Negative sea level anomalies with extreme low tides in the South-West Indian Ocean shape Reunion Island’s fringing coral reef flats

•An unusual negative sea level anomaly occurred in the Western Indian Ocean in 2015.•Reef flat benthic communities massively died following the sea level anomaly event.•A 50 % decline in coral cover is measured from both in situ and remote sensing data.•Coral cover variation on Reunion Island reef flat are shaped by these disturbances.