Effect of nutrients and pH on the phytoplankton growth and structure in different environments of the Lower Paraná floodplain

Se evaluó experimentalmente la importancia del N como factor limitante para el desarrollodel fitoplancton en distintos ambientes acuáticos, distribuidos sobre un eje transversal alcauce principal del Paraná Inferior.Se analizaron además las diferencias espaciales en lacomposición de esta comunidad y el efecto del N y el pH sobre su estructura,principalmente sobre la abundancia de algas mixotróficas y fijadoras de N2. La primer parte del estudio se llevó a cabo en tres ambientes (rio Paraná, laguna Montiel,bañado El Ciego) aledaños a Villa Constitución (Santa Fe). Aquí se analizaron en cuatroocasiones (mayo'96 - febrero'97) las características limnológicas de estos cuerpos de aguay se realizaron bioensayos in vitro con agregado de N y P. La segunda parte correspondióa un estudio intensivo (octubre'98 - mayo'00)de la laguna Grande (Otamendi, Buenos Aires), donde se realizaron bioensayos in situ con agregado de nutrientes y de Na2CO3para elevar artificialmente el pH del agua. Desde el cauce principal hacia la planicie de inundación se observó un marcado gradientelimnológico. A lo largo de este eje disminuyeron la concentración de sólidos ensuspensión, de NID y la profundidad, y aumentaron la transparencia, la relación Secchi:profundidad, la concentración de nutrientes totales (NT y PT) y la biomasafltoplanctónica. En el río, donde la luz es limitante, dominaron diatomeas típicamentepotamoplanctónica adaptadas a vivir con bajas intensidades lumínicas y alta turbulencia (Aulacoseira granulata y sus variedades), mientras que en el otro extremo del gradientedonde el principal factor limitante es la falta de NID, el fitoplancton estuvo dominadoprincipalmente por fitoflagelados mixotróficos (Cryptomonas, Euglena, Peridinium) de lasasociaciones W e Y (sensu Reynolds, 1997) y por pequeñas Chlorococcales C-estrategasde la asociación X1. El grado de conectividad con el cauce principal determina laimportancia relativa de la luz y el N como factores limitantes. El NID sería potencialmentelimitante cuando su concentración disminuye por debajo de los 100 μg L-1. La ventaja de losfitoflagelados dominantes en los ambientes más alejados del curso principal no sería sólola mixotrofiasino además su capacidad para mantenerse en suspensión en un ambientevegetado relativamente calmo, mientras que las algas autotróficas obligadas sin movilidadpropia dependen de condiciones de turbulencia para ser dominantes. La abundancia decianobacterias fijadoras de N2 de la asociación H (Anabaena) en los ambientes donde el Nes limitante está condicionada no solo por la baja concentración de NID sino que ademásrequerirían valores de pH elevados. Por otro lado, Cyclotella meneghiniana fue dominantedurante el verano'00 en la laguna Grande debido principalmente a los altos valores de pHregistrados durante este período.The aim of this work is to evaluate the importance of N as limiting factor for phytoplanktongrowth in different environments from a floodplain stretch of the Lower Paraná River. Thechanges in natural phytoplanktonic community as well as the main physico-chemicalparameters were also studied along this section. Experiments were performed in order toassess the effect of N and pH on the phytoplankton structure, principally on the abundanceof mixotrophic algae and N2-fixing Cyanobacteria. The first part of the study was carried out in three environments (the main channel, a lakeand a swamp) across the Lower Paraná River floodplain opposite to Villa Constitución city (Santa Fe). Each site was seasonally sampled (May'96 - February'97), in vitro bioassayswith addition of N and P were also performed. The second part was an intensive study (October'98 - May'00)of the Grande lake (Otamendi). In situ bioassays with addition ofnutrients and Na2CO3 (to rise pH) were performed using bottles and mesocosms. A decrease in depth, suspended solids and DIN(dissolved inorganic N)was observed fromthe main channel towards the swamp. whereas transparency, Secchi:depth ratio. totalnutrients (TP and TN) and phytoplankton biomass increased. In the mainstream, wherelight is the major limiting factor for phytoplankton growth, typical potamoplanktonic speciesadapted to grow in turbid and turbulent environments dominated (Aulacoseira granulataand its varieties). Oppositely, in the swamp phytoplankton was mainly composed ofmixotrophic phytoflagellates (Cryptomonas, Euglena, Peridinium) from associations W and Y (sensu Reynolds. 1997) and small-size green algae, typically C-strategists (association X1). NlD is the main limiting factor in the latter environment. The connectivity degreebetween floodplain environments and the main channel determines the relative importanceof light and N as limiting factors. NID concentration below 100 μg L-1 would indicate potential N-limitation. Phytoflagellates, dominating in low connectivity and N-limiting water bodies.would be favored not only by their mixotrophic behavior, but also by their capacity tomaintain suspension in a vegetated and relativer calm environment; whereas autotrophicalgae lacking motility depend on turbulent conditions (less macrophytes) to becomedominant. The abundance of N2-fixing Cyanobacteria from association H (Anabaena) in N limitingenvironments depends on the low DIN concentration, as well as on the high pHvalues. On the other hand, Cyclotella meneghiniana dominated Grande lake during thesummer'00 due to the high pH values encountered during this period.Fil: Unrein, Fernando. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Summer phytoplankton structure and dynamics in an Antarctic lake (Potter Peninsula, South Shetland Islands)

