Abundance, size and biomass of long-spined sea urchins (Centrostephanus rodgersii) and red sea urchins (Heliocidaris tuberculata) in New South Wales, Australia

Context Detailed demographic information for the commercially harvested long-spined sea urchins (Centrostephanus rodgersii) and red sea urchins (Heliocidaris tuberculata) on nearshore reefs of New South Wales is unavailable. Aims This is the first detailed study of abundances and sizes of these sea urchin species on shallow reefs of New South Wales where the fishery operates. Methods Divers counted sea urchins and measured their sizes in transects in the nearshore mosaic habitat and in extensive barrens habitat at 51 sites along ~800 km of coast. Key results Centrostephanus was found at most sites in both habitats, whereas Heliocidaris was found at lower densities and at fewer sites. Heliocidaris was rare in the far south and in barrens habitat. Centrostephanus was, on average, smaller in barrens habitat than in the nearshore mosaic habitat, and size structures shifted towards smaller individuals from north to south. Conclusions Centrostephanus occurred at higher densities than did Heliocidaris and had a broader distribution along the coast and across the nearshore reefs where the fishery operates. Implications This study provides a historical baseline for these commercially and ecologically important species. The small biomass of Heliocidaris (~3% that of Centrostephanus) and its restricted distribution suggest it is vulnerable to overfishing.