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VENTI ANNI DI EVOLUZIONE TEMPORALE DI UN POPOLAMENTO BENTONICO SU SUBSTRATI ARTIFICIALI. TEMPORAL EVOLUTION OF BENTHIC ASSEMBLAGE ON ARTIFICIAL REEFS OVER TWENTY YEARS.
No full textQuesta ricerca si propone di descrivere e analizzare l’evoluzione a lungo termine di un popolamento bentonico di substrato duro, fin dalle prime fasi di colonizzazione. Per raggiungere questo obbiettivo si è deciso di lavorare su substrati artificiali che
consentono di quantificare con precisione le aree e i tempi degli insediamenti bentonici grazie alla loro semplicità strutturale. Si è, pertanto, scelto di proseguire lo studio sul popolamento
bentonico della barriera artificiale sommersa di Fregene di cui erano disponibili dati per un periodo di 10 anni, dal 1981 al 1992, in modo tale da descrivere e analizzare l’evoluzione
temporale del popolamento per un arco di tempo di 20 anni.
I campionamenti, effettuati in immersione, si sono svolti nel 2001, in diversi periodi dell’anno. Le modalità e le tecniche di campionamento sono state simili a quelle adottate nei periodi precedenti, così che i dati raccolti potessero essere comparati con quelli del passato. L’area di studio è caratterizzata da acque eutrofiche, idrodinamismo medio e scarsa illuminazione. Il popolamento attuale è caratterizzato principalmente dalla presenza di colonie massicce e tridimensionali di due specie di briozoi, Schizoporella errata e Turbicellepora magnicostata, che ricoprono tutto il substrato. La presenza di queste biocostruzioni ha
modificato in maniera evidente la struttura edifica della barriera, aumentando sia la superficie del substrato colonizzabile, sia la sua eterogeneità. Questo ha determinato una maggiore diversificazione del popolamento che viene così ad essere costituito da una maggiore numero di specie rispetto al passato.
Dall’analisi descrittiva e strutturale, l’evoluzione temporale del popolamento è risultata caratterizzata da 5 diverse fasi, ognuna con una particolare associazione bentonica: 1) insediamento delle specie pioniere; 2) dominanza di Mytilus galloprovincialis; 3) regressione di Mytilus galloprovincialis; 4) abbondanza di specie di substrato mobile; 5) prevalenza di biocostruzioni a briozoi. Il succedersi di queste associazioni è stato messo in relazione
all’apporto di materiale in sospensione proveniente dal fiume Tevere le cui acque influenzano fortemente l’area dove è posizionata la barriera. Da un punto di vista bionomico la barriera si trova in una zone di transizione, caratterizzata da fattori abiotici tipici sia del piano infralitorale, come l’elevato idrodinamismo e l’eutrofia, sia del circalitorale, come la scarsa illuminazione.
L’attuale coesistenza nel popolamento di molte specie tipiche di coralligeno con specie appartenenti a biocenosi del piano infralitorale contribuisce al mantenimento di una elevata
biodiversità. Dopo 20 anni il popolamento non è stabile e continua ad evolversi. Si può ipotizzare che con il tempo, se le condizioni ambientali rimarranno costanti, questo popolamento possa evolvere verso una biocenosi di tipo coralligeno.The aim of the present thesis is the study of the long-term development of a benthic community over a period of twenty years. Such a long-term study, including its start from a new
substratum, could represent a helpful insight in understanding the most important changes occurring in the community structure during and after the colonization process. To this end, the choice was to work on artificial substrata that, for their structural simplicity, allow to exactly quantify the areas and the times of benthic settlement. The artificial reef of Fregene was selected because past benthic assemblage data were already available for the period 1981 to 1992. This artificial reef is located in the mid Tyrrhenian Sea, 5 miles north of the two mouths of the Tevere River (Latium, Italy) and 1,5 miles offshore Fregene (Rome, Italy). The artificial reef was deployed for fisheries enhancement in 10-14 m of water on a sand-silty seabed in March 1981. The reef was composed of 280 concrete cube-shaped blocks (with 2 m long sides) arranged in groups of five, four at the base and one on the top, so as to form a pyramid and covering a total area of 6 ha. The area is characterised by a soft bottom. The Tevere river carries suspended materials and a noteworthy organic load since it transports Rome’s effluent, thus conditioning the eutrophic state of the area. The actual benthic assemblage was studied and the data were compared with data collected in the past. Benthic samplings were carried out by scuba diving in 2001, in four different periods.
During each sampling time two standard surfaces of 400 cm2 were scraped from the vertical walls of the same top block. The methodology used is the same as that adopted in the previous
periods, so that the 2001 data could be compared with past collected data.
