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Cawley, Kaelin M ¹ ; McKnight, Diane M ²

¹ University of Å·ÃÀ¿Ú±¬ÊÓƵ at Boulder
² University of Å·ÃÀ¿Ú±¬ÊÓƵ at Boulder

Harmful algal blooms (Hרs) are a global concern in freshwater and coastal ecosystems because they can lead to anoxia in aquatic ecosystems, taste and odor concerns in reservoirs, and paralytic shellfish poisoning (PSP) outbreaks in the coastal ocean. They are a result of both natural ecological processes and anthropogenic nutrient inputs (Anderson et al., 2002). However, Hרs occur with slightly different timing and severity each year. Greater predictive skill would protect human health and decrease the economic impacts of closing shellfish harvesting areas. Studies have linked increases in inorganic nutrient concentrations to Hרs, but have been unable to develop a consistent method of predicting Hרs and PSP outbreaks based solely on nutrient inputs (Anderson et al., 2002).

Studies of algal modes of nutrition have shed some light on potential weaknesses in Hר prediction models. Many harmful algal species that were previously thought to be strictly photosynthetic have been shown to be mixotrophs (Jeong et al., 2005). Mixotrophs are both photosynthetic and capable of consuming prey, detrital particles, and DOM in order to sustain metabolic activity. Therefore, the presence of prey, particulate matter, and DOM is likely another important factor controlling Hר timing and severity.

In order to better understand Hר formation in the field we have performed a set of experiments intended to understand A. fundyense growth under controlled conditions in the presence of DOM.

The A. fundyense used for the experiments described here was obtained from the Provasoli-Guillard National Center for the Culture of Marine Phytoplankton (CCMP1719). Cultures for the experiment were grown in triplicate under three conditions: L1 medium in filtered seawater (‘No DOM’ on figures), L1 medium with ~2.5 mg/l DOM in filtered seawater (‘+ Pony Lake FA’ on figures), and low nutrient levels with ~2.5 mg/l DOM added in filtered seawater (‘Low Nutrient + PLFA’ in figures). These cultures were sampled for cell counts and DOM analysis using UV-VIS spectroscopy, and fluorescence spectroscopy.

Cell growth rates remained statistically similar for the three cultures (figure 1.). Preliminary analysis of the spectral data shows significant changes to the DOM pool in cultures with added DOM alteration by A. fundyense. In the cultures with added DOM, DOC initially decreased 15% followed by an increase of 12-14%. This is evidence that the algae initially take up DOM and then excrete DOM as they grow.

Anderson, D.M., 1997, Bloom dynamics of toxic Alexandrium species in the northeastern U.S.: Limnology and Oceanography, v. 42, p. 1009-1022.

Anderson, D.M. et al., 2002, Harmful algal blooms and eutrophication: nutrient sources, composition, and consequences: Estuaries, v. 25, p. 704-726.

Gagnon, R., et al., 2005, Growth stimulation of Alexandrium fundyense (Dinophyceae) by humic substances from the Manicougan River (Eastern Canada): Journal of Phycology, v. 41, p. 489-497.

Jeong H.J., et al., 2005, Feeding by phototrophic red-tide dinoflagellates: five species newly revealed and six species previously known to be mixotrophic: Aquatic Microbial Ecology, v. 40, p. 133-150.