Range expansion of the sea urchin Centrostephanus rodgersii leads to loss of taxonomic diversity in a kelp bed habitat, eastern Tasmania

The long spined sea urchin Centrostephanus rodgersii (Diadematidae) has recently undergone poleward range expansion to eastern Tasmania (southeast Australia). This species is associated with barrens habitat which has been grazed free of macroalgae, and therefore has potentially important consequences for reef structure and biodiversity. This study used urchin removal experiments from barrens patches in eastern Tasmania to monitor the subsequent response of the macroalgae relative to unmanipulated barrens patches. In removal patches, there was a rapid proliferation of canopy-forming macroalgae (Ecklonia radiata and Phyllospora comosa), and within 24 months the algae community structure had converged with that of nearby areas without urchins. Faunal species richness was comparatively low in barrens habitat, with C. rodgersii grazing activity resulting in an estimated minimum net loss of approximately 150 taxa compared with intact macroalgal habitats.