The global carbon cycle is in part modified by marine biological processes, which can impact the amount of carbon that is transported from surface waters to the deep ocean. In this project, we observed interactions between planktonic grazers and marine snow aggregates – sinking particles that form in the surface ocean and have been shown to play an important role in the global carbon cycle and marine food webs. Although the small scale of these biological processes makes them challenging to study, we were able to use high-resolution cameras and computational techniques to analyze the images to directly observe the behavior of zooplankton interacting with marine snow aggregates, and the resulting effects on the aggregates themselves. In a first set of experiments, we applied two methodologies to confirm the ingestion of marine snow by a common species of copepods off the coast of Southern California, Calanus pacificus. Results from these experiments show that the consumption of marine snow by these copepods depends on properties related to the composition of the marine snow, and in some cases can even match or exceed their consumption of individual phytoplankton. In a second study, we observed copepods foraging in layers of marine snow aggregates, which have been commonly observed in coastal waters. We found that copepod behavior and ingestion is altered by the presence of a marine snow layer and a sharp density gradient, indicating that copepods respond to physical and/or chemical cues at the layer, thus providing insight into how different conditions in natural systems would impact these interactions. One of the most important findings arose from experiments in which we observed copepods interacting and ingesting marine snow on very small scales using high-speed cameras. These observations demonstrated that these interactions can result in the fragmentation and deformation of marine snow aggregates – a process which had never previously been directly observed. Since marine snow aggregates breaking up into smaller particles would likely result in them sinking more slowly, this has important implications for the rate that carbon is sequestered in the deep ocean. Lastly, we developed a mathematical model simulating how the chemical plume behind a sinking marine snow aggregate will be altered when that particle crosses a sharp density gradient and slows down; this phenomenon could affect the rate that these particles are ingested by zooplankton since these chemical plumes are used by organisms to chemically detect these particles. All of these findings collectively contribute to a better understanding of how interactions between zooplankton and aggregates affect the marine carbon cycle. This project also included an educational initiative, for which a new interdisciplinary course on Mathematical Modeling in Ecology was developed to teach undergraduate students how to apply advanced mathematical and computational techniques to address important ecological problems. Funding from this grant also provided experience for a postdoctoral scholar, multiple graduate students, and over 20 undergraduate students in conducting research on this topic using laboratory methods and computational techniques, thus training a new generation of oceanographic scholars to tackle problems at the interface of ecology and mathematics.

Last Modified: 11/18/2024
Modified by: Jennifer Prairie