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Post-larval development in deep-sea echinoderms
No full textThe post-larval phase is an essential period in the life history of marine invertebrates; vulnerable to high mortality, it ultimately influences the distribution and abundance of adult populations. The post metamorphic ontogenesis of thirty species of deep-sea echinoderms, belonging to three classes (Ophiuroidea, Asteroidea and Echinoidea), is described using scanning electron microscopy. The life history of Ophiocten gracilis is also examined as a case study for future research on post-larval organisms. The analysis of development in ophiuroids reveals that species can be identified from a very early post metamorphic stage, even in congeneric species, contrary to the findings of other authors. The ontogeny of homologous structures is similar within related groups, but may give rise to different adult structures indifferent taxa. The mouth papillae within the ophiurids are serially homologous, originating from the jaw, but the fourth mouth papilla may have a different origin. In the families Ophiactidae, Ophiacanthidae and Amphilepididae examined, the mouth papillae have different origins, as, for instance, the adoral shieldspine or tentacle scale. Data on the post-larval development of Ophiura affinis suggest that this species is more closely related to the genus Ophiocten and a change in the generic status is proposed. Ophiocten gracilis is a bathyal brittle star occurring on both sides of the North Atlantic and its life history is studied in the eastern side of the North Atlantic. In this area, O. gracilis spawns in February/March of each year producing a large number of eggs. Fecundity is estimated to be around 40,000 eggs/ind, with the population of the Hebridean Slope being able to produce probably up to 16 million eggs/m2. Post-larvae start settling in May and numbers settling reached over 3,200 post-larvae/m2. The settling speed of post-larvae in the water column is estimated to be around 500 m/day, settling faster in warmer than colder water. Settling speeds appear to be similar for post-larvae ranging from 0.6 to 0.9 mm in disk diameter. Size at settlement is around 0.6 mm in disk diameter and 5-6 arm segments. The settlement of post-larval O. gracilis on the bottom of the Hebridean Slope also represented a considerable fraction of the particulate organic carbon (POC) flux in the area, reaching over 7% of the total daily flux. This is likely to have a considerable impact in the benthic community as competition and predation and as an additional food source for demersal and benthic organisms. The occurrence of post-larvae of O. gracilis in sediment traps also represented a large problem for POC flux measurements, with ophiuroids consuming part of the flux. In future works with sediment traps, such errors must be taken into account and ophiuroids must be included in the total POC flux. The deep-sea juvenile asteroids of the NE Atlantic could be distinguished to species level from a very early stage of development. The ontogenesis of Porcellanaster ceruleus shows that this species is likely to undergo a shift in habitat and diet during the juvenile phase. This is evidenced by the appearance of the epiproctal cone, the changing of the furrow and apical spines, the early development of the cribriform organ adjacent to the madreporite and the appearance of sediment in the stomach. P. ceruleus is probably a predator on meiofauna and small macrofaunal organisms during the early stages of life, changing to a burrowed life style ingesting sediment particles. Most juvenile sea stars analysed during the present study showed wider bathymetric distribution than their adult counterparts, suggesting that events occurring during the early stages of life are important for the maintenance of the local population structure and diversity in the deep NE Atlantic.The post-metamorphic development of three deep-sea spatangoid echinoids is very similar, but the morphology and formation of fascioles facilitate the distinction of the species examined. Whereas in Hemiaster expergitus and Spatangus raschi the fascioles present in the post-larvae develop to form the adult fascioles, in Brissopsis lyrifera post-larvae there is a juvenile fasciole, which disappears during ontogenesis giving way to the adult fascioles. The function of the juvenile fasciole is unknown in B.lyrifera. The development of the periproct in all spatangoids examined is similar to that described by other authors, with the periproct being initially endocyclic and migrating towards the rear of the animal as development progresses. Post-larvae of the genus Echinus could not be separated into different species, which may be linked to the recent diversification of the genus in the North Atlantic. The widespread settlement of echinoderm post-larvae reported in the present thesis and in other works is thought to have been very important for the colonization of the deep-sea through the supply of stages to deeper areas and selection of pressure adapted animals and subsequent speciation
Reproduction, dispersal and settlement of the bathyal ophiuroid Ophiocten gracilis in the NE Atlantic Ocean
No full textAbstract Ophiocten gracilis is an ophiuroid found at bathyal depths in the North Atlantic Ocean. The adults show strong seasonal reproduction, with an ophiopluteus in the surface plankton. Settling postlarvae were collected in sediment traps moored at 1000 and 1400 m depth in the NE Atlantic during Julian Days 142 to 212 (May to July) in 1996. During this period, growth of postlarvae in the traps was linear and the diet consisted of phytodetritus and foraminifera. Experiments suggest that postlarvae sink at rates of up to 500 m dm1, although this may well be slower in the natural environment. The high fecundity, seasonality and high population density resulted in high fertilization success, and many of the offspring were advected outside the normal adult range, where they were able to settle but did not survive to adulthood
Early juvenile development of deep-sea asteroids of the NE Atlantic Ocean, with notes on juvenile bathymetric distributions
No full textThe postmetamorphic ontogenesis of 11 deep-sea asteroid species is described. Juvenile bathymetric distributions are compared to adults. The deep-sea juvenile asteroids of the NE Atlantic could be distinguished to species level from a very early stage of development. In all species, except Porcellanaster ceruleus and Plinthaster dentatus, the arms grow faster than the body. In Porcellanaster ceruleus and Plinthaster dentatus, early growth is nearly isometric. In the appearance of the epiproctal cone, the change in form of the furrow and apical spines, the early development of the cribriform organ adjacent to the madreporite and the appearance of sediment in the stomach indicate that Porcellanaster ceruleus is likely to undergo a shift in habitat and diet during the juvenile phase. Porcellanaster ceruleus is probably a predator on meiofauna and small macrofauna during the early stages of life, changing to a burrowing lifestyle ingesting sediment particles. Juvenile sea stars showed wider bathymetric distributions than their adult counterparts, suggesting that events occurring during the early stages of life are important for the maintenance of the local population structure and diversity in the deep NE Atlantic
Ophiuroid growth within deep-sea sediment traps: a problem for carbon flux measurements at continental margins
No full textEarly post-metamorphic ontogenesis of deep-sea spatangoids (Echinoidea, Spatangoida) of the NE Atlantic Ocean
No full textThe early juvenile development of 3 species of irregular deep-sea echinoids of the NE Atlantic was examined using scanning electron microscopy. Although the post-metamorphic development of these 3 spatangoids is very similar, the morphology and development of fascioles (specialized bands of heavily ciliated minute spines) facilitates distinguishing the species. In Hemiaster expergitus and Spatangus raschi, the fascioles present in the early juvenile develop to form adult fascioles. In Brissopsis lyrifera, a juvenile fasciole of unknown function disappears during ontogenesis, and new adult subanal and periproct fascioles arise. Fascioles of S. raschi and B. lyrifera are present at a very early stage of development (0.7 mm test length), whereas in H. expergitus the fasciole appears much later (3 mm test length). Animals smaller than 0.8 mm test diameter have not yet developed a functional mouth and are still considered as endotrophic postlarval stages. Mouth development is similar for all spatangoids examined
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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