Document Type



Virginia Institute of Marine Science

Publication Date



Journal Of Shellfish Research





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A simulation model was developed to investigate the population dynamics of the protistan parasite, Perkinsus marinus, within its host, the eastern oyster, Crassostrea virginica. The main objective was to evaluate the relationship between P. marinus population dynamics and environmental conditions in order to predict the onset and termination of P. marinus epizootics in Chesapeake Bay oyster populations. Information derived from laboratory experiments and from direct field observations of P. marinus dynamics in the James River for the years 1990 to 1993 was utilized for model development. The individual-based model, which is driven by temperature and salinity, tracks the average within-host parasite density at a daily time step. The model was verified against monthly field observations of parasite abundance for the years 1994 to 1999 at three oyster bars located along a 0-20-ppt salinity gradient in the James River, Virginia. Simulated populations exhibited a distinct seasonal periodicity with annual density maximums and minimums occurring in October and May, respectively. Parasite abundance decreased in an upriver direction with decreasing salinity along the salinity gradient. Predicted parasite densities significantly correlated with actual observed densities at all three locations; however, the strength of the association decreased from bar to bar in an upriver direction. Predicted parasite abundance exhibited a dynamic steady state for all three oyster bars during the 6-year time series. Simulations run without the input of a midsummer transmission event resulted in a destabilization and extinction of the parasite from the oyster population located farthest upriver. but the parasite remained enzootic during the six year simulation at the two lower river stations. This suggests that a single transmission event may be sufficient for P. marinus to become enzootic in specific year classes of oyster populations located in moderate to high salinity areas, while periodic transmission events are required for the parasite to persist in low salinity areas. Simulation results suggest that fairly accurate quantitative predictions of P. marinus abundance can be made using in situ temperature and salinity data and a relatively simple model.


Perkinsus; Model; Disease; Parasite; Oyster; Temperature; Salinity

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Creative Commons Attribution-Noncommercial-Share Alike 3.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License.