CHANGES IN SUBTIDAL HABITAT FOLLOWING MASS MORTALITY OF SEA-URCHINS IN BOTANY-BAY, NEW-SOUTH-WALES

On two occasions, between June and October 1986 and April/May 1988, mass mortality of the sea urchin Centrostephanus rodgersii occurred at Bare Island in Botany Bay, New South Wales. Following the widespread disappearance of C. rodgersii in August 1986, the abundance of filamentous and foliose algae increased and crustose corallines declined. There was also a large, but shortlived, increase in the density of limpets, particularly Patelloida alticostata, which then fell to nearly zero after 15 months. In October 1986, the habitat found at other sites in Botany Bay was consistent with a recent disappearance of C. rodgersii. At all sites a complex assemblage of non-crustose algae developed, the species composition of which differed among sites. A large recruitment of C. rodgersii was observed at all affected sites in February 1987 and January 1988. These individuals grew quickly and reached a mean size of approximately 35 mm test diameter at the end of their first year.