Diatomeas centrales de la Ría de Puerto Deseado, Santa Cruz, Argentina, III -S.O. Coscinodisciineae, familia Coscinodiscaceae, Familia Heliopeltaceae y Familia Thlassiosiraceae

Este trabajo es el tercero de una serie ya iniciada y trata sobre el estudio del contenido diatomológico cualitativo de muestras procedentes de la Ría de Puerto Deseado. En la presente contribución acepto los conceptos propuestos por Simonsen (1979) referidos a la agrupación de algunas especies del género Melosira dentro del género Aulacosira. La metodología usada en este trabajo ya ha sido descripta anteriormente (Ferrario1972). Las muestras fueron incorporadas a la colección de la División Plantas Celulares, adjudicandole la numeración de acuerdo a la norma de la división, figura como LP (C)

Consideraciones taxonómicas sobre Diatomeas epífitas del intermareal rocoso marplatense.I

Fourteen species and varieties of epiphytic diatom of intertidal seagras were studied using light and electron microscope for some of them. The ecological distribution of Navicula tripunctata (i\hiller) BOIYis extended to littoral environment. Licmophora juergensii Agardh, Nitzschia parvula mith and ,. marina Grunow are new records for Argentina.Catorce especies y valiedades de diatomeas epífitas de macroalgas intermarcales fueron estudiadas usando microscopio óptico y electrónico de barrido. La distribución ecológica de Navicula tripunctata (Müller) Bory es ampliada a ambientes marinos litorales. Licmophora juergensii Agardh, Nitzschia parvula Smith y marina Grunow son nuevas citas para Argentina

Estudio taxonómico del fitoplancton de los alrededores de La Plata (Prov. Buenos Aires, Argentina) II- Bacillariophyceae

Treinta y seis especies, variedades y formas del Orden Pennales son descriptas e ilustradas. Nítzschía amphíbía fa. rostrata Hustedt se cita por primera vez para la Argentina

Response of a natural Antarctic phytoplankton assemblage to changes in temperature and salinity

The climate around the Western Antarctic Peninsula (WAP) is rapidly changing and dramatically affecting marine coastal waters. Increases in air and seawater temperatures, not matter how small, can alter coastal biological communities due to both temperature increases as well as salinity reduction from glacier melting. The aim of this study was to evaluate the individual and combined effects of elevated sea surface temperature (+4 °C) and decreased salinity (−4) on growth and assemblage composition of natural summer phytoplankton from Potter Cove (King George Island, South Shetlands, northern WAP), using an outdoor microcosm experiment. Pigment composition was analyzed by high performance liquid chromatography (HPLC/Chemtax) and species composition by light and electron microscopy. Increases in phytoplankton biomass during the first 3 days at elevated-temperatures coincided with an increase in the abundance and the specific growth rate of small centric diatoms (Chaetoceros socialis and Shionodiscus gaarderae, mostly observed in temperate waters) and unidentified small phytoflagellates <5 μm. In contrast, pennate diatoms significantly decreased. At the end of the experiment on day 7, under nitrate and phosphate limitation, chlorophytes abundances increased under low salinity whereas prasinophytes decreased in all treatments. This study suggests that climate change could notably affect Antarctic phytoplankton composition by favouring temperate-water species previously undetected in Antarctic waters, such us S. gaarderae. Moreover, the observed changes in phytoplankton structure, associated with an increase of nano- over micro-size taxa, could have important implications for future Antarctic food webs

Co-occurrence of <i>Dinophysis tripos</i> and pectenotoxins in Argentinean shelf waters

The species Dinophysis tripos is a widely distributed marine dinoflagellate associated with diarrheic shellfish poisoning (DSP) events, which has been recently identified as a pectenotoxin (PTX) producer. In two sampling expeditions carried out during austral autumns 2012 and 2013 along the Argentine Sea (≈38–56° S), lipophilic phycotoxins were measured by tandem mass spectrometry coupled to liquid chromatography (LC–MS/MS) in size-fractionated plankton samples together with microscopic analyses of potentially toxic phytoplankton. PTX-2, PTX-11 and PTX-2sa were recurrently detected in the 50–200 μm fractions, in association to D. tripos. PTX-2 was also widely distributed among the 20–50 μm fractions, mostly related to Dinophysis acuminata. Okadaic acid or its analogs were not detected in any sample. This is the first report of D. tripos related to PTX in the Argentine Sea and the first record of PTX-11 and PTX-2sa for this area. The morphological variability of D. tripos, including the presence of intermediate, small and dimorphic cells, is described. Also, the micro- and mesoplanktonic potential grazers of Dinophysis spp. were explored.Facultad de Ciencias Naturales y Muse

Distribution and ecology of <i>Pseudo-nitzschia</i> species (Bacillariophyceae) in surface waters of the Weddell Sea (Antarctica)

The distribution of six Pseudo-nitzschia species and their relationship with environmental conditions were studied for the first time in a vast zone of the Weddell Sea (∼61–77°S, Antarctica). Both qualitative and quantitative phytoplankton samples, collected during summer 2004, were examined using light and scanning electron microscopy. Phytoplankton abundance and composition showed great variability along our study area. Diatoms were the most conspicuous phytoplankton group in the northern area while small flagellates were generally dominant in the southern stations. The genus Pseudo-nitzschia was broadly distributed and significantly contributed to total diatom densities. A marked contrast in Pseudo-nitzschia species distribution was observed in three main zones divided by the Weddell Front (WF) and the Antarctic Slope Front (ASF). P. subcurvata and P. turgiduloides were the most abundant species in the neritic Weddell Sea zone, south of the ASF, mainly near the ice-edge in shallower waters and in conditions of long photoperiod. In contrast, P. prolongatoides and P. lineola dominated north of the ASF; the first was associated with deeper and nutrient-rich waters whereas the latter showed a weak relation with environmental variables examined. Finally, P. turgidula and P. heimii were mostly observed in the Weddell–Scotia Confluence Zone in the warmest and far from ice covered waters, north of the WF. A brief morphological Pseudo-nitzschia species description is given in the Appendix, including morphometrics and pictures.Facultad de Ciencias Naturales y Muse