Estimating mortality in natural assemblages of oysters

To evaluate methods for calculating mortality in bivalve molluscs, we analyzed historical data from dredge surveys of both planted and natural oyster (Crassostrea virginica) grounds in Delaware Bay to compare total box-count mortality estimates with those made by accumulating short-term mortality rates obtained from fresh boxes identified by shell condition and degree of fouling. Box-count and cumulative-mortality patterns and values agreed best on grounds with planted oysters, where a cohort with very few dead oysters was broadcast on previously cleaned bottom and was followed over time. This situation is analogous to an artificially created reef with oysters either deployed or naturally set on it. When deaths predominated in late summer and early autumn, the two estimates were similar throughout the following year; when mortality was greatest in spring or early summer, the estimates were similar only through autumn of the same year. Correspondence was much weaker on natural beds, where new individuals constantly recruited to the population and variable numbers of boxes were always present. Nevertheless, total box-count mortality estimates made during autumn stock surveys were significantly correlated with cumulative mortalities calculated for the preceding year. We also estimated disarticulation rates of artificially created boxes by deploying them at three seasons and eight sites in Delaware Bay. Disarticulation time depended on the length of exposure at summer temperatures, with the average time to 50% disarticulation for boxes deployed in spring and in summer being 225 and 345 days, respectively. Disarticulation rates increased with decreasing size, and increasing salinity and temperature. Finally, we compared total box-count and cumulative-mortality estimates with those made using the disarticulation data. Annual averages for the three methods were within 5 percentage points of each other. Our data indicate that total box-count mortality estimates from fall stock surveys can provide a reliable index to total mortality for the previous year, although it cannot describe the seasonal patterns obtainable using the cumulative-mortality method. *** DIRECT SUPPORT *** A02BY003 00003     

Fish assemblages in natural versus well-established recolonized seagrass meadows

Studies of fish assemblages between natural and newly recolonized (<4 yr) seagrass meadows have shown no significant differences in community composition between meadow types. However, comparison of natural and well-established (31 yr) recolonized seagrass meadows in the Indian River Lagoon, Florida, showed that, although patterns in fish assemblages are complex and not always consistent, differences were evident. Species richness was higher in natural meadows during spring and autumn while density and species richness were higher in recolonized meadows during summer. Juveniles of all but the five most abundant species were more common in one or the other meadow type. Additionally, species composition was distinctly different between recolonized and natural seagrass meadows, as indicated by UPGMA cluster analysis based on the Morisita-Horn similarity index, Spearman'sr _s (r _s>0.05 in all but one case), and a maximum of only 58.5% species in common. There were also significant differences in the length-frequency distribution for six of seven abundant species. Our results suggest that a well-established recolonized seagrass meadow has the potential to maintain species complements distinct from nearby natural meadows. Reasons for our differing results may include differences in seagrass morphology and collecting techniques between our study and the former studies. Additionally, species may have a longer time to establish specific habitat-use patterns in well-established compared to newly-formed recolonized meadows. Recolonized seagrass meadows appear to be as suitable a habitat as natural meadows for juvenile and small adult fishes.     

Molluscan assemblages from archaeological deposits

Research about the impact of prehistoric human subsistence strategies upon prey populations of shellfish is based on the assumption that trends in shell size are directly related to collection strategies. A shell midden on San Juan Island, Washington, where archaeological research is sponsored by the University of Washington and hosted by the National Park Service, provides large samples of shells from separate archaeological deposits. the shells from each deposit produce size-frequency distributions that vary in shape (modality). Because several factors (the original prey population, the method of collection and transport, the environment of deposition, and post-depositional processes) affect the size-frequency distribution differentially, the shell measurements do not provide the direct archaeological information expected.     

A reinterpretation of two chertbreccias from the Proterozoic basins of India

Several horizons of a unique lithotype called “chertbreccia” are interbedded within the Proterozoic platform sediments of the Peninsular India. These cherty rocks with brecciated texture appearing as blocky masses were earlier diversely interpreted as being products of disparate processes such as fault-zone breccias, collapse breccias, and so on. Two of these horizons, one from the Kaladgi Basin (Dharwar Craton) and the other from the Dhar Forest Inlier of the Vindhyanchal Basin (Bundelkhand — Aravalli Craton) are compared in context of their geological setting, field relations and petrological constitution. A model of the mode of development of these peculiar rocks is reconstructed, taking into account their characters and limitations of previous interpretations. They are interpreted as transported debris deposits of syntectonogenic material released during the episodic activity of the growth faults of the Kaladgi and Vindhyanchal Basins that was diagenetically silicified.     

