Abstract. In recent years, the far northern and northern Great Barrier Reef suffered a category 5 tropical cyclone in 2014 (Ita), a category 4 tropical cyclone in 2015 (Nathan), and a significant coral bleaching event due to an underwater heatwave in 2016. Each of these events had severe implications for the health of coral reefs within the Great Barrier Reef Marine Park. Using novel developments in underwater imaging and machine learning for automated image processing, I will present a synoptic analysis of coral reef trajectories since 2012 and discuss the impacts of each disturbance and their combined effect on outer reef slope communities at ~10 m depth in the far northern and northern Great Barrier Reef. All surveys used imagery collected from a customised diver propelled vehicle and camera system, and the imagery was processed using convoluted neural networks (Deep Learning) for automated pattern recognition. Changes in coral cover and the abundance and composition of benthic organisms between 2012 and 2016 were evaluated to assess the extent of damage caused by tropical cyclones Ita (2014) and Nathan (2015), and the thermal induced coral bleaching event (2016), as well as to provide an indication of the cumulative impacts of both these recent stressors. In summary, coral cover on outer reef shelf communities at ~10 m depth declined between 2012 and 2016, with an average loss of coral cover ~25%. Losses in coral cover between 2012 and 2014 was localised in sites that were affected by tropical cyclone Ita. The highest and most widespread loss in coral cover occurred between 2014 and 2016, after the impact of tropical cyclone Nathan and the coral bleaching event (average 32% loss). In the majority of cases, the losses in coral cover were accompanied by increases in turf algal cover. Encrusting hard corals from the families Acroporidae and Poritidae showed the highest mortality, followed by massive colonies from the families Faviidae and Mussidae, and branching and tabular Acroporidae. This is consistent with published coral susceptibility to bleaching and robustness to cyclones. The 2016 coral bleaching was the most severe coral bleaching event recorded on the Great Barrier Reef to date and it had the greatest influence on the changes observed in the far northern and northern Great Barrier Reef between 2012 and 2016, when compared to the impacts of tropical cyclones Nathan and Ita alone. However, the most severe impacts on coral cover occurred when the effect of these disturbances was combined.
Biography. Manuel is a Post-Doctoral Fellow with the Global Change Institute at the University of Queensland. His current research focuses on harnessing on novel technologies to understand large-scale patterns and drivers of coral reefs benthic communities in different reefs around the world. A central theme of his work is the importance of spatial scale – in particular, accounting for spatial heterogeneity to generalise across broader scales. Over the past four years, Manuel has led the data collection and analysis of the XL Catlin Seaview Survey – Shallow Reef research – and a sister project, the Global Reef Record, dedicated to data storage and sharing.