Factors affecting habitat occupancy of fish assemblage in the Gulf of Trieste (Northern Adriatic Sea)

Species composition, richness and abundance of the fish assemblage were studied over six different inshore macrohabitats in the southern part of the Gulf of Trieste (Northern Adriatic Sea) using the visual counts technique. Fifteen environmental variables were taken into consideration in order to determine microhabitat preferences of fish species, using canonical correspondence analysis and electivity indices. The results suggest that the structure of the fish assemblage in shallow habitats is affected by a large number of interplaying factors. Depth, type of bottom and vegetation cover – incorporating both abiotic and biotic variables – are some of the factors responsible for coastal fish distribution. Microhabitat preferences for 29 fish species are presented in the depth range from 0.5 to 3 m.     

Trophic ecology of the Patagonian skate, Bathyraja macloviana, on the Argentine continental shelf

When this article was originally published     

Perspectives for Distributed Observations of Near-Earth Space Using a Russian–Cuban Observatory

The creation of a specialized network of large, wide-angle telescopes for distributed observations of near-Earth space using a Russian–Cuban Observatory is considered. An extremely important goal of routine monitoring of near-Earth and near-Sun space is warding off threats with both natural and technogenic origins. Natural threats are associated with asteroids or comets, and technogenic threats with man-made debris in near-Earth space. A modern network of ground-based optical instruments designed to ward off such threats must: (a) have a global and, if possible, uniform geographic distribution, (b) be suitable for wide-angle, high-accuracy precision survey observations, and (c) be created and operated within a single network-oriented framework. Experience at the Institute of Astronomy on the development of one-meter-class wide-angle telescopes and elements of a super-wide-angle telescope cluster is applied to determine preferences for the composition of each node of such a network. The efficiency of distributed observations in attaining maximally accurate predictions of the motions of potentially dangerous celestial bodies as they approach the Earth and in observations of space debris and man-made satellites is estimated. The first estimates of astroclimatic conditions at the proposed site of the future Russian–Cuban Observatory in the mountains of the Sierra del Rosario Biosphere Reserve are obtained. Special attention is given to the possible use of the network to carry out a wide range of astrophysical studies, including optical support for the localization of gravitational waves and other transient events.     

Taking Better Advantage of Fold Axis Data to Characterize Anisotropy of Complex Folded Structures in the Implicit Modeling Framework

Mathematical Geosciences - When too few field measurements are available for the geological modeling of complex folded structures, the results of implicit methods typically exhibit an...     

Accelerating the solution of linear systems appearing in two-phase reservoir simulation by the use of POD-based deflation methods

We explore and develop a Proper Orthogonal Decomposition (POD)-based deflation method for the solution of ill-conditioned linear systems, appearing in simulations of two-phase flow through highly heterogeneous porous media. We accelerate the convergence of a Preconditioned Conjugate Gradient (PCG) method achieving speed-ups of factors up to five. The up-front extra computational cost of the proposed method depends on the number of deflation vectors. The POD-based deflation method is tested for a particular problem and linear solver; nevertheless, it can be applied to various transient problems, and combined with multiple solvers, e.g., Krylov subspace and multigrid methods.

     

Biogeochemical and ecological functioning of the low-salinity water lenses in the region of the Rhone River freshwater influence,NW Mediterranean Sea

A quasi-synoptic survey of a eulerian small grid was carried out twice during mid-spring 2002 in the Gulf of Lions, NW Mediterranean Sea. Analysis of hydrological core parameters reveal for the first time, in the region of freshwater influence (ROFI) of the Rhone River, the presence of low-salinity water (LSW) lenses. The present work details the biogeochemical and ecological functioning of the two LSW lenses from a combined analysis of nutrients and organic matter content, taxonomic assemblages of phytoplankton, primary productivity measurements and nitrogen regeneration fluxes. During the first survey, the lens observed is only detached in part from the Rhone River plume and is considered as a juvenile lens. In contrast, the second lens is totally detached from the plume forming a confined 3D structure with a large vertical development and is considered as having a more advanced maturity. A second survey, 4 days later, provided the opportunity to propose a complete sequence of ecological functioning of the LSW lenses, from their formation to a late stage of maturity just before dispersion. Nitrate contents and dissolved organic matter remain in high concentrations during the juvenile stages while the little available phosphate is rapidly exhausted. In such, an unbalanced-nutrient environment picoplankton appear to out-compete bacterioplankton for phosphate and other resources such as ammonium. In turn, the dominance of such prokaryotic assemblages could have involved the rapid development of microzooplankton. The sudden increase in phosphate observed in a more advanced stage of lens maturity is attributed to intense P-regeneration driven by the large abundance of microzooplankton. This top-down control does not seem to enable the prokaryotic assemblages to bloom again but the high concentrations of phosphate and nitrate favour the development of larger phytoplankton. These autotrophic communities rapidly exhaust nutrients and then decline in the confined ecosystem of the LSW lens that subsequently evolves towards oligotrophic conditions. In the observed last stage, small-sized phytoplankton again dominates the microbial assemblages and the trophic regime is mainly based on regenerated production. The long lifetime of the LSW lens compared to that of the Rhone River plume enables a deep transformation of the initial characteristics of the Rhone River freshwaters both in terms of nutrients balance and microbial food webs, especially through trophic cascading effects. Hence, we show that the LSW lenses have the potential to transfer nutrients and organic matter offshore but the nature (inorganic vs. organic) of the dominant compound exported will depend on the maturity of the lens at the time of its dispersion.