Legacy effects of a mild mass bleaching event on coral survival and growth

Updated: 2026-06-29

List of authors: Lechene Marine1,2, Burn Deborah1, Álvarez-Noriega Mariana1, Becker Madison1, Toor Maren1, Gordon Sophie1, Aston Eoghan1, Hoogenboom Mia2, Ferrari Renata1 Institutional affiliations: 1 Australian Institute of Marine Science, Townsville, Queensland, 4810 Australia 2 College of Science and Engineering, James Cook University, Townsville, Queensland, 4810, Australia Contact Information for corresponding author: Marine Lechene, m.lechene@aims.gov.au, marine.lechene@my.jcu.edu.au Abstract Coral bleaching can cause substantial mortality, with well-documented consequences for reef structure and function. However, comparatively little is known about the sublethal demographic impacts of bleaching, despite their potential to strongly influence population persistence and recovery. In particular, it remains unclear whether phenotypic responses of corals to heat stress (e.g., remaining unbleached, partially bleached or fully bleached) scale predictably with lethal and sublethal outcomes, or whether even mildly affected corals experience lasting demographic consequences of thermal stress. This study examined changes in coral growth and survival dependent on phenotypic bleaching response, following a mild (4 – 5 DHW) but spatially extensive bleaching event in the central Great Barrier Reef, Australia, in 2022. By using large-area orthomosaics, we were able to virtually tag and track > 5000 colonies before, during, and after bleaching to quantify coral growth, bleaching response, and partial and whole colony mortality. We assessed how bleaching severity influenced vital rates of dominant coral taxa, accounting for taxonomic identity, colony size, water clarity, sea surface temperature, and water velocity. Initial colony size, heat stress and bleaching severity significantly influenced survival and growth in the year following bleaching. Severely bleached colonies showed declines in survival probability and growth compared to non-bleached and partially bleached colonies. Importantly, even the survival and growth of colonies that did not bleach declined during the year with heat stress compared with the year prior. These results suggest that the ecological consequences of mild bleaching events may be substantially underestimated when assessments focus only on visibly bleached colonies. We also demonstrate that partially and fully bleached colonies differ significantly in demographic responses, emphasising the importance of accounting for bleaching severity in ecological assessments and forecasting efforts.