Abstract
In this study, we created a series of models that were designed to forecast the decadal percent chance that there would be a mass coral bleaching event in a given year, under a given Representative Concentration Pathway (RCP) emission scenario. All models shared the same general framework, but differed in key bleaching parameters such as bleaching threshold temperature and critical degree heating amount, given in Degree Heating Days (DHD). The first 3 models used experimentally determined parameters from Dr. Chris Langdon’s recent heat stress experiments that were performed on Acropora cervicornis. The experimentally derived parameters reflected what would be required to cause 10%, 50%, and 90% mortality of genotypes involved in the experiment. By creating models using each of these sets of bleaching thresholds and critical DHD’s, we were able to test the impact that genotypic thermal tolerance could have on a coral species’ future chances of survival against the looming threat of ocean warming. Results showed an overall decrease in decadal % chance of mass bleaching events as the thermal tolerance of the genotypes used in the model increased; this showed us that if corals continue to adapt to the warming climate, the more genetically fit genotypes will have far reduced chances of mass mortality events due to thermal stress through the end of the century. Additionally, we created 2 more models that used parameters recommended by NOAA’s Coral Reef Watch (CRW) program, which suggest a bleaching threshold of the area’s maximum monthly mean temperature (MMM) + 1°C and a critical degree heating amount of 4-6 °C-weeks. The results from the 2 models that used these suggested values were greatly different from the predictions based on experimental data, showing almost no percent chances in mass bleaching events through the end of the century. Comparing the results from these 2 models to the previous 3 showed us that in order to create accurate models to forecast mortality due to mass bleaching, the parameters used need to be experimentally determined in order to be as species specific as possible.