Sea Urchin Recruitment: Effect of Substrate Selection on Juvenile Distribution

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Abstract
Intertidal field observations have shown that juvenile purple sea urchins Strongylocentrotus purpuratus are found in higher densities near adults. The same is true for subtidal populations of juvenile red sea urchins S. franciscanus. These distribution patterns could be influenced by any of 3 elements: substrate selection, early juvenile mortality or juvenile migration. Using laboratory-reared larvae, experiments were designed to gauge the effect of substrate selection on juvenile distributions of these 2 sea urchin species. In both laboratory and field experiments, larval sea urchins showed no enhanced settlement in the presence of adults or adult-associated substrates. These results imply that early juvenile mortality or migration provide the greater influence on juvenile distributions.