Mixed Assemblages Research Articles

First genetic characterisation of Giardia in human isolates from Jordan

Little is known about the epidemiology of Giardia in Jordan and to date, no genotyping studies have been conducted on Giardia isolates from Jordanians. In the present study, a total of 49 microscopy-positive faecal samples from Jordanian patients suffering from giardiasis were analysed at two loci: the triose phosphate isomerase (tpi) gene and the glutamate dehydrogenase (gdh) gene. At the tpi locus, a total of 28 samples amplified and assemblage A was identified in 46.4% (13/28) samples, while assemblage B was identified in 50% (14/28) samples and a mixed assemblage A and B was identified in one sample (3.6%) (Table 1). At the gdh locus 48 isolates amplified and of these assemblages A was identified in 43.7% (21/48) of isolates and assemblage B in 56.3% (27/48) of isolates. No mixed infections were detected at the gdh locus. Subtyping at the gdh locus identified sub-assemblage AII in 43.7% (21/48) of isolates and sub-assemblages BIII and BIV in 25% (12/48) and 31.2% (15/48) of isolates, respectively, with more genetic diversity in AII isolates than BIII or BIV isolates. Novel sub-types within each sub-assemblage were identified suggesting unique endemicity and anthroponotic transmission of Giardia in Jordanian patients suffering from giardiasis. Further studies are required to better understand the epidemiology and transmission of Giardia in Jordan.

Toward disentangling stages in mixed assemblages of flake debris from biface reduction: An experimental approach

Their abundance in the archaeological record makes assemblages of lithic debris popular subjects of analysis. Archaeologists study them to identify both kinds and stages of reduction, using approaches that range in scale from attribute analysis to typology and size distributions. Experiments demonstrate meaningful pattern in flake assemblages by both kind and stage. Yet empirical assemblages often are mixtures of flake debris from various reduction kinds and stages. Mixing confounds the patterns often found in controlled experimental data. To address this problem, we use Stahle and Dunn's (1982) data and a similar constrained-regression method, QUADPROG in R, to allocate hypothetical mixed assemblages of biface-reduction stages to their constituent stages. In combining their Stages 2 and 3, a measure that Stahle and Dunn themselves advocated, QUADPROG improves their allocation results. Methods like these deserve further testing on a wider range of flake assemblages to address the challenge that mixing poses.

Differences in coastal subsidence in southern Oregon (USA) during at least six prehistoric megathrust earthquakes

Stratigraphic, sedimentologic (including CT 3D X-ray tomography scans), foraminiferal, and radiocarbon analyses show that at least six of seven abrupt peat-to-mud contacts in cores from a tidal marsh at Talbot Creek (South Slough, Coos Bay), record sudden subsidence (relative sea-level rise) during great megathrust earthquakes at the Cascadia subduction zone. Data for one contact are insufficient to infer whether or not it records a great earthquake—it may also have formed through local, non-seismic, hydrographic processes. To estimate the amount of subsidence marked by each contact, we expanded a previous regional modern foraminiferal dataset to 174 samples from six Oregon estuaries. Using a transfer function derived from the new dataset, estimates of coseismic subsidence across the six earthquake contacts vary from 0.31 m to 0.75 m. Comparison of subsidence estimates for three contacts in adjacent cores shows within-site differences of ≤0.10 m, about half the ±0.22 m error, although some estimates may be minimums due to uncertain ecological preferences for Balticammina pseudomacrescens in brackish environments and almost monospecific assemblages of Miliammina fusca on tidal flats. We also account for the influence of taphonomic processes, such as infiltration of mud with mixed foraminiferal assemblages into peat, on subsidence estimates. Comparisons of our subsidence estimates with values for correlative contacts at other Oregon sites suggest that some of our estimates are minimums and that Cascadia's megathrust earthquake ruptures have been heterogeneous over the past 3500 years.

Enumeration of Parasitic Chytrid Zoospores in the Columbia River via Quantitative PCR.

