Shifting baselines on the Great Barrier Reef: major changes in inshore coral communities since European settlement
Project Leader: Dr Jian-Xin Zhao, UQ
Using a novel uranium/thorium method that permits precise dating of the year of death from coral fragments, this study has shown for the first time that European modification of Queensland catchments corresponded with a shift in both the health and composition of inshore coral communities. The observed shift in community structure included the loss of previously dominant Acropora corals, and has been attributed to the synergistic impacts of increasing sediment runoff and climatic factors. Detailed results from over 40 sediment cores from Pandora and Havannah Reefs suggest that coral communities exist in stable states for extended periods (> 400 yrs) punctuated by periods of instability, and that once established, stable states persist for longer periods than unstable communities. Comparison of mortality frequency distribution patterns across sampling sites from the central and southern Great Barrier Reef shows that there have been three common recent peaks in inshore coral mortality (despite local variability), likely correlating with the early phase of European settlement (1850-1890) and warm phases of the Pacific Decadal Oscillation (1930-1940 and 1980-2000). If borne out by further sampling, this implies the presence of large-scale common stressors or more likely ‘triggers’ driving coral mortality in inshore reef areas since European settlement. In a classic local example of the globally-recognised shifting baselines phenomenon, these results clearly indicate that management of inshore coral reef communities should not aim to maintain present-day condition. While achievement of a pre-disturbance condition for these reefs is probably not a useful management objective either, managers can use these results to make more informed decisions about condition targets for the inshore Great Barrier Reef.
Honours Thesis by Jill K. Quaintance, The Centre for Marine Studies, The University of Queensland. The project received support from MTSRF Project 1.1.4.