Growth and size-structure of stegophiura sp. (Echinodermata: Ophiuroidea) on the continental slope off central Chile: A comparison between cold seep and non-seep sites

The growth and size-structure of the bathyal ophiuroid brittle star, Stegophiura sp., were analysed from skeletal growth bands and disc diameter frequencies. Specimens were collected in trawl samples taken on the continental slope off central Chile (̃36S) at two sites within the recently discovered Concepcin Methane Seep Area (CMSA) and at two control non-seep sites. Growth bands were measured as radii of vertebral ossicles from scanning electron microscope (SEM) micrographs and used to provide size-at-age data. The von Bertalanffy and the Gompertz growth models provided good fit to size-at-age data. The size-structure distributions observed in the study area suggest that small-bodied (<10mm disc diameter) individuals of Stegophiura sp. are more abundant near seep sites, probably attracted there by the presence of methane-derived authigenic carbonates, which provide a preferred habitat for ophiuroids and benthic fauna in general. Furthermore, size-at-age data from measurements of the ossicle growth bands indicate relatively rapid growth of Stegophiura sp. populations at seep sites. Assuming that the growth rings are annual, the maximum Stegophiura sp. age was estimated to be 15 years. The growth performance of this species falls within the range of values reported for sub-Antarctic and bathyal species.