Research Projects

If you are interested in joining the Dyhrman Microbial Oceanography Group please email Dr. Sonya Dyhrman.

Defining the biogeochemical drivers of diatom physiological ecology.

How do diatom species respond to changes in biogeochemistry across marine provinces?  Ongoing work in the North Atlantic seeks to shed light on this question by using quantitative metabolic fingerprinting (QMF) to follow shifts in diatom community composition and metabolism across three oceanic provinces (coast, Gulf Stream, open ocean).  These locations differ dramatically in many factors, including nutrient profiles, predicted patterns of nutrient limitation as well as diatom species composition and abundance.

Mesoscale eddy influences on the taxonomic diversity and expressed functional profiles of large eukaryotic phytoplankton in the North Pacific Subtropical Gyre.

Physical and biological forces influence primary production in the oligotrophic ocean and change across broad temporal and spatial scales. Large eukaryotic phytoplankton, such as diatoms and haptophytes, despite relatively rare occurrence in oligotrophic waters, are responsible for the majority of organic matter flux to the ocean interior and higher trophic levels. Mesoscale eddies are known to have a dramatic impact on phytoplankton community structure and function, enhancing primary productivity and potential carbon export. For this work, we are looking at mesoscale eddy influences on the taxonomic diversity and expressed functional profiles of surface communities of large eukaryotic phytoplankton and their associated heterotrophic bacteria (microbiome) from the North Pacific Subtropical Gyre across annual time-scales.

Resolving the effects of resource availability, predation and competition on brown tide dynamics using metatranscriptomics.

Aureococcus forms dense ecosystem-destructive blooms in the systems where it occurs, but understanding the drivers of these bloom dynamics is still a challenge.  Working in embayments in coastal New York, we are applying a novel dual metatranscriptome sequencing approach to profile the eco-transcriptomic responses of A. anophagefferens and co-occurring phytoplankton over the course of a bloom and in culture.  We are evaluating the expression of known nutrient stress markers to identify factors driving bloom dynamics.  By comparing the responses of Aureococcus and co-occuring phytoplankton, we hope to also describe potential competitive outcomes in a changing ocean.

Dynamics of dissolved organic phosphorus production, composition and bioavailability along a natural marine phosphate gradient.

Primary production and carbon cycling in a number of oceanic regions, including the western North Atlantic, are controlled by dissolved organic phosphorus (DOP), yet its production, composition, and bioavailability is poorly constrained. The overarching goal of this collaborative work is to use paired field and laboratory efforst to provide foundational information on the way DOP molecular characteristics translate into P-bioavailability to marine phytoplankton, and in turn how phytoplankton growing under different DIN:DIP impact the composition and bioavailability of DOP.  This work will use a unique combination of analytical and 'omics (coupled transcriptomic/metabolomic)-based approaches.

Gene expression coordination and metabolic function interactions between Trichodesmium and its microbiome over day–night cycles.

Trichodesmium is a widespread, N2 fixing marine cyanobacterium that drives inputs of newly fixed nitrogen and carbon into the oligotrophic ecosystems where it occurs. Colonies of Trichodesmium ubiquitously occur with heterotrophic bacteria that make up a diverse microbiome, and interactions within this Trichodesmium holobiont could influence the fate of fixed carbon and nitrogen.  We are using metatranscriptome sequencing to identify possible interactions between the Trichodesmium host and microbiome over day-night cycles. To date, we have shown significantly coordinated patterns of gene expression between host and microbiome, many of which had significant day-night periodicity. To fully understand and forecast future ocean dynamics, studies of Trichodesmium must consider the role of the microbiome.

Ecology and evolution of microbial interactions in a changing ocean.

The effect of ocean acidification on calcifying organisms has been well-studied, but less is known about how changing pH will affect phytoplankton. Previous work from our group showed that the mutualistic interaction between the globally abundant cyanobacterium Prochlorococcus and its "helper" bacterium Alteromonas broke down under projected future CO2 conditions, leading to a strong decrease in the fitness of Prochlorococcus. It is possible that such interspecies interactions between microbes are important for many ecological processes, but a lack of understanding of how these interactions evolve makes it difficult to predict how important they are. This project will use laboratory evolution experiments to discover how evolution shapes the interactions between bacteria and algae like Prochlorococcus, and how these co-evolutionary dynamics might influence the biogeochemical processes that shape Earth's climate.

CO2-induced responses in physiology and gene expression among eukaryotic phytoplankton.

With rising atmospheric CO2, phytoplankton face shifts in ocean chemistry including increased dissolved CO2 and acidification that will likely influence the relative competitive fitness of different phytoplankton taxa. We are working to identify the physiological and gene expression responses of different phytoplankton under different concentrations of CO2.  To date, our group has looked at the response of six species of phytoplankton including a diatom, a raphidophyte, two haptophytes, and two dinoflagellates to ambient (~400 ppm) and elevated (~800 ppm) CO2.  Eukaryotic phytoplankton have diverse gene complements and gene expression responses to CO2 perturbations and this effort highlights the value of cross-phyla comparisons for identifying gene families that respond to environmental change.  Understanding the diversity in genetic complement and gene expression response to elevated CO2 can improve predictions of the relative success of phytoplankton taxa in future ecosystems, their impacts on biogeochemical cycles, and harmful algal bloom frequency.