1,721,014 research outputs found
A spatial and temporal study of Pseudocalanus acuspes, P. minutus and P. moultoni in the Svalbard – Barents Sea region and their potential as environmental indicator species in a changing Arctic
Full text linkMany species of small copepods are morphologically similar and thus often grouped together at genus level rather than studied as individual species. However, species within the same genus may differ quite a lot in life history strategies and traits. In this study, I used a species-specific polymerase chain reaction to explore the abundance, distribution and size range of Pseudocalanus sibling species in the Svalbard – Barents Sea region. The main aim was to investigate if they have distinct environmental preferences and the potential to be used as valid environmental indicator species. Temporal patterns in species composition were investigated monthly year-round in a high Arctic fjord (Billefjorden, Svalbard) over an entire year, while spatial patterns in species composition were investigated during a three-week cruise in the Barents Sea across the Polar Front from 73º S to 78º N.
P. acuspes was the most abundant species in Billefjorden and it dominated year-round except in June when the overall Pseudocalanus abundance was low and P. minutus were dominating. P. minutus was also present year-round in Billefjorden comprising 20 - 42 % of the total Pseudocalanus abundance from May to August 2021, while in the other months they had a lower total abundance between 4 and 15 %. P. moultoni was only present in 7 out of 12 months in Billefjorden, with the highest abundance in June and July (16-20 % of the Pseudocalanus community).
P. minutus had the overall largest average CIV and CVs, and while P. acuspes had the overall largest adults, P. moultoni had the overall largest single individuals. The gap and inconsistency between body size in CV and adult females, could be explained by differences in feeding strategy and timing of reproduction. P. minutus overwintered as CIV and CV in Billefjorden and started to reproduce in February and peaked in April when most CV had moulded into adults and hence were using their lipids reserves on maturation and reproduction rather than growing larger during the spring showing a capital breeding strategy. P. acuspes on the other hand overwintered as CIII and CIV, and adults had a late peak in July after CV were grazing during the spring and becoming adults during the summer displaying an income breeding strategy.
In the Barents Sea, P. acuspes was the most abundant species at the northernmost (T1, P2) and at the Polar Front stations (T3, T4, and T5). P. moultoni on the other hand, was the most abundant species at the southernmost stations (P1, C and the reference station), but barely present at the stations furthest North (1.3 – 3.2 % of the total Pseudocalanus abundance).
My study demonstrates the importance of sampling the entire populations (CI-adults) and not only parts of it when investigating species distributions, and preferable throughout the entire year to avoid biases due to seasonality in population structures and advective events (i.e., Billefjorden)
Mesozooplankton distribution in Svalbard waters. Calanus spp. and its relationship to hydrographic variability
Full text linkThis thesis investigates mesozooplankton abundance, composition and distribution in Svalbard waters in relation to hydrography. Sampling was carried out in the archipelago of Svalbard mainly during summer and autumn between 2000 and 2004. From cluster analysis four species assemblages were distinguished and these reflected differences in hydrography and bottom depth. In particular the distribution of the Atlantic Calanus finmarchicus relative to that of the Arctic Calanus glacialis was associated with different hydrographic regimes. Differences in the species assemblages primarily resulted from variations in species densities rather than from taxonomical variation. For species of Atlantic and Arctic origin significant relationships with temperature and salinity were found. Regression models were used to quantify the influence of water mass characteristics on the abundance of the three different Calanus species that co-occur in the study area. About 50% of the variability in abundance of each Calanus species could be accounted for by variability in temperature and salinity. C. finmarchicus abundance was positively related to warmer and more saline waters, as expected from its distributional southern core area. Conversely, the Arctic species C. hyperboreus was more abundant in colder and fresher waters. The numbers of C. glacialis decreased with increasing temperature and salinity in shallow areas, while the opposite trend was found in deep locations. Salinity and temperature between 50 - 150 m depth were in most cases better predictors for Calanus spp. abundance than near-surface conditions. Variability in the vertical distribution of the three Calanus species and Metridia longa reflected life history and behavioural adaptations on diel and seasonal scale. Diel vertical migration was observed for copepodite stages of M. longa but generally not for Calanus spp. The copepodite stage composition indicated a south to north delay in the succession of Calanus development and that the descent to overwintering depth had started at time of sampling. The vertical distribution patterns of C. finmarchicus and M. longa were found to be consistent with the hypothesis that the developmental stages distributed according to preferences for light intensity. This thesis includes one of few year-round studies on Calanus population dynamics from the high Arctic. The three Calanus species co-existed in the studied fjord. The estimated length of the life cycle of C. glacialis (1-2 years) and C. finmarchicus (1 year) were in agreement with previous studies in Svalbard and the Arctic in general. For C. hyperboreus a one year life cycle was observed which is among the shortest life cycle duration reported for this species. Differences in winter mortality rates for the three Calanus populations indicate that these affect the species composition in the study area. The observed statistical relationships between Calanus abundance and hydrography indicate that changes in ocean climate as a consequence of global warming may alter the relative composition of the three Calanus species in Svalbard waters. However, lack of such relationship between Calanus biomass and hydrography suggests that a changing climate may induce a shift in size structure rather than in biomass which may have repercussions on the pelagic food web
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
Distribution of Zooplankton in relation to biophysical gradients associated with frontal systems
No full textPolarFront August 2023 Cruise Report
No full text<p><strong>PolarFront August 2023 Cruise Report</strong><br>Cruise dates: 2023-08-15/2023-08-28<br>Ship: R/V Helmer Hanssen</p>
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
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