Ultraviolet-B radiation effects on natural phytoplankton assemblages of central San Francisco Bay

Since the discovery of a depletion of the stratospheric ozone layer over Antarctica in 1979, scientific attention has been directed towards the effects of increased doses of ultraviolet radiation on phytoplankton in other ecosystems. Little is known about the effects of ultraviolet-B (280–320 nm) radiation (UVBR) on temperate estuarine phytoplankton. Freshly collected phytoplankton samples from Central San Francisco Bay were exposed to ambient UVBR in quartz bottles and monitored for biomass and nutrient uptake rates for comparison with phytoplankton dispensed into bottles made of polycarbonate that effectively filtered out the UVBR to evaluate response to natural UVBR exposure. Short-term (10–12 h) exposure experiments were carried out monthly from October 1998 to October 1999. No significant effect of UVBR on chlorophylla concentrations was found but a clear deleterious effect of UVBR on nutrient uptake was observed.     

Mineral assemblages and oxygen and sulphur fugacities in natural water-rock interaction processes

Several mineral assemblages capable of buffering oxygen and sulphur fugacity and theoretical calculations were used to determine the fugacities of these two gas species over a temperature range between 150° and 350°C. Computed values were compared with those calculated from the composition of the geothermal fluids of Larderello, Travale, Bagnore and Piancastagnaio (Italy), The Geysers (USA) and Cerro Prieto (Mexico). The possible hydrothermal mineral assemblages that best fit the field data are those containing minerals frequently found in many geothermal fields: epidote, chlorite, K-feldspar, quartz and pyrite. These assemblages can be used in place of the classical buffers based on iron oxides and sulphides.     

Holocene pollen assemblages from coastal wetlands: differentiating natural and anthropogenic causes of change in the Thames estuary,UK

Simultaneous changes in the representation of wetland and dry land taxa are a common feature of mid and late Holocene pollen diagrams from the coastal wetlands of North‐West Europe. Distinguishing both the areas affected and between natural and anthropogenic causes can be problematic. High temporal resolution, improved taxonomic procedures and multivariate statistics have been applied to two Thames estuary sites, along with simulation models, to resolve these issues. Large Poaceae pollen grains appear to be derived from wild grasses rather than cereals, while modelling indicates that even extensive clearance in dry land areas produces relatively minor changes in pollen assemblages where fen carr is the in situ vegetation. It is concluded that rapid/abrupt simultaneous pollen stratigraphic events in coastal wetlands are likely to have been caused by wetland vegetation changes alone. Simultaneous events, dating from c. 2150–1300 cal a BC, can be distinguished at 12 Thames estuary pollen sites. During this interval inter‐tidal environments expanded creating areas attractive to human populations for pasturage. This exploitation is likely to have led to further changes in wetland vegetation and increased clearance activity on adjacent dry land areas. In such circumstances disentangling the processes causing vegetation change is challenging, although considerably aided by the techniques adopted in this paper. Copyright © 2012 John Wiley & Sons, Ltd.     

A thermodynamic model for Fe–Mg dioctahedral K white micas using data from phase-equilibrium experiments and natural pelitic assemblages

The purpose of this study is to derive a solid-solution model for potassic white micas (KWM) encountered in rocks of various bulk compositions, over a wide range of P-T conditions. A compilation of phengite compositions lead us to propose a seven-thermodynamic-component (muscovite, Fe²⁺-Al-celadonite, Mg-Al-celadonite, annite, phlogopite, pyrophyllite and paragonite) ionic solid-solution model which accounts for the Tschermak, Fe-Mg, di/trioctahedral, pyrophyllitic and paragonitic substitutions observed in nature. A four-site mixing model with symmetric Margules parameters to model the Tschermak substitutions, asymmetric Margules parameters to model the other substitutions, and ideal intersite interaction has been adopted. In contrast to previous models, the relevant thermodynamic data and solid-solution properties are calibrated with independent sets of published experiments conducted for the KMASH, KFASH, KFMASH, and KNASH systems, as well as about 200 natural data involving KWM assemblages. The constraints span a wide range of pressure and temperature conditions (150 to 750 °C, 0.5 to 30 kbar), so that our model does not need to be extrapolated outside the calibration range to be used for P-T thermobarometric purposes. The calculated thermodynamic data are interconsistent with the TWQ thermodynamic database and solid-solution models, including that recently published for chlorites.     

