The role of marine aggregates in the ecological epidemiology of Quahog Parasite X (QPX) disease of northern quahogs (= hard clams) Mercenaria mercenaria

Date of Completion

January 2008


Biology, Oceanography|Health Sciences, Epidemiology




Ecological epizootiology is the study of environmental influences on the health of animals including disease incidence, persistence and transmission. It is a conceptual approach that unifies molecular biology, environmental sciences, and epidemiology for the purpose of identifying causes, classifying risks, and controlling health problems. Ecological epizootiology has been successfully applied in terrestrial systems, but its adaptation to marine ecosystems is relatively new. My dissertation uses this approach to evaluate the role of marine aggregates (i.e., marine snow, organic aggregates, flocs) in the ecology of Quahog Parasite X (QPX), a disease of northern quahogs (=hard clam), Mercenaria mercenaria. Marine aggregates are a ubiquitous feature of aquatic ecosystems, but have no terrestrial counterpart. They have the potential to serve as a link between aquatic pathogens (e.g., QPX) and benthic hosts (e.g., hard clams) in two ways: (1) as environmental reservoirs for pathogens embedded in aggregates; and (2) as vectors for aggregate-bound pathogens transported between hosts. The results of this research include the descriptive epizootiology of QPX disease in hard clams, along with the first quantitative assay for the QPX organism, and data to support QPX as a facultative pathogen. Evidence that QPX is facultative is critical because it supports that once QPX is established in a location, eradication will be difficult because QPX is capable of surviving on environmental resources other than hard clams. In this research, marine aggregates were characterized using underwater video surveys coupled with direct collection of suspended aggregates in modified settling cones. The results provide a starting point for determining the temporal and spatial scales at which aggregates influence persistence and transmission of aquatic pathogens. Overall, these results have important implications for the way in which aquatic pathogens are collected, quantified, and monitored for water quality assessments in shallow-water ecosystems. ^