The evolution of the benthic assemblage from 1981 to 2001 was analysed by descriptive and structural analysis. Changes in benthic assemblages and hydrological trends of the Tevere river
were investigated using the cumulative sum series method.
The twenty year development of the benthic community, starting from the new substratum, is composed of different phases characterized by different benthic assemblages. In particular
five different phases are distinguished: 1. pioneer species recruitment (settlement) (5.81-6.81); 2. Mytilus galloprovincialis dominance (8.81-83); 3. M. galloprovincialis regression (84-85); 4.
soft bottom species abundance (91-92); 5. bryozoan bioconstruction dominance (2001).
The dynamic succession of the observed benthic assemblages exhibited a good correlation with the Tevere river flow. The monthly cumulative sum series shows a clear upward trend
between 1981 and 1985. This trend was subsequently reversed in the successive period (1990-
2000). The succession of benthic assemblages is followed by a temporal increase in number of species. According to McArthur’s and Wilson’s “Island biogeographic theory” the succession
observed after 20 years should not have yet reached a steady-state equilibrium. From a biocoenosis point of view, the reef is located in a transition zone, characterised by abiotic factors which are typical of the infralittoral zone (high hydrodynamism and eutrophic water) and the circumlittoral zone (reduced illumination). A mussel dominated assemblage,
characteristic of shallow exposed and eutrophic environments, was present in the first period.
The increasing sedimentation present in 1981-85 caused the mussels to die. The assemblage was therefore subsequently characterised by the presence of species typical of sciaphilous muddy infralittoral hard bottoms. The ensuing dramatic decrease of the Tevere terrigenous particles favoured the presence of suspension-feeding organisms, such as bryozoans. These organisms, together with serpulids, barnacles and vermetids, formed a bioconstruction that for morphology and composition is similar to a “coralligenous” bioconstruction, thereby favouring the settlement of many typical coralligenous habitat species.
The coexistence of coralligenous species with infralittoral species favours the maintenance of a high biodiversity. If the environmental conditions shall remain constant, it is possible to
forecast that this complex assemblage may evolve into a real “coralligenous” assemblage
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
The polychaete community of the Fregene artificial reef (Tyrrhenian Sea, Italy): a 20-year study (1981-2001).
No full textthe fourth is a phase of mud accumulation between dead balanids, with the presence of laminar bryozoans (1991–92), and the last corresponds to a phase dominated by bryozoan bioconstruction (2001). The increased complexity in the benthic assemblage and substratum on the reef is also shown by an increased differentiation and distribution of polychaete functional groups. Increasing environmental heterogeneity on the reef is the basic factor that affected biodiversity by generating new niches that could be occupied by additional species with different ecology. The similarity of the benthic assemblage observed on the reef in 2001 with natural bioconstructions suggest that after two decades the ecological succession has lead to a settlement at a steady-state of equilibrium with the surrounding environment.; the third is a phase characterized by Mytilus galloprovincialis dominance and
regression (1983–85); The artificial reef of Fregene, Italy, was built in 1981 as a multipurpose structure with the intent of protecting the coastal environment from illegal trawling and also improving fishery production. It is located at 10–14 m depth on a sandy-silty seabed in the Tyrrhenian Sea, 5 nmi north of the outlet of the Tevere River (Latium, Italy) and 1.5 nmi offshore the town of Fregene (Latium, Italy). The development of the polychaete community on the reef was studied from May 1981 to December 2001 in order to examine long-term community dynamics and verify to what extent changes in polychaete assemblage could depict the development of the benthic assemblage. At each sampling time, two standard surfaces of 400 cm2 were scraped from the vertical walls of the same block. Temporal changes in the development of the polychaete community were detected by univariate (S, N, ExpH', 1/Simpson, J') and multivariate (CLUSTER, nMDS) analysis of the faunal data. Functional structure of the community was also analyzed. Changes in the community structure were shown by an overall increasing trend in the total number of species and individuals. The 20-year development of the polychaete community was divided into five different phases representing different benthic assemblages on the reef: the first two periods correspond to settlement of pioneer species (1981–82
Polychaetes of Fregene Artificial Reef after 20 years from its construction (Latium, Tyrrhenian Sea): preliminary study.
No full textPUBBLICO CONCORSO , PER TITOLI ED ESAMI, AD 2POSTI DI COLLABORATORE TECNICO ENTI DI RICERCA IN PROVA - VI LIVELLO PROFESSIONALE DELL'ISTITUTO SUPERIORE DI SANITA' - DIP.TO DI MALATTIE INFETTIVE, PARASSITARIE E IMMUNOMEDIATE (LETT. B) - PUBBLICATO NELLA G.U. - 4° SERIE SPECIALE - N. 39 DEL 23/05/2006.
No full textVariations 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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