El Niño-Southern Oscillation (ENSO) derived heatwaves can lead to coral mass bleaching events and death of bleaching-impacted corals. Therefore, the increasing number, duration and earlier annual onset of these events threaten tropical reef ecosystems and emphasise the necessity to investigate coral bleaching in detail. Studying past hyperthermal events is important to estimate the future capacity of tropical coral reefs to cope with marine heatwave-derived bleaching events. To shed light on how often coral mass bleaching has occurred over geological time, we need a robust proxy for bleaching events in the coral skeleton. To address this issue, we investigate geochemical signals in the skeleton of three massive corals (Porites sp.) from Lizard Island (Great Barrier Reef, Australia) in correlation with known bleaching events. The three coral skeleton samples, collected in August 2022, were scanned using micro-Computed Tomography (μ-CT), Laser Ablation-Inductively Coupled Mass Spectrometry (LA-ICPMS) and Confocal Raman Microscopy (CRM). Using the internal morphology and Li/Mg-thermometer results, an age model was generated and compared to years of known bleaching events. Preliminary data show a disagreement between the μ-CT and LA-ICPMS data. In addition, the well-established Sr/Ca thermometer shows a different cyclicity than the Li/Mg signal. The growth and calcification of stony corals are important for reef accretion dominating over its erosion. Different element-to-calcium ratios and derived annual growth rates will be discussed concerning the bleaching events and evaluated on their capability to be used as a proxy for historical mass bleaching events. The first results indicate a reduced apparent growth rate after years of coral mass bleaching events. Finally, the calcification of the three colonies before and after known mass bleaching events will be evaluated using the CRM-derived aragonite saturation state of the calcifying fluid (ΩAr).
Flöter, S., Pisapia, C., Basso, D., De Leau, E., Martinez-Colon, M., Stainbank, S., et al. (2024). Signature of bleaching events in coral skeleton - A case study for Porites from Lizard Island, Australia. In Bridging knowledge gaps between tropical, temperate, and cold-water coral reefs. Book of abstracts of the 2024 European Coral Reef Symposium. Città della Scienza & Stazione Zoologica Anton Dohrn, Naples, Italy, 2-5 July 2024.. Napoli.
Signature of bleaching events in coral skeleton - A case study for Porites from Lizard Island, Australia
Basso, D;
2024
Abstract
El Niño-Southern Oscillation (ENSO) derived heatwaves can lead to coral mass bleaching events and death of bleaching-impacted corals. Therefore, the increasing number, duration and earlier annual onset of these events threaten tropical reef ecosystems and emphasise the necessity to investigate coral bleaching in detail. Studying past hyperthermal events is important to estimate the future capacity of tropical coral reefs to cope with marine heatwave-derived bleaching events. To shed light on how often coral mass bleaching has occurred over geological time, we need a robust proxy for bleaching events in the coral skeleton. To address this issue, we investigate geochemical signals in the skeleton of three massive corals (Porites sp.) from Lizard Island (Great Barrier Reef, Australia) in correlation with known bleaching events. The three coral skeleton samples, collected in August 2022, were scanned using micro-Computed Tomography (μ-CT), Laser Ablation-Inductively Coupled Mass Spectrometry (LA-ICPMS) and Confocal Raman Microscopy (CRM). Using the internal morphology and Li/Mg-thermometer results, an age model was generated and compared to years of known bleaching events. Preliminary data show a disagreement between the μ-CT and LA-ICPMS data. In addition, the well-established Sr/Ca thermometer shows a different cyclicity than the Li/Mg signal. The growth and calcification of stony corals are important for reef accretion dominating over its erosion. Different element-to-calcium ratios and derived annual growth rates will be discussed concerning the bleaching events and evaluated on their capability to be used as a proxy for historical mass bleaching events. The first results indicate a reduced apparent growth rate after years of coral mass bleaching events. Finally, the calcification of the three colonies before and after known mass bleaching events will be evaluated using the CRM-derived aragonite saturation state of the calcifying fluid (ΩAr).
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