Sea Urchin Recruitment: Effect of Substrate Selection on Juvenile Distribution

Intertidal field observations have shown that juvenile purple sea urchins Strongylocentwtus purpuratus are found in higher densities near adults . The same is true for subtidal populations of juvenile red sea urchins 5. franciscanus. These distribution patterns could be influenced by any of three elements: substrate selection, early juvenile mortality or juvenile migration. Using laboratory-reared larvae, we conducted experiments designed to gauge the effect of substrate selection on juvenile distributions of these two 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.