Trophic dynamics in the northern Humboldt Current system: insights from stable isotopes and stomach content analyses

The northern Humboldt Current system (NHCS) off Peru is one of the most productive world marine regions. It represents less than 0.1% of the world ocean surface but presently sustains about 10% of the world fish catch, with the Peruvian anchovy or anchoveta Engraulis ringens as emblematic fish resource. Compared with other eastern boundary upwelling systems, the higher fish productivity of the NHCS cannot be explained by a corresponding higher primary productivity. On another hand, the NHCS is the region where El Niño, and climate variability in general, is most notable. Also, surface oxygenated waters overlie an intense and extremely shallow Oxygen Minimum Zone (OMZ). In this context, the main objective of this study is to better understand the trophic flows in the NHCS using both stomach content and stable isotope analyses. The study focuses on a variety of organisms from low trophic levels such as zooplankton to top predators (seabirds and fur seals). The approach combines both long-term and specific studies on emblematic species such as anchoveta, and sardine Sardinops sagax and a more inclusive analysis considering the 'global' food web in the recent years (2008 – 2012) using stable isotope analysis. Revisiting anchovy and sardine we show that whereas phytoplankton largely dominated anchoveta and sardine diets in terms of numerical abundance, the carbon content of prey items indicated that zooplankton was by far the most important dietary component. Indeed for anchovy euphausiids contributed 67.5% of dietary carbon, followed by copepods (26.3%). Selecting the largest prey, the euphausiids, provide an energetic advantage for anchoveta in its ecosystem where oxygen depletion imposes strong metabolic constrain to pelagic fish. Sardine feed on smaller zooplankton than do anchoveta, with sardine diet consisting of smaller copepods and fewer euphausiids than anchoveta diet. Hence, trophic competition between sardine and anchovy in the northern Humboldt Current system is minimized by their partitioning of the zooplankton food resource based on prey size, as has been reported in other systems. These results suggest an ecological role for pelagic fish that challenges previous understanding of their position in the foodweb (zooplanktophagous instead of phytophagous), the functioning and the trophic models of the NHCS. Finally to obtain a more comprehensive vision of the relative trophic position of NHCS main components we used stable isotope analyses. For that purpose we analyzed the δ13C and δ15N stable isotope values of thirteen taxonomic categories collected off Peru from 2008 - 2011, i.e., zooplankton, fish, squids and air-breathing top predators. The δ15N isotope signature was strongly impacted by the species, the body length and the latitude. Along the Peruvian coast, the OMZ get more intense and shallow south of ~7.5ºS impacting the baseline nitrogen stable isotopes. Employing a linear mixed-effects modelling approach taking into account the latitudinal and body length effects, we provide a new vision of the relative trophic position of key ecosystem components. Also we confirm stomach content-based results on anchoveta Engraulis ringens and highlight the potential remarkable importance of an often neglected ecosystem component, the squat lobster Pleuroncodes monodon. Indeed, our results support the hypothesis according to which this species forage to some extent on fish eggs and larvae and can thus predate on the first life stages of exploited species. However, the δ13C values of these two species suggest that anchoveta and squat lobster do not exactly share the same habitat. This would potentially reduce some direct competition and/or predation.

Trophic ecology of jumbo squid and predatory fishes in the Northern Humboldt Current System

