1,721,013 research outputs found
Regional and temporal variation of Oithona spp. biomass, stage structure and productivity in the Irminger Sea, North Atlantic
Full text linkOithona spp. standing stock and production is considered relatively stable in space and time as a result of continuous breeding, low metabolism, reduced predation mortality and the ability of these small cyclopoids to exploit microbial food webs more efficiently than larger copepods. However, through a review of the published literature we show that Oithona spp. biomass can vary widely both over the year and with latitude. Thus, the present study set out to investigate the basin scale variability in biomass, stage structure and reproduction of Oithona spp. in relation to changes in hydrographic, physico-chemical and biological parameters encountered during three cruises conducted between April and November 2002 in the Irminger Sea, North Atlantic. Here we found that Oithona spp. biomass varied significantly with temperature and with dinoflagellates biomass concentration. On the other hand, O. similis egg production rates (EPR) increased with both ciliates and dinoflagellates concentrations, rather than with temperature. The inverse relationship we found between Oithona spp. naupliar recruitment with Calanus spp. and fish larvae abundance suggests that predation pressure may contribute to control the spatial variation in the stage structure and biomass of Oithona spp. and that the nauplii of this genus may serve as a food source for other planktonic organisms prior to the spring phytoplankton bloom
Comparison of five methods for estimating growth of Calanus helgolandicus later developmental stages (CV–CVI)
No full textThe activity of the enzymes aminoacyl-tRNA synthetases (AARS) in adult females and males and copepodites stage V of Calanus helgolandicus was studied at the L4 time-series station in the English Channel from June 2002 to December 2003. AARS activity was explored as an index of somatic growth in the laboratory as well as in the field by comparison with other methods of measuring growth: (1) the direct method (Heinle in Chesapeake Sci 7:59–74, 1966), (2) the weight increment (WI) method, (3) the Hirst and Bunker (HB) equation (Limnol Oceanogr 48(5):1988–2010, 2003) and (4) the egg production (EPR) method. AARS activity showed a significant correlation with the direct measurement of growth in the laboratory (R 2=0.55). However, the correlation was lower for growth assessed either with the WI or the HB approaches in the field (R 2=0.05–0.17). Female AARS activity showed a positive correlation with specific EPR during the reproductive season (R 2=0.40) but no relationship was found during the non-reproductive period
Latitudinal variation in plankton size spectra in the Atlantic Ocean
No full textThe size distribution of the pelagic community has the potential to compare ecosystems with different species composition as well as to identify the main functional properties of the system. Plankton size spectra are an effective approach of summarising the size structure of the community and have the potential to indicate the transfer of energy up the trophic food web. However, data on which open ocean plankton biomass-size structure can be constructed are scarce. Here we present the latitudinal distribution in the Atlantic Ocean of normalised biomass-size spectra (NB-S), plankton biomass and abundance, as well as mean zooplankton size between 70°N and 50°S. Samples were collected from three Atlantic Meridional Transect (AMT) cruises during May/June 2003, September/October 2003 and April/June 2004, as well as from a Marine Productivity (MarProd) cruise farther north in the Irminger Sea during spring 2002. The biomass-size distribution covered a body size range from nano- to mesoplankton and was based on a depth range of 50–0 m on the AMT and 120–0 m on the Irminger Sea cruise. The distribution of normalised biomass versus size was linear on a double log plot at all of the 95 stations. The slopes of the NB-S spectra ranged from ?0.93 to ?1.26 and ?1.12 to ?1.46 on the AMT and Irminger Sea cruises, respectively. A “dome-shaped” pattern in the slopes of community size spectra was observed in the Atlantic, indicating a decrease in the trophic transfer efficiency of energy with increasing latitude and phytoplankton biomass. Mesozooplankton biomass, abundance, and mean size followed a distribution similar to ecosystem productivity
Feeding and egg production of Oithona similis in the North Atlantic
No full textAlthough cyclopoids of the genus Oithona are considered the most abundant copepods in the marine environment, there is still very little information about what sustains their population and almost constant reproduction rate throughout the year. Feeding and egg production rate (EPR) of O. similis were measured at coastal and oceanic stations during 3 cruises in the North Atlantic between April and November 2002. O. similis ingested ciliates preferentially to other components of the nano- and microplankton (herein nano-microplankton), which only became a more important component of the copepod diet when the abundance of the former decreased to low concentrations. EPR did not show significant seasonal differences, with 2.13 ± 0.67 eggs female–1 d–1 in spring, 1.61 ± 0.32 eggs female–1 d–1 in summer and 1.60 ± 0.15 eggs female–1 d–1 in winter. The ingestion rates measured at many oceanic stations and in winter were often too low to sustain EPR.
Egg production efficiency (GGE) >100% indicated that sustained EPR might have relied, particularly in winter, on alternative food sources such as a more carnivorous diet and/or on the faecal pellets of euphausids
North Atlantic Oscillation and spring bloom phytoplankton composition in the English Channel
No full textThe spring phytoplankton composition has been investigated at a 50 m deep station off Plymouth in the English Channel for 6 years (1993–1999). The percentage of diatoms during the spring bloom was significantly correlated with the North Atlantic Oscillation index. A similar relationship between phytoplankton and North Atlantic Oscillation has also been found in a Swedish lake, suggesting a possible link between atmospheric forcing and phytoplankton composition
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
Feeding of Calanus finmarchicus nauplii in the Irminger Sea
No full textRecent studies have shown that the passage from nauplius to copepodite is a key event in the population dynamics of Calanus finmarchicus. As a first step towards understanding if and how trophic interactions influence this event, we investigated the feeding of C. finmarchicus nauplii IV-VI in the Irminger Sea during spring and summer in a series of incubation experiments. Generally, feeding efficiencies were highest on large cells, whereas small flagellates were ingested at very low rates. Colonies of Phaeocystis sp. were not ingested. Among the larger cells, the diatoms Chaetoceros pelagicus and Tropodineis sp. and the ciliate Strombidium sp. were the main food sources. We observed a negative relationship between the percentage of diatoms in the food environment and the filtration rate on Strombidium sp. We therefore suggest that the combination of low feeding efficiency on small cells and the generally low concentrations of ciliates in oceanic waters explains why C. finmarchicus relies on phytoplankton blooms for recruitment from nauplius to the first copepodite stage
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
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