantified relative to the tidal datum for Palau. Low MSL events occur in cycles at intervals of 5-7 years in Palau, and are the critical factor limiting upward growth of reefs with rising sea levels. The oceanographic conditions underpinning ENSO conditions in Palau (2014-2016) are examined in detail