A comparison of sea urchin recruitment at sites on the Atlantic and Pacific coasts of North America

A technique was developed for sampling post-metamorphic sea urchins (<1mm test diameter) and other motile fauna from discrete substrates and utilized to look at temporal and spatial patterns of recruitment. Studies were conducted at sites along the coast of New Hampshire in the Gulf of Maine and in the Santa Barbara Channel off of Southern California. In the Gulf of Maine, Strongylocentrotus droebachiensis recruitment was limited to heavy settlement (up to 1 urchin/cm2) in June, decreasing quickly until no further settlement was observed after the middle of July. Settlement appeared to be random and recruitment was enhanced by prior removal of all motile fauna from substrates. There were no differences in settlement on rocks taken from a kelp bed, a newly established urchin ground and one five years old. Follow up studies showed that survival of urchins was patchy, indicating that populations of S. droebachiensis in the Gulf of Maine are the result of differential survival and not selective settlement. Similar studies conducted at sites in the Santa Barbara Channel indicated that settlement of S. purpuratus occurred over a number of months and in much lower densities. Again, urchin populattons appeared to be the result of differential survival.