Fine-Scale Intertidal Distribution and Recruitment Patterns of the Gumboot ChitonCryptochiton stelleri(Polyplacophora: Mopaliidae)

Abstract

The gumboot chiton Cryptochiton stelleri Middendorff, 1847, is the largest intertidal invertebrate herbivore in the northeast Pacific, but little is known about the fine-scale distribution of this species within its range. In this study, extensive intertidal surveys were used to determine the distribution of C. stelleri within six rocky intertidal sites on the southern coast of Oregon, USA, and found that gumboot chitons show a patchy and clumped distribution. At all six sites, individuals were found at highest densities within small coves, and small specimens (< 15 cm long) were found almost exclusively in sea urchin pits. Age-frequency histograms were created for populations of C. stelleri at all six sites and showed sporadic cohort success, likely as a result of sporadic recruitment. Successful cohorts were indicated by peaks in the age-frequency histograms and were compared between sites in order to determine whether or not successful cohorts occurred at the same time at all sites. There was low similarity between sites, and a negative correlation was found between distance between sites and percent similarity in age-frequency peaks. Combined with other factors, this suggests that larval settlement and cohort success of C. stelleri is driven by local factors, not such large-scale factors as upwelling or El Niño.