We are broadly interested in quantifying the links and feedback between global ocean changes and microbially-mediated biogeochemistry. Projects in the lab span microbial physiology, evolution, and ecology to large-scale ocean biogeochemical cycles (carbon, oxygen, nutrients). Below is a brief overview of some of the ongoing projects.
Ocean microbiomes and ecosystem function (Bio-GO-SHIP)
We are deeply involved in an effort to quantify ocean plankton biodiversity functional potential across the globe. The project is part of Bio-GO-SHIP (see website for more details). The goal is to sample most ocean regions within a decade. From this, we can learn many things, including patterns of biodiversity, how plankton diversity and abundance are responding to current (and presumably future) ocean changes, linkages between shifting biodiversity and ecosystem functions, and much more.
Plankton as sentinels of ocean changes
Marine microorganisms adapt or acclimate rapidly to ocean environmental change via genome-wide mutations or transcriptional changes. Therefore, we can use microbes as living biosensors for ocean change. We have applied this principle to provide the first global estimation of N, P, and Fe ocean limitations (Ustick et al., 2021). We are also managing a long-term time series in California where, for example, El Niño events can help us understand the effect of future warming on local marine ecosystems.
Ecological stoichiometry of marine plankton
The ocean carbon and nutrient cycles are coupled via the resource demands of surface ecosystems. Phytoplankton are nutrient limited in most ocean regions. Thus, the maximal level of CO2 fixation is regulated by the carbon-to-nutrient biomass ratio. For nearly a century, this C:N:P ratio was assumed to be fixed at 106:16:1 (aka the Redfield Ratio). Through a myriad of projects, our lab has demonstrated the C:N:P ratio (i) varies between oceans, (ii) is regulated by a hierarchy of environmental factors, and (iii) is likely important for ocean productivity and carbon sequestration. In the next phase of this project, we aim to (i) understand the detailed molecular regulation of C:N:P, (ii) build genome-scale models to mechanistically predict changes in phytoplankton macromolecular allocations under different environmental conditions, (iii) map the biogeography of C:N:P in polar regions, and (iv) simulate how the ocean-wide C:N:P will be affected by climate change.
We use a combination of lab cultures, fieldwork, and modeling in this project.
Ocean deoxygenation
Ocean observations suggest a decline in the oxygen of more than 2% since 1960 and this can become a very serious threat to marine life. One of the major unknowns for the regulation of ocean oxygen levels is the biological demand. Our lab is trying to understand the detailed coupling between carbon being sequestered in the deep ocean and the biological oxygen demand. This coupling is determined by an obscure biogeochemical factor called the respiration quotient. However, this biogeochemical factor is likely very important for future oxygen levels. Our lab is trying to measure the respiration quotient across ocean environments to understand how it is regulated and might change with rising ocean temperature and increased nutrient limitation.
Combining remote sensing and ‘omics to detect ocean changes
In collaboration with Mike Behrenfeld and Toby Westberry at Oregon State University, we have a new project that links genomic nutrient stress biomarkers with satellite remote sensing of phytoplankton physiological status and community composition. Our research objective is to develop a remote sensing algorithm that distinguishes nitrogen, phosphate, and iron stress in surface ocean phytoplankton populations. We will then apply this algorithm to global ocean color data to understand the regional shifts in nutrient limitation and to understand the vulnerability of coastal and pelagic ecosystems to future water column stratification.
This project combines fieldwork and ‘big data analysis.
Microbes in the Coastal Region of Orange County (MICRO)
The California coastal zone is a critical, mid-latitude eastern boundary upwelling system home to diverse species that are threatened by both warming and terrestrial inputs from 26.3 million coastal residents. In this system, El Niño acts as a natural analog for climate change impacts at timescales relevant to microbial communities. However, little is known about in situ bacterial responses to anomalous warming and associated nutrient limitation in coastal environments. In order to characterize these responses, our laboratory has been collecting weekly samples at the Newport Beach Pier since 2009. Data collected by our lab include nitrate, high-sensitivity soluble reactive phosphorus (P), particulate organic C, N, and P, and microbial community genomic DNA.
In October of 2021, a pipeline break off the coast of Huntington Beach leaked thousands of gallons of oil and impacted the MICRO time series location. In response, our lab worked with collaborators at UCI and beyond to form the Southern California Oil Spill Project to characterize the impacts of this spill.
For more information on the MICRO time series, please see our MICRO resources page.