Browsing by Author "Von Dassow, Peter"

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    Carbon assimilation by the picoplanktonic community inhabiting the secondary chlorophyll maximum of the anoxic marine zones of the eastern tropical north and south pacific
    (FRONTIERS MEDIA SA, 2022) Aldunate, Montserrat; Von Dassow, Peter; Vargas, Cristian A.; Ulloa, Osvaldo
    Anoxic marine zones (AMZs) constitute pelagic systems distinguished from the oxygen minimum zones (OMZs) by the complete absence of detectable oxygen and the accumulation of nitrite in mid-waters. At the top of the oxygen-depleted layer and below the oxycline, nutrients are abundant; light intensity is very much reduced (<1% of incident light) and a secondary chlorophyll maximum (SCM) is developed. The shoaling of the oxygen-depleted layer, product of the AMZ expansion, could enhance this SCM, which has little-known biogeochemical effects. Here, we show that the SCM is contributing a measurable signal in the particulate organic carbon (POC), enough to alter the δ13CPOC in the top of the oxygen-depleted layer. This data showed significant differences among stations with and without the development of a SCM, being 3.0‰ heavier when a SCM is developed, and indicating photosynthetic activity and/or remineralization in the top of the AMZ. More depleted δ13CPOC values were also found when no SCM was present indicating stronger chemoautotrophic activity, potentially driven by anammox and sulfur-oxidizing bacteria activity. Assimilation rate data show that when sufficient light and Prochlorococcus are present, photosynthesis exceeds chemoautotrophic carbon fixation, and can exceed heterotrophic assimilation of glucose or acetate. However, in the majority of the stations, assimilation rates of both glucose and acetate exceeded carbon fixation rates under light stimulation, suggesting that often the SCM is still a net heterotrophic system
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    Does environmental heterogeneity explain temporal β diversity of small eukaryotic phytoplankton? Example from a tropical eutrophic coastal lagoon
    (2017) Alves-de-Souza, Catharina; Benevides, Tatiane S.; Santos, Juliana B. O.; Von Dassow, Peter; Guillou, Laure; Menezes, Mariangela
    The temporal beta diversity of small eukaryotic phytoplankton in a tropical urban coastal lagoon (Rodrigo de Freitas Lagoon, Brazil) was characterized throughout two annual cycles (2012-2103) with twice-weekly sampling. Small eukaryotic phytoplankton (< 20 mu m) were very abundant (above 1 x 10(3) and up to 6.2 x 10(5) cells mL(-1)). Small eukaryotes were also the most diverse phytoplankton group, showing high temporal variability at the species level that was represented by seven taxonomic divisions. Temporal beta diversity was positively related to environmental heterogeneity on a short-time scale. Although abundance peaks of the main species were positively related to NH4 inputs, selection of species ultimately depended on the simultaneous interaction among several physical-chemical variables acting hierarchically on different temporal scales (first seasonally and then on a short-time scale). Considering the numerical importance of small size fraction phytoplankton, information relevant to the management and conservation of coastal lagoons could be incomplete if the floristic composition and temporal species turnover of pico- and nanophytoplankton species are not properly determined.
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    From molecules to ecosystem functioning: insight into new approaches to taxonomy to monitor harmful algae diversity in Chile
    (2022) Mardones, J. I.; Krock, B.; Marcus, L.; Alves-de-Souza, C.; Nagai, S.; Yarimizu, K.; Clément, A.; Correa, N.; Silva, S.; Paredes, J.; Von Dassow, Peter
    Harmful algal blooms (HABs) are a major concern for Chilean scientists and governmental authorities, due to their deleterious effects on the aquaculture industry, resulting in complex sanitary, economic, and social problems. Increasingly, intense and frequent HABs events have distressed the aquaculture industry in recent years, especially for the occurrence of previously unreported toxic microalgae species. In the context of HAB monitoring programs, we review recent major advances in new approaches that have enabled deeper understanding of HAB species diversity in Chile. In particular, molecular approaches have revealed exceptional cryptic diversity, and chemotaxonomic approaches exposed the presence of new phycotoxins belonging to still undetected HAB species using conventional light microscopy. New advances in the detection of ichthyotoxins through the use of a fish cell line assay promises an early incorporation of this technique in routine monitoring of community composition. Emerging imaging flow cytometry is progressively pushing monitoring to more automated capabilities, and citizen science is gradually involving local communities in the complex phenomenon of harmful algal blooms
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    Physical-chemical factors influencing the vertical distribution of phototrophic pico-nanoplankton in the Oxygen Minimum Zone (OMZ) off Northern Chile: The relative influence of low pH/low O2 conditions
    (2022) Piscoya, Edson; Von Dassow, Peter; Aldunate, Montserrat; Vargas, Cristian A.
    The vertical distribution of phytoplankton is of fundamental importance in the structure, dynamic, and biogeochemical pathways in marine ecosystems. Nevertheless, what are the main factors determining this distribution remains as an open question. Here, we evaluated the relative influence of environmental factors that might control the coexistence and vertical distribution of pico-nanoplankton associated with the OMZ off northern Chile. Our results showed that in the upper layer Synechococcus-like cells were numerically important at all sampling stations. Pico-nano eukaryotes and phototrophic nanoflagellates (PNF) also showed high abundances in the upper layer decreasing in abundance down to the upper oxycline, while only Prochlorococcus showed high abundances under oxycline and within the oxygen-depleted layer. Statistical analyses evidenced that temperature, oxygen, and carbonate chemistry parameters (pH and dissolved inorganic carbon, DIC) influenced significantly the vertical distribution of phototrophic pico-nanoplankton. Additionally, we experimentally-evaluated the combined effect of low pH/low O2 conditions on a nanophytoplankton species, the haptophyte Imantonia sp. Under control conditions (pH = 8.1; O2 = 287.5 μM, light = 169.6 μEm−2s−1), Imantonia sp. in vivo fluorescence increased over fifty times, inducing supersaturated O2 conditions (900 μM) and an increasing pH (8.5), whereas upon an experimental treatment mimicking OMZ conditions (pH = 7.5; O2 = 55.6 μM; light = 169.6 μEm−2s−1), in vivo fluorescence declined dramatically, suggesting that Imantonia sp. did not survive. Although preliminary, our study provides evidence about the role of low pH/low O2 conditions on the vertical distribution of nanophytoplankton, which deserve future attention through both fieldwork and more extended experimental experiences
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