One of the central issues in biological oceanography is to understand the processes that regulate the biomass and distribution of phytoplankton in the ocean. The fate of most phytoplankton is to be consumed by grazers, and it is now generally accepted that marine planktonic protists are the most important grazers on phytoplankton, and that grazing by protists can fundamentally affect phytoplankton biomass and distribution in the ocean. Protists can become temporarily very abundant (up to tens of thousands per liter) and can grow nearly as rapidly as phytoplankton do, which gives them great potential to regulate phytoplankton populations. Adaptations by protists to feed selectively on the fastest growing species of phytoplankton and to reduce predation by metazoan zooplankton should enhance the coupling between phytoplankton growth and grazing, and therefore promote planktonic ecosystem stability. Compared to larger metazoan zooplankton such as copepods, relatively little is known about the morphological and behavioral adaptations in protists for selective feeding and predator avoidance.
The PIs will study details of selective feeding behavior and predator avoidance behavior of free-swimming planktonic protists in 3-dimension using high-speed video. Under the same conditions, they will measure flow fields imposed by individual free-swimming protists using a time-resolving stereo micro-particle image velocimetry (microPIV) system. To gain a mechanistic understanding, they will also conduct empirical data-driven, reality-reproducing computational fluid dynamics (CFD) simulations of the protist-imposed flow fields. The results will be used to test the hypothesis that diversity and flexibility in propulsive morphology facilitates protists to achieve sophisticated swimming behaviors and sensory perception capabilities that adapt them for selective feeding and predator avoidance. These capabilities may also serve as important driving forces for protistan biodiversity, represented by various sizes, shapes, propulsive morphologies and motility patterns.
Two graduate students will participate in this project and will receive training in plankton ecology and marine biology; in theoretical/computational/experimental plankton fluid mechanics; and in setting up and using sophisticated optical systems. Conducting research in the field of small-scale biological-physical interactions in plankton ecology requires interdisciplinary knowledge, and this training will benefit their preparation for conducting interdisciplinary research. The PIs will construct an easily-followed and interactive online learning module based on their results, and will make video clips of protistan behavior available to educators and the public at large through their web sites.