Distribución geográfica y variación interanual del género Pseudo-nitzschia [Bacillariophyceae] en aguas de la plataforma del Mar Argentino y Antártida

Tesis presentada para optar al Grado de Doctor en Ciencias NaturalesFil: Almandoz, Gastón Osvaldo. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentin

First Investigations on the Andvord Bay Phytoplankton Community (Antarctica). Composition and Space-Time Dynamics

El oeste de la Península Antártica (PA) alberga el mayor sistema de fiordos glacio-marinos de la Antártida. Los fiordos de las costas de Danco/Graham, al oeste de la PA, son sitios de gran conglomeración de krill y ballenas y presentan a la vez una elevada abundancia y riqueza de fauna bentónica, lo que sugiere que se trata de sitios de elevada productividad primaria. Sin embargo, el conocimiento que se tiene sobre el fitoplancton en este tipo de ambientes es aún muy limitado. Estos fiordos, además, se ven particularmente afectados por el calentamiento global. En los fiordos del Ártico se ha demostrado que el deshielo glaciar tiene una influencia positiva en el crecimiento del fitoplancton costero, aunque en la PA este tipo de estudios aún son escasos. Mediante el análisis con microscopía óptica y electrónica de muestras de columna de agua, este trabajo de tesis propone brindar los primeros datos sobre la composición, estructura y dinámica de la comunidad fitoplanctónica de la Bahía Andvord, así como de otros fiordos del oeste de la PA, en distintas estaciones del año (primavera, verano y otoño). Dichas muestras fueron colectadas en dos campañas oceanográficas (primavera 2015 y otoño 2016) en la Bahía Andvord, y en otros fiordos y canales del oeste de la PA (entre 63 y 67°S) mediante un proyecto de ciencia ciudadana llamado Fjord Phyto durante los veranos 2016-2019. En particular, este trabajo busca analizar la influencia que tienen los cambios en la columna de agua provocados por el aporte de agua de deshielo glaciar sobre la comunidad fitoplanctónica.Universidad Nacional de La Plat

El microscopio electrónico de barrido

¿Sabías que el Microscopio Electrónico de Barrido (MEB) permite observar detalles de la topografía superficial de diversos especímenes en 3 dimensiones, aumentando hasta 300.000 veces su tamaño original. De esta forma, se pueden realizar análisis ultraestructurales de cualquier tipo de organismo animal o vegetal, minerales, fósiles, restos arqueológicos, etc., que resultan imperceptibles a simple vista. El Museo de la Plata cuenta con un Servicio de Microscopía Electrónica de Barrido que fue inaugurado el 3 de agosto de 1987. Gracias a un convenio de intercambio entre la Universidad Nacional de La Plata y la Prefectura de Tokushima-Japón, y a las gestiones realizadas por el destacado paleontólogo Dr. Rosendo Pascual, llegó el primer MEB.Sección: ¿Sabías que...?Fundación Museo La Plat

El microscopio electrónico de barrido

¿Sabías que el Microscopio Electrónico de Barrido (MEB) permite observar detalles de la topografía superficial de diversos especímenes en 3 dimensiones, aumentando hasta 300.000 veces su tamaño original. De esta forma, se pueden realizar análisis ultraestructurales de cualquier tipo de organismo animal o vegetal, minerales, fósiles, restos arqueológicos, etc., que resultan imperceptibles a simple vista. El Museo de la Plata cuenta con un Servicio de Microscopía Electrónica de Barrido que fue inaugurado el 3 de agosto de 1987. Gracias a un convenio de intercambio entre la Universidad Nacional de La Plata y la Prefectura de Tokushima-Japón, y a las gestiones realizadas por el destacado paleontólogo Dr. Rosendo Pascual, llegó el primer MEB.Sección: ¿Sabías que...?Fundación Museo La Plat

Distribución de nutrientes inorgánicos y clorofila-a a través de los frentes de la Plataforma Continental Patagónica Argentina durante verano y otoño