Se estudió la estructura y dinámica del fitoplancton estival de un lago antártico marítimo de Península Potter (SEIC N°13, Shetland del Sur). Se analizaron las fluctuaciones de las principales variables físico-químicas y del fitoplancton entre el 1 enero 1996 y el 13 febrero 1996, dando especial énfasis al efecto del descongelamiento sobre la composición de esta comunidad. Al comienzo del estudio el lago se hallaba aun parcialmente congelado; durante el proceso de deshielo tanto los parámetros abióticos como bióticos presentaron notables cambios. Junto con el aumento de la temperatura se observó un incremento en el pH, la conductividad y en la densidad y biomasa fitoplanctónica. La concentración de clorofila-a presentó valores típicos de lagos oligomesotróficos. La concentración de PRS (fósforo reactivo soluble) siempre fue inferior a 4 µg/L, mientras que el PT (fósforo total) osciló alrededor de 16 µg/L. Los dos grupos de algas mejor representados en términos de abundancia, de biomasa y de riqueza fueron las Chlorophyta y las Bacillariophyceae. El fitoplancton estuvo dominado claramente por Pseudodictyosphaerium jurisii (Hind.) Hind. (Chlorococcales). Como consecuencia de su elevada densidad, hacia fines del estudio se observó un brusco descenso de la equitatividad y la diversidad específica. Otras especies de Chlorophyta típicamente planctónicas también estuvieron presentes aunque en menor densidad. Las Bacillariophyceae, en su mayoría representadas por especies ticoplanctónicas, fueron subdominantes, especialmente durante la última fase de descongelamiento. Esto se vio reflejado en un aumento de la riqueza y diversidad específicas y una disminución del índice de similitud (SIMI) aplicado a pares de muestras consecutivas en el tiempo.The structure and dynamics of the phytoplankton community of a lake from Potter Peninsula (SSSI N° 13, South Shetland Islands) were analyzed during the 1995- 1996 summer together with the main limnological features of this system. The surface of the water body was partially covered by ice (60%) at the beginning of the study. Important changes in the abiotic parameters and in the phytoplankton composition were observed during the melting process. Temperature, pH, conductivity and phytoplankton density and biomass increased during the ice-free period. Chlorophyll-a values were typical of oligoñmesotrophic lakes. SRP (soluble reactive phosphorus) values were always lower than 4 µg/L, while TP (total phosphorus) concentration fluctuated around 16 µg/L. Chlorophyta and Bacillariophyceae were the dominant groups in terms of density, biomass and species richness. Pseudodictyosphaerium jurisii (Hind.) Hind. (Chlorococcal) was the dominant species. A decrease in species equitability and diversity was observed as a consequence of the high density achieved by this species during the end of February. Other planktonic taxa of Chlorophyta were also present in low number. Bacillariophyceae, mainly represented by tychoplanktonic species, showed a small peak just at the final phase of ice thawing. Thus, an increase in species richness and diversity and a decrease in the similarity index (SIMI) applied to consecutives samples were observed during this period

Environmental dynamics as a structuring factor for microbial carbon utilization in a subtropical coastal lagoon

