Influences of Larval Settlement Location and Rate on Later Growth and Mortality in a Sessile Marine Invertebrate Population (Spirorbis spirillum)

Abstract

Planktonic larvae of the tube-buildlng polycheate Spirorbis spirillum (Linnaeus) settle abundantly along seagrass blades of Thalassia testudinum Banks ex Konig in bays of the northern Gulf of Mexico. Detailed demographic parameters of settled Individuals were measured in situ by using biological stains that mark the leading margin of tubes containing living S. spirillum and this method yielded similar results when compared with independent estimates of settlement rate, growth, and mortality. Larvae tended to settle near the base of growing seagrass blades and subsequent survivorship and tube growth were highest for Individuals nearest the base. Survivorship that is positively affected by settlement location and not negatively affected by the density of conspecifics suggests that temporal changes In settlement can have a significant Influence on benthic population size over time. This was supported by a positive correlation between population size and settlement and suggests that local extinction is potentially less likely to occur because planktonic larvae may be transported distances greater than the scale of ecological processes acting on the benthic stage.