Diversity and depth-related patterns of mobile invertebrates associated with kelp forests

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.