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71.
72.
P. Pato C. Lopes M. Vlega A.I. Lilleb J.M. Dias E. Pereira A.C. Duarte 《Estuarine, Coastal and Shelf Science》2008,76(4):787-796
The objective was to estimate the seasonal and inter-tidal variability of dissolved and particulate mercury fluxes between the Ria de Aveiro (Portugal) and the Atlantic Ocean. The mercury fluxes were estimated by means of a two-dimensional vertically integrated hydrodynamic model. Results showed that the particulate fraction plays an important role in the transport of mercury while the contribution of the seston fraction to the transport of mercury was always <0.5%. During spring tides, in summer, about 2% of mercury transported in seston was present in an organic form. The mass balance for the mercury fractions revealed that the mercury export to the Atlantic Ocean varied with season and tidal regime, mainly in terms of the relative importance of the dissolved and particulate fractions. An approximate range of values for the annual mass balance between 42 and 77 kg shows that the export of dissolved and particulate mercury makes little impact on the near shore region of the Atlantic Ocean and that the recovery of the lagoon from mercury contamination is likely to remain a long-term issue. 相似文献
73.
Eduardo Jaramillo Sandra Cifuentes Cristian Duarte & Heraldo Contreras 《Marine Ecology》2008,29(S1):37-42
The semi-terrestrial isopod, Tylos spinulosus Dana, is a common inhabitant of the upper shore levels of sandy beaches of north-central Chile (ca. 26–30°S). During daylight hours, this isopod remains buried in the sand, while during the night emerges for feeding on stranded organic detritus, leaving exit holes on the beach surface. After feeding, isopods return to dig in their burrowing zones leaving surface irregularities such as cone-shaped mounds of sand. The burrowing preference of T. spinulosus was studied in the field, by: (i) releasing 30 isopods on artificially prepared sand circles (2 m diameter) having exit holes and mounds similar to those left by the isopods and on circles without holes and mounds, and (ii) counting active and buried isopods 15 min after their release in the experimental arenas. The circles had two densities of holes and mounds: treatments 1 and 2 had 100 and 200 holes, respectively, while treatments 3 and 4 had 100 and 200 mounds, respectively. Other 30 isopods were released on sand circles without these holes and mounds (treatment 5). A significantly higher number of isopods buried in circles with holes and mounds (either inside or outside them), compared with experimental arenas without such structures. These results show that the beach surface heterogeneity resulting from holes and mounds would be one of the processes explaining the patchiness of T. spinulosus and thus, its zonation on the intertidal zones of sandy beaches of north-central Chile. 相似文献
74.
Iris E. Hendriks Miguel Cabanellas-Reboredo Tjeerd J. Bouma Salud Deudero Carlos M. Duarte 《Estuaries and Coasts》2011,34(1):60-67
We assess the sheltering effect of Posidonia oceanica meadows on drag forces exerted on shells of the fan mussel Pinna nobilis. We examine a range of shell sizes under four unidirectional flow speeds (0.05–0.34 m s−1) and two oscillating regimes. Three meadow densities are evaluated and a control without vegetation. We found that the attenuating
effect of the meadow on drag forces experienced by bivalves is determined by the form of the hydrodynamic energy, e.g., as
unidirectional flow or wave action. In tidal currents, the meadow protects most sizes of bivalves, with a higher efficiency
for dense meadows, while in wave dominant zones the meadow reduces drag forces for bivalves with shell areas below a threshold
of 0.019 m2, whereas larger animals experience increased drag forces within the meadow independent of meadow density. Reduction of shoot
density in seagrass meadows might therefore not affect the effectiveness of the canopy to reduce drag forces on associated
species like the fan mussel in wave-dominated areas while increased storm frequency could result into losses of larger individuals
during periods of high wave action. 相似文献
75.
Neus Garcias-Bonet Timothy D. Sherman Carlos M. Duarte Núria Marbà 《Estuaries and Coasts》2011,34(6):1161-1168
The presence of the pathogenic protist Labyrinthula sp., the causative agent of seagrass wasting disease and mass mortality events, was assessed in 18 seagrass meadows in the
Balearic region (western Mediterranean). This protist was found in 70% of seagrass meadows investigated and in all seagrass
species present in the region (i.e., Posidonia oceanica, Cymodocea nodosa, and Zostera noltii). Labyrinthula spp. cultures isolated from seven P. oceanica and one Thalassia testudinum meadows were used as inocula to perform cross-infection experiments in order to test seagrass vulnerability to Labyrinthula spp. infection. These isolates produced lesions on P. oceanica and other seagrass species (Zostera marina, Z. noltii, and C. nodosa). P. oceanica and Z. noltii, both species autochthonous to the Mediterranean Sea, were the seagrasses most vulnerable to infection by the tested isolates.
One of the P. oceanica isolates of Labyrinthula sp. also infected the Atlantic seagrass Z. marina, and all of the Mediterranean seagrasses were infected by Labyrinthula sp. isolated from the T. testudinum, native to the Caribbean and Gulf of Mexico. This work confirms that Labyrinthula sp. is commonly found on seagrasses of the Mediterranean Sea and demonstrates that Labyrinthula sp. can infect seagrasses in different genera, in contrast to previous studies where Labyrinthula sp. was considered to be genus-specific. This finding points out the broadly pathogenic nature of some Labyrinthula sp. isolates. Finally, this work identifies Labyrinthula sp. as a possible detrimental agent for P. oceanica. 相似文献
76.
