MIXOTROPHY AND NITROGEN UPTAKE BY PFIESTERIA PISCICIDA (DINOPHYCEAE) |
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Authors: | Alan J. Lewitus Bonnie M. Willis Kenneth C. Hayes JoAnn M. Burkholder Howard B. Glasgow Jr. Patricia M. Glibert Marianne K. Burke |
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Affiliation: | Belle W. Baruch Institute for Coastal Research, Baruch Marine Laboratory, University of South Carolina, P.O. Box 1630, Georgetown, South Carolina 29442; Department of Botany, Box 7612, North Carolina State University, Raleigh, North Carolina 27695-7612; Horn Point Laboratory, University of Maryland Center for Environmental Science, Cambridge, Maryland 21613; USDA Forest Service, Southern Research Station, Charleston, South Carolina 29414 |
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Abstract: | The nutritional versatility of dinoflagellates is a complicating factor in identifying potential links between nutrient enrichment and the proliferation of harmful algal blooms. For example, although dinoflagellates associated with harmful algal blooms (e.g. red tides) are generally considered to be phototrophic and use inorganic nutrients such as nitrate or phosphate, many of these species also have pronounced heterotrophic capabilities either as osmotrophs or phagotrophs. Recently, the widespread occurrence of the heterotrophic toxic dinoflagellate, Pfiesteria piscicida Steidinger et Burkholder, has been documented in turbid estuarine waters. Pfiesteria piscicida has a relatively proficient grazing ability, but also has an ability to function as a phototroph by acquiring chloroplasts from algal prey, a process termed kleptoplastidy. We tested the ability of kleptoplastidic P. piscicida to take up 15N-labeled NH , NO , urea, or glutamate. The photosynthetic activity of these cultures was verified, in part, by use of the fluorochrome, primulin, which indicated a positive relationship between photosynthetic starch production and growth irradiance. All four N substrates were taken up by P. piscicida , and the highest uptake rates were in the range cited for phytoplankton and were similar to N uptake estimates for phagotrophic P. piscicida . The demonstration of direct nutrient acquisition by kleptoplastidic P. piscicida suggests that the response of the dinoflagellate to nutrient enrichment is complex, and that the specific pathway of nutrient stimulation (e.g. indirect stimulation through enhancement of phytoplankton prey abundance vs. direct stimulation by saprotrophic nutrient uptake) may depend on P. piscicida 's nutritional state (phagotrophy vs. phototrophy). |
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Keywords: | cryptophytes fish kills harmful algal bloom kleptoplastidy nutrient loading Pfiesteria piscicida primulin starch toxic dinoflagellates |
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