In situ stalk growth rates in tropical western Atlantic sea lilies (Echinodermata : Crinoidea)

Despite their greater familiarity as fossils, stalked crinoids, or sea lilies, remain important components of hard-substrate assemblages at bathyal depths in both tropical western Atlantic and Pacific regions. To determine stalk growth rates, specimens collected along the western margin of Little Bahama Bank using the submersibles Johnson Sea Link I and II were measured, tagged with color-coded cable ties, returned to the sea floor either to the site at which they were collected or to different habitats or depths, and recovered several months to over a year later. This paper examines stalk growth rates in Neocrinus decorus, Cenocrinus asterius, and the subspecies of Endoxocrinus parrae (E. parrae parrae, E. parrae prionodes and E parrae carolinae) and their variations relative to depth and current flow. Studies were carried out at three different depth sites: 249 in, 372-435 in and 540-576 m. N. decorus produces substantially more stalk per year than any subspecies of E. parrae or C asterius (10-17 cm y(-1) versus no more than 3.6 cm y(-1)) but contributes no more than twice as much skeletal volume to the sediment because of its more slender stalk. To examine environmental control of growth, E. parrae parrae was transplanted beyond its local depth range to the habitat at which deeper-dwelling E. parrae prionodes occurs (572 m). E. parrae parrae grew at 0.6 +/- 0.4 cm y(-1) (n = 6) here, significantly more slowly than in 404 in and more slowly than E. parrae prionodes (2.1 +/- 0.6 cm y(-1); n=4), supporting the hypothesis that these two morphs exhibit distinct growth strategies. Growth rates for E. parrae parrae and N. decorus do not differ significantly between adjacent high and lower current-velocity habitats at the same depth, although both exhibit significantly shorter stalk lengths and crown elevations on raised topography apparently subject to stronger flow. (c) 2007 Elsevier B.V. All rights reserved.