S. Tavares H. OliveiraJ.P. Coelho M.E. PereiraA.C. Duarte M.A. Pardal 《Estuarine, Coastal and Shelf Science》2011,94(4):315-321
Mercury accumulation throughout the lifespan of Liza aurata (Risso, 1810) was analysed in four tissues (muscle, gills, liver and brain) in two southern European coastal ecosystems with distinct mercury contamination. Specimens from four to five age classes were captured in two sampling sites in the Ria de Aveiro (Laranjo bay and Mira), a system historically contaminated by industrial mercury, and in one site in the Mondego estuary, assumed as a mercury-free ecosystem. Mercury concentration in all tissues was found to be significantly higher in the Ria de Aveiro (Laranjo bay) compared to the Mondego, in accordance with the environmental contamination (water, sediments and suspended particulate matter). Significant differences inside the Ria de Aveiro (between the Mira and Laranjo bay) were only detected in the liver. This tissue registered the highest levels of mercury (ranging from 0.11 to 4.2 μg g−1) in all sampling sites, followed by muscle, brain, and gills. In all sampling sites and tissues was denoted a mercury dilution pattern along the lifecycle (except in liver at the Mondego, the reference area where the concentrations are always very low). An exponential trend was found in the metal age variation patterns in Laranjo (the most contaminated area) and a linear trend in the Mira and the Mondego (the least contaminated areas). Organic mercury concentration in muscle generally accounted for over 95% of total mercury concentration, and followed the same accumulation pattern of total mercury. This fish species is of lesser importance in mercury transfer to adjacent coastal areas and although the consumption of fish from Laranjo may present some risk for the humans, this risk decreases with fish age/size. 相似文献
77.
Felipe Alexander Vargas Bazán Edison Castro Prates de Lima Marcos Queija de Siqueira Elizabeth Frauches Netto Siqueira Carlos Alberto Duarte de Lemos 《Applied Ocean Research》2011,33(4):344-365
In riser structural systems, the region where the riser is connected to the platform is critical due to the development of high stress levels. To reduce the stress concentration in this region, bend stiffeners and stress joints are used in order to provide a gradual stiffness transition between the riser and the platform. The present paper presents an optimization design approach for bend stiffeners and stress joints, using a slender beam procedure for the connection joint analysis and an evolution strategies multi-objective optimization algorithm. This approach produces similar results when compared to a finite element analysis of the complete riser, but with significant reduction of computational costs. Numerical examples are presented, showing the efficiency and robustness of the suggested methodology. 相似文献
78.
V. A. Sarychev S. A. Mirer A. A. Degtyarev E. K. Duarte 《Celestial Mechanics and Dynamical Astronomy》2007,97(4):267-287
Attitude motion of a satellite subjected to gravitational and aerodynamic torques in a circular orbit is investigated. In
special case, when the center of pressure of aerodynamic forces is located on one of the principal central axes of inertia
of the satellite, all equilibrium orientations are determined. Necessary and (or) sufficient conditions of stability are obtained
for each equilibrium orientation. Evolution of domains where stability conditions take place is investigated. All bifurcation
values of parameters corresponding to qualitative change of domains of stability are determined. 相似文献
79.
L. S. Farenzena P. Iza R. Martinez F. A. Fernandez-Lima E. Seperuelo Duarte G. S. Faraudo C. R. Ponciano M. G. P. Homem A. Naves de Brito K. Wien E. F. da Silveira 《Earth, Moon, and Planets》2005,97(3-4):311-329
Experimental results on fast ion collision with icy surfaces having astrophysical interest are presented. 252Cf fission fragments projectiles were used to induce ejection of ionized material from H2O, CO2, CO, NH3, N2, O2 and Ar ices; the secondary ions were identified by time-of-flight mass spectrometry. It is observed that all the bombarded frozen gas targets emit cluster ions which have the structure XnR±, where X is the neutral ice molecule and R± is either an atomic or a molecular ion. The shape of the positive or negative ion mass spectra is characterized by a decreasing yield as the emitted ion mass increases and is generally described by the sum of two exponential functions. The positive ion water ice spectrum is dominated by the series (H2O)nH3O+ and the negative ion spectrum by the series (H2O)nOH− and (H2O)nO−. The positive ion CO2 ice spectrum is characterized by R+ = C+, O+, CO+, O2+ or CO2+ and the negative one by R− = CO3−. The dominant series for ammonia ice correspond to R+ = NH4+ and to R− = NH2−. The oxygen series are better described by (O3)nOm+ secondary ions where m = 1, 2 or 3. Two positive ion series exist for N2 ice: (N2)nN2+ and (N2)nN+. For argon positive secondary ions, only the (Ar)nAr+ series was observed. Most of the detected molecular ions were formed by one-step reactions. Ice temperature was varied from ∼20 K to complete sublimation. 相似文献
80.
This article reviews the literature involving benthic invertebrates that are cited in association with hull fouling, reporting the species that occur on the Brazilian coast and evaluating the importance of this vector for the introduction of nonindigenous and cryptogenic invertebrates in Brazil. It discusses some of the strategies that were used by the species that allowed for their overseas transport and made it easier to cross natural barriers that otherwise would have been obstacles to their dispersion. The compiled data list 343 species (65% nonindigenous and 35% cryptogenic), mainly from the northwestern Atlantic Ocean. The traveling fauna, composed mostly of cosmopolitan species (70.3%), is primarily euryhaline and marine stenohaline, with sessile and sedentary habits. After delineating the shipborne species’ ecological profiles and traveling strategies and evaluating their overlapping vectors, we concluded that hull vessels were the main vector of introduction to the Brazilian coast for 89.8% of the compiled species. 相似文献