Through lethal infection, fungal parasites of phytoplankton ("chytrids") repackage organic material from the large, effectively inedible, colonial diatoms they infect into much smaller zoospores, which are easier for zooplankton to consume. However, their small size and lack of distinguishing morphological features render it difficult to distinguish zoospores from other small flagellates in mixed assemblages in the natural environment. In this study, we developed and tested a method to quantify chytrid zoospores in field studies using quantitative PCR (qPCR) targeting the internal transcribed spacer 2 (ITS2) region within the rRNA gene cluster. To achieve accurate quantification, the assay was designed to be highly specific for a parasite (Rhizophydium planktonicum) of the diatom Asterionella formosa; however, the approach is applicable to additional host-parasite systems. Parasitic zoospores were detected and quantified in the freshwater reaches of the lower Columbia River, as well as in the salt-influenced estuary and river plume. The coincidence between zoospore abundances and a prevalence of small zooplankton during blooms of large, colonial diatoms in the spring suggests that Columbia River zooplankton may be poised to benefit nutritionally from chytrid zoospores, thus providing a mechanism to retain organic carbon within the system and reduce losses to downstream export. We estimate that ∼15% of the carbon biomass tied up in blooms of the dominant diatom species is transformed into zoospores through the parasitic shunt during spring. The small size of the parasitic fungi that infect phytoplankton makes it difficult to identify and quantify them in natural systems. We developed and tested a method to quantify these organisms (chytrid zoospores) using a molecular technique that targets the internal transcribed spacer region within the rRNA gene cluster. Using this method, we quantified the abundance of the motile stage of a specific parasite in the freshwater and saltwater-influenced regions of the Columbia River in the U.S. Pacific Northwest. Parasitic chytrid zoospores were found to be present throughout the year and at higher abundances during the spring, when phytoplankton blooms occur. The presence of these organisms indicates not only that they may be responsible for the death of host phytoplankton cells but that they may also provide a readily available food source to small consumers (zooplankton) in the food web of the Columbia River.

Multiscale Imaging of Fixed-Cutter-Drill-Bit-Generated Shale Cuttings

Summary Shales account for more than 75% of the formations drilled worldwide, and fixed-cutter bits are used to drill most of the footage. Cutter/rock interactions after the initial failure of rock are shown to be a major source of drilling inefficiency. Analytical and numerical modeling was implemented to understand these interactions and their controlling factors, but a comprehensive model does not exist. This is mainly because of the complex nature of the problem that depends on several factors that include rock characteristics, pressure-and-temperature environment, bit design, and drilling-fluid properties. Having such a large range of factors requires a cross-disciplinary approach to tackle the problem. This paper is focused on fabric analysis of the rock cuttings. Recent developments in fabric-analysis techniques allow the study of the size, shape, composition, and spatial arrangement of particles and matrix constituents in fine-grained rocks. This has led to an increased understanding of compaction phenomena, shear strength, porosity, permeability, fracturing, electrical propagation, and seismic properties of the rock. Despite this, the changes in rock fabric during interaction with the drill bit are not well-understood. This work takes advantage of those techniques by analyzing the shale cuttings at the macro-, micro-, and nanolevels to understand how shales break and deform under confining pressure to better understand drill-bit/rock interactions. Cuttings recovered from a well in Tuscaloosa, Louisiana, drilled with fixed-cutter bits were analyzed in multiple scales: macro, micro, and nano. Shallower and deeper sections were drilled with water-based mud and oil-based mud (OBM), respectively. Samples were gathered from seven depth intervals ranging from 13,500 to 21,320 ft. The microscale analysis was performed with a X-ray computed-tomography scanning technique, whereas nanoscale analysis was performed with a scanning electron microscope (SEM). Shale-cuttings fabric was characterized by images produced by energy-X-ray-descriptive spectroscopy (EDS) and backscattered-electron microscopy of ion-milled samples. Cuttings were generally formed in the shape of layered ribbons in which the mud-facing side is uneven and serrated whereas the cutter side is smooth and has a darkened clay film. The size of the ribbons and thickness of the layers were larger in areas drilled with OBM. Cuttings accumulation in the form of a ball attached to some of the ribbons from drilling in OBM provided evidence that cutter balling can occur during field drilling operations. SEM-EDS analysis of cuttings showed significant accumulation of barite, a component in the drilling fluid, on the external surface of the serrated sides of the ribbons. In addition, scattered barite zones were found inside the cuttings. X-ray diffraction analyses indicated a mixed mineral assemblage dominated by quartz and smectite with minor illite, kaolinite, chlorite, mixed-layered materials, and traces of calcite and pyrite. It was hypothesized that the absence or scattered appearance of barite in some zones of produced cuttings, particularly the cutter side of the ribbon and the cutter ball, may relate to higher deformation of cuttings at those zones. In addition, the mechanism of cutter balling was explained with an analogy with metal-cutting theories. This was supported by comparison between the geometry of shale cuttings from this field and copper cuttings from single-cutter experiments. Structural analysis of cuttings from actual field drilling reinforced the relevance of the observations made during laboratory experiments. It also provided unique insights, observations, and incentives for additional investigation of how cuttings are formed and what influences dysfunctions or inefficiencies. This is a significant step in understanding shale/cutter interactions that severely affect the bit penetration rate, especially under high confining pressure.

