ABSTRACT: Understanding linkages between pattern and process across scales is one of the major issues in contemporary ecology. The extent to which our perception of the importance of scale is contingent on the specific ecological variable examined is still unknown. We compared patterns in size, biomass, density and cover of the red alga Rissoella verruculosa over multiple spatial scales (from 10s of cm to 10s of km) in the north-west Mediterranean and used a transplant experiment to investigate the underlying causes of variation. All response variables exhibited similar patterns of local variation. These included spatial heterogeneity across the vertical gradient of the shore and alongshore variability at scales of 10s to 100s of m. In contrast, size, biomass and density of fronds, but not percentage cover, displayed significant large-scale variation. The reciprocal transplant experiment showed that the larger size attained by R. verruculosa at one location could be reversed when the alga was taken to another location about 70 km away, emphasizing large-scale differences in local processes rather than intrinsic differences between populations. It was found that morphological plasticity enabled this alga to display different patterns in size, biomass and density between locations. These results show that an analysis restricted to mean percentage cover would not have revealed the sensitivity of R. verruculosa to large-scale processes, emphasizing the advantages of simultaneously comparing variation in several attributes of populations to examine linkages between pattern and process across scales.