Date of Award

Spring 2014

Document Type

Restricted Thesis

Terms of Use

© 2014 Mark P. Levine-Weinberg. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts


Biology Department

First Advisor

Rachel Merz


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, the aggregating anemone, is found from Baja California to Alaska and forms intertidal, clonal colonies that respond aggressively to nearby nonclonemates. It was hypothesized that anemones living higher in the intertidal would have less energy to allocate towards aggression than those in the lower intertidal. Clones were sampled from both the low and high intertidal at Cattle Point, San Juan Island, WA and, in the laboratory, were pitted 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. A principal components analysis indicated that high intertidal clones tend to disengage from battle sooner and make less frequent tentacle contact with their opponents than low intertidal clones. There were significantly more acrorhagi per body mass in animals from the low intertidal compared with those from the high intertidal. As global temperatures continue to rise, A. elegantissima may be pressured to abandon aggressive behavior. Consequently, solitary, rather than clonal, forms of anemones may become favored in the intertidal.