Cumulative effects of cyclones and bleaching on coral cover and species richness at Lizard Island

Abstract

Coral reefs are being subjected to an increase in the frequency and intensity of disturbance, such as bleaching and cyclones, and it is important to document the effects of such disturbance on reef coral assemblages. Between March 2014 and May 2017, the reefs of Lizard Island in the northern section of the Great Barrier Reef were affected by 4 consecutive disturbances: severe tropical cyclones Ita and Nathan in 2014 and 2015, and mass bleaching events in 2016 and 2017. Loss of coral cover following the cyclones was patchy and dependent on the direction of the waves generated. In contrast, loss of cover following bleaching was much more uniform. Overall, coral cover declined 5-fold from 36% pre-cyclone Ita to 7% post-bleaching in 2017, while mean species richness dropped from 10 to 4 species per transect. The spatial scale and magnitude of the loss of coral cover in the region suggests that it will be many years before these reefs recover.