Late Middle Palaeolithic lithic technocomplexes (MIS 5–3) in the northeastern Aquitaine Basin: Advances and challenges

Establishing and interpreting patterns of lithic assemblage variability is of great interest to archaeologists as they shed light on cultural adaptations in the deep past. Nowhere has this topic provoked more interest and debate than in the Middle Palaeolithic of southwestern France. The region's rich archaeological record has produced numerous sites, many of which have been recently excavated and thus provide a reliable dataset for better structuring Mousterian lithic variability. Researchers working with these types of datasets frequently employ the chaine operatoire concept to approach lithic assemblage variability; however, the validity of such analyses has recently been questioned. Here we present results of a combined quantitative and qualitative technological analysis of a large sample of assemblages from numerous well-contextualised sites in the northeastern Aquitaine Basin. We selected clearly identifiable diagnostic elements typical of different flake production systems that can be quantified by different analysts in a replicable fashion. Our results show strong differences in assemblage composition in terms of dominant production systems as well as a smaller number of mixed assemblages that combine two or more flake production methods. When considered together, these results provide not only a means for defining lithic technocomplexes and subsequently comparing assemblages but also for investigating elements of Neanderthal material culture variability.

Abundance and distribution of Arctic cod (Boreogadus saida) and other pelagic fishes over the U.S. Continental Shelf of the Northern Bering and Chukchi Seas

We conducted acoustic-trawl (AT) surveys of the northern Bering and Chukchi Seas during ice-free periods in 2012 and 2013. The mixed species assemblages in the study area required refinement of standard AT survey methods, and adjustment of trawl catches for the effects of trawl selectivity. Sensitivity analyses indicate that the AT abundance estimates are relatively robust to the assumptions of the analysis. These surveys indicate that midwater fishes are dominated by age-0 Arctic cod (Boreogadus saida), age-0 saffron cod (Eleginus gracilis), capelin (Mallotus villosus), and Pacific herring (Clupea pallasii). In both years, age-0 Arctic cod were distributed principally ≥69.5°N, age-0 saffron cod were abundant in coastal areas between 66.5 and 69.5°N, and Pacific herring were distributed south of 67°N. These three fishes exhibited consistent associations with temperature, salinity and bottom depth: e.g., age-0 Arctic cod were abundant at lower mean water column temperatures than saffron cod. In contrast, capelin were distributed throughout the study area, and were not consistently associated with environmental measures. There was a geographic trend in body length, with smaller Arctic cod, saffron cod and capelin in northern areas, but smaller herring in the south. Arctic cod, saffron cod, herring and capelin were all >2 times more abundant in 2013 than 2012. Sizeable populations of age-0 Arctic cod were observed in the northern Chukchi Sea, which suggests that this area is an important nursery ground. However, relatively few older Arctic cod were observed in this and other surveys of the area, which suggests that either overwinter mortality of age-0 Arctic cod is high, and/or these fish are not retained on the Chukchi shelf.

