Project: Collaborative Research: Quantifying the impact of oxylipin chemical signaling on microbial community dynamics and biogeochemical cycling

NSF Award Abstract:
Diatoms are eukaryotic phytoplankton that are responsible for ~25% of photosynthesis globally. Many species of diatoms produce chemical signals called oxylipins under stressful circumstances such as nutrient limitation, wounding due to grazing, and viral infection. These chemical signals are detrimental to many organisms that make up microbial food webs in the ocean, like other eukaryotic phytoplankton, microzooplankton and copepods that graze on phytoplankton, and free-living bacteria. However, particle-associated bacterial communities are stimulated by low doses of oxylipins, and diatoms can use these chemical signals to communicate amongst themselves about impending stress. Because these microbial food webs play a critical role in the Earth's carbon cycle and these ecosystems ultimately support fisheries, it is important to understand the role chemical signaling plays as diatom blooms spin up and crash in productive upwelling regions. Here the investigators propose a field expedition with a series of deck-board incubations to study the effects of oxylipins on community dynamics in the California Current Ecosystem. The team also proposes a series of laboratory-based predator-prey studies to quantify the effects of oxylipins on microzooplankton grazers by documenting behavior with microvideography. The major questions that will be addressed include: 1) how does the concentration and diversity of oxylipins change over the course of a bloom? 2) what is the net impact of oxylipin signaling on community dynamics? 3) how do oxylipins impact carbon export and nutrient recycling (N, P, Si)? Outreach activities undertaken during the lifetime of this grant have the primary goals of introducing young people to microbial oceanography, training a diverse oceanographic workforce, and creating content that can be accessed by inquiring minds after the lifetime of this grant. To accomplish this, undergraduate and graduate scientists are being trained during this project through direct participation on the planned cruise, in the lab, and in classrooms through virtual live-streaming cruise activities and in-person teaching. Some of these students are recruited specifically from programs that increase participation from underrepresented groups. This project also uses cruise data to design data-analysis tutorials and workshops in order to engage the broader science community. Middle and high school students from local urban areas are also being trained on educational day trips in the coastal waters around Cape Cod. A curriculum is being developed for grade 8-12 classrooms related to the work of this project.

This is the first study to profile the full diversity of oxylipins produced across dissolved, cellular, and detrital (i.e., marine snow) fractions. It is the first study to simultaneously assess in situ drivers of oxylipin production (nutrient stress, grazing, and viral infection) within an ecosystem. The project is also be the first to fully characterize oxylipin concentrations and diversity over the course of a bloom within an Eastern Boundary Current. The ultimate goal of this project is to understand how oxylipin-mediated signaling impacts the fate of carbon, so the team will be monitoring export efficiency, net primary productivity, bacterial productivity, and nutrient recycling throughout the field campaign. This project adds to the relatively small number of metatranscriptomic datasets from sinking particle communities and marine lipidomic datasets available in public repositories. The data generated by the Lagrangian Study can be used to ask more general questions about connectivity between the surface and deep ocean, community succession, and the geochemical evolution of blooms. Finally, the proposed research transforms our collective understanding of how chemical signaling impacts grazing behavior and the mechanism of oxylipin grazing deterrence by simultaneously assessing grazing rates, selection, and behavior of microzooplankton in the presence of exogenous oxylipins and when offered high and low oxylipin-producing prey. State-of-the-art microvideography visualizes and quantifies microzooplankton grazing behaviors, and the system will be adapted for measurements of natural communities at sea.

This project is funded by the Biological and Chemical Oceanography Programs in the Division of Ocean Sciences. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.