Meeting Abstract

P3.14  Monday, Jan. 6 15:30  The intertidal front lines: A comparison of the aggressive response in high and low intertidal clones of the anemone Anthopleura elegantissima LEVINE-WEINBERG, M.P.*; MERZ, R.A.; Swarthmore College; Swarthmore College mlevine1@swarthmore.edu

Sessile organisms must contend with different challenges depending on their vertical position in the rocky intertidal zone. Those individuals in the lower part of their species’ intertidal range typically experience greater predation and competition while their relatives in the higher intertidal are exposed to more frequent, extreme and longer lasting variation in physical factors. Anthopleura elegantissima are found from Baja California to Alaska and form intertidal, clonal colonies that make an aggressive response to nearby non-clonemates. We hypothesized that anemones living higher in the intertidal would have less energy to allocate towards aggression than those in the lower intertidal. We sampled clones from both the lower and higher intertidal at Cattle Point, San Juan Island, WA and, in the laboratory, pitted them in battles against individuals from a single clone from a rock ledge adjacent to the Friday Harbor Labs. Post-battle counts of acrorhagi (specialized battle tentacles), as well as time-lapse videos of the battles, were analyzed for metrics of aggression. There were significantly more acrorhagi in animals from the lower intertidal than those in the higher intertidal. No behavioral battle metric showed a significant difference between the higher intertidal and lower intertidal clones; however, in 11 of 13 metrics lower intertidal clones ranked as more aggressive. Based on the results of the individual analyses of metrics, higher intertidal animals seem to have an increased fighting efficiency, behaving as aggressively as lower intertidal animals, but with fewer acrorhagi. The rank analysis suggests that upper intertidal clones are more limited in their aggression.