It is remarkable that although the importance of depth is firmly rooted in the discipline of marine ecology, so little is understood about depth-related patterns of invertebrates in kelp forests, particularly in temperate Australia. We tested for the existence of broad scale patterns in depth-related diversity and abundance of mobile invertebrates in kelp holdfasts (Ecklonia radiata) across several spatial scales along 500 km of coastline. There was a greater abundance and richness of common taxa in holdfasts from shallow relative to deep waters. Strikingly, a disproportionately large percentage (60%) of species was unique to holdfasts from shallow reefs, suggesting that shallow environments create conditions that facilitate a rich biodiversity of invertebrate fauna. We conclude that depth-related variation in kelp forests may not be completely idiosyncratic, and coherent research programs of a broader scale and scope may unify subsets of fragmented knowledge that previously provided little insight into general depth-related patterns of invertebrate assemblages.