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

The Jamaican gorgonians Pseudopterogcrgia 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 delineate the functional consequences of fexibility. Comparison of the drag forces exerted on flexible and arS~cially 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 deformatiori 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 c m . s !. 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 consequence of flexibility.