Goyen, S, Camp, EF, Fujise, L, Lloyd, A, Nitschke, MR, LaJeunensse, T, Kahlke, T, Ralph, PJ & Suggett, D 2019, 'Mass coral bleaching of P. versipora in Sydney Harbour driven by the 2015–2016 heatwave', Coral Reefs, vol. 38, no. 4, pp. 815-830.View/Download from: UTS OPUS or Publisher's site
© 2019, Springer-Verlag GmbH Germany, part of Springer Nature. High-latitude coral communities are distinct from their tropical counterparts, and how they respond to recent heat wave events that have decimated tropical reefs remains unknown. In Australia, the 2016 El Niño resulted in the largest global mass coral bleaching event to date, reaching as far south as Sydney Harbour (~ 34°S). Coral bleaching was observed for the first time (affecting ca., 60% of all corals) as sea surface temperatures in Sydney Harbour remained > 2 °C above the long-term mean summer maxima, enabling us to examine whether high-latitude corals bleached in a manner described for tropical corals. Responses of the geographically cosmopolitan Plesiastrea versipora and southerly restricted Coscinaraea mcneilli were contrasted across two harbour sites, both in situ and among samples-maintained ex situ in aquaria continually supplied with Sydney Harbour seawater. While both coral taxa hosted the same species of microalgal endosymbiont (Breviolum spp; formerly clade B), only P. versipora bleached both in situ and ex situ via pronounced losses of endosymbiont cells. Both species displayed very different metabolic responses (growth, photosynthesis, respiration and calcification) and bleaching susceptibilities under elevated temperatures. Bacterial microbiome profiling, however, revealed a convergence of bacterial community composition across coral species throughout the bleaching. Corals species found in temperate regions, including the generalist P. versipora, will therefore likely be highly susceptible to future change as heat waves grow in frequency and severity unless their thermal thresholds increase. Our observations provide further evidence that high-latitude systems are susceptible to community reorganisation under climate change.
Fujise, L, Nitschke, MR, Frommlet, JC, Serôdio, J, Woodcock, S, Ralph, PJ & Suggett, DJ 2018, 'Cell Cycle Dynamics of Cultured Coral Endosymbiotic Microalgae (Symbiodinium) Across Different Types (Species) Under Alternate Light and Temperature Conditions', Journal of Eukaryotic Microbiology, vol. 65, pp. 505-517.View/Download from: UTS OPUS or Publisher's site
Nitschke, MR, Gardner, SG, Goyen, S, Fujise, L, Camp, EF, Ralph, PJ & Suggett, DJ 2018, 'Utility of photochemical traits as diagnostics of thermal tolerance amongst great barrier reef corals', Frontiers in Marine Science, vol. 5, no. FEB.View/Download from: UTS OPUS or Publisher's site
© 2018 Nitschke, Gardner, Goyen, Fujise, Camp, Ralph and Suggett. Light availability is considered a key factor regulating the thermal sensitivity of reef building corals, where excessive excitation of photosystem II (PSII) further exacerbates pressure on photochemical pathways already compromised by heat stress. Coral symbionts acclimate to changes in light availability (photoacclimation) by continually fine-tuning the photochemical operating efficiency of PSII. However, how this process adjusts throughout the warmest months in naturally heat-tolerant or sensitive species is unknown, and whether this influences the capacity to tolerate transient heat stress is untested. We therefore examined the PSII photophysiology of 10 coral species (with known thermal tolerances) from shallow reef environments at Heron Island (Great Barrier Reef, Australia), in spring (October-November, 2015) vs. summer (February-March, 2016). Corals were maintained in flow-through aquaria and rapid light curve (RLC) protocols using pulse amplitude modulated (PAM) fluorometry captured changes in the PSII photoacclimation strategy, characterized as the minimum saturating irradiance (Ek), and the extent of photochemical ([1-C], operating efficiency) vs. non-photochemical ([1-Q]) energy dissipation. Values of Ekacross species were > 2-fold higher in all coral species in spring, consistent with a climate of higher overall light exposure (i.e., higher PAR from lower cloud cover, rainfall and wind speed) compared with summer. Summer decreases in Ekwere combined with a shift toward preferential photochemical quenching in all species. All coral species were subsequently subjected to thermal stress assays. An equivalent temperature-ramping profile of 1°C increase per day and then maintenance at 32°C was applied in each season. Despite the significant seasonal photoacclimation, the species hierarchy of thermal tolerance [maximum quantum yields of PSII (Fv/Fm), monitored at dawn and dusk] did not shift...