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Using siliceous spicules in the Posidonia oceanica “matte” to discover past dynamics of the sponge community
No full textInvasione della specie aliena Caulerpa racemosa e cambiamento di fase nella prateria di Posidonia oceanica di Bergeggi.
No full textBiogenic silica in the Posidonia oceanica “matte”, a tool to discover past dynamics of the sponge community
No full textThe skeleton of most Porifera species consists of siliceous spicules that, after the sponge death, persist for a long time in the sediment. The reduced suspension occurring within the meadows of the seagrass Posidonia oceanica makes these habitats a stable deposit for sponge spicules. Spicules trapped into the network of rhizomes progressively buried, named “matte”, represent a sedimentary sequence interpretable on a temporal scale. By means of a vertical corer we collected samples of sediment at 0.5, 1, 1.5 and 2 m depth along the matte profile in order to quantify the amount of biogenic silica used to assess past dynamics of the sponge community in four P. oceanica meadows of the Ligurian sea. The content in biogenic silica was determined by spectrophotometric analysis of the sediments. While at Prelo Bay the values are constant in the core sample, a general decreasing trend with depth was observed in the meadows of Punta Pedale, while in the site of Punta Manara the major amount of silica was found deeper in the matte. The temporal variations of sponge abundance were probably due to historical anthropogenic factors. In the meadow of Bergeggi, BSi concentrations, significantly lower compared to all other sites, were likely caused from inputs from the close Savona harbor and strong bottom currents avoiding spicule deposition
Studio del phase shift nella prateria di Posidonia oceanica di Bergeggi: considerazioni sul comportamento della specie aliena Caulerpa racemosa
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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
Population structure change in a temperate reef coral after a quarter of century
No full textSeawater warming is affecting corals worldwide. Mass mortality events are increasingly frequent, and the bioconstruction potential of coral reefs is jeopardized. Revisiting sites surveyed in the past may represent a valuable tool to better understand the health state and ongoing trend of coral reefs. In the Mediterranean Sea the only reef-building coral is the endemic species Cladocora caespitosa. Several mortality events of this coral, due to thermal anomalies, have been reported in the last decades. An impressive change occurred in a population of C. caespitosa revisited 25 years after: smaller colonies became the prevalent size class and larger colonies disappeared, highlighting a loss in the bioconstruction potential. Data collected on C. caespitosa colonies in the Eastern Ligurian Sea (NW Mediterranean) revealed that mortality rate was correlated with colony size, while reproductive potential apparently increased, suggesting hormesis (i.e., enhanced reproductive output under pre-lethal conditions)
Unexpected slow recovery of seagrass leaf epiphytes after the impact of a summer heat wave and concomitant mucilage bloom
No full textThe epiphytes of seagrass leaves constitute a peculiar community, comprised of a number of species specialized for this living substrate. Several studies report on the response of epiphytes to different pressures but no in-formation exists about the effects of summer heatwaves, which have become frequent events in the last decades. This paper represents the first attempt to investigate the change in the leaf epiphyte community of the Medi-terranean seagrass Posidonia oceanica due to the heatwave occurred in summer 2003. Thanks to a series of data collected seasonally between 2002 and 2006, and punctual data in the summers of 2014 and 2019, we assessed the change over time in the leaf epiphyte community. Temperature data trends were analysed through linear regression, while multivariate analyses (i.e., nMDS and SIMPER) were applied to cover data in order to assess changes over time in the epiphyte community. As a whole, the two most abundant taxa were the crustose coralline alga Hydrolithon and the encrusting bryozoan Electra posidoniae, which displayed the highest average cover values in summer (around 19%) and spring (around 9%), respectively. Epiphytes proved to be sensitive to temperature highs, displaying different effects on cover, biomass, diversity and community composition. Cover and biomass exhibited a dramatic reduction (more than 60%) after the disturbance. In particular, Hydrolithon more than halved, while E. posidoniae dropped sevenfold during summer 2003. While the former recovered comparatively quickly, the latter, as well as the whole community composition, apparently required 16 years to return to a condition similar to that of 2002
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