Population Structure, Recruitment and Mortality of Two Sea Urchins (Strongylocentrotus franciscanus and S. purpuratus) in a Kelp Forest
1981; Inter-Research; Volume: 5; Linguagem: Inglês
10.3354/meps005255
ISSN1616-1599
Autores Tópico(s)Coastal wetland ecosystem dynamics
ResumoThe red sea urchin Strongylocentrotus franciscanus and the purple sea urchin S. purpuratus are important members of southern California kelp bed communities.We investigated their population structures in terms of patterns of recruitment and mortality at 3 sites in the Point Loma kelp forest near San Diego, California, USA.Recruitment was annual and substantial at all sites.Several predators consume adult S. purpuratus but only the spiny lobster Panulirus interruptus and the California sheephead fish Semicossyphus pulcher (a large labrld) prey on large S. franciscanus.Urchin test collections, small scale urchin distribution patterns and grazing mortahty of the giant kelp Macrocystis pyrifera suggest that lobsters and sheephead, both of which are harvested, control urchin populations.In the presence of these predators, the size-frequency distributions of S. franciscanus populations are bimodal, apparently because juveniles (up to 40 mm) are protected by the spine canopies of adults, urchins of intermediate size (50-80 mm) are very vulnerable to predators and large adults (> 90 mm) attain a partial refuge in size.The population structure of S. purpuratus is unimodal, evidently because this species is less dependent on the spine canopy association and its short spines and smaller adult test dimensions do not allow it a refuge in size from predation.
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