Sierra Cast

Date of Award


First Advisor

Erin McMullin

Second Advisor

Sarah Snyder


Phytoplankton are the primary producers of the sea, and exhibit seemingly infinite diversity. Despite their importance on a global scale, very little is understood about their activity and behavior. Under specific conditions, phytoplankton will proliferate extensively in what is known as an algal bloom. There are many positive attributes to phytoplankton blooms, particularly due to their prominent role in the carbon cycle, however there are also many detriments worth noting. Blooms can cause hypoxia zones as dead cells sink to the ocean floor and choke the oxygen from the water, and depending on the species in bloom, dangerous levels of biotoxins can be produced, contaminating the water and food chain, building up within the tissues of the oceanic organisms that feed on them. Three such toxigenic genera are Pseudonitzschia, Dinophysis, and Alexandrium, the first being the central focus of this thesis. Species from each of these genera produce harmful toxins and have been implicated in the causation of human shellfish poisonings. Little is known or confirmed about what factors lead to an algal bloom, nor what contributes to the strength, duration, or toxicity of the bloom. In this thesis I examine a large body of data that details the cell counts of these three genera, along with various environmental factors, these being the nutrient levels of nitrate, silicate, ammonium, and phosphate, the presence of other genera in bloom alongside these organisms, precipitation, water temperature, and salinity.

Through data analysis I was able to statistically make correlations between specific nutrients and cell counts of species in the genus Pseudonitzschia. I identified various relationships among phytoplankton genera that tended to bloom simultaneously, illuminating pieces of the complex relationships that these organisms form with each other. I was able to make conclusions about the significance of water temperature, salinity, and precipitation on the ability of Pseudonitzschia, Dinophysis, and Alexandrium to proliferate into blooms. All of these factors contribute to the formation of algal blooms, and though each can be isolated and analyzed on their own, the interactions between them are also important in understanding why algal blooms form, and what constitutes their size, duration, and toxicity.

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