Quantification of Pfiesteria piscicida growth and encystment parameters using a numerical model

Abstract

In the past decade, there has been growing interest in understanding the physiological ecology and life cycle of toxic forms of Pfiesteria piscicida. However, transformations among noninducible (NON-IND; formerly described as nontoxic) stages have received less attention despite the fact that NON-IND stages are found in nature and may be ecologically important as prey and predators. NON-IND stages are also mixotrophic and have the ability to retain and utilize prey chloroplasts in a process termed 'kleptoplastidic mixotrophy'. Quantifying growth, grazing and encystment rates from P. piscicida laboratory experiments is confounded by the interrelationship between mixotrophy and life stage transformations. By fitting a numerical model to a laboratory experiment on NON-IND P. piscicida, we were able to isolate the potential mechanisms that cause encystment and speculate on the interrelationship between adverse conditions (i.e. low light and limiting prey) and life stage transformations. The structure of the laboratory experiment allowed for the estimation of several growth and encystment parameters including grazing rates, gross growth and assimilation efficiencies, as well as the retention time of chloroplasts. Model results suggest a link between encystment and mixotrophic ability. Furthermore, the model results suggest that encystment rates and gross growth and assimilation efficiencies calculated from the model are lower than expected.

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

“…3A). Laboratory observations have confirmed that the light does, indeed, enhance the growth of zoospores (Anderson et al 2003b). In the model, this effect is due to the photosynthetic activity of kleptochloroplasts of zoospores, which is consistent with experimental studies on Pfiesteria nutrient uptake 39 (C) Sensitivity of the model-estimated time period of the plateau phase of change in zoospore abundance, the maximal abundance at the plateau phase and the abundance at the end of the 14 d experiment to additional model parameters used in the third modeling experiment.…”

“…However, the decaying processes of the photosynthetic activity of kleptochloroplasts are not well understood. Anderson et al (2003b) assumed that the photosynthetic potential of kleptochloroplasts decreases linearly with age, eventually ceasing at a set retention time. For the sake of simplicity, we do not include the retention effect of kleptochloroplasts in this model, i.e.…”

“…Therefore, we set the maximum weight-specific grazing rate for zoospore to be equal to 5 d -1 (see Table 2). The values of the maximum phytoplankton-specific growth rate and the phytoplankton-specific mortality rate were calculated from laboratory experiments (Anderson et al 2003b). The other parameters listed in Table 2 are based on published values (Fasham et al 1990, Stickney et al 2000.…”

Modeling the influence of nutrients, turbulence and grazing on Pfiesteria population dynamics

“…The high shear rate of 3 was chosen as a maximum potential value that might be encountered in an estuarine environment like Pocomoke Flats where Pfiesteria outbreaks have occurred and also because Stoecker et al (2006) show experimentally that a shear rate value of 3 has a significant negative impact on Pfiesteria feeding and growth rate. 3: From Anderson et al (2003). 4: Assuming the maximum grazing rate of TOX-A strains is substantially lower (by a factor of 3) than for NON-IND strains, based upon Burkholder et al (1997).…”

Grazing activity of Pfiesteria piscicida (Dinophyceae) and susceptibility to ciliate predation vary with toxicity status

“…The preponderance of information on the nutritional capabilities of P. piscicida has come from studies with cultures maintained on algae for lengthy periods, presumably not actively toxic (e.g. Lewitus et al, 1999a;Eriksen et al, 2002;Feinstein et al, 2002;Anderson et al, 2003;Alavi, 2004;Lin et al, 2004). A high herbivorous growth capacity was indicated in these studies, with rapid depletion of prey, maximum growth rates ranging from 0.8 to 1.4 day À1 , and maximum ingestion rates ranging from 3 to >10 prey flagellated cell À1 day À1 .…”