A quantitative real-time PCR assay for identification and enumeration of the occasionally co-occurring ichthyotoxic Pseudochattonella farcimen and P.verruculosa (Dictyochophyceae) and analysis of variation in gene copy numbers during the growth phase of single and mixed cultures.

The ichthyotoxic genus Pseudochattonella forms recurrent extensive blooms in coastal waters in Japan, New Zealand and Northern Europe. It comprises of two morphologically similar species, P.verruculosa and P.farcimen, which complicates visual species identification and enumeration of live and fixed material. Primers designed previously could not quantitatively distinguish species in mixed assemblages. To address this issue we developed two primer sets: one revealed itself to be genus specific for Pseudochattonella and the other species-specific for P.verruculosa. By subtracting cell estimates for P.verruculosa from combined results we could calculate cell numbers for P.farcimen. This approach has overcome the challenges posed by the very limited sequence availability and low gene variability between the two species. The qPCR assay was extensively tested for specificity, efficiency and sensitivity over an entire growth cycle in both single and mixed assemblages. Comparison of cell abundance estimates obtained by qPCR assay and microscopy showed no statistically significant difference until stationary and death phases. The assay was also tested on environmental samples collected during a small Pseudochattonella bloom in Denmark in March-April 2015. It was impossible to distinguish P.farcimen and P.verruculosa by light microscopy but qPCR showed both species were present. The two methods provided nearly identical cell numbers but the assay provided discrimination and enumeration of both species.

Wood and bark phytoliths of West African woody plants

Abstract Long-term wood anatomical research has shown that 10% of the world's trees and shrubs produce silica in their wood, but silica production in bark had never been systematically investigated. We present here the results of the first comprehensive study on phytoliths in bark and compare them with data on wood phytoliths. We studied 103 bark samples from 92 species and 35 wood samples from 31 species mainly distributed in the West African savannas, altogether representing 34 plant families. The presence of silica in >90% of the studied bark samples indicates that silica production in bark is much more common than in wood. We developed a classification with three anatomical and five morphological classes and recorded their abundance in the processed phytolith samples. With a few exceptions, the phytoliths of bark and wood belong to different classes and can be clearly distinguished from each other. Wood produces Globulars s.l. and Aggregates with their own shape independent from the cells in which they had been formed. In bark, unspecific Blockies and Silica particles/Accumulations are omnipresent while 31% of the species have specific morphotypes with consistent morphologies. These phytoliths reflect the anatomy of the cells and tissues and develop either through silification of the cell lumen or the cell walls. They belong to the anatomical classes Sclerenchyma (with two subclasses Fibres and Sclereids), Cork/Parenchyma, and Cork aerenchyma. Phytoliths in bark and wood have taxonomic relevance, but the distribution is uneven on different taxonomic levels. Some Urticalean Rosids, Bignoniaceae and Capparaceae develop diagnostic phytoliths in the bark. Wood and bark phytoliths can be identified in special archaeological and palaeoecological contexts, but because they are from vegetative tissues, redundancy with similar morphotypes from other plant organs and taxonomic groups has to be considered in mixed assemblages.

