Relict sand dredging for beach nourishment in the central Tyrrhenian Sea (Italy): effects on benthic assemblages

The aim of this study is to analyse the effects in space and time of relict sand-dredging activities on macrobenthic assemblages, in an area situated offshore Montalto di Castro (central Tyrrhenian Sea, Italy), and to analyse the recolonisation processes of macrobenthos in the dredged areas. The area in question is characterised by relict sand deposits (Holocenic paleo-beaches), used for beach nourishment along the Latium coast. The effects of sand extraction on benthic assemblages were investigated before, during and after three dredging operations. The sites analysed are located within the dredged areas (inside stations) and in neighbouring, not dredged, areas (outside stations). The results showed that the impact of sand extraction was confined to the dredged stations and to the areas in proximity to the dredged areas. During dredging activities, the structure of benthic assemblages within the impacted stations was characterised by low species richness and diversity. Both the direct removal of sediment and the re-suspension and consequent deposition of fine sediment affected benthic assemblages of the impacted stations. A few months after the dredgings, a recolonisation process was still observed at all the impacted stations. A gradual recolonisation process was observed at those stations affected by only one dredging, whereas a different recolonisation was observed at those stations affected by two dredgings over time. This study suggests that differences of re-colonisation processes of benthic assemblages are related to the intensity of dredging operations in terms of dredging frequency.     

Managing shark fishermen in southern Australia: A critique

This paper analyses effects of a shift from input to output controls in Australia's Southern Shark Fishery. We show that the use of two management tools—individual transferable quotas and a “partnership approach”—was flawed and argue that primary contributing causes were the unjustified expectation that quota management would serve as a ‘technical fix’ to a variety of presumed problems, the discounting of social effects and the extreme lack of stability in the organizational structure within which this fishery was situated.     

Reproductive biology of Parazoanthus axinellae (Schmidt, 1862) and Savalia savaglia (Bertoloni, 1819) (Cnidaria,Zoantharia) from the NW Mediterranean coast

Despite the wide distribution of zoanthids, little is known about their pattern of reproduction. Here we investigate the reproductive biology of two Mediterranean species, the common Parazoanthus axinellae (Schmidt) and the rare Savalia savaglia (Bertoloni). For both species, samples were collected during an annual cycle, from January to December 2005, in the Western Mediterranean (Ligurian Sea, Italy). Both species are gonochoric. In P. axinellae the sex‐ratio (n colonies = 30) showed a slight predominance of male colonies (M/F = 1.35), whereas in the population of S. savaglia (n colonies = 15) a predominance of females was found (M/F = 0.3). In P. axinellae the first gametocytes were visible in March, whereas in S. savaglia they became visible in May. Both species reproduce at the end of autumn when seawater temperature begins to decrease. Parazoanthus axinellae (10 m depth) spawns eggs and sperms in November, whereas S. savaglia (67 m depth) spawns in December. In P. axinellae sexes were segregated on a rocky wall, with males occurring deeper, whereas male and female colonies of S. savaglia were irregularly dispersed in the population. The maximum number of oocytes differed between the species, being higher in P. axinellae than in S. savaglia.     

Shell‐shape and morphometric variability in Mytilus galloprovincialis from micro‐tidal environments: responses to different hydrodynamic drivers

