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1. Tiny Phytoplankton: The Most Powerful Organisms of the Oceans!

   https://doi.org/10.3389/frym.2021.600102  

   Glibert, Patricia M. (August 2021, Frontiers for Young Minds)

   null (Ed.)

   Although sharks, whales, and other large organisms come to mind when one thinks about the most important or most powerful organisms of the sea, in fact, the most powerful are the tiny phytoplankton. Phytoplankton, which are microscopic algae, hold this power because they harvest the light from the sun, making food for all other organisms. Phytoplankton are the foundation for the ocean ecosystem. Through the process of photosynthesis, they also make oxygen and are responsible for almost half of the oxygen in the world. However, some phytoplankton can also be harmful and can kill fish or damage ecosystems. These harmful phytoplankton can also make people sick. The phytoplankton are tiny but mighty! 

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2. Impact of Lagrangian Sea Surface Temperature Variability on Southern Ocean Phytoplankton Community Growth Rates

   https://doi.org/10.1029/2020GB006880  

   Zaiss, Jessica; Boyd, Philip W.; Doney, Scott C.; Havenhand, Jon N.; Levine, Naomi M. (August 2021, Global Biogeochemical Cycles)

   Abstract Ocean phytoplankton play a critical role in the global carbon cycle, contributing ∼50% of global photosynthesis. As planktonic organisms, phytoplankton encounter significant environmental variability as they are advected throughout the ocean. How this variability impacts phytoplankton growth rates and population dynamics remains unclear. Here, we systematically investigated the impact of different rates and magnitudes of sea surface temperature (SST) variability on phytoplankton community growth rates using surface drifter observations from the Southern Ocean (>30°S) and a phenotype‐based ecosystem model. Short‐term SST variability (<7 days) had a minimal impact on phytoplankton community growth rates. Moderate SST changes of 3–4°C over 7–45 days produced a large time lag between the temperature change and the biological response. The impact of SST variability on community growth rates was nonlinear and a function of the rate and magnitude of change. Additionally, the nature of variability generated in a Lagrangian reference frame (following trajectories of surface water parcels) was larger than that within an Eulerian reference frame (fixed point), which initiated different phytoplankton responses between the two reference frames. Finally, we found that these dynamics were not captured by the Eppley growth model commonly used in global biogeochemical models and resulted in an overestimation of community growth rates, particularly in dynamic, strong frontal regions of the Southern Ocean. This work demonstrates that the timescale for environmental selection (community replacement) is a critical factor in determining community composition and takes a first step towards including the impact of variability and biological response times into biogeochemical models. 

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3. The ecological and biogeochemical state of the North Pacific Subtropical Gyre is linked to sea surface height

   https://doi.org/10.1357/002224019828474241  

   Barone, Benedetto; Coenen, Ashley R.; Beckett, Stephen J.; McGillicuddy, Dennis J.; Weitz, Joshua S.; Karl, David M. (December 2019, Journal of Marine Research)

   Sea surface height (SSH) is routinely measured from satellites and used to infer ocean currents, including eddies, that affect the distribution of organisms and substances in the ocean. SSH not only reflects the dynamics of the surface layer, but also is sensitive to the fluctuations of the main pycnocline; thus it is linked to events of nutrient upwelling. Beyond episodic upwelling events, it is not clear if and how SSH is linked to broader changes in the biogeochemical state of marine ecosystems. Our analysis of 23 years of satellite observations and biogeochemical measurements from the North Pacific Subtropical Gyre shows that SSH is associated with numerous biogeochemical changes in distinct layers of the water column. From the sea surface to the depth of the chlorophyll maximum, dissolved phosphorus and nitrogen enigmatically increase with SSH, enhancing the abundance of heterotrophic picoplankton. At the deep chlorophyll maximum, increases in SSH are associated with decreases in vertical gradients of inorganic nutrients, decreases in the abundance of eukaryotic phytoplankton, and increases in the abundance of prokaryotic phytoplankton. In waters below ∼100 m depth, increases in SSH are associated with increases in organic matter and decreases in inorganic nutrients, consistent with predicted consequences of the vertical displacement of isopycnal layers. Our analysis highlights how satellite measurements of SSH can be used to infer the ecological and biogeochemical state of open-ocean ecosystems. 

