oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2019 ( 6 )

2018 ( 8 )

2017 ( 10 )

2016 ( 19 )

Custom range...

Search Results: 1 - 10 of 3322 matches for " Michelle Graco "
All listed articles are free for downloading (OA Articles)
Page 1 /3322
Display every page Item
VARIABILIDAD ESPACIO-TEMPORAL DE CONDICIONES HIDROFíSICAS EN BAHíA INDEPENDENCIA, PISCO - PERú, DESDE 1995 AL 2004
Daniel Quispe,Michelle Graco,David Correa,Jorge Tam
Ecología Aplicada , 2010,
Abstract: Bahía Independencia cuenta con un importante sistema marino cuya estructura y funcionalidad, ha sido objeto de diferentes estudios biológicos. A partir de informes de evaluaciones in situ (IMARPE, DHN) y de datos satelitales (QuikSCAT), se logró describir la variabilidad espacio-temporal de las condiciones hidrofísicas, en base a vientos, circulación marina, temperatura y salinidad. Para ello se aplicó análisis de estadística descriptiva, pruebas de correlación, análisis multivariado, análisis de varianza (ANOVA) y mapas con escalas de color. Se identificaron patrones de distribución espacial cuya formación se atribuye a factores locales. En superficie se manifiesta un gradiente latitudinal de temperatura y en menor proporción de salinidad, con valores altos al norte de la bahía, debido al repliegue de aguas por acción del viento y a la influencia de Laguna Grande, una formación semi-encerrada en el extremo norte de la bahía. A nivel de fondo, en la zona norte la distribución de temperatura y salinidad reflejan el proceso de afloramiento, evidenciado por aguas que circulan de manera transversal al eje mayor de la bahía. En cambio, en la zona sur la circulación logra acoplarse en ambos niveles de profundidad con flujos en sentido horario y antihorario, generando peque as zonas con características similares de salinidad. A la bahía incursionan con mayor frecuencia las Aguas Ecuatoriales Subsuperficiales (AESS) afloradas, en algunos períodos aguas superficiales de mezcla con influencia de las aguas subtropicales superficiales (ASS) y en condiciones extremas El Ni o, como en 1998, las ASS, más cálidas y salinas.
ANáLISIS COMPARATIVO ENTRE CLOROFILA-A SATELITAL E IN SITU EN EL ECOSISTEMA DE AFLORAMIENTO PERUANO, ENTRE 1998 - 2007
Daniel Quispe,Ruth Calienes,Jorge Tam,Michelle Graco
Ecología Aplicada , 2010,
Abstract: El ecosistema de afloramiento peruano posee una alta variabilidad espacial y temporal en su producción primaria, que puede ser inferida a partir de observaciones de clorofila-a in situ y vía satélite. Las diferencias entre la clorofila-a in situ del IMARPE (Clai) y clorofila-a satelital del SeaWiFS (Clas) fueron estudiadas usando valores coincidentes en el espacio y tiempo, para conocer la relación entre Clai y Clas a partir de un modelo de regresión lineal simple. Asimismo, se determinó el ajuste entre ambas observaciones en las diferentes estaciones del a o, calculando la raíz del cuadrado medio del error. La hipótesis fue que las observaciones de Clai sobreestiman la variabilidad de Clai y que en verano hay un mejor ajuste entre los valores de Clai y Clas, respecto a las otras estaciones del a o. La ecuación general que relaciona ambas variables fue: Clai = 0.9925 Clas 0.9055. Se encontró que el ajuste con transformación log10 fue máximo en primavera (r = 0.84, RCME = 0.31) y mínimo en oto o (r = 0.72, RCME = 0.37). La clorofila-a fue sobreestimada en condiciones de verano y oto o, y subestimada en invierno y primavera por el SeaWiFS.
