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Cell carbon content and biomass assessments of dinoflagellates and diatoms in the oceanic ecosystem of the Southern Gulf of Mexico
Full text linkThis study assessed the cell carbon content and biomass for genera of dinoflagellates and diatoms in the oceanic ecosystem of the Southern Gulf of Mexico. Carbon content estimates were based on biovolume calculations derived from linear dimension measurements of individual cells and the approximate geometric body shape of each genus. Then, biomass assessments were performed for both groups in two gulf regions (Perdido and Coatzacoalcos) using these carbon content factors and cell abundances. After four seasonal cruises, 11,817 cells of dinoflagellates and 3,412 cells of diatoms were analyzed. Diverse body shapes and cell sizes were observed among 46 dinoflagellate genera and 37 diatom genera. Nano-cells of dinoflagellates (68% <20 μm) and micro-cells of diatoms (77% 20–200 μm, mostly 50–75 μm) were predominant. According to this cell-size structure, on average, diatoms contained 40% more carbon per cell than dinoflagellates. Contrasting carbon content estimates were observed within the genera of both microalgae. Large carbon averages (>10,000 pg C cell-1) were attributed to Gonyaulacal and some occasional genera of dinoflagellates (e.g., Pyrocystis and Noctiluca) and centric diatoms. In contrast, values up to 3 orders of magnitude lower were found for Peridinial and Gymnodinial dinoflagellates and pennate diatoms. Based on these carbon content estimates, which can be considered representative for most of this oceanic ecosystem, seasonal and regional differences were found in the biomass assessments conducted for these functional groups. Overall, dinoflagellates (mostly low-carbon Gymnodinales) had larger depth-integrated biomass than diatoms (mainly rich-carbon centric forms) within the euphotic zone. An exception to it was the late-summer cruise at the Coatzacoalcos region when a surface bloom of centric diatoms was observed in stations influenced by river runoff. This work contributes useful reference information for future ecological studies and models for understanding the biogeochemical functioning of this open-ocean ecosystem. © 2021 Linacre et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Estructura comunitaria de los eufáusidos en la parte sur del sistema de la corriente de California durante octubre de 1997 (evento El Niño) y octubre de 1999 (evento La Niña)
No full textSe describe la estructura comunitaria de los eufáusidos entre Punta Baja (30ºN) y Punta Abreojos (26. 7ºN), Baja California, durante un evento El Niño (Octubre 1997) y uno La Niña (Octubre 1999). Se encontraron un total de 24 especies, pertenecientes a 7 géneros. La abundancia de eufáusidos durante el evento cálido (Octubre 1997) fue de un 32% mayor que la encontrada en el periodo frio (Octubre 1999) debido principalmente a una mayor contribución de larvas. El porcentaje de postlarvas (juveniles y adultos) y larvas (furcilias y caliptopis) para Octubre 1997 fue de un 36 y 64%, respectivamente, mientras que para Octubre 1999 estos porcentajes fueron de un 57 y 43%, respectivamente. La especie más abundante durante el evento El Niño fue Nyctiphanes simplex (84%), seguida de Euphausia eximia (2%) y Stylocheiron affine (2%). Para el evento La Niña, Nyctiphanes simplex (67%) sigue siendo la especie más abundante y Nematoscelis difficilis (20%) incrementó fuertemente su abundancia El resto de las especies presentaron bajas abundancias, pero la presencia de algunas de ellas en la zona, podría deberse a las condiciones oceanográficas particulares registradas en ambos períodos. Tal es el caso de Euphausia pacifica que estuvo presente sólo durante Octubre 1999, incluso en las estaciones de más al sur, siendo una especie de aguas frías que normalmente se encuentra presente en la parte más norte de la Corriente de California. En contraste, la presencia en Octubre 1997 de especies con afinidades tropicales y ecuatoriales tales como Euphausia diomedeae, E. distinguenda, E. lamelligera, E. tenera y Nematoscelis gracilis, podría deberse al calentamiento de las aguas durante El Niño 1997-98, asociado a un flujo hacia el norte de aguas subtropicales, que producen la introducción de estas especies a la zona.Community structure of euphausiids is described between Punta Baja (30oN) and Punta Abreojos (26.7oN), Baja California, during events El Niño (October 1997) and La Niña (October 1999). Adults, juveniles, and larval stages (furcilias and calyptopes) of the euphausiids of both periods were quantified and identified finding 24 species, belonging 7 genera. Euphausiids abundance during the warm event (October 1997) was 32% higher than in the cold period of October, due mainly to a higher contribution of larves. The percent of the poslarval and larval stages in October 1997 were 36 and 64%, respectively, while in October 1999 these percent were 57 and 43%, respectively. The most abundant species during El Niño was Nyctiphanes simplex (84%), followed by Euphausia eximia (2%) and Stylocheiron affine (2%). During La Nifia event, Nyctiphanes simplex (67%) continued being the most abundant species, and Nematoscelis diflicilis (20%) increased their abundance notoriously. Other species presented low abundance, but their presence in the area could be due particular oceanographic conditions of both periods. Such is the case of Euphausia pacified while was present during the cold period in October 1999 including southern stations. This species has affinity by cold waters being found in the northern part of the California Current. In contrast, in October 1997 species with tropical and equatorial affinity, such as, Euphausia diomedeae, E. distinguenda, E. lamelligera, E. tenera y Nematoscelis gracilis, were recorded, due to the warming of the waters in El Niño 1997-98, associated to a flow northward of subtropical waters with the introduction fi'om these species to the area
