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1. Organoclay flocculation as a pathway to export carbon from the sea surface

   https://doi.org/10.1038/s41598-024-79912-z  

   Sharma, Diksha; Menon, Vignesh_Gokuladas; Desai, Manasi; Niu, Danielle; Bates, Eleanor; Kandel, Annie; Zinser, Erik_R; Fields, David_M; O’Toole, George_A; Sharma, Mukul (December 2024, Scientific Reports)

   Abstract Marine microorganisms play a critical role in regulating atmospheric CO₂concentration via the biological carbon pump. Deposition of continental mineral dust on the sea surface increases carbon sequestration but the interaction between minerals and marine microorganisms is not well understood. We discovered that the interaction of clay minerals with dissolved organic matter and a γ-proteobacterium in seawater increases Transparent Exopolymer Particle (TEP) concentration, leading to organoclay floc formation. To explore this observation further, we conducted a microcosm experiment using surface seawater collected from the Spring 2023 phytoplankton bloom in the Gulf of Maine. Unfiltered (natural community) and filtered (200 μm and 3 μm) seawater was sprayed with clay (20 mg L^− 1and 60 mg L^− 1) and incubated. All clay treatments led to a tenfold increase in TEP concentration. 16S rRNA gene amplicon sequence analyses of seawater and settled organoclay flocs showed the dominance of α-proteobacteria, γ-proteobacteria, and Bacteroidota. The initial seawater phytoplankton community was dominated by dinoflagellates followed by a haptophyte (Phaeocystissp.) and diatoms. Following clay addition, dinoflagellate cell abundance declined sharply while diatom cell abundance increased. By analyzing organoclay flocs for 18S rRNA we confirmed that dinoflagellates were removed in the flocs. The clay amendment removed as much as 50% of phytoplankton organic carbon. We then explored the fate of organoclay flocs at the next trophic level by feeding clay and phytoplankton (Rhodomonas salina) toCalanus finmarchicus. The copepod ingestedR. salinaand organoclay flocs and egested denser fecal pellets with 1.8- to 3.6- fold higher sinking velocity compared to controls. Fecal pellet density enhancement could facilitate carbon sequestration through zooplankton diel vertical migration. These findings provide insights into how atmospheric dust-derived clay minerals interact with marine microorganisms to enhance the biological carbon pump, facilitating the burial of organic carbon at depths where it is less likely to exchange with the atmosphere. 

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2. Shore and mid-channel surveys reveal distinct phytoplankton-bacterial population associations along an urban estuary

   https://doi.org/10.3354/ame02012  

   Humphries, GE; Ambrosone, M; Roldan-Ayala, Z; Brown, M; Greenfield, DI (September 2024, Aquatic Microbial Ecology)

   A growing body of literature has highlighted the importance of phytoplankton-bacterial associations to marine and estuarine ecological and biogeochemical function, but their population linkages remain sparsely characterized within urban estuaries. Since many developed coastlines are heavily impacted by anthropogenic nutrient inputs, elucidating their phytoplankton-bacterial dynamics provides insight into nutrient cycling, productivity, and can help inform water quality management. This study compared surface (0.5 m depth) physical water quality, cell abundances of major phytoplankton taxa and bacteria, as well as concentrations of chlorophylla(chla) and dissolved organic matter (DOM) in the nitrogen (N)-enriched Western Long Island Sound (WLIS), USA, between mid-channel and shore sites (in 2020 and 2021). Shore bacterial and phytoplankton abundances as well as DOM concentrations (primarily dissolved organic N and carbon [DOC]), were significantly higher than mid-channel, especially during summer, indicative of terrestrial loading influencing microbial assemblages as well as N and C cycling. Abundances of key phytoplankton taxa were better indicators of bacterial abundances than chla, as bacterial abundances positively and significantly correlated with those of dinoflagellates, especially the most common generaProrocentrum(mid-channel, shore) andHeterocapsa(shore only), but not with diatoms. However, pennate diatom abundances negatively and significantly correlated with DOC concentrations in the mid-channel. Results highlight the impact of terrestrial inputs on WLIS microbial assemblage dynamics, presumably by favoring bacteria and dinoflagellate population coupling, as well as shed new ecological insight into how phytoplankton and bacterial communities respond to nutrient loadings in urban estuaries. 

