Fish assemblage structure on sandy beaches with different anthropogenic influences and proximity of spawning grounds

Fish assemblages in an insular (preserved) and a continental (disturbed) sandy beach were compared to assess any changes that could be attributed to anthropogenic influences and/or the proximity of the fish spawning grounds. We expected that the closer geographical position to the spawning grounds and the small amount of anthropogenic disturbance on the insular beach would be likely to provide more suitable conditions for early fish development compared with the continental beach. A total of 192 samples (96 in each beach) were taken, yielding 68 fish species, mostly young‐of‐the‐year. Fish assemblage structure differed significantly between the two beaches. Moreover, the insular beach had higher number of species, number of individuals and biomass compared with the continental beach. The commercially important Clupeiformes Harengula clupeola, Anchoa tricolor and Anchoa januaria, Perciformes Micropogonias furnieri and Mugiliformes Mugil liza were typical species on the insular beach, partitioning the seasonal use of the beach. On the other hand, a few abundant non‐commercial species, mainly the Atheriniformes Atherinella brasiliensis and the Perciformes Eucinostomus argenteus and Diapterus rhombeus, occurred all year round at the continental beach. The high fish richness and abundance and the more conspicuous species turnover across seasons on the insular beach are probable indications of more complex and dynamic organization of the communities favored by better geographical position and less anthropogenic disturbance in the area.     

Assessing the factors driving the changes in the spatio-temporal distribution of Hepatus pudibundus (Decapoda,Brachyura) over a 20-year interval in a region under the influence of El Niño (ENSO)

This study aimed to compare the spatio-temporal distribution of demographic groups of Hepatus pudibundus in the Ubatuba Bay, São Paulo, Brazil, over a 20-year interval. Two 1-year samplings were conducted: the 1st period (P1) ran from September 1995 to August 1996 and the 2nd period (P2) ran from September 2016 to August 2017. Samples were taken from five stations that differed in depth (5, 10, and 15 m) and location (exposed area and sheltered area), aboard a shrimp fishing boat. Over the 20-year period, the percentage of fine sediment increased in all stations. In total, we captured 865 H. pudibundus individuals in the P1 and 4,222 in the P2. The higher abundance seen in the P2 may have been caused by the effects of an intense ENSO event in Ubatuba, as well as co-occurring protective actions against fisheries activities in the region. The spatial distribution also changed after 20 years: In the P1, H. pudibundus were more concentrated in the 15 m station and exposed area, but they shifted to the sheltered area in the P2. This change may be related to the increase of fine sediments in this area, and to the fact that it is naturally protected from fisheries. According to the correspondence analysis, the abundance of males and juveniles was correlated with spring and winter, respectively. In the P1, females were more abundant in spring, whereas in the P2 they were more abundant in summer, which may be explained by a higher nutrient availability to the larvae in the summer of the P2. Our comparisons over the 20-year interval revealed that the spatio-temporal distribution of H. pudibundus has changed and that the population is well established in Ubatuba Bay.     

Inhomogeneous Dark Radiation Dynamics on a de Sitter Brane

Assuming spherical symmetry we analyse the dynamics of an inhomogeneous dark radiation vaccum on a Randall and Sundrum 3-braneworld. Under certain natural conditions we show that the effective Einstein equations on the brane form a closed system. On a de Sitter brane and for negative dark energy density we determine exact dynamical and inhomogeneous solutions which depend on the brane cosmological constant, on the dark radiation tidal charge and on its initial configuration. We also identify the conditions leading to the formation of a singularity or of regular bounces inside the dark radiation vaccum. This revised version was published online in July 2006 with corrections to the Cover Date.     

Climatic and geologic controls on the piezometry of the Querença-Silves karst aquifer,Algarve (Portugal)

Karst aquifers in semi-arid regions, like Querença-Silves (Portugal), are particularly vulnerable to climate variability. For the first time in this region, the temporal structure of a groundwater-level time series (1985–2010) was explored using the continuous wavelet transform. The investigation focused on a set of four piezometers, two at each side of the S. Marcos-Quarteira fault, to demonstrate how each of the two sectors of the aquifer respond to climate-induced patterns. Singular spectral analysis applied to an extended set of piezometers enabled identification of several quasi-periodic modes of variability, with periods of 6.5, 4.3, 3.2 and 2.6 years, which can be explained by low-frequency climate patterns. The geologic forcing accounts for ~15 % of the differential variability between the eastern and western sectors of the aquifer. The western sector displays spatially homogenous piezometric variations, large memory effects and low-pass filtering characteristics, which are consistent with relatively large and uniform values of water storage capacity and transmissivity properties. In this sector, the 6.5-year mode of variability accounts for ~70 % of the total variance of the groundwater levels. The eastern sector shows larger spatial and temporal heterogeneity, is more reactive to short-term variations, and is less influenced by the low-frequency components related to climate patterns.     

