Meeting Abstract

P2.135  Jan. 5  Interactions of ambient and feeding currents in the branchial crown of the “Christmas tree worm,” Spirobranchus giganteus WALDROP, L.D.*; KIER, W.M.; Univ. of California, Berkeley; Univ. of North Carolina, Chapel Hill lwaldrop@berkeley.edu

Active suspension feeders create their own feeding currents, but are also exposed to moving water in their environment. One such suspension feeder is the serpulid polychaete Spirobranchus giganteus, which is common on coral reefs. This �Christmas tree worm� is named for its branchial crown consisting of two lobes shaped like Christmas trees. Each lobe bears ciliated tentacles arranged in whorls around a central stalk like a spiral staircase. Cilia on the tentacles create feeding currents that draw water from the abfrontal (bottom) to frontal (top) surface of each whorl. In still water, the excurrent stream of filtered water from a proximal (lower) whorl becomes the incurrent flow of the whorl distal to it. Ambient water flow perpendicular to the crown can prevent such refiltration by maintaining a separation between the proximal whorl�s excurrent flow and the incurrent flow of its distal neighbor. In this study, we examined how ambient flow velocity affected the feeding currents of S. giganteus by videotaping the lobe configuration and the paths of dyed water through the branchial crowns of worms in a flume. For the upstream lobe perpendicular to the ambient current, complete separation of the excurrent and incurrent flow occurred at ambient water speeds between 3 and 5 cm/s. The upstream lobe became more compact and bent over in velocities greater than 5 cm/s, and it slowed the ambient current encountered by the trailing lobe, which achieved maximal separation of excurrent and incurrent flow at velocities between 5 and 13 cm/s. Thus, ambient flow reduced refiltration of water within the branchial crown of S. giganteus, but the velocity range in which this reduction occurred was different for the upstream and the downstream lobes as the crown was reconfigured by ambient water movement.