Adriana Lopes dos Santos

• Sim, Clarence Wei Hung; Walde, Marie; Strindberg, Hanna; Kaur, Avneet; Panse, Sophie Le & Gourvil, Priscillia [Show all 9 contributors for this article] (2026). Labyrinthula merlionensis sp. nov.: A Novel Labyrinthulid Infecting Marine Diatoms. Journal of Eukaryotic Microbiology. ISSN 1066-5234. 73(5). doi: 10.1111/jeu.70111. Full text in Research Archive
• Sim, Clarence Wei Hung; Ribeiro, Catherine Gérikas; Gall, Florence Le; Probert, Ian; Gourvil, Priscilla & Lovejoy, Connie [Show all 8 contributors for this article] (2025). Temporal dynamics and biogeography of sympagic and planktonic photosynthetic microbial eukaryotes during the under-ice Arctic bloom. ISME Communications. 5(1). doi: 10.1093/ismeco/ycaf075. Full text in Research Archive Show summary

  Photosynthetic microbial eukaryotes play a pivotal role as primary producers in the Arctic Ocean, where seasonal blooms within and below the ice are crucial phenomena, contributing significantly to global primary production and biogeochemical cycling. In this study, we investigated the taxonomic composition of sympagic algae and phytoplankton communities during the Arctic under-ice spring bloom using metabarcoding of the 18S rRNA gene. Samples were obtained from three size fractions over a period of nearly three months at an ice camp deployed on landfast ice off the coast of Baffin Island as part of the Green Edge project. We classified the major sympagic and phytoplankton taxa found in this study into biogeographical categories using publicly available metabarcoding data from more than 2800 oceanic and coastal marine samples. This study demonstrated the temporal succession of taxonomic groups during the development of the under-ice bloom, illustrated by an overall transition from polar to polar-temperate taxa, particularly in the smallest size fraction. Overlooked classes such as Pelagophyceae (genera Plocamiomonas and Ankylochrysis), Bolidophyceae (Parmales environmental clade 2), and Cryptophyceae (Baffinella frigidus) might play a greater role than anticipated within the pico-sized communities in and under the ice pack during the pre-bloom period. Finally, we emphasize the importance of microdiversity, taking the example of B. frigidus, for which two ecotypes linked to pelagic and sea ice environments have been identified.

• Gochev, Camelia Shopen; Demory, David; Santos, Adriana Lopes dos; Carlson, Michael C. G.; Gutiérrez-Rodríguez, Andrés & Weitz, Joshua S. [Show all 7 contributors for this article] (2025). Cold Surface Waters of the Sub-Antarctic Pacific Ocean Support High Cyanophage Abundances and Infection Levels. Environmental Microbiology. ISSN 1462-2912. 27(1). doi: 10.1111/1462-2920.70031. Full text in Research Archive Show summary

  Cyanobacterial distributions are shaped by abiotic factors including temperature, light and nutrient availability as well as biotic factors such as grazing and viral infection. In this study, we investigated the abundances of T4-like and T7-like cyanophages and the extent of picocyanobacterial infection in the cold, high-nutrient-low-chlorophyll, sub-Antarctic waters of the southwest Pacific Ocean during austral spring. Synechococcus was the dominant picocyanobacterium, ranging from 4.7 × 103 to 1.2 × 105 cells∙mL−1, while Prochlorococcus abundances were relatively low overall, ranging from 1.0 × 103 to 3.9 × 104 cells∙mL−1. Using taxon-specific, single-virus and single-cell polony methods, we found that cyanophages were on average 15-fold, and up to 50-fold, more abundant than cyanobacteria in these waters. T4-like cyanophages (ranging from 1.7 × 105 to 6.5 × 105 phage·mL−1) were 2.7-fold more abundant than T7-like cyanophages (ranging from 3.1 × 104 to 2.8 × 105 phage·mL−1). Picocyanobacteria were primarily infected by T4-like cyanophages with more Synechococcus (4.8%–12.1%) infected than Prochlorococcus (2.5%–6.2%), whereas T7-like cyanophages infected less than 1% of both genera. These infection levels translated to daily mortality in the range of 5.7%–26.2% and 2.9%–14.3% of the standing stock of Synechococcus and Prochlorococcus, respectively. Our findings suggest that T4-like cyanophages are significant agents of cyanobacterial mortality in the cold, low-iron, sub-Antarctic waters of the South Pacific Ocean.

• Ribeiro, Catherine Gérikas; Santos, Adriana Lopes dos; Trefault, Nicole; Marie, Dominique; Lovejoy, Connie & Vaulot, Daniel (2024). Arctic phytoplankton microdiversity across the marginal ice zone: Subspecies vulnerability to sea-ice loss. Elementa: Science of the Anthropocene. 12(1), p. 1–26. doi: 10.1525/elementa.2023.00109. Full text in Research Archive Show summary

