Date of Award


Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)


Marine Biology


Robert S. Steneck

Second Committee Member

Malcolm L. Hunter, Jr.

Third Committee Member

Paul Rawson


Invasions by non-native species have altered the structure and function of marine ecosystems. However, processes and scales of these invasions are still unclear for many species and ecosystems. This work is a contribution to the understanding of the physical and biotic factors driving temporal and spatial dynamics in the abundance and richness of marine non-native species in fouling communities in coastal Gulf of Maine. Field observations, and field and laboratory experiments on fouling communities, allowed me to test hypotheses regarding physical drivers such as temperature and salinity, and biotic drivers such as predation and competition. In local scale studies, I found that rivers with significant freshwater discharge lower the salinity to lethal limits of non-native fouling species, affecting their successful colonization in estuaries. At a regional scale, in areas with adequate salinities for survival, warm thermal regimes correspond well with nonnative colonizing biota’s abundance and species richness, with a possible invasive threshold at summer temperatures > 16°C. The colonial ascidians Botrylloides violaceus and Botryllus schlosseri showed the strongest response to warmer sea temperatures. The colder northeastern coast of Maine is less invaded than warmer southwestern Maine. I also investigated biological interactions as drivers of invasions. Colonial encrusting tunicates are virtually immune to benthic predators, which could explain their high abundances in some areas. Local predators such as green crabs (Carcinus maenas), rock crabs (Cancer irroratus) and hermit crabs (Pagurus acadianus) preyed on solitary species, possibly resisting the colonization of solitary species in the benthos. Humanbuilt floating structures may offer a predator-free habitat that facilitates colonization by solitary species. I also studied the role of native fouling bivalves in resisting or facilitating invasions. Tunicates readily recruit to the blue mussel (Mytilus sp.) but the mussel rapidly succumbs to overgrowth. The jingle shell (Anomia simplex) does not facilitate tunicate recruitment but it is able to maintain a tunicate free halo around itself that reduces mortality from the colonizing ascidians. This work on drivers of non-native species in coastal Gulf of Maine is a contribution to the understanding of non-native species impacts and might help envision possible future impacts in a climate change scenario.