Resting Stages and the Population Dynamics of Harmful Algae in ...

(Baker et al., 2007). It was discoveredthat P. parvum have the ability to deploya poison that paralyzes prey, prevents grazing, and reduces competition especiallyduring nutrient limited environments (Tillman, 2003; Roelke et al., 2007;Graneli et al., 2008; Brooks et al., 2010). This poison was found to be not one,but multiple poisons that are released simultaneously whose chemical structureshave yet to be clearly defined (Igarashi et al., 1999). These toxins can have verypotent effects on non-planktonic species, especially fish, causing massive fishkills numbering over 30 million in total (Southard et al., 2010). Toxic eventsduring winter may be especially severe since temperature and salinity are farfrom optimal for P. parvum, which appears to enhance its toxicity (Baker etal. 2007, 2009). P. parvum have also shown that, during certain stressful conditions,it can assume a markedly reduced metabolic state. In this paper thisstate is referred to as the non-motile state, which may possibly be a cyst formation(Green et al., 1982). Therefore, for analytical purposes, we assume thatthis non-motile state has negligible rates of reproduction, nutrient consumption,toxin release, and meaningful movement compared to those of the active, motilestate. Thus, a better understanding of this non-motile state may shed light onharmful algal bloom cycles and environment-dependent toxin release of the P.parvum algae.It has been established that the success of a newly introduced organismdepends on its ability to reproduce successfully. Since environmental factorsplay a large role in P. parvum bloom dynamics, our study attempts to modelcertain environments to observe motile and non-motile cell transitions. The twoenvironments used for the model are batch and chemostat cultures. The batchculture allows an organism to be isolated in a controlled environment with alimited source of a specific nutrient. Since the batch is a closed system, neworganisms and nutrient cannot be added. The chemostat model was establishedto show the rate of successful multiplication of a newly introduced organismin an open system (Powell, 1965). Further, this chemostat model includes adilution of a vessel in which both cell and nutrient populations are introducedand evacuated in equal amounts (Monod, 1950; Johansson and Graneli, 1999).We have proposed a theoretical model that can demonstrate the impact of cellconversion rates on population dynamics.2 Batch Culture ModelThe batchculture model usesthe variablesand parameterslisted in Table1. Werepresent the population dynamics by the following three differential equations:2