Evidence for a positive relationship between juvenile abalone Haliotis midae and the sea urchin Parechinus angulosus in the South-Western Cape, SouthAfrica
E. Day et Gm. Branch, Evidence for a positive relationship between juvenile abalone Haliotis midae and the sea urchin Parechinus angulosus in the South-Western Cape, SouthAfrica, S AFR J MAR, 22, 2000, pp. 145-156
Citations number
46
Categorie Soggetti
Aquatic Sciences
Journal title
SOUTH AFRICAN JOURNAL OF MARINE SCIENCE-SUID-AFRIKAANSE TYDSKRIF VIR SEEWETENSKAP
Previous field observations have suggested an association between the urchi
n 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 Sou
th-western Cape, South Africa. These showed that both species occupy primar
ily hard substrate, showing preferences for encrusting coralline algae. The
y also confirmed a strong. positive relationship between urchins and juveni
le abalone. Of the juvenile abalone sampled, more than 98% were found benea
th sea urchins. All small(3-10 mm) and medium-sired (11-20 mm) juvenile aba
lone 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 t
hat urchins are of critical importance to the continued survival of viable
abalone populations. There has been a dramatic decrease in natural populati
ons of sea urchins over the past five years in the heart of the abalone fis
hing grounds, and the present findings suggest that this will lead to recru
itment failure of abalone. because juvenile abalone seem dependent on the u
rchins. The long-term consequences for the industry may be crucial.