ISOLATING SETTLEMENT FROM RECRUITMENT OF SEA-URCHINS

Recruitment of benthic marine invertebrates with planktonic larvae is composed of three components: larval supply; settlement and metamorphosis of larvae; and survival and growth in the benthic environment. We offer a technique that isolates settlement from the other processes for the sea urchin Strongylocentrotus. Settlement samplers constructed of common and inexpensive materials were deployed in a central California kelp forest for 1 yr and sampled monthly. The samples effectively induced larval sea urchins Strongylocentrotus purpuratus (Stimpson) to settle both in the laboratory and in the field. Other invertebrates occurred in the samplers as both adults and juveniles, and predation on settled sea urchins in the samplers probably influenced the results. We suggest that long-term use of settlement samplers will contribute to a better understanding of the population dynamics of sea urchins and other benthic invertebrates with planktonic larvae.