Modelling the impacts of tropical cyclones on coral cover across the Great Barrier Reef

Tropical cyclones (TCs) are major acute stressors on coral reefs and significantly contribute to coral decline, with increasing frequency and intensity due to climate change posing further challenges for the Great Barrier Reef (GBR). This project models multiple TCs over the GBR to assess coral reef damage using bed shear stress (BSS) as a proxy and evaluates future impacts of sea level rise (SLR) through simulations based on IPCC AR6 SSP projections (SSP1-1.9 and SSP2-4.5). Using Thetis, a flow solver for simulating coastal flows, BSS impacts were analysed in tide-only and tide-and-wind (cyclonic) environments. Statistical analysis showed significant trends in algae (τ = 0.19, p < 0.001) and “Other” (e.g. sponges, tunicates and abiotics) (τ = -0.22, p < 0.001), with algae cover increasing as BSS intensified, while other benthic decreased, suggesting physical damage or dislodgement creates space for algal growth. No significant changes in hard or soft coral cover in response to BSS were found. Simulations altering bathymetry based on the SLR projections revealed that the response of BSS to SLR varies across reefs, with deeper reefs experiencing stronger cyclonic BSS than shallower ones due to differences in wave energy. Coral species also respond differently to hydrodynamic forces, indicating the importance of species-specific analysis. These findings highlight the difficulty of generalising results across the GBR due to variations in bathymetry, coral species, and environmental conditions. A reef-specific approach is necessary to accurately predict how individual reefs will respond to TCs and SLR in the future.