Tidal conditions differently influence inter‐tidal organisms in terms of general physiological and metabolic responses. In this study we investigated the morphological response in shells of Mytilus galloprovincialis native to different micro‐tidal coastal environments in the Northern Adriatic Sea. Our purpose was to highlight the ecophenotypic variability across tidal levels and to elucidate how tidal currents and waves produced by anthropogenic activities may play a part in modulating shell morphology. Three sampling sites were selected: an open‐sea area 15 km off‐shore and two sites within the lagoon of Venice, the first near one of its three inlets, and the other one in the proximity of Venice city centre. At each sampling site, organisms were seasonally collected at different depths within their vertical zonation, either in the inter‐tidal zone – i.e. at both the highest and lowest tide zonation limits, and subtidally. The mussel shells were analysed by investigation of their morphometric relationships (height/length and width/length ratios) and by elliptic Fourier analysis of the shell contours. Shell thickness and condition index were also evaluated for a better comprehension of energy allocation/partitioning. Estimates based on long‐term measurements, visual observation, wind statistics and wave growth laws allowed an evaluation of the forces acting on shells. At the open‐sea site, the observed phenotypic variability of both shell shape and thickness was clearly related to the tidal vertical zonation. At the two lagoon sites, the currents generated by tidal flow through the inlet and the waves caused by the frequent passage of boats influenced both shell shape and thickness. A trade‐off between protection and growth was apparent along the tide gradient, as emphasized by the differences in the partitioning and allocation of energy between shell and flesh production.     

Size matters more than method: Visual quadrats vs photography in measuring human impact on Mediterranean rocky reef communities

The performances of two commonly used non-destructive sampling procedures for rocky benthic assemblages (i.e. photography and visually assessed quadrats) were compared. A damaging human activity, date mussel (Lithophaga lithophaga) harvesting (DMH), was chosen. Directly impacted sites were compared with reference conditions (controls). Both visual quadrats and photography were equally able to detect differences between impacted situations and controls. However, visual quadrats showed high variability among replicates and estimated higher species richness for controls, while photography did so for impacts. Pooling photos in a ‘sum photo quadrat’ showed that differences between the two methods are due to sampling unit size rather than sampling procedure itself. As a small sampling unit is unavoidable with photography, visual quadrats should be preferred in investigating shallow rocky reefs for their larger size; however, longer working time underwater with quadrats does not allow for numerous replicates. Pooling many photos to reach sampling sizes comparable with those of quadrats may be a valid alternative to reconcile image resolution and areal coverage.     

Procida volcanic history: new insights into the evolution of the Phlegraean Volcanic District (Campania region,Italy)

New stratigraphic, major- and trace-element, and Sr-, Nd- and Pb- isotopic data on volcanic deposits older than 14 ka from the island of Procida, Italy, are presented and compared with published analyses from the rest of the Phlegraean Volcanic District (PVD). Procida rocks range in composition from basalt to shoshonite and trachyte and show ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios varying within the ranges 0.70523–0.70678, 0.512539–0.512630, 18.99–19.29, 15.67–15.69 and 39.10–39.39, respectively. The presence of a compositional gap in the range SiO₂=54–59 wt % is evidence of magma bimodality, and suggests that the feeding magmatic system was formed by at least two different reservoirs located at different depths. Geochemical and isotopic variations with increasing differentiation can be explained by fractional crystallization mechanisms, that in some cases were associated with crustal contamination that occurred in both deeper and shallower reservoirs; the most evolved magmas formed in the shallower one. Mixing/mingling processes also occurred. The variation of isotopic composition through time observed both for Procida and for Campi Flegrei and Ischia rocks is evidence of strong affinity between magmas that erupted on the entire PVD until about 40 ka. This indicates that they share a common origin and a common plumbing system. Most of the PVD eruptive centers active until about 40 ka lie within a NE-SW-oriented volcano-tectonic belt extending from the southeastern part of Ischia, through Procida and Torregaveta volcano to the northeastern sector of the present Campi Flegrei caldera. This not only indicates the existence of a link between regional structures and volcanism in the area, but also suggests that PVD magma genesis and evolution were strongly regulated by extensional tectonics. In the last 40 ka the mafic rocks erupted along this extensional structure – from Torregaveta and the islands of Ischia and Procida – indicate that it still represents an important crustal discontinuity that focuses mantle-derived magmas. Procida trachybasalts are enriched in large ion lithophile elements (LILE) and light and middle rare earth elements (LREE and MREE), and show slight negative anomalies in the high field strength elements (HFSE) relative to average MORB. A slight depletion in HREE is present. Trace element and isotope systematics can be referred to a lithospheric mantle source. The lithospheric mantle source carries intra-plate and slab-derived components, the latter probably inherited from a previous subduction event.     

