Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

Edward G Durbin


Polar marine ecosystems are highly productive, with strong seasonal phytoplankton blooms, and high abundances of vertebrate predators. A key link between these phytoplankton and megafauna are the zooplankton, which package and transform phytoplankton biomass, making it available to the fish, mammals, seabirds, and other predators in the ecosystem. I investigated three groups of these important small eukaryotes. In the Bering Sea I analyzed the diet of three morphologically very similar congeners of Pseudocalanus copepods. The two copepod species with largely overlapping geographic ranges were found to have different diets, suggesting feeding differences may serve as a mechanism of niche partitioning between these two species, reducing competition and allowing them both to persist simultaneously. In the West Antarctic Peninsula region the distribution of krill, and the diversity and distribution of microeukaryotes were analyzed in winter. Krill were concentrated within the fjords along the coast, with the few krill found in more offshore stations small, young-of-the-year individuals. Microeukaryotes in the peninsula region included organisms from nearly every major eukaryotic lineage. Microeukaryote assemblages were different in surface waters, deep-waters, and sediments, with further differences by geographic location. Sequences for multiple phytoplankton groups in sediment samples suggest the importance of resting stages, and of the sediments as a seed bank for the highly seasonal phytoplankton bloom. Enhanced understanding of the ecology of these polar ecosystems may potentially allow for improvements in modeling and fisheries management in these regions, and also serves as a baseline against which future changes may be compared.