This work provides a contribution to a better understanding of the trophic ecology of important predators in the Northern Humboldt Current System, the jack mackerel (Trachurus murphyi), the chub mackerel (Scomber japonicus) and the jumbo squid (Dosidicus gigas) by the characterization of the highly variable feeding patterns of these species at different spatiotemporal scales. We provided new knowledge on the comparative trophic behaviour of these species, defined as opportunistic in previous investigations. For that purpose we applied a variety of statistical methods to an extensive dataset of 27,188 non-empty stomachs. We defined the spatial organization of the forage fauna of these predators and documented changes in prey composition according to predators’ size and spatiotemporal features of environment. Our results highligh the key role played by the dissolved oxygen. We also deciphered an important paradox on the jumbo squid diet: why do they hardly forage on the huge anchovy (Engraulis ringens) biomass distributed of coastal Peru? We showed that the shallow oxygen minimum zone present off coastal Peru could hamper the co-occurrence of jumbo squids and anchovies. In addition, we proposed a conceptual model on jumbo squid trophic ecology including the ontogenetic cycle, oxygen and prey availability. Moreover we showed that the trophic behaviour of jack mackerel and chub mackerel is adapted to forage on more accessible species such as for example the squat lobster Pleurocondes monodon and Zoea larvae. Besides, both predators present a trophic overlap. But jack mackerel was not as oracious as chub mackerel, contradictorily to what was observed by others authors. Fish diet presented a high spatiotemporal variability, and the shelf break appeared as a strong biogeographical frontier. Diet composition of our fish predators was not necessarily a consistent indicator of changes in prey biomass. El Niño events had a weak effect on the stomach fullness and diet composition of chub mackerel and jack mackerel. Moreover, decadal changes in diet diversity challenged the classic paradigm of positive correlation between species richness and temperature. Finally, the global patterns that we described in this work, illustrated the opportunistic foraging behaviour, life strategies and the high degree of plasticity of these species. Such behaviour allows adaptation to changes in the environment.

Evaluación técnica de la red de encierre activada por buzos o bolichito de fondo

La “red de encierre activada por buzos” o “bolichito de fondo” es un arte de pesca que por sus características técnicas y de operación es clasificado como no determinado y no reglamentado. Se realizó una evaluación técnica de este arte de pesca, que indica que su cobertura espacial está limitada a la capacidad de buceo, restringida a zonas muy someras, presenta baja respuesta de selectividad y alto poder de pesca al compararla con otras artes de pesca artesanales utilizadas en la misma área costera; tiene elevada extracción de juveniles y de fauna acompañante los que generalmente están en mayores porcentajes de estadios inmaduros (II) y maduración inicial (III). Se recomienda prohibir su uso.

Shield morphology of curly overhair in 22 genera of Soricidae (Insectivora, Mammalia)

The structure of the shield of curly overhairs was studied in 22 genera of shrews, using scanning electron microscopy. The cross section of the shield is quadriconcave with two sides showing particular scale patterns or a relief which can be grouped into 4 morphological types: 1) a smooth type with, at most, shallow U-shaped notches; 2) a type with uniserial, V-shaped tiled notches; 3) a type with a groove and irregular notches; 4) a type with a deep ridged groove. Myosorex, which occupies a basal phyletic position, shows type 3. This type is therefore interpreted as an ancestral character state. It is found also in Feroculus and in some Sylvisorex. In the Crocidurinae, this type evolved into type 2 (Scutisorex and some Indomalayan Crocidura), and finally into type 1 (Suncus and most Crocidura). In the Soricinae, it evolved into type 4, which is common to all genera except Megasorex and Notiosorex. These two genera possess type 1 which is interpreted as being a synapomorphous character of these genera. The regression of the complex structure under dry climatic conditions supports the hypothesis that the function of the grooved form of hair is water repulsion.

Nuclear well logging in soils. Calibration of slim hole nuclear tools gamma-gamma and neutron-thermal neutron.

The calculation of elasticity parameters by sonic and ultra sonic wave propagation in saturated soils using Biot's theory needs the following variables : forpiation density and porosity (p, ø), compressional and shear wave velocities (Vp, Vs), fluid density, viscosity and compressibility (Pfi Ilfi Ki), matrix density and compressibility (p" K), The first four parameters can be determined in situ using logging probes. Because fluid and matrix characteristics are not modified during core extraction, they can be obtained through laboratory measurements. All parameters necessitate precise calibrations in various environments and for specific range of values encountered in soils. The slim diameter of boreholes in shallow geophysics and the high cost of petroleum equipment demand the use of specific probes, which usually only give qualitative results. The measurement 'of density is done with a gamma-gamma probe and the measurement of hydrogen index, in relation to porosity, by a neutron probe. The first step of this work has been carried out in synthetic formations in the laboratory using homogeneous media of known density and porosity. To establish borehole corrections different casings have been used. Finally a comparison between laboratory and in situ data in cored holes of known geometry and casing has been performed.

