Biology subjects

Brzezinski, M. A.

Publications and source records attributed to Brzezinski, M. A..

3 recordsLinked to original sources

bioRxiv2025

Phytoplankton phenology through gene expression during the North Atlantic spring bloom decline

While phytoplankton dynamics in the annual North Atlantic spring bloom have been well characterized, the physiological underpinnings driving these changes and their net impact on the biogeochemistry of the region are less understood. Phytoplankton metabolism is both affected by, and influences the regions nutrient cycling, primary production, and ultimately, the fate of carbon export. Thus, developing an understanding of these processes is critical. Phytoplankton biomass, biological rates, and gene expression data along with associated environmental parameters were measured as part of the NASA EXport Processes in the Ocean from RemoTe Sensing programs campaign to the North Atlantic to evaluate the relationships amongst these processes within the four most dominant phytoplankton groups (diatoms, dinoflagellates, haptophytes, and chlorophytes) during the spring bloom. We observe a transition from a period dominated by active diatom growth (defined as Phase I) to a period dominated by non-diatom phytoplankton groups (Phase II). Silicic acid depletion appears to limit overall production and reduce competition from diatoms, likely leading to enhanced contributions of haptophytes in Phase II. Expression of key protein-encoding genes involved in cell maintenance, photosynthesis, and nitrogen and vitamin metabolisms varied amongst the taxa throughout the observation period. Expression patterns of diatom genes involved in silicon transport suggest an apparent uncoupling between genes involved in nitrate uptake and photosynthesis, resulting in an increase in silicification independent growth. Our analysis demonstrates the utility in combining gene expression with biological rate processes to provide a more holistic view of phytoplankton bloom dynamics and phenology.

ecology↗

bioRxiv2023

Quantitative analysis of food web dynamics in a low export ecosystem

Food webs trace the flow of organic matter and energy among producers and consumers; for pelagic marine food webs, network complexity directly influences the amount and form of carbon exported to the deep ocean via the biological pump. Here we present a synoptic view of mixed layer food web dynamics observed during the late summer 2018 EXport Processes in the Ocean from Remote Sensing (EXPORTS) field campaign in the subarctic Northeast Pacific at the long-running time-series site, Ocean Station Papa. Carbon biomass reservoirs of phytoplankton, microzooplankton, and bacterioplankton, were approximately equal while mesozooplankton biomass was 70% lower. Live organisms composed [~]40% of the total particulate organic carbon within the mixed layer: the remainder was attributed to detritus. Rates of carbon transfer among reservoirs indicated production and assimilation rates were well balanced by losses, leaving little organic carbon available for export. The slight positive net community production rate generated organic carbon that was exported from the system in the form of food web byproducts, such as large fecal pellets generated by mesozooplankton. This characteristically regenerative food web had relatively slow turnover times with small-magnitude transfers of carbon relative to standing stocks that occurred amidst a high background concentration of detrital particles and dissolved organic matter. The concurrent estimation of food web components and rates revealed that separated processes dominated the transfer of carbon within the food web compared to those that contributed to export. Plain Language SummaryThe biological carbon pump drives a downward flux of organic matter from the sunlit surface ocean to the vast ocean interior. Ecological interactions in the surface ocean directly affect the amount and type of carbon that is exported to the deep ocean. In this study, we present a synthesis of the late summer mixed layer food web in the Northeast Pacific that was extensively characterized during the 2018 EXport Processes in the Ocean from Remote Sensing (EXPORTS) field campaign. We found the majority of carbon was recycled within the mixed layer by microbes through multiple transfers between producers and consumers. Larger organisms, mesozooplankton and salps, only consumed a small amount of carbon but through the formation of sinking fecal pellets were the main mechanism of transporting carbon out of the system. The study highlights the need to concurrently study microbial and large organism dynamics to develop a predictive understanding of the fate of organic carbon in the oceans. Key PointsO_LIThe microbial loop dominated carbon flow in the late summer mixed layer food web of the North Pacific, most net production was respired leaving little carbon available for export. C_LIO_LIActive production and consumption of organic carbon occurred amid a high background of detrital particulate organic carbon (58% of total) with slow turnover time, 66 d. C_LIO_LIMesozooplankton which had relatively minor carbon consumption rates created the majority of export production due to efficient repackaging of consumed material. C_LI

ecology↗

bioRxiv2018

Divergent gene expression among phytoplankton taxa in response to upwelling

Frequent blooms of phytoplankton occur in coastal upwelling zones creating hotspots of biological productivity in the ocean. As cold, nutrient-rich water is brought up to sunlit layers from depth, phytoplankton are also transported upwards to seed surface blooms that are often dominated by diatoms. The physiological response of phytoplankton to this process, commonly referred to as shift-up, is characterized by rapid growth rates and increases in nitrate assimilation. To examine the molecular underpinnings behind this phenomenon, metatranscriptomics was applied to a simulated upwelling experiment using natural phytoplankton communities from the California Upwelling Zone. An increase in diatom growth following five days of incubation was attributed to the genera Chaetoceros and Pseudo-nitzschia. Here we show that certain bloom-forming diatoms exhibit a distinct transcriptional response that coordinates shift-up where diatoms exhibited the greatest transcriptional change following upwelling; however, comparison of coexpressed genes exposed overrepresentation of distinct sets within each of the dominant phytoplankton groups. The analysis revealed that diatoms frontload genes involved in nitrogen assimilation likely in order to outcompete other groups for available nitrogen during upwelling events. We speculate that the evolutionary success of diatoms may be due, in part, to this proactive response to frequently encountered changes in their environment.

microbiology↗