Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Trick, Charles G.


Heterosigma akashiwo (Y.Hada) Y.Hada ex Y.Hara & M.Chihara is a golden-brown phytoflagellate with high potential to kill fish. These cells create large, nearly mono-specific blooms that persist from weeks to months. Although bloom persistence and frequency remain a mystery, environmental factors such as light, temperature, salinity and CO2 level are proposed as drivers for both bloom initiation and toxicity. As timing and locations of nature blooms are difficult to predict, most of the information on this species comes from laboratory experiments on isolated cells. In this age, when multiple stressors occur simultaneously the traditional “One-factor-at-a-time” (OFAT) approach limits our understanding of how the cells respond to environmental change. Here, I consider the simultaneous effect of multiple parameters and their interaction by employing a design-of-experiment (DOE) approach. The results suggested that the DOE approach is an appropriate method to determine the impact of multi-environmental factors on both bloom formation and toxicity of H. akashiwo.

Similarly, the measurement of “fish killing” activities requires the use of an experimental proxy when cells are grown in the laboratory. There is a critical need to understand toxicity in “fish-kill” species. Two commonly employed assays, the rainbow trout cell line RTgill-W1 cytotoxicity assay (RCA) and the erythrocyte lysis assay (ELA) were evaluated against combinatorial environmental conditions (temperature, pCO2, salinity). Increased temperature and pCO2 reduced the expression of toxicicty based on these two assays.

With regards to the future conditions of warmer temperatures, and elevated levels of CO2, which impact the salinity, water temperature, and the absorbance of CO2, in many coastal regions worldwide, it is expected these abiotic changes will likely increase the potential growth rate and biomass yield but reduce the toxicity of fish-killing flagellate H. akashiwo in North America.

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