Fungal species diversity affects leaf decomposition after drought

The number of studies on the importance of biodiversity in stream ecosystem processes increased in the last years; however, little is still known on its role in scenarios of flow intermittency. In this study, we conducted a microcosm experiment to test the diversity‐insurance hypothesis on microbial decomposing oak leaves exposed to a drought event. Three microbial diversity levels were tested, single species and mixture assemblages of three or eight species of aquatic hyphomycetes. We also evaluated changes in leaf litter quality promoted by leaves desiccation to the shredder Schizopelex festiva. Fungal mixed assemblages resulted in higher decomposition and fungal sporulation rates than single species. This pattern was maintained after drought and decomposition was rapidly reassumed with rehydration. Fungal‐mediated decomposition seems to be more stimulated in the presence of rich (vs. single) fungal assemblages even after desiccation, particularly when species addition occurs at lower levels of richness. Shredder consumption was not affected by leaf desiccation, although feeding rates were consistently higher on leaves conditioned with eight fungal species and likely affected by the identity of the dominant taxa. Bottom‐up effects are expected on the food webs of detritus‐based streams affected by droughts; the intensity of these effects seems to be dependent on the level of decline promoted on decomposers richness by the environmental perturbation.

Influence of temperature and congener presence on habitat preference and fish predation in blue (Paralithodes platypus Brandt, 1850) and red (P. camtschaticus Tilesius, 1815) king crabs (Anomura: Lithodidae)

Rebuilding fisheries is a difficult process and many stocks that are declared overfished fail to recover even in the absence of fishing pressure. The Pribilof Islands stock of the blue king crab ( Paralithodes platypus Brandt, 1850) in Alaska, USA is one of these recovery failures. To explore how environmental and ecological factors might interact to suppress this stock, we conducted a suite of laboratory experiments to assess the effects of temperature changes and the presence of red king crab ( Paralithodes camtschaticus Tilesius, 1815) on blue king crab habitat preference and fish predation survival. Age-0 blue king crabs exhibited plasticity in habitat preference mediated by changes in water temperature, as well as the presence and density of juvenile red king crabs. While blue king crabs are often associated with shell-hash habitat, increases in water temperature, as well as the presence of red king crab at high densities, caused blue king crab juveniles to shift into habitats with an algal mimic present, a habitat type shown to reduce the predation efficacy of red king crabs. In contrast, red king crabs exhibited fewer changes in habitat preference with changes in water temperature and the presence of a congener. Blue king crabs are therefore behaviorally plastic, switching from strategies of predator avoidance when predator encounter rates are likely low, to predator deterrence strategies when encounter rates are higher. Fish predation trials further support the idea that blue king crabs are more focused on predator avoidance than are red king crabs. In fish predation trials run separately for the two crab species, blue king crabs had higher survival (60%) than red king crabs (33%) when exposed to fish predators. Our results indicate that age-0 blue king crabs can be less vulnerable to fish predation than red king crabs, but future research should assess how fish predation rates change when presented with higher densities of red and blue king crab in mixed assemblages as the observed habitat shifts could affect predation survival.

Production, exportation and preservation of silicoflagellates in Alfonso Basin, Gulf of California

Limited areas of sea floor have the physiochemical conditions that allow for the formation and preservation of high resolution (yearly or close to yearly) laminated sediments that can function as a historic proxy for past oceanographic and climate conditions. We evaluated and established the fidelity of the sedimentary record in recording these signals by analyzing silicoflagellates production, changes in species composition, skeletal settling and their subsequent burial in bottom sediments at Alfonso Basin. The data series from December 2005 to February 2008 showed similar tendencies in both the vertical flux and overlying euphotic zone (Zeu) production of silicoflagellates. Both series were numerically dominated by Octactis pulchra with maxima values being recorded for the mixed water column period. Observed differences occurred during the studied years in both magnitude and in flux composition. The presence of a mixed assemblage with (warm–temperate–cold) species such as Dictyocha fibula var. robusta, Dictyocha epiodon and Distephanus speculum could be explained by a synchronization of trends between a predominantly positive Pacific Decadal Oscillation and a positive North Pacific Gyre Oscillation climate phases that were the background conditions underlying the early 2006 through 2007 El Niño event. A Morisita's similarity index value of 97.5% between winter trap and Zeu samples combined with an annualized settling factor of 0.45, suggests that Alfonso Basin is a favorable settling environment for silicoflagellates. However, core-top sediments showed an attenuation of record fidelity (burial factor=0.25) resulting in a modified record for the production and settling of skeletons. O. pulchra that were not preserved in sediments as the dominant species and with this removal, the signal was also lost of the highest silicoflagellate production season (Mixing-cyclonic eddy periods) from the sedimentary record of the Alfonso Basin.

