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Evidence for a positive relationship between juvenile abalone Haliotis midae and the sea urchin Parechinus angulosus in the South-Western Cape, South Africa
Day, E.; Branch, G.M. (2000). Evidence for a positive relationship between juvenile abalone Haliotis midae and the sea urchin Parechinus angulosus in the South-Western Cape, South Africa. S. Afr. J. Mar. Sci./S.-Afr. Tydskr. Seewet. 22: 145-156
In: South African Journal of Marine Science = Suid-Afrikaanse Tydskrif vir Seewetenskap. Marine & Coastal Management: Cape Town. ISSN 0257-7615, more
Peer reviewed article  

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Keyword
    Marine

Authors  Top 
  • Day, E.
  • Branch, G.M.

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 substrate, 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 (similar to 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 Africa, indicating that urchins are of critical importance to the continued survival of viable abalone populations. There has been a dramatic decrease in natural populations of sea urchins over the past five years in the heart of the abalone fishing grounds, and the present findings suggest that this will lead to recruitment failure of abalone, because juvenile abalone seem dependent on the urchins. The long-term consequences for the industry may be crucial.

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