Variation in abundances of herbivorous invertebrates in temperate subtidal rocky reef habitats

Abstract

The present study assessed variation in the abundances of large herbivorous invertebrates in south-western Australia. There was some habitat partitioning between different parts of the reef: of the most frequently recorded species, the sea urchins Phyllacanthus irregularis and Centrostephanus tenuispinus were found primarily at the base of steep rock faces, whereas the gastropods Turbo torquatus and Australium squamifera were found primarily on open sections of reef. The sea urchin Heliocidaris erythrogramma was evenly distributed between these two habitats. For C. tenuispinus and H. erythrogramma, differences among locations (separated by tens to hundreds of kilometers) were the main source of variation in abundances. Phyllacanthus irregularis was more evenly distributed among locations. Abundances of sea urchins at each reef varied little over 26 months, suggesting low mortality and low recruitment. Turbo torquatus and A. squamifera varied significantly in abundance among reefs separated by < 10 km, although these differences were influenced by fluctuations over time. Broad patterns in abundances were evident: overall, abundances of herbivorous invertebrates were low, but certain areas supported high abundances. This suggests that herbivory may be a minor process in this region; however, the importance of herbivory at reefs with and without high abundances of herbivores deserves further attention.