Interspecific competition and protistan grazing affect the coexistence of freshwater betaproteobacterial strains.

The competitive strength of four cosmopolitan freshwater betaproteobacterial isolates was investigated in the presence or absence of bacterivorous flagellates during continuous cultivation in artificial minimal medium at two dilution rates. Bacteria reached similar abundance and growth rate in monocultures, but in co-cultures, two strains (Acidovorax sp. and Massilia sp.) displayed significantly higher numbers and growth rates. These potential cross-feeding benefits were also supported by a high nutritional versatility of the two strains. In contrast, Hydrogenophaga sp. was seemingly less competitive or even inhibited by co-cultivation, and Limnohabitans planktonicus displayed striking abundance fluctuations. The latter two strains were least versatile in the uptake of different carbon sources and thus suffered more from interspecific competition. Moreover, remarkable strain-specific responses appeared when bacteria experienced increasing loss rates due to grazing and/or raised dilution rates. Limnohabitans planktonicus developed no successful defence strategy and was close to extinction. Massilia sp. formed grazing-resistant filaments exclusively at low dilution, but was highly reduced at increased flow-through. Acidovorax sp. was selectively ingested, but compensated grazing losses with accelerated growth rates and formed (co-)aggregates together with Hydrogenophaga sp. to escape predation at high flow-through. These species-specific interactions, growth responses and defence strategies strongly modulate mixed microbial assemblages and the microbial food web.

Seasonal variations of phytoplankton dynamics in Nunatsiavut fjords (Labrador, Canada) and their relationships with environmental conditions

We assessed phytoplankton dynamics and its environmental control in four Labrador fjords (Nachvak, Saglek, Okak, and Anaktalak) during summer, early fall and late fall. Primary production and chlorophyll a (chl a) biomass were measured at seven optical depths, including the depth of subsurface chl a maximum (SCM). Phytoplankton abundance, size structure and taxonomy were determined at the SCM. Principal component analysis and non-metric multidimensional scaling were used to analyze relationships between production, biomass and community composition in relation to environmental variables. We observed a marked seasonal variability, with significant differences in phytoplankton structure and function between summer and fall. Surprisingly, primary production and chl a biomass were not significantly different from one fjord to another. The highest values of primary production (1730mgCm−2day−1) and chl a biomass (96mgchlam−2) were measured during the summer bloom, and those high values indicate that Labrador fjords are highly productive ecosystems. The summer community showed relatively high abundance of nanophytoplankton (2–20μm) while the fall community was characterized by low primary production and chl a biomass as well as relatively high abundance of picophytoplankton (<2μm). The low value of carbon potentially exported out of the euphotic zone throughout the study (≤31% of total primary production) suggests that phytoplankton production was mainly grazed by microzooplankton rather than being exported to greater depths. We observed a mixed assemblage of diatoms and flagellates in summer, whereas the fall community was largely dominated by flagellates. Seasonal variations in phytoplankton dynamics were mainly controlled by the strength of the vertical stratification and by the large differences in day length due to the northerly location of Labrador fjords. This study documents for the very first time phytoplankton structure and function in Labrador fjords, and provides an essential foundation for further research and for monitoring environmental changes in arctic and subarctic coastal areas.

Consecutive wildfires affect stream biota in cold- and warmwater dryland river networks

AbstractClimate change and fire suppression have altered fire regimes globally, leading to larger, more frequent, and more severe wildfires. Responses of coldwater stream biota to single wildfires are well studied, but measured responses to consecutive wildfires in warmwater systems that often include mixed assemblages of native and nonnative taxa are lacking. We quantified changes in physical habitat, resource availability, and biomass of cold- and warmwater oligochaetes, insects, crayfish, fishes, and tadpoles following consecutive megafires (covering >100 km2) in the upper Gila River, New Mexico, USA. We were particularly interested in comparing responses of native and nonnative fishes that might have evolved under different disturbance regimes. Changes in habitat and resource availability were related to cumulative fire effects, fire size, and postfire precipitation. The 2nd of 2 consecutive wildfires in the basin was larger and, coupled with moderate postfire discharge, resulted in increased siltatio...

