Date of Award

Spring 1998

Document Type


Degree Name

Master of Science (MS)


Ocean & Earth Sciences

Committee Director

Eileen E. Hofmann

Committee Member

Larry P. Atkinson

Committee Member

Susan E. Ford

Committee Member

John M. Klinck

Committee Member

Eric N. Powell


An oyster population model coupled with a model for Haplosporidium nelsoni, the causative agent of the oyster disease MSX, was used with salinity time-series constructed from Delaware River flow measurements to study environmentally-induced variations in the annual cycle of this disease. Simulations with this model were designed to investigate the effect of increased or decreased spring freshwater discharge, the timing of high freshwater runoff, the presence or absence of a fall or late spring phytoplankton bloom, and the occurrence of a warm winter on MSX prevalence and intensity in Delaware Bay oyster populations. Model simulations for the lower Bay site reproduced the annual cycle observed in the lower Delaware Bay. Simulations at upper Bay (low salinity) and lower Bay (high salinity) sites produced MSX prevalences and intensities that were consistent with field observations. Warm winters prevented the loss of MSX infections during the winter, causing higher MSX infection levels in the spring and almost 100% mortality by July. These simulations demonstrate the importance of salinity and temperature in altering and controlling the MSX annual cycle.


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