Relationships and interactions between temperate reef fish communities, physical habitat structure and marine protection.

Habitat heterogeneity and complexity are important factors responsible for structuring the associated faunal and algal compositions of temperate marine communities. Despite the efforts of traditional management approaches, the continued worldwide decline in commercial fisheries has led to a growing awareness and appreciation of ecosystem-based approaches as a potential means to sustainably managing and conserving the biodiversity of the World's oceans. Such an approach requires knowledge of the relevant environmental parameters, resources and habitats at multiple scales that are important in shaping the spatial distributions and abundances of marine communities. The magnitude of sampling effort required to sufficiently quantify marine biodiversity across whole ecosystems is generally prohibitive at broad management scales which has led to the need for more time and cost effective surrogate approaches utilising physical habitat data. Disentangling the separate importance of natural spatial and temporal habitat variability effects from those of spatial marine planning efforts is vital to ensuring successful management outcomes. To achieve this, scientists and managers first need to understand how specific aspects of the physical environment structure temperate reef-fish communities and at which scales they become relevant. The current availability of this information is limited across temperate marine environments of Southern Australia and Tasmania. This thesis investigates patterns in the community structure responses of temperate reef fish communities along the South Australian and Tasmanian coasts in response to aspects of their surrounding habitat structure. The first and second chapters of this thesis investigate how fish community structure varies in response to variability in the physical characteristics, heterogeneity and complexity of reef habitat; and how these responses in fish community assemblage structure vary with the spatial scale at which they are measured. Across large, inter-bioregional scales it is principally climatic and biogeographical differences between varying geographic positions which are important in structuring much of the temperate reef fish community structure around Australia, while at smaller, intra-bioregional and local scales, the importance of ecologically proximal physical variables, such as exposure, biogenic cover, refuge space and habitat substratum begin to come into effect suggesting an increasing importance of physical habitat heterogeneity and complexity towards finer ends of the scales investigated. The third chapter of this thesis investigates the potential of remotely sensed measures of habitat complexity (i.e. multibeam sonar derivative products) as surrogates to understanding how reef-fish community structure responds to the surrounding habitat. The bathymetry derived measures of habitat structure that were investigated were limited predictors of temperate reef fish community structure at fine resolutions with the most important variables identified being those acting as proxies of the predominant swell exposure. The final chapter attempts to disentangle the effects of natural community responses of reef-fish communities to their habitat structure from those related directly to marine protection. The results were largely uninformative but highlight the need for larger scale studies considering additional factors such as local anthropogenic pressure and recruitment variability in order to adequately apply this analysis approach across Tasmanian MPAs and maximise the ability to detect reserve effects. Overall, this thesis provides an improved understanding of the importance of physical structure in determining rocky reef marine assemblages and highlights some of the potential physical surrogate measures which should and should not be applied to predict spatial variability driven by such structure for use in all forms on marine spatial management.