Abstract
Limited information is available on the bleaching susceptibility of coral species that dominate high latitude reefs along the eastern seaboard of Australia. The main aims of this study were to: (i) monitor coral health and spatial patterns of coral bleaching response at the Solitary Islands Marine Park (SIMP) and Lord Howe Island Marine Park (LHIMP), to determine variability of bleaching susceptibility among coral taxa; (ii) predict coral bleaching thresholds at 30 °S and 31.5 °S, extrapolated from published bleaching threshold data; and (iii) propose a subtropical northern New South Wales coral bleaching model from biological and physical data. Between 2005 and 2007 minor bleaching was observed in dominant coral families including Pocilloporidae, Poritidae and Dendrophylliidae in the SIMP and Pocilloporidae, Poritidae and Acroporidae (Isopora and Montipora spp.) in the LHIMP, with a clear difference in bleaching susceptibility found between sites, both within and between locations. Bleaching susceptibility was highest in Porites spp. at the most offshore island site within the SIMP during summer 2005. Patterns of subtropical family bleaching susceptibility within the SIMP and LHIMP differed to those previously reported for the central Great Barrier Reef (GBR). These differences may be due to a number of factors, including temperature history and/or the coral hosts association with different zooxanthellae clades, which may have lower thermal tolerances. An analysis of published estimates of coral bleaching thresholds from the Caribbean, South Africa, GBR and central and northern Pacific regions suggests that the bleaching threshold at 30–31.5 °S ranges between 26.5–26.8 °C. This predicted threshold was confirmed by an extensive coral bleaching event on the world’s southernmost coral reef at Lord Howe Island, during the 2010 austral summer season. These results imply that dominant coral taxa at subtropical reefs along the eastern Australian seaboard are highly susceptible to thermal stress; which, in turn, could lead to a future decline in total live coral cover if predicted rising seawater temperatures lead to more frequent coral bleaching events in future.
Highlights
The recent increase in coral bleaching occurrence and severity has resulted in a substantial decline in live hard coral cover on many coral reefs throughout the world [1,2,3]
A severe coral bleaching event was reported throughout the southern Great Barrier Reef (GBR)
The high latitude bleaching model presented in this study predicts that at eastern Australian subtropical locations, some scleractinian coral genera from the families Acroporidae (e.g., Isopora and Montipora), Dendrophylliidae (e.g., Turbinaria), Pocilloporidae (e.g., Pocillopora and Stylophora) and Poritidae (e.g., Porites) will be more susceptible to thermal stress than coral genera from the families Faviidae (e.g., Goniastrea and Favites), Mussidae (e.g., Acanthastrea) and Siderastreidae (e.g., Psammocora)
Summary
The recent increase in coral bleaching occurrence and severity has resulted in a substantial decline in live hard coral cover on many coral reefs throughout the world [1,2,3]. The combined effect of increased seawater temperature coinciding with recent strong El Niño-Southern Oscillation (ENSO) events and periods of high light intensity has caused unprecedented bleaching episodes on a global scale. With seawater temperature predicted to rise, mass-bleaching events will continue, which may result in the loss of many ecologically and economically important habitats [2,18,19].
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