Spatial and temporal distribution of nickel and cadmium related to Synechococcus spp and Prochlorococcus spp abundance in the Mexican region of the Gulf of Mexico
No full textEn la región oceánica y oligotrófica del golfo de México dominan las poblaciones de Synechococcus spp. y Prochlorococcus spp., las cuales han mostrado en otros ecosistemas una estrecha asociación con Cd y Ni, sugiriendo que estos picoautótrofos son actores importantes para la biogeoquímica de estos metales en la columna de agua. El objetivo de este estudio fue conocer la asociación entre las abundancias de estas cianobacterias y la concentración disuelta de Cd y Ni en la región de aguas profundas del golfo de México durante tres campañas oceanográficas: XIXIMI-4 (agosto - septiembre 2015), XIXIMI-5 (junio 2016) y XIXIMI-6 (agosto - septiembre 2017). Los resultados mostraron que la concentración de Cd y Ni tienen una gran variabilidad regional y temporal, influenciada en mayor medida por la actividad de mesoescala, y por otros forzantes físicos como los aportes continentales hacia la plataforma y la interacción de estructuras anticiclónicas con el talud, que permiten un transporte costa-océano. La distribución de Cd y Ni en la columna de agua también se vio influenciada por los procesos locales de remineralización de los metales que fueron consumidos en la zona eufótica por diversos grupos fitoplanctónicos. Las relaciones estequiométricas de metal:nutriente, evidenciaron una variabilidad temporal entre las campañas, proponiendo que los cambios estacionales de la columna de agua, así como la cantidad y el origen de la materia orgánica, pueden estar influyendo en el cambio de estas razones. Comparativamente con la región norte del Atlántico oeste (~19 - 21°N), las aguas del golfo mostraron características fisicoquímicas similares. Los análisis estadísticos de este estudio revelaron una tendencia generalmente opuesta de ambas cianobacterias con el Cd y Ni, sugiriendo un cierto control de estos metales en el crecimiento de estos organismos, ya sea por un consumo inmediato o por un efecto tóxico después de un cierto umbral de concentración. Los resultados de este estudio destacaron la importancia de los factores físicos, químicos y biológicos en la distribución de Cd y Ni en el golfo y particularmente, el papel que ejercen las poblaciones de cianobacterias en modificar sus concentraciones dentro de la zona eufótica.Picoautotrophs like, Synechococcus spp. and Prochlorococcus spp. are dominant populations in the oceanic and oligotrophic region of the Gulf of Mexico. They exhibit a close relationship with Cd and Ni, hence, they are important actors on the biogeochemistry of these metals in the water column. The objective of this research was to study the association between the abundance of these cyanobacterial populations and the dissolved concentrations of Cd and Ni at the deep region of the Gulf of Mexico during three oceanographic campaigns: XIXIMI-4 (August - September 2015), XIXIMI-5 (June 2016) and XIXIMI-6 (August - September 2017). The results showed regional and temporal variability in the Cd and Ni concentrations, mainly influenced by the mesoscale activity and other physical forcing such as, river inputs to the continental shelf and the interaction between anticyclonic structures and the continental slope, allowing a cross-shelf transport. Local processes like, metal remineralization after consumption in the euphotic zone by different phytoplankton groups, also influenced the Cd and Ni distributions in the water column. The metal:nutrient stoichiometry displayed a temporal variability among campaigns, associated to the seasonal changes in the water column, and also the amount and origin of the organic matter. Comparisons made with the northern region of the Western Atlantic (~19 - 21°N), indicated that the Gulf of Mexico waters presented similar physicochemical characteristics. Statistical analyses revealed a generally opposed trend between both cyanobacterial populations and the two metals, suggesting a control over their growth, by immediate consuming or by a toxic effect after surpassing a concentration threshold. The results of this study highlights the importance of the physical, chemical, and biological factors on the Cd and Ni distributions in the Gulf of Mexico and, in particular, the role of the cyanobacterial populations to modify the concentrations of these metals into the euphotic zone
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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