Date of Award

Spring 2010

Project Type


Program or Major


Degree Name

Doctor of Philosophy

First Advisor

James E Byers


This research examines the ecological factors that shape trematode parasite communities of mudsnail Ilyanassa obsoleta at three different spatial scales. Nine species of trematode which obligately infect I. obsoleta during larval stages but use numerous estuarine species as second intermediate and definitive hosts are considered. The work provides the most geographically extensive examination to date of this trematode parasite community.

At the broadest scale, I. obsoleta trematodes were examined across their distributional range (Chapter 2) which includes both native and introduced populations. The results demonstrate that introduced trematode communities are characterized by lower abundance and diversity compared to native communities and therefore conform to the pattern predicted by the enemy release hypothesis. The ecological factors that contribute to the establishment of specific L. obsoleta trematodes in the introduced range are considered.

A regional scale analysis of I. obsoleta trematode communities is presented in Chapter 3. Trematode abundance and diversity along with a wide variety of biological, chemical, and physical factors was examined at fifteen salt marsh sites located throughout northern New England, USA. Although the abundance of numerous hosts were measured as part of this work, variables found to be most strongly correlated with trematode abundance and diversity at sites (revealed through multiple regression analysis) were of physical and chemical origin including sediment nitrogen, roads, trace metals and the distance of sites from the ocean. The results are explored in the context of a variety of candidate mechanisms.

Chapter 4 focuses on I. obsoleta trematodes at a local scale within a single salt marsh site. The work examines intra- and inter-annual patterns of trematode infection in snails associated with four distinct salt marsh habitat types. Experiments were conducted to assess the importance of key processes in determining infection patterns including acquisition of infection by I. obsoleta, mortality, movement, and demographics of the snail hosts. Results indicate that patterns of infection among the salt marsh habitats are subject to strong shifts over time. Changing demographics and snail movement (but not infection input) are likely to be the strongest factors contributing to changing infection patterns across habitats in this system.