Fish kill due to golden algae at Lake Whitney, Texas
Prymnesium parvum, also called “golden algae”, occurs worldwide and is responsible for large fish kills in coastal and inland water environments. Blooms of golden algae have been identified in fresh and brackish water environments from Australia to Texas, where they have impacted community revenues from tourism, fishing, and hatchery production. Blooms in Texas have affected over 20 reservoirs in five river basins, killing over 17.5 million fish with economic losses of several million dollars. Dr. James Grover and colleagues at Texas A&M University (Dr. Dan Roelke) and Baylor University (Dr. Bryan Brooks) are investigating the ecology of golden algae, with sponsorship from the Texas Parks & Wildlife Department
(http://www.tpwd.state.tx.us/landwater/water/environconcerns/hab/ga/). This research integrates laboratory and field experiments with mathematical modeling and toxicology. Previous research has established that blooms in Texas occur in winter, under conditions of temperature and salinity that are not optimal for growth of the algae, but which do enhance the toxicity of golden algae to fish. The absence of golden algae blooms in warmer weather, which supports more rapid growth, remains unexplained. Ongoing research will address hypotheses that the competitors (other algae) and grazers present in summer suppress the growth of golden algae.
Dr. Grover, Dr. Brooks and Dr. Roelke
The mixotrophic protozoan Ochromonas danica (dashed outline) with chloroplasts (red) and ingested bacterial cells (green).
Drs. James Grover and Thomas Chrzanowski are investigating the impact of variable stoichiometry on predation and competition by developing microbial experimental models, in a project funded by NSF (2005-2008). This project addresses how variations in the chemical composition (“stoichiometry”) of microorganisms affect their interactions with other species. Experiments in this project examine how variations in composition of the nutrient elements carbon, nitrogen, and phosphorus affect the relationship of bacterial prey with the larger microorganisms that consume them. This project will provide insights into processes governing abundances of microorganisms in nature, including some species of “harmful algae” whose lifestyle includes feeding upon bacteria.
Dr. Chrzanowski and Dr. Grover
from K. Schug et al., unpublished report
Dr. James Grover is collaborating with Drs. Kevin Schug and Laura Mydlarz to extract and characterize toxins produced by “golden algae” (Prymnesium parvum). The known toxins are complex, high molecular-weight compounds for which standards are not available, and the presence of additional uncharacterized toxins remains possible. This research has developed a microscale hemolytic assay for the operational quantification of toxic activity, and is applying this assay to chemical fractions separated from whole cell extracts and from the aqueous medium of cultures. Through this means, toxic constituents will be isolated and then characterized. Additional toxicological testing by Dr. Bryan Brooks at Baylor University will examine the toxicity to fish of isolated compounds.
This project is sponsored by the US Department of Energy through a contract with the Texas Water Resources Institute, and involves investigators from Texas A&M University, Baylor University and the University of Texas at Arlington. The goal is to use high resolution spatial mapping of lake characteristics and mathematical modeling to identify factors affecting two water quality problems within the lake. Problems under investigation involve outbreaks of high numbers of bacteria indicating low water quality (E. coli, other fecal bacteria indicators), and harmful blooms of "golden algae" (Prymnesium parvum). Lake Granbury is a long, narrow reservoir whose shoreline is essentially completely developed, mostly as residential property. Only a minority of the residences around the lake is hooked to municipal sewage, and most homes rely on septic systems for sewage disposal. Leakage from these systems is one potential factor contributing to water quality problems.
Jason W. Baker, PhD Dissertation
Growth of Prymnesium parvum (“golden algae”) in relation to environmental factors
Jason’s dissertation research focused on how the population growth rate and toxicity of “golden algae” (Prymnesium parvum) are related to temperature, salinity, light, and nutrient concentration. He used laboratory experiments and regression modeling to find quantitative expressions governing these relationships. The equations that Jason derived have become the basis for a suite of mathematical models under development to simulate the dynamics of “golden algae” in lakes. These algae tend to bloom and cause fish kills in Texas lakes during cooler weather. Jason’s research showed that such conditions are suboptimal for the growth of P. parvum, but that such suboptimal conditions also increase toxicity to fish.
Ratheesh Ramachandrannair, MS Thesis
Growth of Prymnesium parvum in semicontinuous laboratory cultures
Ratheesh grew populations of Prymnesium parvum (“golden algae”) in the laboratory in semicontinuous cultures to examine how various conditions affected abundance, toxicity, and the ability to compete with other algal species growing in the same cultures. His research showed that when confronted by competitors under such culture conditions, many of the P. parvum individuals became inactive and formed cysts. Betty Scarborough, PhD Dissertation Role of encystment and germination in population dynamics of Prymnesium parvum Betty is currently working on her dissertation. Her work began with the observation that under some growth conditions many individuals in a population of Prymnesium parvum (“golden algae”) become inactive and form cysts. Her ongoing research is systematically examining the conditions under which cysts form and then germinate.
Ken Crane, PhD Dissertation
Theoretical studies of mixotrophy and other nutritional strategies of microorganisms
Ken is currently working on his dissertation. He has constructed theoretical models examining the various nutritional strategies employed by aquatic microorganisms. In these models up to four populations following different strategies interact in a food web. The four nutritional strategies are: (1) Osmotrophy, in which heterotrophic microorganisms consume dissolved organic substances; (2) Phagotrophy, in which heterotrophic microorganisms prey upon osmotrophic organisms; (3) Phototrophy, in which autotrophic microorganisms produce organic matter by photosynthesis; and (4) Mixotrophy, in which microorganisms pursue a mixture of phagotrophic and phototrophic strategies. These efforts focus on predicting conditions under which mixotrophs persist with other types of microorganisms, in part because this is commonly observed in natural habitats, and in part because many harmful algae pursue a mixotrophic nutritional strategy.
James Harman, Undergraduate Honors Thesis
Role of mixotrophy in the population dynamics of Prymnesium parvum
James conducted experiments examining the role of mixotrophic nutrition in the population dynamics of Prymnesium parvum (“golden algae”). This species was grown in semicontinuous cultures in the presence of bacteria, at different ratios of supply of organic carbon to inorganic phosphorus (C:P ratio). In similar experiments with other species, purely phototrophic algae are usually eliminated from cultures with high C:P ratios due to competition with bacteria. Mixotrophic algae can persist in such cultures by eating some of the bacteria. In James’ experiments, P. parvum persisted in cultures with high C:P ratios, but only at low population densities, and was more abundant at low C:P ratios. This result suggests that mixotrophic nutrition can enable P. parvum to persist under some conditions, but is not sufficient to allow it to thrive.