Aspects of Population Structure of Parechinus Angulosus Leske,Around the Cape Peninsula

Aspects of the community structure of Parechinus angulosus, a locally dominant echinoid, were studied in two inshore temperature environments on the Cape Peninsula for a year. Stratified, random transects of 10 stations were run seasonally across the aireas of maximum density at each locality and urchins were counted, measured and sexed. Percentage substrate cover was calculated, and variation in urchin size with distance from shore was investigated. Individual and combined effects of locality, season, distance (and depth) and sex were tested. Results indicate that urchins found at the cold- water locality, were on the average smaller, more numerous and included more size classes than the other. Urchin density did not vary with distance from shore at either locality, but was dependent on kelp, the occurrence of which is controlled by the nature of the substrate and by light penetration. A test of sex ratios was significant, males being more numerous. No seasonal effect on urchin distribution could be shown. There was no interaction of factors, except a small one between locality and season.