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Published August 31, 2019 | Version 1
Journal article Open

Refugia under threat - mass bleaching of coral assemblages in high-latitude eastern Australia

Authors/Creators

  • 1. 1Australian Research Council Centre of Excellence for Coral Reef Studies, School of Biological Sciences, The University of Queensland, St. Lucia, QLD 4067, Australia
  • 2. School of Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, U.K.
  • 3. Fisheries Research, New South Wales Department of Primary Industries, Coffs Harbour, NSW 2450, Australia
  • 4. School of Life and Environmental Sciences, The University of Sydney, Sydney, NSW 2006, Australia
  • 5. Solitary Islands Underwater Research Group, Coffs Harbour, NSW 2450, Australia
  • 6. 2School of Life and Environmental Sciences, The University of Sydney, Sydney, NSW 2006, Australia
  • 7. National Marine Science Centre, Southern Cross University, Coffs Harbour, NSW 2450, Australia
  • 8. Marine Geophysical Laboratory, Physics Department, College of Science and Engineering, James Cook University, Townsville, QLD 4814, Australia
  • 9. Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia
  • 10. Anatomy and Histology, Bosch Institute, F13, The University of Sydney, Sydney, NSW 2006, Australia
  • 11. Coral Reef Watch, U.S. National Oceanic and Atmospheric Administration, College Park, MD 20740, U.S.A.
  • 12. School of Life Sciences, University of Technology Sydney, PO Box 123, Broadway, NSW, 2007, Australia

Description

Environmental anomalies that trigger negative physiological responses and mortality are occurring with increasing frequency due to climate change. At species’ range peripheries, environmental anomalies are particularly concerning because species often exist at their environmental tolerance limits and may not be able to migrate to escape unfavourable conditions. Here, we investigated the bleaching response and mortality of 14 coral genera across high-latitude eastern Australia during a global heat stress event in 2016. We evaluated whether the severity of assemblage-scale and genus-level bleaching responses was associated with cumulative heat stress and/or local environmental history, including long-term mean temperatures during the hottest month of each year (SSTLTMAX), and annual fluctuations in water temperature (SSTVAR) and solar irradiance (PARZVAR). The most severely-bleached genera included species that were either endemic to the region (Pocillopora aliciae) or rare in the tropics (e.g. Porites heronensis). Pocillopora spp., in particular, showed high rates of immediate mortality. Bleaching severity of Pocillopora was high where SSTLTMAX was low or PARZVAR was high, whereas bleaching severity of Porites was directly associated with cumulative heat stress. While many tropical Acropora species are extremely vulnerable to bleaching, the Acropora species common at high latitudes, such as A. glauca and A. solitaryensis, showed little incidence of bleaching and immediate mortality. Two other regionally-abundant genera, Goniastrea and Turbinaria, were also largely unaffected by the thermal anomaly. The severity of assemblage-scale bleaching responses was poorly explained by the environmental parameters we examined. Instead, the severity of assemblage-scale bleaching was associated with local differences in species abundance and taxon-specific bleaching responses. The marked taxonomic disparity in bleaching severity, coupled with high mortality of high-latitude endemics, point to climate-driven simplification of assemblage structures and progressive homogenisation of reef functions at these high-latitude locations.

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Additional details

Funding

European Commission
TRIM - Vulnerable trait-combinations in corals and fishes and their management 747102