Life in the Supralittoral Fringe: Microhabitat Choice, Mobility and Growth in the Tropical Perwinkle Cenchritis (=Tectarius) muricatus (Linneaus, 1758)

The littorinid snail, Cenchritis muricatus, inhabits supralittoral vertical rocky walls along Caribbean shores, at times surpassing 14 meters above mean sea level. As the sole macrofaunal representative of this habitat, this marine gastropod presumably experiences extraordinary conditions of thermal load and desiccation. In order to understand the effect of behavioral choices on periwinkle survivorship and growth, snail distribution, microhabitat utilization, and crawling speed were documented in St John (US Virgin Islands). In general, snails rarely inhabited open surfaces; instead, periwinkles were commonly observed in microhabitats that may reduce water and heat stresses (e.g., > 75% in crevices and depressions). Snails found on occasional buttonwood trees (Conocarpus erectus) were larger than elsewhere. Although typically found in repose, C. muricatus crawling speed on moist, shaded, and smooth substrata averaged more than 3 cm.min- 1, but did not vary with slope. Repeated mark-recapture of tagged periwinkles exhibited high recovery rates (ca. 35% after 4 yr), absence of mortality, and a projected cessation of growth at 16.5 mm (shell height). Nearly 10% of marked individuals were recaptured every year. Dead, tagged snails were never noted; indeed, seven individuals were only recovered once, a full 4 yrs after release. Site-specific growth rates were absent. Projections using von Bertalanffy growth functions (VBGF) suggest that periwinkles will require 15+ years to achieve the maximum shell height. These VBGF models cannot address extraordinary individuals reaching 22 mm. C. muricatus's remarkable supralittoral distribution may be explained by physiological tolerance, selection of microhabitats, lack of predators and long lifespan.