Browsing by Author "Alves-de-Souza, Catharina"

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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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    Salinity-Growth Response and Ichthyotoxic Potency of the Chilean Pseudochattonella verruculosa
    (2019) Mardones, Jorge, I; Fuenzalida, Gonzalo; Zenteno, Katherine; Alves-de-Souza, Catharina; Astuya, Allisson; Dorantes-Aranda, Juan Jose
    Despite salmon farmers suffering the worst damage from a harmful algal bloom in Chile's history (US$800M) due to a massive outbreak of the dictyochophyte Pseudochattonella verruculosa in 2016 (similar to 7000-20,000 cells ml(-1)), the effect of environmental drivers and the potency of lytic toxins produced by the local clones of this species remain still largely unexplored. Based on the drastic oceanographic anomalies observed in the Chilean fjords during the 2016-El Nino "Godzilla" event, the role of salinity (15 to 35 psu) on Pseudochattonella cell growth and cytotoxicity was studied by culturing, scanning electron microscopy (SEM) and using a rainbow trout cell line RTgill-W1 assay to define: (1) vegetative growth rates, (2) cell taxonomy, (3) ichthyotoxicity of monoclonal cultures at 25 and 35 psu in salinity, (4) differences in toxicity of lysed cells and supernatant at different cell concentrations (from 10 to 100,000 cells ml(-1)), and (5) temporal stability of lytic compounds. This study formally confirms the presence of P. verruculosa in Chilean waters using the large subunit (LSU) of the nuclear ribosomal RNA gene. The Chilean P. verruculosa ARC498 strain showed maximum cell densities at 30 psu (max. 84,333 +/- 4,833 cells ml(-1)) and maximum growth rates (mu(max)) at 20 psu (1.44 cells d(-1)). Cultures at 15 psu showed suppressed maximum cell density (max. 269 +/- 71 cell ml(-1)) but high mu(max) were recorded at the beginning of the exponential growth (1.31 cells d(-1)). No significant differences were observed between lysed cells and supernatant treatments in the two salinity levels, suggesting that the most lytic portion is released into the cell-free media instead of remaining cell bound. Cytotoxicity was correlated to cell abundance, reducing gill cell viability down to 80 and 65% compared to controls at 10,000 and 100,000 cells ml(-1), respectively. Unexpectedly, lytic compounds from P. verruculosa ARC498 at 35 psu showed to be less toxic than cultures at 25, where a noticeable presence of peripheral mucocysts were observed by SEM. Lytic compounds from in vitro experiments are weakly toxic even at high cell concentrations, highly unstable and rapidly degraded in the light after 5 days of storage at 15 degrees C. Our results point to the important effect of salinity on growth and ichthyotoxic potency of Pseudochattonella species and highlight the need for a deeper insight into the role of mucocysts in fish gill damage, which would provide a greater understanding as to the harmful modes of action of this species.