Meredith successfully defended her Ph.D dissertation titled ‘The Influence of Phytoplankton Productivity and Molecular Physiology on Biogeochemical Dynamics of Two Contrasting Ocean Environments’. Meredith examined primary productivity dynamics as part of the NASA EXPORTS program field campaigns in the North Pacific and North Atlantic. She used a combination of physiological and molecular methods to elucidate how phytoplankton respond to their environment and influence the export of carbon from the surface ocean. She also conducted laboratory studies on Bathycoccus, an important picoeukaryote from the North Pacific. Meredith will be starting a post-doc at the University of East Anglia this summer.
Congratulations to Prisca Lim who defended their M.Sc. thesis titled ‘Drivers of marine phytoplankton diversity and connectivity in the Galápagos Archipelago spanning an ENSO cycle’. Prisca analyzed DNA sequences from our Galápagos cruises from 2014 – 2022 spanning the El Niño in 2015/16 and the La Niña event from 2020-2022. Phytoplankton composition and size structure are highly dependent on the environmental conditions across the region which exhibit both high spatial and temporal variability. Publication soon to follow.
Former PhD student Carly Moreno has led a study just published in mSystems examining how diatom natural assemblages respond to changes in environmental conditions in waters adjacent to the Western Antarctic Peninsula using metatranscriptomic approaches. She also opportunistically examined a bloom of the centric diatom Actinocyclus in coastal waters.
Ph.D student Johnson Lin is the lead author on a study recently published in Limnology and Oceanography where we examined how diatoms respond to upwelling when under various iron states at narrow and wide shelf regions in the California Current System.
Former undergraduate student Emily Pierce led a publication on comparing different methods for identification of diatoms in dynamic coastal communities. In this study, Emily compared 18s rRNA gene analysis with FlowCam imaging and light microscopy. Her findings show some consistencies, although cross-method comparisons should proceed with caution.
Our first paper contribution to the NASA EXPORTS program was recently published in Elementa: Science of the Anthropocene. In this study, Ph.D. candidate Meredith Meyer provides our findings on trends in new and regenerated production during the North Pacific EXPORTS field campaign. Meredith and coauthors show that the majority of net primary production (NPP) is performed by small cells growing on regenerated sources of nitrogen. Yet, any variations in NPP are primary driven by changes in nitrate-based new production.
Our second publication investigating the protistan communities in the Galápagos Archipelago was published recently in Frontiers in Marine Sciences. Former post-doc Se Hyeon jang led this effort to examine how environmental conditions influence marine protists with an emphasis on the micrograzer communities. We also report observation from a red tide bloom in Elizabeth Bay, Isabela Island. A bloom of the dinoflagellate Scripsiella lachrymosa was being actively grazed by another dinoflagellate, Polykrikos kofoidii.
Our new publication led by former graduate student Erika Neave was recently published in Environmental Microbiology. This publication is the first highlighting my groups research in the Galápagos Archipelago where we participated on annual research cruises that spanned the 2015/16 El Niño event. In this study, we found that the composition of the marine protist community was significantly influenced by deep water masses. This suggests that the ocean currents are a major source of plankton seed populations to the surface waters in the Galápagos and thus substantially influences plankton composition when these currents change as a result of El Niño-Southern Oscillation (ENSO) events.
The video below was made by UNC undergraduate Heidi Hannoush, who was a student in my Marine Phytoplankton (MASC444) class last semester. She was inspired by all the phytoplankton groups she learned about and so made this video for an assignment in another class. Enjoy!
In a recent study published in Nature Geosciences led by Chana Kranzler from the Thamatrakoln Lab at Rugers University, we examined how iron limitation in diatoms may affect viral infection. Molecular datasets used in the study were derived from incubation experiments led by members of the Marchetti lab during the IrnBru cruise in the California Upwelling Zone in 2014 and a Line P cruise in the Northeast Pacific in 2015. The study found an interesting ecological trade-off in how growth limitation by low iron availability may result in diatoms being less vulnerable to viral infection by slowing down mortality and reducing viral replication.
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