Determinación de sistemas de flujo regionales y locales en las depresiones tectónicas del Baix Empordà y La Selva (NE de España) en base a datos hidroquímicos e isotópicos

The Baix Empordà-Selva-Gavarres aquifer system is related to the fault set that created the tectonic basins of Empordà and Selva areas (NE Spain) during the Neogene. In this work, we describe groundwater hydrogeological, hydrochemical and isotopical (3H, δD, δ18O, and the 87Sr/86Sr ratio) characteristics of this system in order to illustrate the relevance of fault zones in groundwater flow-paths and the recharge. In that way, we identify two flow systems, with distinct hydrochemistry and isotopes. A local flow system originates at the Gavarres Range, and it flows towards the basins of the Baix Empordà and Selva, with an approximate residence time of 20 years. Additionally, a regional flow system has only been identified in the Selva basin. This one is related to the main fault zones, as preferential flow paths. Its recharge is located in mountain ranges with higher altitudes, namely the Transversal and Guilleries Ranges, with residence times larger than 50 years. Isotopical data has also shown mixing processes between both flow systems and rainfall recharge while multivariate statistical analysis of principal components has shown the main processes that control hydrochemistry of each flow systems

Crystal structure of yeast peroxisomal multifunctional enzyme: structural basis for substrate specificity of (3R)-hydroxyacyl-CoA dehydrogenase units.

(3R)-hydroxyacyl-CoA dehydrogenase is part of multifunctional enzyme type 2 (MFE-2) of peroxisomal fatty acid beta-oxidation. The MFE-2 protein from yeasts contains in the same polypeptide chain two dehydrogenases (A and B), which possess difference in substrate specificity. The crystal structure of Candida tropicalis (3R)-hydroxyacyl-CoA dehydrogenase AB heterodimer, consisting of dehydrogenase A and B, determined at the resolution of 2.2A, shows overall similarity with the prototypic counterpart from rat, but also important differences that explain the substrate specificity differences observed. Docking studies suggest that dehydrogenase A binds the hydrophobic fatty acyl chain of a medium-chain-length ((3R)-OH-C10) substrate as bent into the binding pocket, whereas the short-chain substrates are dislocated by two mechanisms: (i) a short-chain-length 3-hydroxyacyl group ((3R)-OH-C4) does not reach the hydrophobic contacts needed for anchoring the substrate into the active site; and (ii) Leu44 in the loop above the NAD(+) cofactor attracts short-chain-length substrates away from the active site. Dehydrogenase B, which can use a (3R)-OH-C4 substrate, has a more shallow binding pocket and the substrate is correctly placed for catalysis. Based on the current structure, and together with the structure of the 2-enoyl-CoA hydratase 2 unit of yeast MFE-2 it becomes obvious that in yeast and mammalian MFE-2s, despite basically identical functional domains, the assembly of these domains into a mature, dimeric multifunctional enzyme is very different.

Calibration of high-resolution geophysical data with tracer test measurements to improve hydrological predictions

Relationships between porosity and hydraulic conductivity tend to be strongly scale- and site-dependent and are thus very difficult to establish. As a result, hydraulic conductivity distributions inferred from geophysically derived porosity models must be calibrated using some measurement of aquifer response. This type of calibration is potentially very valuable as it may allow for transport predictions within the considered hydrological unit at locations where only geophysical measurements are available, thus reducing the number of well tests required and thereby the costs of management and remediation. Here, we explore this concept through a series of numerical experiments. Considering the case of porosity characterization in saturated heterogeneous aquifers using crosshole ground-penetrating radar and borehole porosity log data, we use tracer test measurements to calibrate a relationship between porosity and hydraulic conductivity that allows the best prediction of the observed hydrological behavior. To examine the validity and effectiveness of the obtained relationship, we examine its performance at alternate locations not used in the calibration procedure. Our results indicate that this methodology allows us to obtain remarkably reliable hydrological predictions throughout the considered hydrological unit based on the geophysical data only. This was also found to be the case when significant uncertainty was considered in the underlying relationship between porosity and hydraulic conductivity.

