Date Thesis Awarded


Access Type

Honors Thesis -- Access Restricted On-Campus Only

Degree Name

Bachelors of Science (BS)




Jonathan Allen

Committee Members

Matthias Leu

Adam Potkay


Marine invertebrates typically exhibit biphasic life histories: larval development occurs in the plankton, while adults inhabit the benthos. The transition between these phases involves attachment to a substrate by a competent larva, metamorphosis, and survival as a benthic juvenile. The perimetamorphic period, which encompasses these events, is difficult to study in the field, and, as a result, perimetamorphic ecology is poorly understood. I performed laboratory experiments to assess the settlement preferences of the sea star Asterias forbesi and found that A. forbesi larvae exhibit substrate specificity in settlement. Shells of the blue mussel, Mytilus edulis, were most preferred, with coralline algae (Lithoamnion spp.) and Irish sea moss (Chondrus crispus) also inducing high levels of settlement. Little settlement occurred on biofouled rocks, and no settlement was observed when no cue was offered. Additionally, while larvae settled readily on shells of dead M. edulis, they avoided settling on live juvenile mussels, a known food source. Post-settlement survival and growth of A. forbesi in the presence of different numbers of juvenile mussels was also examined. Mean survival increased when more mussels were offered, possibly because the presence of an alternative food source reduced cannibalism among juveniles; however, differences among treatments were not statistically significant. The effects of within- and between-species relatedness on rates of predation among juveniles were also tested. Recently settled, relatively large A. forbesi were provided smaller juveniles of two types, distinguished by fluorochrome staining. In one set of experiments, focal A. forbesi selected between siblings and unrelated juveniles. In other trials, focal juveniles were offered unrelated juvenile conspecifics and juveniles of Asterias rubens. Rates of cannibalism were not affected by levels of intraspecific relatedness, but A. forbesi preferentially consumed A. rubens over conspecifics. Our results indicate that selective settlement may create high-density aggregation of juvenile sea stars in which cannibalism among juveniles may be a major source of mortality.

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