Ecology of Harmful Algae

Collaborators – Richard Kiesling, James Grover, Bryan Brooks, Yesim Buyukates

Graduate Students – Reagan Errera

Developing a predictive understanding of Prymnesium parvum toxic bloom formation and its control

Prymnesium parvum, also called golden algae, occurs worldwide and is responsible for large fish kills in coastal and inland water environments. The occurrences of the blooms have diminished local community revenues from tourism, fishing, and hatchery production. In 1985, the state of Texas officially confirmed a P. parvum bloom along the Pecos River. Since the initial identification, P. parvum blooms have affected over 20 reservoirs in five river basins. Within the past four years, several major fish kills attributable to toxins released by P. parvum blooms have occurred in large surface-water reservoirs in the Brazos River basin. Between January and May of 2001 through 2004, Lakes Possum Kingdom, Granbury, and Whitney, and TPWD’s Dundee fish hatchery all have experienced significant fish kills associated with P. parvum blooms. The factors controlling the appearance of P. parvum blooms in these reservoirs have yet to be determined, but the pattern of fish kills raises several questions about the physical, chemical, and biological characteristics that trigger the build-up of P. parvum populations leading to toxin production. Our research focuses developing a predictive understanding of P. parvum toxic bloom formation and its control. Our investigation assess P. parvum bloom dynamics by measuring the in-reservoir response of the phytoplankton community to experimental manipulation of each reservoir's planktonic foodweb, by assessing the population growth physiology of P. parvum under the influence of potential limiting factors, and by assessing the toxicity response of P. parvum under these changing conditions.

Interannual variability in the seasonal plankton succession of a shallow, warm-water lake

Common seasonal plankton succession patterns in temperate lakes are well understood, and were described in the popular PEG-model. Seasonal plankton succession in warm-water lakes, however, is not as well known. Recent theory suggests that some lake systems are characteristic of having alternate system-states, where one of the system-states is characterized by dominance of cyanobacteria, and transition between system-states can be abrupt and undeterminable. Lake Somerville, a shallow, well-mixed, warm-water reservoir located in eastern TX, USA, experiences occasional periods of cyanobacteria dominance, where Microcystis and Oscillatoria can dominate. To increase our understanding of seasonal plankton dynamics in warm-water systems, we analyzed 14-years of plankton data spanning a 22-year period. During this period, succession dynamics characteristic of those described by the PEG-model were observed, as well as succession dynamics expected during periods of cyanobacteria dominance, i.e., greater accumulated phytoplankton biovolume, low secondary productivity, and low light penetration. In addition to the PEG-model and cyanobacteria type system-states, other states of the system that were intermediate between these were observed. Therefore, we conclude the lake does not behave according to the alternate system-states model. The change from year to year in early-year cyanobacteria dominance was abrupt and non-monotonic during this period. In addition, the early year performance of cyanobacteria appeared to influence the plankton succession trajectory for the remainder of the season. While the magnitude of lake-flushing early in the year accounted for ~37% of variability in cyanobacteria prevalence, many of the traditional factors impacting cyanobacteria dominance appeared insignificant. Interestingly, during periods when Microcystis and Oscillatoria dominated the phytoplankton, cyanotoxins (a suite of microcystins and nodularin) were not detected.