The sea star Asterina pectinifera causes deep-layer sloughing in Lithophyllum yessoense (Corallinales, Rhodophyta)

Deep-layer sloughing is a recently described mode of surface shedding in so me encrusting coralline algae. Several causative agents or ecological roles have been suggested for its occurrence, but none have been proven. During ecological studies of urchin-dominated barren grounds in southwestern Hokka ido, the dominant encrusting coralline species, Lithophyllum yessoense, was found to be sloughing beneath the sea star, Asterina pectinifera, in shall ow waters. The sea stars often stayed long in one position and left body-sh aped white scars on the encrusting thalli. Anatomical studies of the scars revealed that a deep layer, well below the vegetative initials and the bott om of submerged conceptacles, was being shed. The upper layer of living col umnar cells in the medulla became new vegetative initials, producing new ep ithallial layers above them. Deep-layer sloughing also occurred on the thal li in running-water aquarium experiments, when thalli were exposed to the s ea stars. Although the thalli were heavily covered with small epiphytic alg ae, clean surfaces were found just below the flakes of the sloughed layer. This mode of surface shedding may play an important role in recovery from d amage on barren grounds where bottom feeders are abundant.