BEHAVIOR OF THE SEA PANSYRENILLA KOLLIKERIPFEFFER (COELENTERATA: PENNATULACEA) AND ITS INFLUENCE ON THE DISTRIBUTION AND BIOLOGICAL INTERACTIONS OF THE SPECIES

Abstract

Field and laboratory observations and experiments demonstrate that R. kollikeri has both morphological and behavioral adaptations to life in its turbulent subtidal, nearshore, sand-bottom habitat. Morphological adaptations include a horizontally expanded rachis which offers less resistance to water flow while not decreasing the size of its feeding surface, and a greatly expanded (relative to rachis height) peduncle for increased anchoring abilities. Behavioral adaptations include decreasing the curvature of the rachis and increasing peduncle length in response to increased water flow, the ability to dig itself out of deposits of sediment which bury the colony and which are characteristic of its habitat and a specific set of behavior patterns which quickly reestablish the colony on the bottom is it is uprooted from the substrate. Since the anchoring abilities of colonies decreases as the colonies become larger, small colonies inhabit the nearshore limit of the species'' distribution. The sea pansy''s morphology also influences its species-specific escape behavior from the predatory nudibranch, Armina californica. Instead of withdrawing into the substrate upon attack, Renilla positions itself so that it is uprooted from the substrate and tumbled away from the predator by prevailing water currents. The sea pansy defends itself from another predator Astropecten armatus with its expanded autozooids. Renilla appears to be restricted to preying upon immobile detrital or planktonic material. The utilization of unicellular algae is suggested.