The Role of Zooplankton in Regulating Carbon Export and Phytoplankton Community Structure: Integrating Models and Observations

Kevin Matthew Archibald, Ph.D., 2021
Michael Neubert, Co-Adivsor
Heidi Sosik, Co-Advisor
In this thesis, I explore two topics in plankton ecology using a combination of models and observations. First, I investigate the role of zooplankton diel vertical migrations (DVM) in contributing to the vertical flux of carbon in the biological pump using a global model driven by satellite measurements of primary productivity. While the significance of DVM to the biological pump has been speculated upon for many years, quantitative estimates of its impact are rare. I estimate that DVM constitutes approximately 16% of the global carbon export flux associated with the biological pump. In later chapters, I build two Nutrient-Phytoplankton-Zooplankton models incorporating different levels of complexity to evaluate the role of nutrient supply and grazing in promoting phytoplankton diversity, using the distribution of biomass between size classes as a proxy. Zooplankton switching plays a significant role in promoting diversity because it allows competing phytoplankton types to coexist in situations that would otherwise lead to competitive exclusion. Finally, I describe patterns in phytoplankton community size structure in the shelfbreak region of the Northeast U.S. Shelf from data collected on a series of cruises. I evaluate these patterns in the context of hypotheses generated based on my analysis of the NPZ models.