AGONISTIC BEHAVIOR IN THE INTERTIDAL SEA ANEMONEANTHOPLEURA XANTHOGRAMMICA

Abstract

The large intertidal sea anemone A. xanthogrammica (Brandt) forms aggregations of genetically distinct individuals at exposed sites along the west coast of North America. Individuals are often in close tentacle contact and remain that way for several years. This species displays the same agonistic behavior, inflation and application of acrorhagi, as does its smaller clone-forming congener A. elegantissima. The behavior is frequent and more common among large individuals than small ones. Field transplants show that non-neighbor anemones elicit the full acrorhagial response but that neighbors in close contact fail to behave agonistically towards each other. Microscopic examination of tissue samples revealed that conflicts between opposite sex anemones were as common as those between same sex anemones, and that neighbors found in close contact were also as likely to be the same sex as the opposite. Field anemone removal experiments in crowded pools and channels were used to compare subsequent movement of anemones released from crowding to movement of anemones never crowded, and of those continuously crowded. Newly released anemones do move away from their neighbors but generally do not move out of tentacle contact. These results support the hypothesis that the application of acrorhagi serves more of a communication function than one of severe intraspecific competition. An anemone that has been attacked receives information on the size and position of its neighbor, and can then move or not depending on available space. If movement is not possible, the agonistic behavior of its neighbor probably decreases or disappears altogether as a result of habituation.