Patterns of benthic community structure are driven by a range of biological and physical processes that act over multiple spatial and temporal scales. Settlement panels were deployed in relatively 'pristine' subtidal habitats off southwest Australia to examine spatial variability in assemblage structure at multiple spatial scales, from cm to 100s of km. Panel assemblages were harvested after 3, 9 and 14 mo of maturation to test the following hypotheses: (1) that the magnitude of variability at large spatial scales increases with assemblage development time, (2) that variability at the smallest spatial scales is consistently high regardless of assemblage development time, and (3) that patterns of spatio-temporal variability differ between taxa. No clear trends in the magnitude of variability at each spatial scale examined, in relation to assemblage development time, were recorded. Sessile assemblages were highly variable at all spatial scales examined, and variability at the smallest-spatial scale (cms) was consistently high. As predicted, the magnitude of variability at the largest spatial scales (i.e. between locations 100s of km apart) was lowest for immature assemblages, but overall patterns of large-scale variability did not alter predictably with maturation time. Subtidal sessile assemblages in southwest Australia, like elsewhere, are structured by a complex, interacting suite of biological and physical processes that vary in their relative importance throughout assemblage maturation. As such, understanding variability patterns is challenging and requires greater appreciation of variability in physical processes across multiple spatial and temporal scales and improved knowledge of the life histories and population structures of key taxa. © Inter-Research 2013.