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4. Rival phytoplankton contribute to the cross protection of Prochlorococcus from oxidative stress

   https://doi.org/10.1128/aem.01128-24  

   Calfee, Benjamin C; Bowden, Emily C; Zinser, Erik R (May 2025, Applied and Environmental Microbiology)

   Bose, Arpita (Ed.)

   ABSTRACT The marine cyanobacteriumProchlorococcusnumerically dominates the phytoplankton communities in all lower latitude, open ocean environments. Having lost the catalase gene,Prochlorococcusis highly susceptible to exogenous hydrogen peroxide (H₂O₂) produced at the ocean’s surface. Protection by H₂O₂-scavenging heterotrophic “helper” bacteria has been demonstrated in laboratory cultures and implicated as an important mechanism ofProchlorococcussurvival in the ocean. Importantly, some other phytoplankton can also scavenge H₂O₂, suggesting these competing microbes may inadvertently protectProchlorococcus. In this study, we assessed the ability of co-occurring phytoplankton, the cyanobacteriumSynechococcusand picoeukaryotesMicromonasandOstreococcus, to protectProchlorococcusfrom H₂O₂exposure when cocultured at ecologically relevant abundances. All three genera could significantly degrade H₂O₂and diminishProchlorococcusmortality during H₂O₂exposures simulating photochemical production and rainfall events. We suggest that these phytoplankton groups contribute significantly to the H₂O₂microbial sink of the open ocean, thus complicating their relationships with and perhaps contributing to the evolutionary history ofProchlorococcus.IMPORTANCEThe marine cyanobacteriumProchlorococcusis the most abundant photosynthetic organism on the planet and is crucially involved in microbial community dynamics and biogeochemical cycling in most tropical and subtropical ocean waters. This success is due, in part, to the detoxification of the reactive oxygen species hydrogen peroxide (H₂O₂) performed by “helper” organisms. Earlier work identified heterotrophic bacteria as helpers, and here, we demonstrate that rival cyanobacteria and picoeukaryotic phytoplankton can also contribute to the survival ofProchlorococcusduring exposure to H₂O₂. Whereas heterotrophic bacteria helper organisms can benefit directly from promoting the survival of carbon-fixingProchlorococcuscells, phytoplankton helpers may suffer a twofold injury: production of H₂O₂degrading enzymes constrains already limited resources in oligotrophic environments, and the activity of these enzymes bolsters the abundance of their numerically dominant competitor. These findings build toward a better understanding of the intricate dynamics and interactions that shape microbial community structure in the open ocean. 

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5. Marine phytoplankton resilience may moderate oligotrophic ecosystem responses and biogeochemical feedbacks to climate change

   https://doi.org/10.1002/lno.12029  

   Martiny, Adam C.; Hagstrom, George I.; DeVries, Tim; Letscher, Robert T.; Britten, Gregory L.; Garcia, Catherine A.; Galbraith, Eric; Karl, David; Levin, Simon A.; Lomas, Michael W.; et al (February 2022, Limnology and Oceanography)

   Abstract Are the oceans turning into deserts? Rising temperature, increasing surface stratification, and decreasing vertical inputs of nutrients are expected to cause an expansion of warm, nutrient deplete ecosystems. Such an expansion is predicted to negatively affect a trio of key ocean biogeochemical features: phytoplankton biomass, primary productivity, and carbon export. However, phytoplankton communities are complex adaptive systems with immense diversity that could render them at least partially resilient to global changes. This can be illustrated by the biology of theProchlorococcus“collective.” Adaptations to counter stress, use of alternative nutrient sources, and frugal resource allocation can allowProchlorococcusto buffer climate‐driven changes in nutrient availability. In contrast, cell physiology is more sensitive to temperature changes. Here, we argue that biogeochemical models need to consider the adaptive potential of diverse phytoplankton communities. However, a full understanding of phytoplankton resilience to future ocean changes is hampered by a lack of global biogeographic observations to test theories. We propose that the resilience may in fact be greater in oligotrophic waters than currently considered with implications for future predictions of phytoplankton biomass, primary productivity, and carbon export. 

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