In partial fulfillment of the requirements for the degree of

Doctor of Philosophy in Biology
In the
School of Biological Sciences

STEPHANIE M. BILODEAU

Will defend her dissertation

DIETARY, HOST, AND HABITAT SELECTION IN MARINE AND FRESHWATER INVERTEBRATES

WEDNESDAY APRIL 1, 2026
1 PM EDT
In person location: Marcus Nanotechnology 1116

Zoom link: https://gatech.zoom.us/j/98935625617?pwd=0NPR6ew7EXEF5Z0nnWfzOjFf4XcuUt…

Thesis Advisor:
Mark Hay, Ph.D.
School of Biological Sciences
Georgia Institute of Technology

Committee Members:
Julia Kubanek, Ph.D.
School of Biological Sciences
Georgia Institute of Technology

Lin Jiang, Ph.D.
School of Biological Sciences
Georgia Institute of Technology

Marc Weissburg, Ph.D.
School of Biological Sciences
Georgia Institute of Technology

Susan Adams, Ph.D.
Southern Research Station
United States Forest Service

ABSTRACT:
Marine and freshwater ecosystems differ in temporal persistence, spatial scale, population connectivity, and variance in abiotic and biotic conditions. Foraging and habitat selection strategies and the cues used to make those selections are therefore likely to differ between marine and freshwater systems as well. However, diet and host selection and the consequences of those choices are understudied in numerous freshwater invertebrates, relative to their marine counterparts. In this dissertation, I assessed aspects of marine and freshwater habitat selection and investigated the consequences of dietary and host preferences in a marine specialist subject to anthropogenic climate change and multiple generalists in naturally variable freshwater environments. First, I showed that larvae in persistent, continuous marine environments typically complete their own habitat selection during settlement, often relying on chemical cues at multiple scales. Conversely, in freshwater, more mobile adults that can move upstream or across terrestrial barriers tend to choose habitat for their offspring, also relying on chemical cues. Next, I investigated chemical tracking behavior and the consequences of host choice in a marine nudibranch corallivore that makes host selection choices throughout its life. I showed that these specialist nudibranchs do not consistently avoid bleached coral hosts, even though juveniles experience high mortality and low growth on bleached corals. To investigate the potential coupling of food and habitat choices in freshwater, I assessed feeding and case-building behavior in a semi-aquatic caterpillar. I showed that the cases provide protect from predation and desiccation, and these generalists can utilize multiple common macrophytes as hosts and food. Macrophyte preferences for food and cases are not consistently the same but do reflect the effects of these macrophytes on caterpillar fitness. Finally, I looked at macrophyte feeding preferences and related fitness effects in multiple species of omnivorous crayfish and showed that in most cases, diets were broadly overlapping, but some feeding space was uniquely occupied. Parentage affects overall offspring quality and offspring performance on specific diets, adult and juvenile feeding preferences can differ, and these differences appear driven by juveniles' need for dietary protein. These results emphasize some ways in which marine and freshwater systems may promote different strategies for food and habitat selection, highlighting the need for further study of freshwater invertebrate consumers.