Coridon Laws

Graduation Semester and Year




Document Type


Degree Name

Doctor of Philosophy in Quantitative Biology



First Advisor

James P Grover


Harmful algae disrupt other organisms and ecosystems by multiple mechanisms. Many taxa of harmful algae produce toxic compounds that likely contribute to such problems. Though there is little evidence that the harmful golden algal species such as Prymnesium parvum are harmful to human health, this species has been linked to many toxic blooms leading to fish kills. A clear relationship between the concentrations of P. parvum cells or P. parvum toxins and fish kills is not well established in natural settings. Filtration techniques to generate cell-free filtrates of P. parvum may create toxigenic artifacts that are a result of high-pressure during filtration. Toxic activity in cultures of P. parvum is not strong unless cultures are already at a high density, suggesting that P. parvum may use other traits to become competitive initially, such as mixotrophy. Mixotrophy has been demonstrated in many protists that take up nutrients via photosynthetic processes in addition to phago- and/or osmotrophy. One goal of this study was to examine whether toxicity in P. parvum targeting a potential competitor could be attributed to diffusion of dissolved substances, or if direct contact was required. Using an experimental apparatus that could separate cells of the two species, or allow direct contact, only arrangements allowing direct contact resulted in a rapid decline of cell density for competitor Rhodomonas salina. An experiment was conducted with cultures in which P. parvum was supplied with limiting phosphorus, either as orthophosphate in sterile medium, or as an equivalent amount of total phosphorus in the form of a culture of the cryptophyte R. salina. Rapid lysis of the latter occurred, along with consumption of phosphorus by P. parvum, and net population growth. Together these observations suggest P. parvum individuals produce toxins that kill potential competitors, and then benefit nutritionally by consuming the victim. Thus, the relationship between P. parvum and R. salina, and perhaps with other potential competitors of the former species, is one of intraguild predation.


Harmful algae, Intraguild predation


Biology | Life Sciences


Degree granted by The University of Texas at Arlington

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