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1. Interactive effects of light, CO2 and temperature on growth and resource partitioning by the mixotrophic dinoflagellate, Karlodinium veneficum

   https://doi.org/10.1371/journal.pone.0259161  

   Coyne, Kathryn J. ; Salvitti, Lauren R. ; Mangum, Alicia M. ; Ozbay, Gulnihal ; Main, Christopher R. ; Kouhanestani, Zohreh M. ; Warner, Mark E. ( October 2021 , PLOS ONE)

   Anil, Arga Chandrashekar (Ed.)

   There is little information on the impacts of climate change on resource partitioning for mixotrophic phytoplankton. Here, we investigated the hypothesis that light interacts with temperature and CO 2 to affect changes in growth and cellular carbon and nitrogen content of the mixotrophic dinoflagellate, Karlodinium veneficum , with increasing cellular carbon and nitrogen content under low light conditions and increased growth under high light conditions. Using a multifactorial design, the interactive effects of light, temperature and CO 2 were investigated on K . veneficum at ambient temperature and CO 2 levels (25°C, 375 ppm), high temperature (30°C, 375 ppm CO 2 ), high CO 2 (30°C, 750 ppm CO 2 ), or a combination of both high temperature and CO 2 (30°C, 750 ppm CO 2 ) at low light intensities (LL: 70 μmol photons m -2 s -2 ) and light-saturated conditions (HL: 140 μmol photons m -2 s -2 ). Results revealed significant interactions between light and temperature for all parameters. Growth rates were not significantly different among LL treatments, but increased significantly with temperature or a combination of elevated temperature and CO 2 under HL compared to ambient conditions. Particulate carbon and nitrogen content increased in response to temperature or a combination of elevated temperature and CO 2 under LL conditions, but significantly decreased in HL cultures exposed to elevated temperature and/or CO 2 compared to ambient conditions at HL. Significant increases in C:N ratios were observed only in the combined treatment under LL, suggesting a synergistic effect of temperature and CO 2 on carbon assimilation, while increases in C:N under HL were driven only by an increase in CO 2 . Results indicate light-driven variations in growth and nutrient acquisition strategies for K . veneficum that may benefit this species under anticipated climate change conditions (elevated light, temperature and p CO 2 ) while also affecting trophic transfer efficiency during blooms of this species. 

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2. Tropical cyclones: what are their impacts on phytoplankton ecology?

   https://doi.org/10.1093/plankt/fbac062  

   Thompson, Peter A. ; Paerl, Hans W. ; Campbell, Lisa ; Yin, Kedong ; McDonald, Karlie S. ( November 2022 , Journal of Plankton Research)

   Following the passage of a tropical cyclone (TC) the changes in temperature, salinity, nutrient concentration, water clarity, pigments and phytoplankton taxa were assessed at 42 stations from eight sites ranging from the open ocean, through the coastal zone and into estuaries. The impacts of the TC were estimated relative to the long-term average (LTA) conditions as well as before and after the TC. Over all sites the most consistent environmental impacts associated with TCs were an average 41% increase in turbidity, a 13% decline in salinity and a 2% decline in temperature relative to the LTA. In the open ocean, the nutrient concentrations, cyanobacteria and picoeukaryote abundances increased at depths between 100 and 150 m for up to 3 months following a TC. While at the riverine end of coastal estuaries, the predominate short-term response was a strong decline in salinity and phytoplankton suggesting these impacts were initially dominated by advection. The more intermediate coastal water-bodies generally experienced declines in salinity, significant reductions in water clarity, plus significant increases in nutrient concentrations and phytoplankton abundance. These intermediate waters typically developed dinoflagellate, diatom or cryptophyte blooms that elevated phytoplankton biomass for 1–3 months following a TC.

    

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3. Characterizing coastal phytoplankton seasonal succession patterns on the West Antarctic Peninsula

   https://doi.org/10.1002/lno.12314  

   Nardelli, Schuyler C. ; Gray, Patrick C. ; Stammerjohn, Sharon E. ; Schofield, Oscar ( February 2023 , Limnology and Oceanography)