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3. 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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4. The interaction of physical and biological factors drives phytoplankton spatial distribution in the northern California Current

   https://doi.org/10.1002/lno.11431  

   Krause, Jeffrey W.; Brzezinski, Mark A.; Largier, John L.; McNair, Heather M.; Maniscalco, Michael; Bidle, Kay D.; Allen, Andrew E.; Thamatrakoln, Kimberlee (February 2020, Limnology and Oceanography)

   Abstract Transitions in phytoplankton community composition are typically attributed to ecological succession even in physically dynamic upwelling systems like the California Current Ecosystem (CCE). An expected succession from a high‐chlorophyll (~ 10μg L⁻¹) diatom‐dominated assemblage to a low‐chlorophyll (< 1.0μg L⁻¹) non‐diatom dominated assemblage was observed during a 2013 summer upwelling event in the CCE. Using an interdisciplinary field‐based space‐for‐time approach leveraging both biogeochemical rate measurements and metatranscriptomics, we suggest that this successional pattern was driven primarily by physical processes. An annually recurring mesoscale eddy‐like feature transported significant quantities of high‐phytoplankton‐biomass coastal water offshore. Chlorophyll was diluted during transport, but diatom contributions to phytoplankton biomass and activity (49–62% observed) did not decline to the extent predicted by dilution (18–24% predicted). Under the space‐for‐time assumption, these trends infer diatom biomass and activity and were stimulated during transport. This is hypothesized to result from decreased contact rates with mortality agents (e.g., viruses) and release from nutrient limitation (confirmed by rate data nearshore), as predicted by the Disturbance‐Recovery hypothesis of phytoplankton bloom formation. Thus, the end point taxonomic composition and activity of the phytoplankton assemblage being transported by the eddy‐like feature were driven by physical processes (mixing) affecting physiological (release from nutrient limitation, increased growth) and ecological (reduced mortality) factors that favored the persistence of the nearshore diatoms during transit. The observed connection between high‐diatom‐biomass coastal waters and non‐diatom‐dominated offshore waters supports the proposed mechanisms for this recurring eddy‐like feature moving seed populations of coastal phytoplankton offshore and thereby sustaining their activity. 

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5. Dinoflagellates alter their carbon and nutrient metabolic strategies across environmental gradients in the central Pacific Ocean

   https://doi.org/10.1038/s41564-020-00814-7  

   Cohen, Natalie R.; McIlvin, Matthew R.; Moran, Dawn M.; Held, Noelle A.; Saunders, Jaclyn K.; Hawco, Nicholas J.; Brosnahan, Michael; DiTullio, Giacomo R.; Lamborg, Carl; McCrow, John P.; et al (January 2021, Nature Microbiology)

   null (Ed.)

   Marine microeukaryotes play a fundamental role in biogeochemical cycling through the transfer of energy to higher trophic levels and vertical carbon transport. Despite their global importance, microeukaryote physiology, nutrient metabolism and contributions to carbon cycling across offshore ecosystems are poorly characterized. Here, we observed the prevalence of dinoflagellates along a 4,600-km meridional transect extending across the central Pacific Ocean, where oligotrophic gyres meet equatorial upwelling waters rich in macronutrients yet low in dissolved iron. A combined multi-omics and geochemical analysis provided a window into dinoflagellate metabolism across the transect, indicating a continuous taxonomic dinoflagellate community that shifted its functional transcriptome and proteome as it extended from the euphotic to the mesopelagic zone. In euphotic waters, multi-omics data suggested that a combination of trophic modes were utilized, while mesopelagic metabolism was marked by cytoskeletal investments and nutrient recycling. Rearrangement in nutrient metabolism was evident in response to variable nitrogen and iron regimes across the gradient, with no associated change in community assemblage. Total dinoflagellate proteins scaled with particulate carbon export, with both elevated in equatorial waters, suggesting a link between dinoflagellate abundance and total carbon flux. Dinoflagellates employ numerous metabolic strategies that enable broad occupation of central Pacific ecosystems and play a dual role in carbon transformation through both photosynthetic fixation in the euphotic zone and remineralization in the mesopelagic zone. 

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