Date of Award

Summer 2008

Document Type

Restricted Thesis

Terms of Use

© 2008 Bradley Dickerson. 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


Marine invertebrates undergo several key developmental transitions during the settlement period, moving from the larval to the adult body plan and from planktonic to benthic life. Before larvae are able to metamorphose, they reach competence, the ability to respond to an environmental trigger and change into settled juveniles upon exposure to cues. Some larvae can delay metamorphosis if the conditions are not yet favorable; this delay may invoke some cost to the organism later in life. In this study, we assessed the consequences of delay of metamorphosis for morphology, settlement timing and survival in two solitary ascidians, the phlebobranch Corella inflata and the stolidobranch species Boltenia villosa. Photographic evidence indicates that B. villosa larvae that experience a delay of metamorphosis show test cell migration and ballooning of the tunic, while no such changes are seen for C. inflata. We found that delaying metamorphosis nearly quadruples the rate of settlement of B. villosa larvae. Delay of metamorphosis did not significantly decrease survival in the field for either species, contrary to previous studies using non-feeding larvae.