Macrofaunal Assemblages in Boreholes of the Sea Urchin <i>Centrostephanus rodgersii</i> in Two Contrasting Rocky Reef Habitats

The long-spined sea urchin Centrostephanus rodgersii has space between the spines and the substratum, which creates a microhabitat for macroinvertebrates and some fishes. We sampled assemblages under sea urchins in self-excavated dwellings (boreholes) in macroalgal and urchin-grazed barrens habitats in rocky reefs in New South Wales, Australia, at sites spanning 400 km. A rich fauna of 80 nominal taxa was recorded, with 1–24 taxa and 1–963 individuals recorded under individual urchins. The fauna was dominated by gastropods (39 taxa), malacostracans (13 taxa), and chitons (8 taxa). Significant differences in associated fauna were observed between the two habitats at two of the four study locations and at one-third of all sites sampled. While the abundance of some groups differed significantly between the two habitats, taxonomic richness and total abundance of animals did not. Temporal variability in macroalgal habitat was noted in assemblages, as well as the abundance of several taxa, at the two sites that were sampled over three times. Our findings point to the importance of long-spined and bioeroding diadematid sea urchins as biogenic habitat to support biodiversity and the implications of their removal.