Date of Graduation

Spring 2017

Document Type

Honors Research Project

Degree Name

Bachelor of Science



Research Sponsor

Dr. Peter Lavrentyev

First Reader

Dr. Randall Mitchell

Second Reader

Dr. Anne Wiley


Diatoms, one of the most common classes of phytoplankton, are autotrophic plankton, and are the primary food source for many organisms. Diatoms play a key role in nearly all oceanic food webs. Under stressful conditions, diatoms can undergo biological changes that produce cytotoxic secondary metabolites such as polyunsaturated aldehydes (PUA’s). This process is a form of allelopathy, utilized by many algae as a defense mechanism against predation, as well as to inhibit competitors. Microzooplankton are an essential part of these aquatic food webs as well, as they are a key herbivore in many oceanic environments. A set of experiments was performed using dissolved PUA (2E,4E-octadienal and 2E,4E-heptadienal), natural phytoplankton and microzooplankton, and the copepod Acartia tonsa. This study focused on the effectiveness of PUA’s in inhibiting microzooplankton predation on marine phytoplankton, as well as the extent of growth rate reduction of diatom competitors. The results of this study showed significant changes in phytoplankton grazing loss rates for picoplankton and larger phytoplankton in the presence of PUA in 8 of 10 experiments. On the other hand, PUA treatments did not induce significant changes in the phytoplankton growth rates.