Nitrogen Cycling in Sediments from Central Chile (36oS): Seasonal and Interannual Variability
Laura Farías,Michelle Graco,Verónica Molina,Dimitri Gutierrez
Investigaciones Marinas , 2002,
Abstract:
Oxygen: A Fundamental Property Regulating Pelagic Ecosystem Structure in the Coastal Southeastern Tropical Pacific
Arnaud Bertrand, Alexis Chaigneau, Salvador Peraltilla, Jesus Ledesma, Michelle Graco, Florian Monetti, Francisco P. Chavez
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0029558
Abstract: Background In the southeastern tropical Pacific anchovy (Engraulis ringens) and sardine (Sardinops sagax) abundance have recently fluctuated on multidecadal scales and food and temperature have been proposed as the key parameters explaining these changes. However, ecological and paleoecological studies, and the fact that anchovies and sardines are favored differently in other regions, raise questions about the role of temperature. Here we investigate the role of oxygen in structuring fish populations in the Peruvian upwelling ecosystem that has evolved over anoxic conditions and is one of the world's most productive ecosystems in terms of forage fish. This study is particularly relevant given that the distribution of oxygen in the ocean is changing with uncertain consequences. Methodology/Principal Findings A comprehensive data set is used to show how oxygen concentration and oxycline depth affect the abundance and distribution of pelagic fish. We show that the effects of oxygen on anchovy and sardine are opposite. Anchovy flourishes under relatively low oxygen conditions while sardine avoid periods/areas with low oxygen concentration and restricted habitat. Oxygen consumption, trophic structure and habitat compression play a fundamental role in fish dynamics in this important ecosystem. Conclusions/Significance For the ocean off Peru we suggest that a key process, the need to breathe, has been neglected previously. Inclusion of this missing piece allows the development of a comprehensive conceptual model of pelagic fish populations and change in an ocean ecosystem impacted by low oxygen. Should current trends in oxygen in the ocean continue similar effects may be evident in other coastal upwelling ecosystems.
Beija-flores (Aves: Trochilidae) e seus recursos florais em uma área de caatinga da Chapada Diamantina, Bahia, Brasil
Machado, Caio Graco;
Zoologia (Curitiba) , 2009, DOI: 10.1590/S1984-46702009000200008
Abstract: this study investigated the species of hummingbird occurring in an area of caatinga vegetation, examining their seasonal activities, the assemblages of plants that they used, as well as the floral characteristics and flowering phenology of that vegetation. these surveys were performed in an area of arboreal caatinga in chapada diamantina, municipality of mucugê, state of bahia, brazil, during 12 expeditions undertaken on a bi-monthly basis between october, 2005 and august, 2007. field activities included observations made of the visiting hummingbird species, their behavior, and the frequency of their visits; as well as the plant species visited, their floral attributes, size, and the flowering phenophase evident on the occasion of each expedition. seven species of hummingbirds were registered, including five residents. phaethornis pretrei (lesson & delattre, 1839) acted as the organizer of this pollination guild. this species and chlorostilbon lucidus (shaw, 1812), these two species were considered the principal pollinators within the community. the hummingbirds visited a total of 29 plant species, of which only 12 are considered ornitophilous. the plant community presented a continuous flowering, with 19 species flowering in both the dry and the rainy season, permitting the year-round permanence of resident hummingbird species.
Fenologia reprodutiva de Prepusa montana Mart. (Gentianaceae) em uma área de campo rupestre da Chapada Diamantina, BA, Brasil
Coelho, Aline;Machado, Caio Graco;
Brazilian Journal of Botany , 2009, DOI: 10.1590/S0100-84042009000200018
Abstract: the phenological, flowering and fruiting strategies of prepusa montana mart. (gentianaceae) in an area of campo rupestre vegetation in the chapada diamantina were investigated in terms of the influence of local rainfall, relative humidity, temperature, and photoperiod. the numbers of buds, flowers, and mature fruits of this species were monitored during monthly visits to the mucugê municipal park between 6/2006 and 8/2007. environmental variables (average accumulated rainfall, average temperature and relative humidity) were monitored at the site, while the regional photoperiod was calculated from geographical data. prepusa montana demonstrated annual flowering of intermediate duration during the dry season. the flowering phenophase did not demonstrate any correlation with rainfall or relative humidity, but was found to be negatively correlated with temperature and photoperiod. fruit maturation initiated during the dry season and was most intense at the start of the rainy season. seed dispersal demonstrated a negative correlation with relative humidity. as this species occurs along water courses, flowering appears to be independent of any water stress during the dry period. the negative correlation between fruit opening and relative humidity is associated with the desiccation processes necessary for diaspore maturation and dispersal. the dissemination of p. montana seeds is apparently facilitated by the wind during the dry season and then by rainfall at the start of the rainy season (while rainfall would also increase the probability of seedling establishment).
