Associations and abundance of sea urchins and abalone on shallow subtidal reefs in southern New South Wales

Abstract

The densities of the abalone Haliotis rubra and the sea urchin Centrostephanus rodgersii were estimated at five localities on the southern coast of New South Wales. Abalone were most abundant at localities south of Eden but were patchy at all localities and sites. There was no clear pattern in the abundance of C. rodgersii among localities but there was considerable variation among sites within localities. Densities of abalone and sea urchins were negatively associated within 10-m² transects at 20% of sites. At the smallest nearest-neighbour scale, the two species were segregated. The population structures of abalone differed considerably among sites; some populations consisted of single size cohorts, whereas others were much more complex. Abalone large enough to be collected legally were rare at all localities and comprised less than 10% of the total population. Possible reasons for the negative associations between H. rubra and C. rodgersii are discussed.