Oceanographic data collected during 2001-2003 on the Patagonian Continental Shelf of Argentina were analyzed in order to study the main chemical features of this large shelf. The variation of inorganic nutrients and chlorophyll-a during summer and fall in an area within 40 to 60 km from the coast are presented. Nitrate is the limiting nutrient in the region and is negatively correlated to chlorophyll-a. All variables show localized variations in summer, which can be related to tidal fronts through the comparison of our data with the critical Simpson parameter of stability (50 J m-3). In fall, nutrient concentrations on the continental shelf were more uniform and generally higher than in summer due to the disruption of these fronts.Datos oceanógraficos recolectados durante 2001-2003 en la Plataforma Continental Patagónica Argentina fueron analizados para estudiar las principales características químicas en esta gran plataforma. Se presenta la variación de los nutrientes inorgánicos y de la clorofila-a a una distancia de 40 a 60 km de la costa. El nitrato es el nutriente limitante en la región y está negativamente correlacionado con la clorofila-a. Todas las variables presentan variaciones localizadas en verano, las cuales pueden ser relacionadas con los frentes de marea a través de la comparación de nuestros datos con el parámetro crítico de estabilidad de Simpson (50 J m-3). En otoño, la concentración de nutrientes en la plataforma continental fue más uniforme y generalmente mayor que en verano debido a la disrupción de dichos frentes.Facultad de Ciencias Naturales y Muse

Diversity of the diatom genus Fragilariopsis in the Argentine Sea and Antarctic waters: Morphology, distribution and abundance

Fragilariopsis species composition and abundance from the Argentine Sea and Antarctic waters were analyzed using light and electron microscopy. Twelve species (F. curta, F. cylindrus, F. kerguelensis, F. nana, F. obliquecostata, F. peragallii, F. pseudonana, F. rhombica, F. ritscheri, F. separanda, F. sublinearis and F. vanheurckii) are described and compared with samples from the Frenguelli Collection, Museo de La Plata, Argentina. F. peragallii was examined for the first time using electron microscopy, and F. pseudonana was recorded for the first time in Argentinean shelf waters. New information on the girdle view is included, except for the species F. curta, F. cylindrus and F. nana, for which information already existed. In the Argentine Sea, F. pseudonana was the most abundant Fragilariopsis species, and in Antarctic waters, F. curta was most abundant. Of the twelve species of Fragilariopsis documented, four occurred in the Argentine Sea, nine in the Drake Passage and twelve in the Weddell Sea. F. curta, F. kerguelensis, F. pseudonana and F. rhombica were present everywhere.Facultad de Ciencias Naturales y Muse

Field observations of the dinoflagellate genus <i>Azadinium</i> and azaspiracid toxins in the south-west Atlantic Ocean

Some dinoflagellate species of the genera Azadinium and Amphidoma (Amphidomataceae) produce azaspiracids (AZA), a group of toxins responsible for gastrointestinal disorders in humans following the consumption of contaminated shellfish. In this study, we investigated the diversity, distribution and abundance of Azadinium and AZA from field plankton samples collected during four oceanographic expeditions that covered an extended area of the Argentine Sea during different seasons. Scanning electron microscopy analyses indicated the presence of five Azadinium species: Az. dexteroporum, Az. luciferelloides, Az. obesum, Az. asperum and Az. cf. poporum. Azadinium-like cells were frequently found and were even an abundant component of plankton assemblages, showing a wide latitudinal distribution, from ~38 to ~55.5°S, and occurring in a wide temperature and salinity range. High cell densities (up to 154000cellsL⁻¹) occurred in northern slope and external shelf waters during spring. AZA-2 was detected in net samples from the 20- to 200-µm fractions by tandem mass spectrometry–liquid chromatography analysis, suggesting a transfer of AZA through the food web. Our results contribute to the knowledge of the worldwide occurrence of Azadinium species and AZA, and highlight the importance of amphidomatacean species as a potential source of AZA shellfish poisoning in the south-west Atlantic Ocean.Facultad de Ciencias Naturales y Muse

Metabarcoding and microscopy characterization of phytoplankton from frontal areas of the Argentine Sea