K-T transition in Deccan Traps of central India marks major marine Seaway across India

Deccan intertrappean sediments in central India are generally considered as terrestrial deposits of Maastrichtian age, but the Cretaceous-Tertiary (K-T) position is still unknown. Here we report the discovery of the K-T transition, a marine incursion and environmental changes preserved within the intertrappean sediments at Jhilmili, Chhindwara District, Madhya Pradesh. Integrative biostratigraphic, sedimentologic, mineralogic and chemostratigraphic analyses reveal the basal Danian in the intertrappean sediments between lower and upper trap basalts that regionally correspond to C29r and the C29R/C29N transition, respectively. Intertrappean deposition occurred in predominantly terrestrial semi-humid to and environments. But a short aquatic interval of fresh water ponds and lakes followed by shallow coastal marine conditions with brackish marine ostracods and early Danian zone P1a planktic foraminifera mark this interval very close to the K-T boundary. This marine incursion marks the existence of a nearby seaway, probably extending inland from the west through the Narmada and Tapti rift valleys. The Jhilmili results thus identify the K-T boundary near the end of the main phase of Deccan eruptions and indicate that a major seaway extended at least 800 km across India. (C) 2009 Elsevier B.V. All rights reserved.

Some like it hot: temperature and acidification modulate larval development and settlement of the sea urchin Arbacia lixula

We studied the effects of temperature and pH on larval development, settlement and juvenile survival of a Mediterranean population of the sea urchin Arbacia lixula. Three temperatures (16, 17.5 and 19 °C) were tested at present pH conditions (pHT 8.1). At 19 °C, two pH levels were compared to reflect present average (pHT 8.1) and near-future average conditions (pHT 7.7, expected by 2100). Larvae were reared for 52-days to achieve the full larval development and complete the metamorphosis to the settler stage. We analyzed larval survival, growth, morphology and settlement success. We also tested the carry-over effect of acidification on juvenile survival after 3 days. Our results showed that larval survival and size significantly increased with temperature. Acidification resulted in higher survival rates and developmental delay. Larval morphology was significantly altered by low temperatures, which led to narrower larvae with relatively shorter skeletal rods, but larval morphology was only marginally affected by acidification. No carry-over effects between larvae and juveniles were detected in early settler survival, though settlers from larvae reared at pH 7.7 were significantly smaller than their counterparts developed at pH 8.1. These results suggest an overall positive effect of environmental parameters related to global change on the reproduction of A. lixula, and reinforce the concerns about the increasing negative impact on shallow Mediterranean ecosystems of this post-glacial colonizer.

Localization and characterization of an active fault in an urbanized area in central Guatemala by means of geoelectrical imaging

The Polochic and Motagua faults define the active plate boundary between the North American and Caribbean plates in central Guatemala. A splay of the Polochic Fault traverses the rapidly growing city of San Miguel Uspantan that is periodically affected by destructive earthquakes. This fault splay was located using a 2D electrical resistivity tomography (ERT) survey that also characterized the fault damage zone and evaluated the thickness and nature of recent deposits upon which most of the city is built. ERT images show the fault as a similar to 50 m wide, near-vertical low-resistivity anomaly, bounded within a few meters by high resistivity anomalies. Forward modeling reproduces the key aspects of the observed electrical resistivity data with remarkable fidelity thus defining the overall location, geometry, and internal structure of the fault zone as well as the affected lithologies. Our results indicate that the city is constructed on a similar to 20 m thick surficial layer consisting of poorly consolidated, highly porous, water-logged pumice. This soft layer is likely to amplify seismic waves and to liquefy upon moderate to strong ground shaking. The electrical conductivity as well as the major element chemistry of the groundwater provides evidence to suggest that the local aquifer might, at least in part, be fed by water rising along the fault. Therefore, the potential threat posed by this fault splay may not be limited to its seismic activity per se, but could be compounded its potential propensity to enhance seismic site effects by injecting water into the soft surficial sediments. The results of this study provide the basis for a rigorous analysis of seismic hazard and sustainable development of San Miguel Uspantan and illustrate the potential of ERT surveying for paleoseismic studies.

