Date of Award


Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy (PhD)


Marine Sciences and Technology

First Advisor

Helen Poynton

Second Advisor

William Robinson

Third Advisor

Jarrett Byrnes


Colonial ascidians are a group of prolific marine invaders found in urban biofouling communities. Despite often high levels of copper pollution in these areas, many species of ascidians thrive in these conditions, while many native species suffer. The role of pollution tolerance in establishment success is often overlooked, and therefore the strategies employed by invaders are poorly understood. The purpose of this dissertation was to provide insight into the mechanisms responsible for invader success. The Invader Tolerance Model (ITM) was developed herein to conceptualize how marine pollution facilitates the establishment and spread of invasive ascidians and identify crucial data gaps to be experimentally tested. The acute and chronic copper toxicity of Botrylloides violaceus, a prominent invader in the Gulf of Maine, and a native counterpart, Aplidium glabrum was first explored to establish relative sensitivities to copper. Then, both species were exposed to sublethal copper concentrations in the presence and absence of interspecific competition to determine if an interaction between these two factors exists. Finally, a comparative transcriptomic approach was employed to identify physiological pathways involved in invader tolerance. This research demonstrates that B. violaceus is consistently more tolerant than A. glabrum and that the invader efficiently utilizes molecular mechanisms to endure in copper-polluted environments.


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