The Argentine Sea is worldwide recognized as a highly productive area, characterized by extensive phytoplankton blooms during spring and summer. Despite the well-known importance of frontal areas for biomass accumulation, phytoplankton diversity remains poorly studied. In an unprecedented approach for the Argentine Sea, we combined microscopy and 18Sv4 metabarcoding analyses for a refined assessment of summer phytoplankton composition in three understudied frontal areas of the Argentine Sea (≈43°−55°S), with contrasting oceanographic conditions. Metabarcoding and microscopy analyses agreed on the detection of the dominant phytoplanktonic groups in the different frontal areas studied; chlorophytes in Valdés Peninsula, dinoflagellates in waters off Blanco Cape, and diatoms in de los Estados Island. The analysis of the phytoplankton community was significantly enriched by combining both techniques, microscopy provided cell abundances and biomass data and metabarcoding provided greater detail on species composition, revealing an important specific richness of dinoflagellates, diatoms and other delicate groups, such as chlorophytes. However, we also considered differences between the methods for certain taxa at a lower taxonomic level (species/genus) of the dominant taxa, such as the underestimation of the diatoms Asterionellopsis glacialis and Pseudo-nitzschia spp. and the overestimation of Chaetoceros contortus by metabarcoding in comparison to microscopic counts. The detection of several taxa belonging to small and delicate groups, previously overlooked due to the lack of distinct morphological features, establishes a baseline for future studies on phytoplankton diversity in the Argentine Sea

Phytoplankton Ecology During a Spring-Neap Tidal Cycle in the Southern Tidal Front of San Jorge Gulf, Patagonia

Tidal fronts are interfaces that separate stratified from mixed waters. The stratified surface zone of a front has lower inorganic nutrient concentrations than the mixed side, and thus, phytoplankton assemblages are expected to differ from one side of the front to the other. Here, we characterize the physics, nutrient dynamics, and biology of the southern front in San Jorge Gulf (SJG), Argentina, during a spring-neap tidal cycle. Baroclinic instabilities influence the shape and position of the front and presumably play an important role in the horizontal transport across the front. The highest phytoplankton biomass concentrations were found in the waters of the stratified side of the front during neap tide, with picophytoplankton, cyanobacteria, and nanophyto-plankton being the main contributors to the total autotrophic biomass. Bacteria contribute the most to heterotrophic biomass. In contrast, during spring tide, the carbon contribution of microphytoplankton was higher than during neap tide. In the mixed side, cells photoacclimate to optimum light conditions, suggesting that cells near the surface, which are probably photoinhibited, and cells below the euphotic zone, which are light-limited, are quickly advected by turbulent vertical motions to depths with optimal irradiance conditions.Facultad de Ciencias Naturales y Muse

Influence of microbial community composition and metabolism on air.sea ΔpCO 2 variation off the western Antarctic Peninsula

We studied CO 2 and O 2 dynamics in the western Antarctic Peninsula (WAP) waters in relation to (1) phytoplankton biomass, (2) microbial community primary production and respiration, and (3), for the first time, phytoplankton composition, during summer and fall in 3 consecutive years (2002, 2003 and 2004). The areal average of ΔpCO 2 (the difference between surface seawater and atmospheric partial pressure of CO 2) for the 3 yr was significantly negative (.20.04 ± 44.3 μatm, p < 0.01) during the summer to fall period in the region, possibly indicating a CO 2 sink. In the southern WAP (i.e. south of Anvers Island), ΔpCO 2 was significantly negative (.43.60 ± 39.06 μatm) during fall. In the northern WAP (north of Anvers Island), ΔpCO 2 values showed a more complex distribution during summer and fall (.4.96 ± 37.6 and 21.71 ± 22.39 μatm, respectively). Chlorophyll a (chl a) concentration averaged 1.03 ± 0.25 μg l.1 and was higher in the south of the peninsula. Phytoplankton composition influenced chl a concentration with higher and lower values for diatom-and phytoflagellate-dominated communities, respectively. A significant negative correlation existed between chl a and ΔpCO 2. From incubation experiments performed in the northern WAP, respiration was low (averaging 5.1 mmol O 2 m.3 d.1), and the net community production (NCP) correlated negatively with ΔpCO 2 and positively with %O 2 saturation. However, despite the high NCP values measured, ΔpCO 2 was significantly positive in the northern WAP during the summer to fall period. Strong mixing and lower chl a concentration may explain this result. In contrast, ΔpCO 2 was significantly negative in the southern WAP, possibly because of high surface water chl a concentration.Facultad de Ciencias Naturales y Muse