Abstract The biogenic structure of foundation species provides critical habitat for coastal marine taxa. In temperate ecosystems, forests of large, canopy‐forming macroalgae ( Macrocystis pyrifera , Nereocystis luetkeana ) support rich communities of fishes and macroinvertebrates. However, it is unclear how the biological assemblages of kelp forests vary with respect to the dominant canopy‐forming species, structural attributes of the kelp forest (e.g., stipe density, frond length, forest biomass, forest area), and ambient environmental conditions. To identify the main influences on the composition of kelp‐associated assemblages, we surveyed 21 kelp forests across an island archipelago in British Columbia. We found that the composition of fish and macroinvertebrate assemblages varied significantly with canopy kelp species. The assemblages of macroinvertebrates were significantly influenced by kelp species, frond length, and forest biomass, as well as some abiotic attributes (i.e., depth, hard substrate). In contrast, the pelagic–demersal and benthic fish assemblages were associated with single attributes of kelp forest structure (i.e., frond length and canopy kelp species, respectively). Our findings indicate that the biological assemblages that are associated with kelp forests, especially macroinvertebrates, may be closely tied to structural features of the canopy. By identifying the distinct assemblages fostered by kelp forests of different canopy species and structure, we can better interpret the response of marine communities to changes in coastal habitat.