Joint Inversion of Body-Wave Arrival Times and Surface-Wave Dispersion for Three-Dimensional Seismic Structure Around SAFOD

We incorporate body-wave arrival time and surface-wave dispersion data into a joint inversion for three-dimensional P-wave and S-wave velocity structure of the crust surrounding the site of the San Andreas Fault Observatory at Depth. The contributions of the two data types to the inversion are controlled by the relative weighting of the respective equations. We find that the trade-off between fitting the two data types, controlled by the weighting, defines a clear optimal solution. Varying the weighting away from the optimal point leads to sharp increases in misfit for one data type with only modest reduction in misfit for the other data type. All the acceptable solutions yield structures with similar primary features, but the smaller-scale features change substantially. When there is a lower relative weight on the surface-wave data, it appears that the solution over-fits the body-wave data, leading to a relatively rough V _s model, whereas for the optimal weighting, we obtain a relatively smooth model that is able to fit both the body-wave and surface-wave observations adequately.     

Sedimentary provenance in the central Ribeira belt based on laser-ablation ICPMSPb/Pb zircon ages

²⁰⁷Pb/²⁰⁶Pb ages from 420 zircons from 9 upper amphibolite and granulite facies quartzites of the post-1.8 Ga metasedimentary cover from the Occidental and Oriental terranes from the Neoproterozoic central Ribeira belt, in eastern Brazil, are discussed. Ages from the Occidental terrane show that Proterozoic ages predominate with a modal class at 2.1–2.2 Ga and that Archean ages are less common and lie within the 2.5–3.6 Ga range. A wider dispersion on Proterozoic ages down to 1.1 Ga and youngest Neoproterozoic ages (550–700 Ma) were also observed and could be related to the Brasiliano/PanAfrican metamorphic events. The data show that detrital sediments of the Occidental terrane were derived predominantly from erosion of a 1.8–2.2 Ga Paleoproterozoic terrane with a small proportion of a 2.6–3.6 Ga Archean crust. Ages from the Oriental terrane are greatly dispersed, but show a significant proportion of ages between 1.7 and 2.1 Ga, although the great majority are between 0.5 and 1.6 Ga. Only 3 out of 144 grains yield Archean ages, between 2.5 and 2.9 Ga. Based on the greatest errors observed on the data from the Oriental Terrane (100–300 Ma), and a continuum of obtained ages between 2072 Ma (Paleoproterozoic) and 517 Ma (Cambrian), the more plausible interpretation is that the dispersion of ages results from partial resetting of the U–Pb system by Brasiliano metamorphism in Proterozoic–Archean zircons, although a Mesoproterozoic source could not be discarded.     

Scenarios of Earthquake-Generated Tsunamis for the Italian Coast of the Adriatic Sea

We calculated the expected impact on the Italian coast of the Adriatic Sea of a large set of tsunamis resulting from potential earthquakes generated by major fault zones. Our approach merges updated knowledge on the regional tectonics and scenario-like calculations of expected tsunami impact. We selected six elongated potential source zones. For each of them we determined a Maximum Credible Earthquake and the associated Typical Fault, described by its size, geometry and kinematics. We then let the Typical Fault float along strike of its parent source zone and simulated all tsunamis it could generate. Simulations are based on the solution of the nonlinear shallow water equations through a finite-difference technique. For each run we calculated the wavefields at specified simulation times and the maximum water height field (above mean sea level), then generated travel-time maps and maximum water height profiles along the target coastline. Maxima were also classified in a three-level code of expected tsunami threat. We found that the southern portion of Apulia facing Albania and the Gargano promontory are especially prone to the tsunami threat. We also found that some bathymetric features are crucial in determining the focalization-defocalization of tsunami energy. We suggest that our results be taken into account in the design of early-warning strategies.