Drag-induced deformation: a functional feeding strategy in two species of gorgonians

Abstract

The Jamaican gorgonians Pseudoptorogorgia acerosa (Pallas) and P. americana (Gmelin) exhibit whole colony flexibility in regions of moderate to high water movement. Juvenile colonies were tested under laboratory conditions to delinate the functional consequences of flexibility. Comparison of the drag forces exerted on flexible and artificially stiffened colonies in different flows to the forces required to detach colonies in the field suggested that the reduction in drag afforded by flexible colony deformation is not critical to preventing dislodgement. A further consequence of colony deformation was the reduction in the range of flow velocities encountered by the polyps relative to mainstream current velocity. Colonies appeared to feed most successfully when exposed to intermediate mainstream velocities of 10–15 cm·s −1. Therefore, the reduction of flow velocities at the level of the polyp broadens the range of ambient velocities over which successful feeding can occur, and as such, may be the most important consequences of flexibility.