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Spatial assemblage structure of shallow-water reef fish in Southwest Australia

Savita Goldsworthy*, Ben Saunders, Jack Parker, Euan Harvey

*Corresponding author:

ABSTRACT: Bioregional categorisation of the Australian marine environment is essential to conserve and manage entire ecosystems, including the biota and associated habitats. It is important that these regions are optimally positioned to effectively plan for the protection of distinct assemblages. Recent climatic variation and changes to the marine environment in Southwest Australia (SWA) have resulted in shifts in species ranges and changes to the composition of marine assemblages. The goal of this study was to determine if the current bioregionalisation of SWA accurately represents the present distribution of shallow-water reef fishes across 2000km of its subtropical and temperate coastline. Data was collected in 2015 using Diver Operated Underwater Stereo-Video surveys from seven regions between Port Gregory (north of Geraldton) to the east of Esperance. This study indicated that: (1) the shallow-water reef fish of SWA formed four distinct assemblages along the coast: one Midwestern, one Central and two Southern Assemblages; (2) differences between these fish assemblages were primarily driven by sea surface temperature (SST), Ecklonia radiata cover, non-Ecklonia radiata (canopy) cover, understorey algae cover, reef type, and reef height; and (3) each of the four assemblages were characterised by a high number of short range Australian and Western Australian endemic species. The findings from this study suggest that four, rather than the existing three bioregions would more effectively capture the shallow-water reef fish assemblage patterns, with boundaries having shifted southwards likely associated with ocean warming.