Structural characterization of laser-treated Cr3C2-NiCr coatings

The interconnected porosity of the Cr3C2-NiCr coatings obtained by high-velocity oxy fuel spraying is detrimental in corrosion and wear resistance applications. Laser treatments allow sealing of their surfaces through melting and resolidification of a thin superficial layer. A Nd:YAG laser beam was used to irradiate Cr3C2-NiCr coatings either in the continuous wave mode or at different repetition rates in the pulsed one. Results indicated that high peak and low mean laser irradiances are not good, since samples presented deep grooves and an extensive crack network. At low peak and higher mean laser irradiances the surface was molten, and only a few shallow cracks were observed. The interconnected porosity was completely eliminated in a layer up to 80 m thick, formed by large Cr7C3 grains imbedded in a NiCr matrix.

Stratigraphic, sedimentological and palaeoenvironmental constraints on the rise of the Urgonian platform in the western Swiss Jura

Urgonian-type carbonates are a characteristic feature of many late Early Cretaceous shallow-marine, tropical and subtropical environments. The presence of typical photozoan carbonate-producing communities including corals and rudists indicates the prevalence of warm, transparent and presumably oligotrophic conditions in a period otherwise characterized by the high density of globally occurring anoxic episodes. Of particular interest, therefore, is the exploration of relationships between Urgonian platform growth and palaeoceanographic change. In the French and Swiss Jura Mountains, the onset and evolution of the Urgonian platform have been controversially dated, and a correlation with other, better dated, successions is correspondingly difficult. It is for this reason that the stratigraphy and sedimentology of a series of recently exposed sections (Eclepens, Vaumarcus and Neuchatel) and, in addition, the section of the Gorges de l'Areuse were analysed. Calcareous nannofossil biostratigraphy, the evolution of phosphorus contents of bulk rock, a sequence-stratigraphic interpretation and a correlation of drowning unconformities with better dated sections in the Helvetic Alps were used to constrain the age of the Urgonian platform. The sum of the data and field observations suggests the following evolution: during the Hauterivian, important outward and upward growth of a bioclastic and oolitic carbonate platform is documented in two sequences, separated by a phase of platform drowning during the late Early Hauterivian. Following these two phases of platform growth, a second drowning phase occurred during the latest Hauterivian and Early Barremian, which was accompanied by significant platform erosion and sediment reworking. The Late Barremian witnessed the renewed installation of a carbonate platform, which initiated with a phase of oolite production, and which progressively evolved into a typical Urgonian carbonate platform colonized by corals and rudists. This phase terminated at the latest in the middle Early Aptian, due to a further drowning event. The evolution of this particular platform segment is compatible with that of more distal and well-dated segments of the same northern Tethyan platform preserved in the Helvetic zone of the Alps and in the northern subalpine chains (Chartreuse and Vercors).

Impact of free-range pigs on mountain pastures in the Swiss Jura

The consequences of foraging by free-range pigs on the vegetation of mountain pastures was investigated. 25 pigs (15 week-old, mean weight 50 kg) were enclosed from June to mid-September in a 2 ha-enclosure in Jura Mountains (Switzerland), fed with a mixture of lactoserum and cereals. The enclosure contained five different plant communities. Eutrophic pastures on deep soil were strongly overturned, but the recolonisation was quick and dominated by the original species. Mesotrophic pastures were less damaged on stony soil but completely destroyed on deep soil, and the recovery was slow, characterised by a shift of plant species in a more eutrophic direction. Four years were not sufficient for complete recovery. Oligotrophic calcareous pastures on shallow stony soil were not damaged. Extensive breeding of pigs in mountain pastures might be harmful to plant species and vegetation, and ought to be restricted to the less sensitive plant communities, with a rotation on two to three different sites.

Majority carrier capture cross section determination in the large deep trap concentration cases

A method to determine the thermal cross section of a deep level from capacitance measurements is reported. The results enable us to explain the nonexponential behavior of the capacitance versus capture time when the trap concentration is not negligible with respect to that of the shallow one, and the Debye tail effects are taken into account. A figure of merit for the nonexponential behavior of the capture process is shown and discussed for different situations of doping and applied bias. We have also considered the influence of the position of the trap level"s energy on the nonexponentiality of the capture transient. The experimental results are given for the gold acceptor level in silicon and for the DX center in Al0.55 Ga0.45As, which are in good agreement with the developed theory.