Changes in the incidence of coral injuries during mass bleaching across Australia’s Coral Sea Marine Park

Abstract

Changes in coral abundance are typically used to assess coral mortality rates following major acute disturbances on coral reefs. However, coral abundance metrics do not consider partial mortality (hereafter injury) or background mortality occurring independently of major disturbances. As such we have little understanding about the influence of major versus routine disturbances on coral assemblages. We compared the incidence of recent (in the last 4-6 wk) coral injury (tissue loss affecting 5-99% of the colony) among different genera and size classes (<5, 5-40 and >40 cm diameter) at 16 reefs throughout Australia’s Coral Sea Marine Park before and during a mass bleaching event in 2020. Despite mass bleaching, the overall incidence of recent injury was consistent and low (<5%) across both years. However, there were marked inter-annual changes in the taxonomic hierarchy for incidence of recent injury. Interestingly, massive Porites exhibited higher incidence of recent injury during the 2020 mass bleaching whilst Acropora and Pocillopora exhibited less recent injury during mass bleaching compared to surveys conducted before the bleaching in 2018-2019. Incidence of recent injury increased with colony size, highlighting the vulnerability of large colonies and possibility of shifts in community size structure. Continued assessment of recent injuries as coral communities recover will be critical to understand their vulnerability to future disturbances and changing environmental conditions.