Fenologia de flora??o e poliniza??o de espécies ornitófilas de bromeliáceas em uma área de campo rupestre da Chapada Diamantina, BA, Brasil
Santana, Cyrio Silveira;Machado, Caio Graco;
Brazilian Journal of Botany , 2010, DOI: 10.1590/S0100-84042010000300009
Abstract: (flowering phenology and pollination of ornitophilous bromeliads in the campo rupestre of chapada diamantina, bahia, brazil). hummingbirds are the major pollinators of bromeliads and the sequential flowering can potentially provide the maintenance of their local populations. in this study we investigated the phenological flowering strategies and the floral visitors of five ornitophilous bromeliads on the high altitude rocky field (campos rupestres) areas of the chapada diamantina, bahia. flowering phenology data were collected in monthly monitored individuals, from july 2006 to december 2007. floral visitors were recorded by naturalistic observations from february 2002 to december 2003 and from july 2006 to december 2007. most species flowered at the end of the dry season and the beginning of the rainy season, but hohenbergia ramageana mez showed continuous flowering. the community showed a sequential and continuous flowering, providing feeding resources for the maintenance of pollinators in the area throughout the year. six hummingbirds, the perching bird, and three species of bees visited the bromeliads flowers. chlorostilbon lucidus (shaw, 1812), phaethornis pretrei (lesson & delattre, 1839), and coereba flaveola (linnaeus, 1759) were their major pollinators. neoregelia bahiana (ule) l. b. sm., with its long corolla tube is the most specialized species, and p. pretrei was its only pollinator, while h. ramageana, with its short corolla tube is the most generalist, considered an important resource for the hummingbirds of the area.
Fenologia da flora??o e biologia floral de bromeliáceas ornitófilas de uma área da Mata Atlantica do Sudeste brasileiro
Machado, Caio Graco;Semir, Jo?o;
Brazilian Journal of Botany , 2006, DOI: 10.1590/S0100-84042006000100014
Abstract: this study dealt with phenology and flower visitors of some bromeliaceae species in an atlantic forest area at parque estadual intervales, southeastern brazil. the taxa studied belonged to the genera tillandsia l. (3 spp.), vriesea lindl. (5 spp.), aechmea ruiz & pav. (3 spp.), billbergia thunb. (1 sp.) and nidularium lem. (2 spp.). sample transects were established in areas with different succession stages, where the bromeliads were localized and marked. flowering phenology surveys were made monthly. the bromeliad community showed a sequential flowering all along the year and most species flowered during the rainy season. the floral visitors were recorded by naturalistic observations. eight hummingbird species visited the bromeliads flowers. among them, phaethornis eurynome lesson and thalurania glaucopis gmelin were the most frequent visitors. bromeliads were divided in two groups by similarity analysis of floral visitors (hummingbirds): a group represented by species visited by trochilinae hummingbirds and another visited by phaethornis eurynome (subfamily phaethornithinae). the competition among bromeliad species for pollinators is reduced due to their spatial distribution and the flowering periods.
