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Advances in the aquatic sciences
RESEARCH ARTICLE (Open Access)

Microalgal blooms in the skeletons of bleached corals during the 2020 bleaching event on Heron Island, Australia

A. J. Fordyce https://orcid.org/0000-0002-8577-8174 A C , T. D. Ainsworth https://orcid.org/0000-0001-6476-9263 B , C. E. Page B , J. L. Bergman B 1 , C. A. Lantz A B 1 and W. Leggat A
+ Author Affiliations
- Author Affiliations

A University of Newcastle, School of Environmental and Life Sciences, Callaghan, NSW 2309, Australia.

B School of Biological, Earth and Environmental Sciences, Level 5, UNSW Sydney, Kensington, NSW 1466, Australia.

C Corresponding author. Email: alexander.fordyce@uon.edu.au

Marine and Freshwater Research 72(11) 1689-1694 https://doi.org/10.1071/MF21050
Submitted: 11 February 2021  Accepted: 12 June 2021   Published: 12 July 2021

Journal Compilation © CSIRO 2021 Open Access CC BY-NC-ND

Abstract

Climate change is increasing the frequency of marine heatwaves around the world, causing widespread degradation of coral reefs. Endolithic microalgae inhabiting the coral skeleton have been highlighted as potentially important mediators of the consequences of heatwaves on coral reefs. These microalgae often bloom during heat stress due to greater light availability, theoretically delaying coral starvation by providing photoassimilates. However, these microalgae also dissolve coral skeletons at an accelerated rate during marine heatwaves, affecting the structural complexity of the reef. Despite their ecological role, no studies have examined endolithic algal blooms during a natural bleaching event. We quantified blooms of endolithic microalgae in the skeletons of lagoon corals bleaching on Heron Island in the austral summer of 2020. At the peak of heat stress, 20–30% of bleached corals across 9 genera at 3 sites had blooms. They were predominantly seen in branching Acropora spp. (37.8, 65.7 and 66.7% at three sites), which are primary reef builders at Heron Island. At the end of the bleaching event, the overall prevalence varied between 5 and 42%, and nearly all blooms were observed in acroporids. The relative high frequency of these blooms highlights the ongoing need to understand the role of these microbes during coral bleaching events.


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