Laguna de Rocha belongs to a series of shallow coastal lagoons located along South America. It is periodically connected to the sea through a sand bar, exhibiting a hydrological cycle where physicochemical and biological gradients are rapidly established and destroyed. Its most frequent state is the separation of a Northern zone with low salinity, high turbidity and nutrient load, and extensive macrophyte growth, and a Southern zone with higher salinity and light penetration, and low nutrient content and macrophyte biomass. This zonation is reflected in microbial assemblages with contrasting abundance, activity, and community composition. The physicochemical conditions exerted a strong influence on community composition, and transplanted assemblages rapidly transformed to resembling the community of the recipient environment. Moreover, the major bacterial groups responded differently to their passage between the zones, being either stimulated or inhibited by the environmental changes, and exhibiting contrasting sensitivities to gradients. Addition of allochthonous carbon sources induced pronounced shifts in the bacterial communities, which in turn affected the microbial trophic web by stimulating heterotrophic flagellates and virus production. By contrast, addition of organic and inorganic nutrient sources (P or N) did not have significant effects. Altogether, our results suggest that (i) the planktonic microbial assemblage of this lagoon is predominantly carbon-limited, (ii) different bacterial groups cope differently with this constraint, and (iii) the hydrological cycle of the lagoon plays a key role for the alleviation or aggravation of bacterial carbon limitation. Based on these findings we propose a model of how hydrology affects the composition of bacterioplankton and of carbon processing in Laguna de Rocha.This might serve as a starting hypothesis for further studies about the microbial ecology of this lagoon, and of comparable transitional systems.Fil: Alonso, Cecilia. Universidad de la República; UruguayFil: Piccini, Claudia. Instituto de Investigaciones Biológicas "Clemente Estable"; UruguayFil: Unrein, Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús). Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús); ArgentinaFil: Bertoglio, Florencia. Universidad de la República; UruguayFil: Conde, Daniel. Universidad de la República; UruguayFil: Pernthaler, Jakob. Universitat Zurich; Suiz

¿Quién se come a quién?: tramas tróficas microbianas y su implicancia en las lagunas pampeanas

Los microorganismos que conforman el plancton son componentes importantes en las relaciones alimentarias que ocurren en los ecosistemas acuáticos, ya que determinan en última instancia la cantidad de materia y energía disponible para los niveles tróficos superiores, representados por los consumidores. Entre estos microorganismos las bacterias que forman parte del plancton (bacterioplancton) registran valores extremadamente elevados de abundancia en las lagunas pampeanas, convirtiéndolas en un caso excepcional para la literatura limnológica.Instituto de Limnología "Dr. Raúl A. Ringuelet

Significant year-round effect of small mixotrophic flagellates on bacterioplankton in an oligotrophic coastal system

14 pages, 7 figures, 1 tableThe seasonal variation in the grazing effect of mixotrophic flagellates on bacterioplankton was assessed during an annual cycle in an oligotrophic coastal station in the northwest Mediterranean Sea. Ingestion rates of fluorescently labeled bacteria were estimated for different size categories of phytoflagellates (PF) and heterotrophic flagellates (HF) in short-term experiments and compared with long-term grazing estimates and published empirical models. The mixotrophic flagellates included haptophyte-like cells, cryptophytes, and dinoflagellates. The group-specific grazing rates (SGR) averaged 1.1 (3–5 µm PF), 1.3 (5–20 µm PF), 4.0 (<5 µm HF), and 15.4 bacteria individual-1 h-1 (5–20 µm HF). Lower SGR but higher abundances of PF resulted in an average mixotroph contribution of 50% to the total flagellate grazing. Remarkably, the effect was relatively high all through the year (35–65%). Regardless of the presence of chloroplasts, flagellates <5 mm in size accounted, on average, for about 80% of total flagellate bacterivory and ingested a large percentage of their cell carbon per day from bacteria. Soluble reactive phosphorus concentration was negatively correlated with the ingestion rate of both groups of PF, suggesting that mixotrophic flagellates would be using their phagotrophic capability to obtain phosphorus when this nutrient is limiting. HF grazing activity showed a marked seasonality, with grazing being higher during the warmer seasons, and clearance rates were positively correlated with water temperature. Total bacterivory accounted for most of the bacterial production. Short-term and long-term bacterivory measurements were highly correlated, confirming that the smallest flagellates were the main causative agent of bacterial loss. The bacterivory values were also well correlated to a published empirical model that considers HF as the only bacterivorous. However, this model underestimated (up to 50%) total flagellate grazing during periods of high effect of mixotrophic flagellatesThis study was supported mainly by a EU project (EVK3-CT-2002-00078) and a Spanish post-doctoral fellowship (SB2001-0166) and also partially funded by three projects supported by the Spanish government (REN2001-2120/MAR; CTM2004-12631/MAR; CTM2004-02586/MAR)Peer reviewe

