MEPS 256:29-44 (2003)  -  doi:10.3354/meps256029

Modeling Pfiesteria piscicida population dynamics: a new approach for tracking size and mass in mixotrophic species

Xinsheng Zhang*, Jon T. Anderson, Raleigh R. Hood

Horn Point Laboratory, University of Maryland Center for Environmental Science, PO Box 775, Cambridge, Maryland 21613, USA

ABSTRACT: We have developed a generalized dynamic, numerical model to study Pfiesteria population dynamics based on available observations and literature. We have incorporated formulations into this model which allow us to track changes in cell size in relation to food availability and other environmental conditions, which can be used for modeling a variety of cell-size dependent physiological functions. With this model, we are able to follow the time dependency of both individual size and abundance of Pfiesteria zoospores in cultures. We also have developed a general, starvation-based trigger mechanism for cyst formation for mixotrophic species like Pfiesteria, which is based on the size of zoospores determined by previous food conditions and the decrease or increase in size determined by the current food conditions. The model results suggest that zoospore concentration can be regulated effectively by both bottom-up control by food availability and the top-down control by zooplankton grazing. Model sensitivity analysis shows that the results are fairly robust with respect to changes in the model parameter values. This paper represents a significant step forward in our efforts to model complicated life-cycle phenomena in dinoflagellates like Pfiesteria and, in so doing, also provides some important new approaches for tracking cell size and cyst formation.

KEY WORDS: Modeling · Pfiesteria size · Pfiesteria abundance · Encystment

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