The intertidal frontlines: A comparison of the aggressive response in higher intertidal and lower intertidal clones of the anemone Anthopleura elegantissima

Abstract

Sessile animals of the intertidal contend with a different set of challenges based on the height at which they live in the intertidal. An abundant intertidal species of the Pacific Northwest is the sea anemone Anthopleura elegantissima. This species forms colonies of genetically identical individuals and has been shown to enact an aggressive response to nonclonemates using specialized battle tentacles known as acrorhagi. We sampled twenty clones from the lower intertidal and twenty from the higher intertidal and battled and analyzed their battles against a single opponent clone. Individual analyses of battle metrics showed no significant difference between the behavior of higher intertidal clones and lower intertidal clones. However, a holistic analysis that looked at the more aggressive respondent, on average, indicated lower intertidal clones were more aggressive. There were significantly more acrorhagi present in animals from the lower intertidal than those in the higher intertidal. We pose the questions of possible increased fighting efficiency in higher intertidal clones and potential phenotypic plasticity in the anemone that may enable any settling larva to adopt an appropriate level of energy allocation to aggressiveness in balance with the physical demands of the higher intertidal. We plan to continue developing aggression metrics and analyzing anemone behavior post-battle.