Phytoplankton phagotrophy across nutrients and light gradients using different measurement techniques

Mixotrophy is important to ecosystems functioning. Assuming that limiting resources induce phagotrophy in mixotrophs, we used a factorial experimental design to evaluate how nutrient and light affects phagotrophy in two mixotrophic phytoflagellates belonging to different lineages. We estimated cell-specific grazing rates (CSGR) by analyzing prey ingestion using microscopy and flow cytometry (FC). Furthermore, we tested if the acidotropic probe LysoTracker green (LyTG) can be used to differentiate autotrophs from mixotrophs. Cryptomonas marssonii (cryptophyte) had higher CSGR in high-nutrient treatments. Although it seems counterintuitive, phytoflagellates likely uses phagotrophy to obtain organic growth factors instead of inorganic nutrients when photosynthesis is more favorable. In contrast, CSGR in Ochromonas tuberculata (chrysophyte) increased when light decreased, suggesting that it uses phagotrophy to supplement carbon when autotrophic growth conditions are suboptimal. Measurements of CSGR obtained by FC and microscopy were significantly correlated and displayed the same trend among treatments, although FC rates tended to be higher. Fluorescence with LyTG did not differ from the control in the non-phagotrophic chlorophyte. Contrarily, addition of LyTG significantly increased the fluorescence in chrysophytes and cryptophytes, although no differences were observed among treatments. This approach allowed for differentiation between phagotrophic and non-phagotrophic flagellates but failed to quantify mixotrophy.Fil: Costa, Mariana R. A.. Universidade Federal do Rio Grande do Norte; BrasilFil: Sarmento, Hugo. Universidade Federal do São Carlos; BrasilFil: Becker, Vanessa. Universidade Federal do Rio Grande do Norte; BrasilFil: Bagatini, Inessa L. Universidade Federal do São Carlos; BrasilFil: Unrein, Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas; Argentin

Microbial assemblages associated with the invasive kelp Undaria pinnatifida in Patagonian coastal waters: Structure and alginolytic potential

Undaria pinnatifida is a brown algae native to Asia that has settled in various regions worldwide, periodically contributing with large quantities of C and nutrients during its annual cycle. In this work, we analyzed a coastal site in Patagonia (Argentina) that has been colonized for three decades by U. pinnatifida, focusing on associated microbial communities in three different compartments. An important influence of algae was observed in seawater, especially in the bottom of the algal forest during the austral summer (January) at the moment of greater biomass release. This was evidenced by changes in DOC concentration and its quality indicators (higher Freshness and lower Humification index) and higher DIC. Although maximum values of NH4 and PO4 were observed in January, bottom water samples had lower concentrations than surface water, suggesting nutrient consumption by bacteria during algal DOM release. Concomitantly, bacterial abundance peaked, reaching 4.68 ± 1.33 × 105 cells mL −1 (January), showing also higher capability of degrading alginate, a major component of brown algae cell walls. Microbial community structure was influenced by sampling date, season, sampling zone (surface or bottom), and environmental factors (temperature, salinity, pH, dissolved oxygen, nutrients). Samples of epiphytic biofilms showed a distinct community structure compared to seawater, lower diversity, and remarkably high alginolytic capability, suggesting adaptation to degrade algal biomass. A high microdiversity of populations of the genus Leucothrix (Gammaproteobacteria, Thiotrichales) that accounted for a large fraction of epiphytic communities was observed, and changed over time. Epiphytic assemblages shared more taxa with bottom than with surface seawater assemblages, indicating a certain level of exchange between communities in the forest surroundings. This work provides insight into the impact of U. pinnatifida decay on seawater quality, and the role of microbial communities on adapting to massive biomass inputs through rapid DOM turnover.Fil: Lozada, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Zabala, Maria Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biología de Organismos Marinos; ArgentinaFil: Garcia, Patricia Elizabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Dieguez, Maria del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Bigatti, Gregorio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biología de Organismos Marinos; ArgentinaFil: Fermani, Paulina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Unrein, Fernando. Universidad Nacional de San Martin. Instituto Tecnologico de Chascomus. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - la Plata. Instituto Tecnologico de Chascomus.; ArgentinaFil: Dionisi, Hebe Monica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentin

