Evidence for a positive relationship between juvenile abalone Haliotis midae and the Sea urchin Parechinus angulosus in the South-Western Cape, South Africa

Abstract

Previous field observations have suggested an association between the urchin Parechinus angulosus and juveniles of the abalone Haliotis midae. To test the generality and nature of this association, surveys were carried out at five sites between Cape Point and Danger Point in the kelp beds of the South-Western Cape, South Africa. These showed that both species occupy primarily hard substrata, showing preferences for encrusting coralline algae. They also confirmed a strong, positive relationship between urchins and juvenile abalone. Of the juvenile abalone sampled, more than 98% were found beneath sea urchins. All small (3–10 mm) and medium-sized(11–20 mm) juvenile abalone were under urchins, whether on flat or vertical reef, or in crevices. A small proportion (∼10%) of larger juveniles(21–35 mm) was not found under urchins, and in these instances they occupied crevices instead. These findings are of particular importance in terms of their implications for the lucrative commercial abalone fishery in South A...