An empirical evaluation of the relationship between coral reef calcium carbonate production and wave energy using geospatial techniques at Lizard Island, Great Barrier Reef, Australia

Coral reefs are complex, dynamic ecosystems occurring over a range of spatial and temporal scales. They provide a range of goods and services to mankind, including shoreline protection and support a large portion of marine life. The value of coral reefs exemplifies the need to empirically evaluate the complex interactions operating on them to efficiently manage these systems in light of anthropogenic induced climate change. This study was on Lizard Island’s coral reef system, situated within the northern lagoon of the Great Barrier Reef, Australia. Carbonate production is an important process, which underpins reef development and island security. Wave energy is one of the most important physical processes influencing coral reef carbonate production by flushing nutrients around the system, and removing metabolic waste. Other important functions include mechanically breaking down and transporting calcium carbonate. The empirical relationship between carbonate production and wave energy has not been addressed in the current literature and warrants a comprehensive investigation. The aim of this thesis was to employ a unique geospatial approach to combine in situ field observations, remote sensing and modelling techniques to develop a spatially continuous distribution model of coral reef calcium carbonate production and to empirically evaluate its relationship against a spatially continuous model of wave energy. Census-based methods and video samples were used to quantify carbonate production using published carbonate production rates of various benthic organisms. Individual benthic models of carbonate producing components included live coral, carbonate sand, green calcareous macroalgae and encrusting calcified algae. Regression analysis used surrogates derived from a digital elevation model of the seafloor and satellite imagery from Worldview-2 to predict the distribution of each component. The spatially continuous carbonate production model was the combined result of each benthic component layer, using their respective carbonate production rates as a weight. Comparing carbonate production and wave energy datasets was performed using global techniques and a series of transects, traversing across the entire reef platform. Results suggest that carbonate production increases with wave energy. However, transect comparisons suggest that a threshold of carbonate production occurs when wave energy exceeds 300 J/m2. These empirical results further the scientific understanding of coral reef ecosystems and can be incorporated into environmental models to predict the impacts of increased wave energy on reef and island development due to rapid climate change