Bioregional distributions and assemblage composition of fish populations with high endemism in south-western Australia: examining the range and scale of influence of physical and biological environmental factors

Aim This study combined large-scale fish abundance surveys with detailed habitat models that combine multibeam and towed video surveys to identify a constraining subset of environmental predictors that influence on patterns of... [ view full abstract ]

Aim This study combined large-scale fish abundance surveys with detailed habitat models that combine multibeam and towed video surveys to identify a constraining subset of environmental predictors that influence on patterns of bioregional fish distributions and assemblage composition. We used a range of contemporary habitat modelling and spatial analyses techniques to elicit these patterns.
Location South-west region of Western Australia
Methods The relative abundance of demersal fish along 1,600 km of continental shelf in Western Australia was analysed using a multivariate regression trees. Initially, 49 environmental variables were considered in the analyses. The key indicator species were identified and the spatial structure of the assemblage composition of the terminal leaves of the tree was then presented on a bioregional scale.
Results The final multivariate regression tree was constrained by six environmental factors of which occurrence of macroalgae was the most important. In addition, distance along shore, aspects of habitat availability and cover of biota were found to be important drivers of patterns in assemblage composition. Structurally complex habitats with vegetative cover were found to support higher endemic species richness, whereas sub-tropical reef habitats typically had high species richness, but low numbers of endemic species.
Main conclusions The relatively stable and biodiverse ecosystem of the south-western Australia may be under threat from predicted tropicalisation of this region, habitat loss and extreme climatic events as a result of global climate change. This may cause dramatic changes to fish assemblage composition and affect resilience to environmental and anthropogenic stresses for the local, endemic species reach, fish communities. The scale of influence of various environmental processes on the assemblage composition of marine species varied between tens of metres to hundreds of kilometres. Thus further emphasising the importance of understanding the scale of species-habitat relationships in order to successfully implement ecosystem-scale management efforts and protect vulnerable marine resources.