Macroalgal Composition Determines the Structure of Benthic Assemblages Colonizing Fragmented Habitats.

Understanding the consequences of fragmentation of coastal habitats is an important topic of discussion in marine ecology. Research on the effects of fragmentation has revealed complex and context-dependent biotic responses, which prevent generalizations across different habitats or study organisms. The effects of fragmentation in marine environments have been rarely investigated across heterogeneous habitats, since most studies have focused on a single type of habitat or patch. In this study, we assessed the effects of different levels of fragmentation (i.e. decreasing size of patches without overall habitat loss). We measured these effects using assemblages of macro-invertebrates colonizing representative morphological groups of intertidal macroalgae (e.g. encrusting, turf and canopy-forming algae). For this purpose, we constructed artificial assemblages with different combinations of morphological groups and increasing levels of fragmentation by manipulating the amount of bare rock or the spatial arrangement of different species in mixed assemblages. In general, our results showed that 1) fragmentation did not significantly affect the assemblages of macroinvertebrates; 2) at greater levels of fragmentation, there were greater numbers of species in mixed algal assemblages, suggesting that higher habitat complexity promotes species colonization. Our results suggest that predicting the consequences of fragmentation in heterogeneous habitats is dependent on the type and diversity of morphological groups making up those habitats.

Ocean acidification increases the accumulation of toxic phenolic compounds across trophic levels.

Increasing atmospheric CO2 concentrations are causing ocean acidification (OA), altering carbonate chemistry with consequences for marine organisms. Here we show that OA increases by 46–212% the production of phenolic compounds in phytoplankton grown under the elevated CO2 concentrations projected for the end of this century, compared with the ambient CO2 level. At the same time, mitochondrial respiration rate is enhanced under elevated CO2 concentrations by 130–160% in a single species or mixed phytoplankton assemblage. When fed with phytoplankton cells grown under OA, zooplankton assemblages have significantly higher phenolic compound content, by about 28–48%. The functional consequences of the increased accumulation of toxic phenolic compounds in primary and secondary producers have the potential to have profound consequences for marine ecosystem and seafood quality, with the possibility that fishery industries could be influenced as a result of progressive ocean changes.

Multiple sources for the origin of the early Cretaceous Xinxian granitic batholith and its tectonic implications for the western Dabie orogen, eastern China

This paper investigates the petrogenesis of the Xinxian granitic batholith and its tectonic implications for the Dabie orogen. Two Xinxian granites yield Early Cretaceous 238U/206Pb ages of 122.7 ± 1.3 Ma and 123.6 ± 2.2 Ma. The granites are metaluminous differentiated I–type granites, with A/NKC ranging from 0.90 to 0.96. The chondrite–normalised REE patterns display significant LREE/HREE enrichments with moderate negative Eu anomalies (Eu/Euδ = 0.30 ~ 0.85). The granites show enrichments in large–ion lithophile elements (LILEs, e.g. Rb, K, Th and U) and depletions in Sr, Ba and high field strength elements (HFSEs, e.g. Nb, Ta and Ti). Inherited zircons of different age (Neoproterozoic, one Early Proterozoic, one Archean and two Triassic inherited metamorphic zircons) are identified. The Early Cretaceous magmatic zircons contain enriched Hf isotopes with e Hf (t) values ranging from −26.9 to −18.7 (average = −22.5), more enriched than their probable alleged source, i.e. the Dabie Complex, represented by the Neoproterozoic and Triassic inherited zircons. Thus, the Archean and Early Proterozoic crustal materials may represent an enriched end member source for the parental magma of the Xinxian granites. Provenance analysis of the magmatic zircons in the North China and Yangtze blocks demonstrates that the Early Proterozoic inherited zircon in Xinxian has North China affinity. Thus, we proposed a multiple–sourced petrogenetic model for the Xinxian granitic batholith, which suggests that the batholith was formed by the remelting of a mixed crustal assemblage, including the Archean and Early Proterozoic crust of the North China Block, the Neoproterozoic crust of the Yangtze Block, as well as some Triassic collision–related ultra–high pressure (UHP) metamorphic rocks.

