323,259 research outputs found
GRB 980425, SN1998bw and the EMBH model
No full textThe EMBH model, previously developed using GRB 991216 as a prototype, is here applied to GRB 980425. We fit the luminosity observed in the 40-700 keV, 2-26 keV and 2-10 keV bands by the BeppoSAX satellite. In addition we present a novel scenario in which the supernova SN1998bw is the outcome of an "induced gravitational collapse" triggered by GRB 980425, in agreement with the GRB-Supernova Time Sequence (GSTS) paradigm [Ruffini, R., Bianco, C.L., Chardonnet, P., Fraschetti, F., Xue, S.-S. On a possible GRB-supernova time sequence. Astrophys. J. 555, L117-L120, 2001c]. A further outcome of this astrophysically exceptional sequence of events is the formation of a young neutron star generated by the SN1998bw event. A coordinated observational activity is recommended to further enlighten the underlying scenario of this most unique astrophysical system. © 2004 COSPAR. Published by Elsevier Ltd. All rights reserved
Human-driven impacts on marine habitats: a regional meta-analysis in the Mediterranean Sea
No full textHabitat destruction is one of the main threats to environmental integrity. Assessing the consequences
of human impacts is crucial both to predict and prevent structural and functional changes of habitats.
However, to date almost all studies on marine threats, from regional to global scales, have been
entirely qualitative and generally based on little more than expert opinion. We have developed a
meta-analytical approach to quantify overall effects of various stressors on different Mediterranean
habitat types and to compare the relative importance of different impacts across a range of habitats.
We first qualitatively reviewed and synthesized 366 experiments (either manipulative or correlative)
collected in the literature. After a selection procedure, we finally quantitatively meta-analyzed 158
experiments. We showed that fisheries (destructive or not), species invasion, aquaculture, sedimentation
increase, water degradation and urbanization have negative effects on Mediterranean habitats
and associated species assemblages. We also explored the overlap between the impacts identified
as important in the Mediterranean and those identified by experts as being important globally, highlighting
the inadequacies of relying on expert opinion alone. Finally, we drew attention to the critical
lack of empirical knowledge about marine systems in many areas of the Mediterranean, which
impedes the implementation of effective conservation measures. Our study is the first to synthesize
experimental analyses on human-driven impacts on marine habitats across such a broad geographic
scale
A three-year time series of elemental and biochemical composition of organic matter in subtidal sandy sediments of the Ligurian Sea (northwestern Mediterranean).
No full textVariations in organic matter composition and microphytobenthic biomass were examined in the surface sandy sediments at a water depth of 10 m in the Gulf of Marconi (NW Mediterranean Sea) over a three year period. Seasonal changes in elemental (organic C and total N) and biochemical (lipids, proteins, carbohydrates) composition of sediment organic matter as well as Chi a were assessed in order to provide information about the origin and fate of sedimentary organic matter, the contribution of microphytobenthic biomass, seasonal and interannual variations of food quantity and quality, and factors related to food availability. Data obtained in this three-year study revealed that organic matter determined with a muffle furnace is clearly an overestimate of the organic content of the sediment and is thus of little significance for benthic ecologists studying community dynamics in relation to food availability. Labile organic matter, utilized to estimate the food potentially available for benthic consumers, accounted for only a small percentage (on average less than 10%) of total organic C. The highest labile fraction was observed in spring, whereas minima were recorded in winter. Analysis of elemental and biochemical composition of organic matter showed an inverse relationship between amount of organic matter and its potential availability to consumers; small quantities of high-quality organic matter were replaced by large quantities of refractory material. The labile portion was mostly microphytobenthic (65% of the labile carbon). Protein:carbohydrate ratios were low and confirmed the role of proteins as a potentially limiting factor for consumers. Significant differences in nutritional quality of the sediment organic matter were observed from year to year, changes due to the increase in specific labile compound content
Meiofaunal vertical zonation on hard-bottoms: comparison with soft-bottom meiofauna
No full textAn annual study on hard-substrate meiofaunal assemblages was carried out at 2 depths (2.5 and 8 m) along a vertical cliff of the Middle Adriatic (Mediterranean Sea) characterised by different macroalgal canopies and structural substrate complexities. The upper sampling area of the rocky cliff was covered by macroalgae, and its upper limit was characterised by the presence of a dense belt of Mytilus galloprovincialis. At 8 m depth, mussels were not present, the algal assemblage was less diversified, and phytal coverage decreased. Dynamics and community structure of meio-fauna-inhabiting hard substrates were compared with those of meiofauna collected from soft sediments at the cliff base (9 m depth). Meiofauna of hard and soft substrates displayed significant differences both in terms of density (7-fold higher in soft substrates) and assemblage structure. Meiofauna from rocky