Diversity of photosynthetic picoeukaryotes in eutrophic shallow lakes as assessed by combining flow cytometry cell-sorting and high throughput sequencing

Photosynthetic picoeukaryotes (PPE) are key components of primary production in marine and freshwater ecosystems. In contrast with those of marine environments, freshwater PPE groups have received little attention. In this work, we used flow cytometry cell sorting, microscopy and metabarcoding to investigate the composition of small photosynthetic eukaryote communities from six eutrophic shallow lakes in South America, Argentina. We compared the total molecular diversity obtained from PPE sorted populations as well as from filtered total plankton samples (FTP). Most reads obtained from sorted populations belonged to the classes: Trebouxiophyceae, Chlorophyceae and Bacillariophyceae. We retrieved sequences from non-photosynthetic groups, such as Chytridiomycetes and Ichthyosporea which contain a number of described parasites, indicating that these organisms were probably in association with the autotrophic cells sorted. Dominant groups among sorted PPEs were poorly represented in FTP and their richness was on average lower than in the sorted samples. A significant number of operational taxonomic units (OTUs) were exclusively found in sorting samples, emphasizing that sequences from FTP underestimate the diversity of PPE. Moreover, 22% of the OTUs found among the dominant groups had a low similarity (<95%) with reported sequences in public databases, demonstrating a high potential for novel diversity in these lakes.Fil: Metz, Sebastián Darío. Universidad Nacional de San Martin. Instituto Tecnológico de Chascomús - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Tecnológico de Chascomús; ArgentinaFil: Dos Santos, Adriana Lopes. Sorbonne University; Francia. Centre National de la Recherche Scientifique; Francia. Nanyang Technological University; SingapurFil: Castro Berman, Manuel. Universidad Nacional de San Martin. Instituto Tecnológico de Chascomús - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Tecnológico de Chascomús; ArgentinaFil: Bigeard, Estelle. Sorbonne University; Francia. Centre National de la Recherche Scientifique; Francia. Nanyang Technological University; SingapurFil: Licursi, Magdalena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Not, Fabrice. Sorbonne University; Francia. Centre National de la Recherche Scientifique; FranciaFil: Lara, Enrique. University of Neuchatel; SuizaFil: Unrein, Fernando. Universidad Nacional de San Martin. Instituto Tecnológico de Chascomús - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Tecnológico de Chascomús; Argentin

The plankton communities from peat bog pools: structure, temporal variation and environmental factors

This is the first characterization of the structure and temporal variation of the plankton communities comprising the complete food web in five peat bog pools related to environmental factors over two consecutive ice-free periods in Tierra del Fuego (548S). Remarkably, picophytoplankton was composed solely of eukaryotic cells, surpassing the dominance expectations for these acidic water bodies, whereas testaceans were virtually absent, even as tychoplankters. Abundances of the different planktonic communities were slightly higher than those reported for Northern Hemisphere peat bogs and humic lakes. Mixotrophic nutrition prevailed among nano- and microphytoplankters, a strategy also common in humic lakes. The structures in spring of the planktonic communities were similar. In contrast, in late summer there were differences in the abundance and biomass of the different trophic compartments among small, shallow water bodies and large ones. These seem to be dictated by distinct pool size-driven patterns of water temperature variation. A general shift in the control of heterotrophic flagellates abundance in the pools occurred, changing from bottom-up regulation in spring to top-down control in late summer related to temperature-dependant variations in zooplankton abundance and composition. We hypothesize that changes in the trophic interactions affecting the entire food web occur over the open water period in these aquatic ecosystems, and that these are dictated by pool morphometry and related abiotic features.Facultad de Ciencias Naturales y MuseoInstituto de Limnología "Dr. Raul A. Ringuelet