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The rapid range expansion of the toxigenic marine haptophytic alga Prymnesium parvum in inland aquatic systems across the southern USA and beyond has prompted great interest in the ecology and evolutionary biology of this invasive bloom-forming species. Researchers have speculated that increased toxicity and heterotrophy in suboptimal environments allow blooms to develop in these new inland habitats that seem to represent extremes relative to P. parvum's perceived optimal niche. We used a laboratory-based study to elucidate the roles of salinity and nutrient availabilities in P. parvum growth and toxicity under environmental conditions representative of hypereutrophic reservoirs of the southwestern USA in which P. parvum blooms are now common. We found evidence that nutrient conditions favoring toxigenesis in P. parvum are suboptimal for growth and bloom formation, whereas conditions conducive to high growth rates are less favorable for toxigenesis. In contrast, both growth and toxicity scaled positively with salinity. Taken in the context of the documented biogeography of P. parvum and that toxigenesis in P. parvum probably evolved in support of heterotrophic nutrient acquisition, our results suggest that P. parvum's apparent range expansion into and across the USA is driven by increasing availabilities of salty and nutrient-rich systems, rather than by its toxigenic abilities. [ABSTRACT FROM AUTHOR]

Abstract: The toxigenic marine flagellate Prymnesium parvum was first recorded in Lake Texoma, OK-TX, USA, an impoundment of the Red and Washita Rivers, following a massive fish kill in January 2004. Results of a 4.5-year monitoring program, spanning five bloom periods, revealed that Prymnesium abundances in the lake were temporally and spatially variable—densities were higher in winter, near-shore, and in Red River-associated sampling sites; the largest blooms were in Lebanon Pool, a large backwater basin often disconnected from the main reservoir. Prymnesium blooms appeared to have been fueled by high nutrient concentrations, and winter-spring densities were positively correlated with chlorophyll a, conductivity, total phosphorus, total nitrogen, and microzooplankton biomass, and negatively correlated with molar total nitrogen:total phosphorus and cladoceran and total crustacean zooplankton biomass. Comparison of Prymnesium densities with hydrological data suggested that Prymnesium blooms in Lebanon Pool were highest when the pool was disconnected from the main reservoir; no bloom occurred in the winter of 2004–2005, the only year since the 2003–2004 invasion in which Lebanon Pool and Lake Texoma were connected during the winter months. [ABSTRACT FROM AUTHOR]

Abstract: Within the last two decades, Prymnesium parvum (golden algae) has rapidly spread into inland waterways across the southern portion of North America and this organism has now appeared in more northerly distributed watersheds. In its wake, golden algae blooms have left an alarming trail of ecological devastation, namely massive fish kills, which are threatening the economic and recreational value of freshwater systems throughout the United States. To further understand the nature of this emerging crisis, our group investigated the chemical nature of the toxin(s) produced by P. parvum. We approached the problem using a two-pronged strategy that included analyzing both laboratory-grown golden algae and field-collected samples of P. parvum. Our results demonstrate that there is a striking difference in the toxin profiles for these two systems. An assemblage of potently ichthyotoxic fatty acids consisting primarily of stearidonic acid was identified in P. parvum cultures. While the concentration of the fatty acids alone was sufficient to account for the rapid-onset ichthyotoxic properties of cultured P. parvum, we also detected a second type of highly labile ichthyotoxic substance(s) in laboratory-grown golden algae that remains uncharacterized. In contrast, the amounts of stearidonic acid and its related congeners present in samples from recent bloom and fish kill sites fell well below the limits necessary to induce acute toxicity in fish. However, a highly labile ichthyotoxic substance, which is similar to the one found in laboratory-grown P. parvum cultures, was also detected. We propose that the uncharacterized labile metabolite produced by P. parvum is responsible for golden algae''s devastating fish killing effects. Moreover, we have determined that the biologically-relevant ichthyotoxins produced by P. parvum are not the prymnesins as is widely believed. Our results suggest that further intensive efforts will be required to chemically define P. parvum''s ichthyotoxins under natural bloom conditions. [Copyright &y& Elsevier]