Kelp grazing by the common sea urchin Parechinus angulosus Leske in False Bay, Cape

Abstract

The effect of grazing by the common sea urchin on a local kelp bed was studied. The need for this investigation was felt in view of the importance of kelp beds to the near-shore ecosystem and reports describing the extent of damage to some Californian and eastern Canadian kelp beds by the grazing activity of certain urchin species. Experimental sites typical of the area were permanently marked. A study site was protected from urchins, while the control was not. Urchins were regularly removed from the study site. Kelps growing on the experimental plots were harvested seasonally, counted and their biomass calculated. Results over one year suggest that although the grazing potential of sea urchins is considerable, little impact was made on kelp beds in the study area. The grazing potential of Parechinus seems to be directed principally at the early sporophytes of Ecklonia maxima rather than at adult plants.