Otolith shape variation provides a marker of stock origin for north Atlantic bluefin tuna (Thunnus thynnus)

Two stocks of bluefin tuna (Thunnus thynnus) inhabit the north Atlantic; the western and eastern stocks spawn in the Gulf of Mexico and the Mediterranean Sea respectively. Trans-Atlantic movements occur outside spawning time whereas natal homing maintains stock structure. Commercial fisheries may exploit a mixed assemblage of both stocks. The incorporation of mixing rates into stock assessment is precluded by uncertainties surrounding stock discrimination. Otolith shape descriptors were used to characterise western and eastern stocks of Atlantic bluefin tuna in the present study and to estimate stock composition in catches of unknown origin. Otolith shape varied with length and between locations and years. Within a restricted size range (200–297-cm fork length (FL)) the two stocks were distinguished with an accuracy of 83%. Bayesian stock mixture analysis indicated that samples from the east Atlantic and Mediterranean were predominantly of eastern origin. The proportion assigned to the eastern stock showed slight spatial variation; however, overlapping 95% credible intervals indicated no significant difference (200–297cm FL: central Atlantic, 73–100%; Straits of Gibraltar, 73–100%; Morocco, 50–99%; Portugal 64–100%). Otolith shape could be used in combination with other population markers to improve the accuracy of mixing rate estimates for Atlantic bluefin tuna.

Palaeobiogeographical constraints on the distribution of foraminifers and rugose corals in the Carboniferous Tindouf Basin, South Morocco

The northern flank of the Tindouf Syncline in southern Morocco exhibits a continuous, well exposed Carboniferous succession with limestones of Late Asbian to Early Bashkirian age containing rich and diverse foraminiferal and rugose coral assemblages. Analysis of these assemblages provides new data on the relatively poorly known Saharan basins. The palaeobiogeographical relationship of the Tindouf Basin with other Palaeotethyan basins is complex. Although there is a predominance of cosmopolitan taxa for the Palaeotethys, it is recognized that there was an influence of basins from NW Europe, such as the UK and Ireland. Some taxa are recorded in both NW Europe and Tindouf without any characteristic contributions from intermediate basins in northern Morocco. The neighbouring Béchar Basin in Algeria presents distinct assemblages. The bulk of the data analyzed suggest that this sector of the western Palaeotethys can be subdivided into four palaeobiogeographical subprovinces: the Atlantic Subprovince (UK, Ireland, N France and Belgium), the Mediterranean Subprovince (Pyrenees, Montagne Noire, Betic Cordillera, Rif (N Morocco) and Balearic Islands), and the Saharan Subprovince (Béchar, Reggan, Ahnet-Mouydir and Tindouf). In between, mobile belts of mixed faunal assemblage characteristics are observed (e.g., SW Spain and Central Meseta) forming the West peri-Gondwanan Subprovince. Analysis of the Tindouf Basin faunas shows that, as in other Saharan basins, there is a high diversity and abundance of foraminiferal taxa, with a higher proportion of survivors and longer stratigraphic ranges; these features also are mirrored by rugose corals. This emphasizes the longevity of the carbonate platform in a tropical setting, where periodic transgressions introduced new assemblages, and oceanic currents are interpreted as one of the main controlling factors for the distribution of the taxa in these subprovinces. Moreover, not only were water temperatures on the platform higher, but also tectonic stability greater. It is considered that the effects of the first phases of the Gondwanan glaciation were minimal on the Tindouf faunas.