   In coastal West Antarctic Peninsula (WAP) waters, large phytoplankton blooms in late austral spring fuel a highly productive marine ecosystem. However, WAP atmospheric and oceanic temperatures are rising, winter sea ice extent and duration are decreasing, and summer phytoplankton biomass in the northern WAP has decreased and shifted toward smaller cells. To better understand these relationships, an Imaging FlowCytobot was used to characterize seasonal (spring to autumn) phytoplankton community composition and cell size during a low (2017–2018) and high (2018–2019) chlorophyllayear in relation to physical drivers (e.g., sea ice and meteoric water) at Palmer Station, Antarctica. A shorter sea ice season with early rapid retreat resulted in low phytoplankton biomass with a low proportion of diatoms (2017–2018), while a longer sea ice season with late protracted retreat resulted in the opposite (2018–2019). Despite these differences, phytoplankton seasonal succession was similar in both years: (1) a large‐celled centric diatom bloom during spring sea ice retreat; (2) a peak summer phase comprised of mixotrophic cryptophytes with increases in light and postbloom organic matter; and (3) a late summer phase comprised of small (< 20 μm) diatoms and mixed flagellates with increases in wind‐driven nutrient resuspension. In addition, cell diameter decreased from November to April with increases in meteoric water in both years. The tight coupling between sea ice, meltwater, and phytoplankton species composition suggests that continued warming in the WAP will affect phytoplankton seasonal dynamics, and subsequently seasonal food web dynamics.

    

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4. Phytoplankton assemblage responses to nitrogen following COVID-19 stay–in–place orders in western Long Island Sound (New York/Connecticut)

   https://doi.org/10.1016/j.marenvres.2024.106371  

   Brown, Maximillian ; Ambrosone, Mariapaola ; Turner, Kyle J. ; Humphries, Georgie E. ; Tzortziou, Maria ; Anglès, Sílvia ; Panzeca, Caterina ; Greenfield, Dianne I. ( April 2024 , Marine Environmental Research)

   This study evaluated water quality, nitrogen (N), and phytoplankton assemblage linkages along the western Long Island Sound (USA) shoreline (Nov. 2020 – Dec. 2021) following COVID-19 stay-in-place (SIP) orders through monthly surveys and N-addition bioassays. Ammonia-N (AmN; NH3+NH4+) negatively correlated with total chlorophyll-a (chl-a) at all sites; this was significant at Alley Creek, adjacent to urban wastewater inputs, and at Calf Pasture, by the Norwalk River (Spearman rank correlation, p<0.01 and 0.02). Diatoms were abundant throughout the study, though dinoflagellates (Heterocapsa, Prorocentrum), euglenoids/cryptophytes, and both nano- and picoplankton biomass increased during summer. In field and experimental assessments, high nitrite+nitrate (N+N) and low AmN increased diatom abundances while AmN was positively linked to cryptophyte concentrations. Likely N+N decreases with presumably minimal changes in AmN and organic N during COVID-19 SIP resulted in phytoplankton assemblage shifts (decreased diatoms, increased euglenoids/cryptophytes), highlighting the ecological impacts of N-form delivered by wastewater to urban estuaries. 

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5. Diminished carbon and nitrate assimilation drive changes in diatom elemental stoichiometry independent of silicification in an iron-limited assemblage

   https://doi.org/10.1038/s43705-022-00136-1  

   Maniscalco, Michael A. ; Brzezinski, Mark A. ; Lampe, Robert H. ; Cohen, Natalie R. ; McNair, Heather M. ; Ellis, Kelsey A. ; Brown, Matthew ; Till, Claire P. ; Twining, Benjamin S. ; Bruland, Kenneth W. ; et al ( July 2022 , ISME Communications)

   In the California Current Ecosystem, upwelled water low in dissolved iron (Fe) can limit phytoplankton growth, altering the elemental stoichiometry of the particulate matter and dissolved macronutrients. Iron-limited diatoms can increase biogenic silica (bSi) content >2-fold relative to that of particulate organic carbon (C) and nitrogen (N), which has implications for carbon export efficiency given the ballasted nature of the silica-based diatom cell wall. Understanding the molecular and physiological drivers of this altered cellular stoichiometry would foster a predictive understanding of how low Fe affects diatom carbon export. In an artificial upwelling experiment, water from 96 m depth was incubated shipboard and left untreated or amended with dissolved Fe or the Fe-binding siderophore desferrioxamine-B (+DFB) to induce Fe-limitation. After 120 h, diatoms dominated the communities in all treatments and displayed hallmark signatures of Fe-limitation in the +DFB treatment, including elevated particulate Si:C and Si:N ratios. Single-cell, taxon-resolved measurements revealed no increase in bSi content during Fe-limitation despite higher transcript abundance of silicon transporters and silicanin-1. Based on these findings we posit that the observed increase in bSi relative to C and N was primarily due to reductions in C fixation and N assimilation, driven by lower transcript expression of key Fe-dependent genes.

    

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