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Abstract
Foundation species such as trees, corals, kelp and seagrasses are found across multiple spatial scales (i.e., local to biogeographic scales) and provide many ecosystem services. Understanding species distributions across multiple spatial scales can inform species resilience and important spatial scales for restoration and management of threatened foundation species. However, only few studies have investigated their distribution patterns across all spatial scales they exist in. The Sydney Rock Oyster, Saccostrea glomerata, is a threatened, reef-building, intertidal foundation species that is found on the Australian south-eastern coast. Remnant reefs in different estuaries consist of patches of different shapes, size and distances (i.e., connectivity) from one another. In this thesis, I utilised this spatial variation to investigate how oyster population characteristics (e.g., body size and density), population processes (e.g., recruitment) and biodiversity provision by remnant S. glomerata reefs vary within patches (e.g., surface elevation), with patch-scale attributes (e.g., patch-area), among patches (e.g., distance between patches) and on a regional scale (i.e., among estuaries). My major finding was that variation at the largest scale (among estuaries) was the best predictor of body size and density of oysters, faunal communities and oyster recruitment. Although smaller scales (i.e., scales within estuary) relationships also occurred for all metrics, these were often in different directions (positive, negative or neutral) across estuaries. This suggests that larger scale processes are setting the context to smaller scale effects on metrics recorded. To investigate the effect of larger scale processes on oyster recruitment, I conducted a field experiment across six estuaries. The major finding was that oyster recruitment across these estuaries was negatively correlated to sedimentation loads in each estuary. In summary, my thesis highlights the need to understand ecological patterns of foundation species across multiple spatial scales and the influence of large-scale processes that may drive ecological patterns at smaller scales. From a restoration perspective, prioritising important spatial scales that maximise population characteristics and ecosystem functions, especially the recruitment of the target species can aid in efforts to promote long-term oyster reef sustainability, enhance restoration success and the services they provide.