Anoxic sediments off Central Peru record interannual to multidecadal changes of climate and upwelling ecosystem during the last two centuries
M. Graco, D. Gutiérrez,L. Farías
Advances in Geosciences (ADGEO) , 2006,
Abstract: The coastal region of central Chile (36° S) is one of the most productive coastal systems, characterized by a marked seasonality in the upwelling regime, that brings subsurface waters rich in nutrient and poor in oxygen (ESSW) into the euphotic zone. This oceanographic condition depends basically on the equatorward wind strength and is modified on different time scales, with the El Ni o-Southern Oscillation (ENSO) phenomenon as the main source of interannual variability in the Pacific Ocean. Here we present an effort to integrate physical and biogeochemical variability associated with in situ information and experiments at coastal stations off central Chile (36° S) in order to improve the knowledge on the pelagic-benthic coupling in this upwelling system during the warm ENSO phase or El Ni o. Carbon fluxes exported from the water column to the sediments and the ammonium exchange across the sediment-water interface are discussed together with oceanographic and benthic conditions. All measurements and estimations were carried out from May 1997 until April 2001 at two stations, one located inside Concepción Bay (~28 m depth), and the other on the continental shelf at ~36° S (~88 m depth). The results show that the pelagic and benthic systems are strongly coupled off central Chile (36° S). Oceanographic variability associated with upwelling events (seasonal scale) and an El Ni o event (interannual scale) was observed. The carbon fluxes exported to the sediments, the benthic conditions (i.e., quantity and quality of the sediment organic matter), and the ammonium exchange across the sediment-water interface, responded to the seasonal regime of upwelling during non El Ni o years as well as to the ENSO related oceanographic variability.
Giant Hydrogen Sulfide Plume in the Oxygen Minimum Zone off Peru Supports Chemolithoautotrophy
Harald Schunck, Gaute Lavik, Dhwani K. Desai, Tobias Gro?kopf, Tim Kalvelage, Carolin R. L?scher, Aurélien Paulmier, Sergio Contreras, Herbert Siegel, Moritz Holtappels, Philip Rosenstiel, Markus B. Schilhabel, Michelle Graco, Ruth A. Schmitz, Marcel M. M. Kuypers, Julie LaRoche
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0068661
Abstract: In Eastern Boundary Upwelling Systems nutrient-rich waters are transported to the ocean surface, fuelling high photoautotrophic primary production. Subsequent heterotrophic decomposition of the produced biomass increases the oxygen-depletion at intermediate water depths, which can result in the formation of oxygen minimum zones (OMZ). OMZs can sporadically accumulate hydrogen sulfide (H2S), which is toxic to most multicellular organisms and has been implicated in massive fish kills. During a cruise to the OMZ off Peru in January 2009 we found a sulfidic plume in continental shelf waters, covering an area >5500 km2, which contained ~2.2×104 tons of H2S. This was the first time that H2S was measured in the Peruvian OMZ and with ~440 km3 the largest plume ever reported for oceanic waters. We assessed the phylogenetic and functional diversity of the inhabiting microbial community by high-throughput sequencing of DNA and RNA, while its metabolic activity was determined with rate measurements of carbon fixation and nitrogen transformation processes. The waters were dominated by several distinct γ-, δ- and ε-proteobacterial taxa associated with either sulfur oxidation or sulfate reduction. Our results suggest that these chemolithoautotrophic bacteria utilized several oxidants (oxygen, nitrate, nitrite, nitric oxide and nitrous oxide) to detoxify the sulfidic waters well below the oxic surface. The chemolithoautotrophic activity at our sampling site led to high rates of dark carbon fixation. Assuming that these chemolithoautotrophic rates were maintained throughout the sulfidic waters, they could be representing as much as ~30% of the photoautotrophic carbon fixation. Postulated changes such as eutrophication and global warming, which lead to an expansion and intensification of OMZs, might also increase the frequency of sulfidic waters. We suggest that the chemolithoautotrophically fixed carbon may be involved in a negative feedback loop that could fuel further sulfate reduction and potentially stabilize the sulfidic OMZ waters.
Page 1 /3322
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.