Marine heatwave hotspots in coral reef environments: physical drivers, ecophysiological outcomes and impact upon structural complexity

Fordyce, Alexander J., Ainsworth, Tracy D., Heron, Scott F., and Leggat, William (2019) Marine heatwave hotspots in coral reef environments: physical drivers, ecophysiological outcomes and impact upon structural complexity. Frontiers in Marine Science, 6. 498.

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View at Publisher Website: https://doi.org/10.3389/fmars.2019.00498
 
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Abstract

A changing climate is driving increasingly common and prolonged marine heatwaves (MHWs) and these extreme events have now been widely documented to severely impact marine ecosystems globally. However MHWs have rarely recently been considered when examining temperature-induced degradation of coral reef ecosystems. Here we consider extreme, localised thermal anomalies, nested within broader increases in sea surface temperature, which fulfil the definitive criteria for MHWs. These acute and intense events, referred to here as MHW hotspots, are not always well represented in the current framework used to describe coral bleaching, but do have distinct ecological outcomes, including widespread bleaching and rapid mass mortality of putatively thermally tolerant coral species. The physical drivers of these localised hotspots are discussed here, and in doing so we present a comprehensive theoretical framework that links the biological responses of the coral photo-endosymbiotic organism to extreme thermal stress and ecological changes on reefs associated after MHW hotspots. We describe how the rapid onset of high temperatures drives immediate heat-stress induced cellular damage, overwhelming mechanisms that would otherwise mitigate the impact of gradually accumulated thermal stress. The warm environment, and increased light penetration of the coral skeleton due to the loss of coral tissues, coupled with coral tissue decay support rapid microbial growth in the skeletal microenvironment, resulting in the widely unrecognised consequence of rapid decay and degeneration of the coral skeletons. This accelerated degeneration of the coral skeletonson a reef scale hinder the recovery of coral populations and increase the likelihood of phase shifts towards algal dominance. We suggest that MHW hotspots, through driving rapid heat-induced mortality, compromise reefs' structural frameworks to the detriment of long term recovery. We propose that MHW hotspots be considered as a distinct class of thermal stress events in coral reefs, and that the current framework used to describe coral bleaching and mass mortality be expanded to include these. We urge further research into how coral mortality affects bioerosion by coral endoliths.

Item ID: 59757
Item Type: Article (Research - C1)
ISSN: 2296-7745
Keywords: bioerosion; coral bleaching; endolithic activity; marine heatwaves; mass mortality; microbioerosion; phase shift
Copyright Information: © 2019 Fordyce, Ainsworth, Heron and Leggat. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
Funders: Australian Research Council (ARC)
Projects and Grants: ARC Discovery grant DP180103199
Date Deposited: 26 Aug 2019 01:21
FoR Codes: 02 PHYSICAL SCIENCES > 0203 Classical Physics > 020399 Classical Physics not elsewhere classified @ 50%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060203 Ecological Physiology @ 50%
SEO Codes: 96 ENVIRONMENT > 9603 Climate and Climate Change > 960310 Global Effects of Climate Change and Variability (excl. Australia, New Zealand, Antarctica and the South Pacific) @ 50%
96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960507 Ecosystem Assessment and Management of Marine Environments @ 50%
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