The Cariris Velhos tectonic event in Northeast Brazil

The Borborema Province in northeastern South America is a typical Brasiliano-Pan-African branching system of Neoproterozoic orogens that forms part of the Western Gondwana assembly. The province is positioned between the São Luis-West Africa craton to the north and the São Francisco (Congo-Kasai) craton to the south. For this province the main characteristics are (a) its subdivision into five major tectonic domains, bounded mostly by long shear zones, as follows: Médio Coreaú, Ceará Central, Rio Grande do Norte, Transversal, and Southern; (b) the alternation of supracrustal belts with reworked basement inliers (Archean nuclei + Paleoproterozoic belts); and (c) the diversity of granitic plutonism, from Neoproterozoic to Early Cambrian ages, that affect supracrustal rocks as well as basement inliers. Recently, orogenic rock assemblages of early Tonian (1000–920 Ma) orogenic evolution have been recognized, which are restricted to the Transversal and Southern domains of the Province.Within the Transversal Zone, the Alto Pajeú terrane locally includes some remnants of oceanic crust along with island arc and continental arc rock assemblages, but the dominant supracrustal rocks are mature and immature pelitic metasedimentary and metavolcaniclastic rocks. Contiguous and parallel to the Alto Pajeú terrane, the Riacho Gravatá subterrane consists mainly of low-grade metamorphic successions of metarhythmites, some of which are clearly turbiditic in origin, metaconglomerates, and sporadic marbles, along with interbedded metarhyolitic and metadacitic volcanic or metavolcaniclastic rocks. Both terrane and subterrane are cut by syn-contractional intrusive sheets of dominantly peraluminous high-K calc-alkaline, granititic to granodioritic metaplutonic rocks. The geochemical patterns of both supracrustal and intrusive rocks show similarities with associations of mature continental arc volcano-sedimentary sequences, but some subordinate intra-plate characteristics are also found.In both the Alto Pajeú and Riacho Gravatá terranes, TIMS and SHRIMP U–Pb isotopic data from zircons from both metavolcanic and metaplutonic rocks yield ages between 1.0 and 0.92 Ga, which define the time span for an event of orogenic character, the Cariris Velhos event. Less extensive occurrences of rocks of Cariris Velhos age are recognized mainly in the southernmost domains of the Province, as for example in the Poço Redondo-Marancó terrane, where arc-affinity migmatite-granitic and meta-volcano-sedimentary rocks show U–Pb ages (SHRIMP data) around 0.98–0.97 Ga. For all these domains, Sm–Nd data exhibit T_DM model ages between 1.9 and 1.1 Ga with corresponding slightly negative to slightly positive ε_Nd(t) values. These domains, along with the Borborema Province as a whole, were significantly affected by tectonic and magmatic events of the Brasiliano Cycle (0.7–0.5 Ga), so that it is possible that there are some other early Tonian rock assemblages which were completely masked and hidden by these later Brasiliano events.Cariris Velhos processes are younger than the majority of orogenic systems at the end of Mesoproterozoic Era and beginning of Neoproterozoic throughout the world, e.g. Irumide belt, Kibaride belt and Namaqua-Natal belt, and considerably younger than those of the youngest orogenic process (Ottawan) in the Grenvillian System. Therefore, they were probably not associated with the proposed assembly of Rodinia. We suggest, instead, that Cariris Velhos magmatism and tectonism could have been related to a continental margin magmatic arc, with possible back-arc associations, and that this margin may have been a short-lived (<100 m.y.) leading edge of the newly assembled Rodinia supercontinent.     

Velocity structure of upper-mantle transition zones beneath central eurasia from seismic inversion using genetic algorithms

We present velocity constraints for the upper-mantle transition zones beneath Central Siberia based on observations of the 1982 RIFT Deep Seismic Sounding (DSS) profile. The data consist of seismic recordings of a nuclear explosion in north-western Siberia along a 2600 km long seismic profile extending from the Yamal Peninsula to Lake Baikal. We invert seismic data from the mantle transition zones using a non-linear inversion scheme using a genetic algorithm for optimization and the WKBJ method to compute the synthetic seismograms. A statistical error analysis using a graph-binning technique was performed to provide uncertainty values in the velocity models.
Our best model for the upper-mantle velocity discontinuity near 410 km depth has a two-stage velocity-gradient structure, with velocities increasing from 8.70–9.25 km s⁻¹ over a depth range of 400–415 km, a gradient of 0.0433 s⁻¹, and from 9.25–9.60 km s⁻¹ over a depth range of 415–435 km, a gradient of 0.0175 s⁻¹. This derived model is consistent with other seismological observations and mineral-physics models. The model for the velocity discontinuity near 660 km depth is simple, sharp and includes velocities increasing from 10.15 km s⁻¹ at 655 km depth to 10.70 km s⁻¹ at 660 km depth, a gradient of 0.055 s⁻¹.