substrates were dominated by crustaceans (copepods, nauplii and amphipods), while soft sediments were largely dominated by nematodes (ca 90%). Significant temporal changes of meiofaunal density were observed on both hard and soft substrates, with higher densities in spring to summer and lowest abundance in winter, Despite a completely different algal assemblage and coverage at 2.5 and 8 m depths, hard substrates displayed very similar meiofaunal densities and community structure. Crustacean taxa were correlated with algal coverage, Polychaetes inhabiting hard substrates increased their relevance with depth, whilst amphipods, being significantly correlated with algal biomass, decreased. Nematodes were related with the structural complexity index, calculated on the basis of macroalgal geometric complexity and biomass, whereas copepod and nauplius densities were related with the total structural complexity (as a sum of the algal complexity). The results of the present study indicate that the nature of the substrate (hard vs soft) is the main factor responsible for the differences observed between hard- and soft-bottom meiofauna assemblages, whereas phytal coverage and substrate complexity influenced the structure of hard bottom meiofaunal assemblages. Finally, the analysis of spatial variability of meiofaunal assemblages indicates that hydrodynamic stress also played an important role in meiofaunal structure and distribution on hard substrates, especially at shallow depth
Coastal fish indicate human-induced changes in the Mediterranean littoral
No full textCoastal fish assemblages were studied to assess two sorts of human impacts in southwestern Apulia (SE Italy, Mediterranean Sea). Fish assemblages were evaluated by visual census along two rocky locations impacted by a sewage outfall discharging nearshore (S) and by date-mussel (Lithophaga lithophaga) fisheries (F), respectively, and at two control locations (Cs). Multivariate analyses showed that fish assemblage structures at S and F differed from those at Cs. Asymmetric ANOVAs indicated that species richness were significantly lower both at S (similar to 27%) and at F (similar to 35%) compared with Cs. Total fish abundance was 5- to 7-fold higher at S than at Cs, while the values recorded at F were comparable to those of Cs. At S, average abundances of planktivorous fish and POM feeders were higher, and those of labrids and sparids of the genus Diplodus were lower, respectively, than at Cs. Labrids of the genus Symphodus and small serranids were significantly less abundant at F than Cs. Data suggested that coastal fish respond to the impact caused by the sewage discharge and provided a framework to assess potential benefits of its future displacement to deeper waters. For the first time, moreover, this study provided suggestive evidence that the habitat destruction caused by the illegal date-mussel fisheries may affect fish assemblages
Life-cycle, growth and secondary production in a Brackish-water population of the polychaete Notomastus latericeus (Capitellidae) in the Mediterranean Sea.
No full textPopulation ecology and production of Bittium latreillii (Gastropoda, Cerithidae) in a Posidonia oceanica seagrass bed
No full textPopulation structure, growth and production of the gastropod Bittium latreillii (Gastropoda, Cerithiidae), were studied in a Posidonia oceanica seagrass meadow off the isle of Ischia (Gulf of Naples, Italy). Sampling was performed ten times at five depths (1, 3, 10, 15, 25 m), during the one year of study. A total of 2780 specimens was counted and measured. The survivorship curve, obtained by plotting the values of abundance of each age class, showed a mortality rate that was low immediately after settlement but markedly increased in individuals exceeding 10 mm shell length. The demographic analysis suggested a life-cycle of about 18 months and a semelparous reproduction. Three cohorts were identified: the first settled in October, a second in late winter (December-February), and a third in June. Winter cohorts showed a very low growth rate until spring when an increase was recorded. Annual secondary production (estimated by the Hynes-Coleman method) ranged between 67.9 (10 m depth) and 733.1 mg m(-2) yr(-1) (25 m), while the P/B value was between 3.5 (15 m) and 5.3 (25 m). Recruitment occurred exclusively at the deepest stands (15-25 m) where the population was characterised by higher values of abundance, biomass, and production, confirming that B. latreillii is a typical species of the deepest stands of P. oceanica seagrass beds
Effects of a short-term environmental change on a brackish-water polychaete community (Aquatina, Lecce, Italy).
No full textAcquatina lake is a brackish basin, connected with the Adriatic Sea along the coast of Apulia (Italy), with a mean salinity of 26 parts per thousand. The abundance and biomass of fifteen polychaete species were recorded by monthly samples in a pilot area of the lake from February 1989 to February 1990. Naineris laevigata was dominant, both in number of individuals and biomass. During 1990, obstruction of freshwater inflow to the lake caused an increase in salinity up to 40 parts per thousand, followed by some changes in the polychaete community. Notomastus latericeus became dominant, and the abundances of the other species decreased except for Naineris laevigata. Salinity assumed normal values after three months, but community responded slowly because the massive presence of N. latericeus inhibited the recovery of other species. An abiotic disturbance, followed by a biotic disturbance, altered the structure of the polychaete community
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