  Seasonal phytoplankton blooms are important Arctic phenomena, contributing to global primary production and biogeochemical cycling. The decline in sea-ice extent and thickness favors a longer open-water period with impacts on phytoplankton dynamics. Arctic net productivity is influenced by microalgae living associated with sea ice, with distinct species thought to be favored by ice-covered and ice-free waters. In this study, we investigated the phytoplankton community structure in Baffin Bay, a semi-enclosed sea where Arctic and North Atlantic water masses interact. We compared communities from the ice-free Atlantic-influenced eastern, the marginal ice zone, and the ice-covered Arctic-influenced western Baffin Bay. The community was characterized using 18S rRNA high-throughput amplicon sequencing and flow cytometry cell counting, and compared to environmental data collected during the Green Edge campaign. We sampled 16 stations grouped by sectors according to sea-ice cover. In the sectors associated with sea ice, phytoplankton formed a highly diverse community of smaller taxa, which contrasted with a low-diversity community in ice-free sectors, dominated by larger centric diatoms and Phaeocystis pouchetii adapted to high light/low nutrient conditions. Several phytoplankton species were flagged as indicators for the under-ice and marginal ice zone sectors, including ice-associated taxa such as the diatoms Melosira arctica and Pseudo-nitzschia seriata, but also subspecies representatives of the early-blooming alga Micromonas polaris and the cryptophyte Baffinella frigidus. The strong association of certain taxa with under-ice and marginal ice zone sectors, including Pterosperma sp., Chrysochromulina sp., Micromonas polaris, and B. frigidus, suggest that they might be indicators of diversity loss due to ongoing sea-ice changes in Baffin Bay. We report new intra-species variability of Micromonas polaris suggesting that seasonal specialists could wax and wane over the bloom and non-bloom periods, highlighting the need for detailed year-long studies and the importance of microdiversity when assessing the diversity and distribution of polar phytoplankton.

• Ong, Denise Rui Ying; Gutiérrez-Rodríguez, Andrés; Safi, Karl A.; Marie, Dominique; Selph, Karen E. & Stukel, Michael R. [Show all 8 contributors for this article] (2024). Consistent cell-specific carbon fixation rates by small eukaryotic phytoplankton in contrasting nutrient-limited conditions. Limnology and Oceanography. ISSN 0024-3590. 70(1), p. 162–177. doi: 10.1002/lno.12751. Full text in Research Archive Show summary

  Small phytoplankton, consisting of pico and nano size fractions, are diverse in size and taxonomy. Yet, the differences in their productivity and taxonomic diversity are poorly described. Here, we measured the cell-specific carbon fixation rates of picocyanobacteria Synechococcus, picoeukaryote, and nanoeukaryote populations, while unveiling their taxonomic composition in oligotrophic subtropical and high-nutrient low-chlorophyll subantarctic waters. We coupled 24 h in situ radiolabeled 14C incubations to flow cytometry sorting and DNA metabarcoding from the same incubated samples, offering a direct account of the community associated with the carbon fixation rates measured. In both water masses, nanoeukaryotes had the highest cell-specific carbon fixation rate, followed by picoeukaryotes and Synechococcus (2.24 ± 29.99, 2.18 ± 2.08, and 0.78 ± 0.55 fgC cell−1 h−1, respectively). The cell-specific carbon fixation rates and growth rates of Synechococcus were threefold higher in subtropical compared to subantarctic waters, while the rates of picoeukaryotes and nanoeukaryotes had no significant difference between the biogeochemically-contrasting water masses. Sorted picoeukaryote populations were dominated by Mamiellophyceae, Pelagophyceae, Prymnesiophyceae, and Chrysophyceae, while nanoeukaryote populations were dominated by Dinophyceae and Prymnesiophyceae. Despite significant differences in their taxonomic composition, the sorted picoeukaryote populations in subantarctic waters and nanoeukaryote populations in subtropical and subantarctic waters were dominated by taxa reported in the literature as able to engage in phago-mixotrophic strategies (Prymnesiophyceae, Chrysophyceae, and Dinophyceae), suggesting that such trophic strategy might be applied by discrete small photosynthetic eukaryote populations to alleviate macronutrient and iron stress.

• Cristi, Antonia; Law, Cliff S.; Pinkerton, Matt; Santos, Adriana Lopes dos; Safi, Karl & Gutiérrez-Rodríguez, Andres (2024). Environmental driving forces and phytoplankton diversity across the Ross Sea region during a summer–autumn transition. Limnology and Oceanography. ISSN 0024-3590. 69, p. 772–788. doi: 10.1002/lno.12526. Full text in Research Archive Show summary

  The Ross Sea is a highly productive system characterized by a seasonal succession of phytoplankton groups. However, most of the current understanding is based on observations on the continental shelf in spring and summer at relatively coarse taxonomic resolution. Here, we characterize community composition (class to species) using V4-18S rRNA gene metabarcoding on transects to and across the Ross Sea (shelf-slope and oceanic subregions) during two voyages covering the Austral summer–autumn progression in successive years. Phytoplankton composition shifted from low-diversity diatom-dominated (50%) communities during the summer to more diverse dinoflagellate-dominated (48%) systems during the lower-productivity autumn season. Prymnesiophyceae abundance was low on both voyages (10%), except on the southeast shelf-slope, where Phaeocystis antarctica dominated a shallow mixed layer, contrary to its reported preference for deep-mixing conditions. Amplicon sequence variant analysis identified distinct spatial patterns for two P. antarctica genotypes yet clustered certain species of Bacillariophyta and Prymnesiophyceae, indicating similar environmental preference for genotypes in these groups. Multivariate analysis of environmental drivers found a higher correlation of community composition variation with salinity and macronutrients, but less so with mixed layer depth, considered a primary determinant of taxonomic composition in the Ross Sea. Comparison between years established that community composition was temporally more stable in oceanic relative to shelf-slope waters. This study of seasonal variation of phytoplankton community composition at finer taxonomic resolution provided insights into species- and strain-specific distribution, ecological preferences, and relationships to environmental conditions in the wider Ross Sea to inform modeling and projection of future regional changes.

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