Date of Award

Spring 2021

Project Type


Program or Major

Biological Sciences

Degree Name

Doctor of Philosophy

First Advisor

Larry G Harris

Second Advisor

Walter J Lambert

Third Advisor

James Haney


Trematode parasites are ubiquitous in marine environments and their importance in ecological function is becoming increasingly recognized, impacting host behaviors, food web dynamics, and community diversity. Trematodes are inextricably tied to their hosts. Therefore, to understand the role of trematodes it is essential to understand their relationships with their hosts. Trematodes typically utilize first intermediate, second intermediate, and definitive hosts to complete their life cycle. Second intermediate hosts are underrepresented in trematode research. Most parasite models and theory are thus incomplete as they rarely include this life stage of the parasite. This research examines the relationship between the trematode Zoogonus rubellus and its first and second intermediate hosts within Great Bay Estuary, New Hampshire, with a particular emphasis on the impact of Z. rubellus on the second intermediate hosts.The spatial and temporal distributions of Z. rubellus within its first intermediate host Ilyanassa obsoleta and second intermediate hosts, nereid worms, were investigated through a series of annual surveys of six sites around Great Bay Estuary (Chapter 1). Sites were simultaneously surveyed for first and second intermediate hosts, which were then dissected in the laboratory to determine parasitic infection rates. The results of the surveys established (1) three nereid worm species, Alitta virens, Neanthes succinea, and Hediste diversicolor, as natural second intermediate hosts for Z. rubellus, (2) the spatial and temporal distribution of Z. rubellus, and (3) the relationship between infection patterns among first and second intermediate hosts. The relationship among first and second intermediate hosts was further investigated in Chapter 2. The first intermediate host is the source of infection for the second intermediate host. This chapter investigated the role of two temporally variable abiotic factors, temperature and salinity, and their effect on the release of infective trematodes. Both temperature and salinity vary substantially within Great Bay Estuary on multiple temporal scales. Both factors were found to significantly impact the release of trematodes from the first intermediate host. Understanding how these abiotic factors affect trematode release is essential to understand the infection risk for second intermediate hosts. The final chapter investigated the impact of Z. rubellus on the biology of the second intermediate hosts. This chapter compared the susceptibility to infection and post-infection effects of Z. rubellus on two nereid worm species, Alitta virens and Hediste diversicolor. These species are both natural hosts to Z. rubellus and sympatric within Great Bay Estuary. Thus, they interact with each other and with Z. rubellus, and infection may differentially affect these host species. The susceptibility to infection differed between these two nereid worm hosts. Hediste diversicolor displayed a density-dependent decrease in predation activity in response to exposure to Z. rubellus. However, neither nereid species displayed long term growth impacts from infection by Z. rubellus. The results of these studies highlight the interwoven relationship among these three groups of species. All three of these species are dominant members of the intertidal mudflat community and their roles are still poorly understood, particularly in light of their interactions with each other. This research establishes the groundwork for understanding the mechanisms that drive their interactions.