Early Cretaceous megaspore assemblages from southeastern Australia

Twenty-nine megaspore species including six new taxa (Bacutriletes otwayensis sp. nov.,Erlansonisporites cerebrus sp. nov., Erlansonisporites decisum sp. nov., Hughesisporites coronatus sp. nov., Hughesisporites dettmanniae sp. nov., and Verrutriletes depressus sp. nov.) are documented from Aptian and Albian strata of the Gippsland and Otway basins, southeastern Australia. Together with six taxa known only from underlying Neocomian strata, these megaspores are used to establish four provisional biozones for the Lower Cretaceous that complement existing biostratigraphic schemes based on miospores and plant macrofossils. Megaspores are best represented in silty floodbasin facies and it is likely that the parent plants predominantly occupied moist understorey to fully aquatic habitats on the floodplain. Megaspores are sparsely represented in most other fluvial facies chiefly due to reworking of floodbasin sediments into higher energy channel and crevasse deposits. The relatively high diversity of lycophyte and fern megaspores contrasts with the scarcity of these plant groups in macrofossil assemblages. The megaspore record suggests that heterosporous cryptogams may have been significantly more prominent in the vegetation of this region than previously suggested. Several megaspores from southeastern Australia are closely comparable to forms from India and Argentina indicating broad similarities between Early Cretaceous heterosporous fern and lycophyte communities across Gondwana. These similarities also suggest that megaspores may be useful for inter-continental biostratigraphic correlation.     

Genetic identification of natural gases from shallow reservoirs in some oil- and gas-bearing basins of China

Natural gases of shallow reservoirs with the carbon isotopic compositions of methane ranging from -50‰ to -60‰ (PDB) were considered as mixed gases of biogenic and thermogenic origins previously and some of them were considered as low-mature (or low temperature thermogenic) gases lately. In this paper natural gases with the carbon isotopic compositions of methane in the above range were identified using the molecular and stable carbon isotopic compositions of methane, ethane and propane. The mixed gases of biogenic and mature thermogenic origins display the characteristics of δ 13 C1 ranging from -50‰to -60‰,δ13C2 ＞ -35‰,Δvalues (δ13C3 -δ13C2) ＜ 5‰ and C1/∑C2 ratios ＜ 40. Immature to low-mature gases display the characteristics of δ 13 C1 ranging from - 50‰ to - 60‰, δ13 C2 ＜- 40‰,Δ values (δ13C3 -δ13C2) ＞7‰, and C1/∑C 2 ratios ＞60.     

Fe-Ti-oxides in metamorphic basites from the Eastern Alps,Austria: a contribution to the formation of solid solutions of natural Fe-Ti-oxide assemblages

The development of Fe-Ti oxide assemblages in basic rocks from the Penninic series of the southern Venediger rea, Austria, during polyphase Alpine metamorphism has been studied. Textural and compositional relations indicate thorough reequilibration of the opaque mineral assemblages during late Barrovian metamorphism at essentially static conditions of lower amphibolite to greenschist facies. In contrast, silicate mineralogy of the preceeding blueschist to eclogite facies metamorphism might still be preserved to a large extent. Chemical adjustment of the Fe-Ti oxide minerals to decreasing P-T conditions is characterized by (1) formation of complex intergrowths of ilmenite and hematite solid solutions (<550° C), (2) the decomposition of hemo-ilmenite ₁ to ferrianilmenite₂+magnetite+rutile and of ilmeno-hematite₁ to titanhematite₂+rutile±magnetite (<450° C), and (3) low-grade oxidation of ferrianilmenite₂ to magnetite+hematite-rutile intergrowths or hematite +rutile and of titanhematite₂ to hematite-rutile intergrowths (≦400° C). Chemical equilibrium is suggested by the regular partitioning of Cr, V, Mg and Mn between coexisting hemo-ilmenite, ilmeno-hematite, and magnetite. The hematite-ilmenite miscibility gap has been delimited on the basis of the bulk compositions of the exsolved phases and the temperature estimates obtained from Fe-Ti oxide thermometry.     

Selective feeding and grazing rates of oyster (Crassostrea virginica) larvae on natural phytoplankton assemblages

Results of laboratory feeding experiments suggest that oyster (Crassostrea virginica) larvae select small phytoplanktonic organisms (<10 μm) over larger-celled forms from natural estuarine assemblages, but that little selection occurs within the small phytoplankton fraction. Laboratory-reared larvae grazed each of five small-celled phytoplankton groups enumerated (coccoids, centrate diatoms, pennate diatoms, dinoflagellates, and flagellates) at rates proportional to phytoplankton group densities in controls (no larvae added). Larval grazing rates (number of cells removed per larva per hour) were inversely proportional to both larval density and experimental duration.     

A study of natural and experimental metasomatic assemblages in an ultramafic-quartzofeldspathic metasomatic system from the haast schist,South Island,New Zealand

The mineralogy of a metasomatic sequence formed between ultramafic and quartzofeldspathic protoliths from the Southern Alps of New Zealand consists of a forsterite-antigorite core surrounded concentrically by zones of antigorite-magnesite, magnesite-talc, talc, tremolite, chlorite and muscovite with discontinuous pods of albite associated with the muscovite zone. On the basis of trace element data the original ultramafite-schist contact is positioned between the present tremolite and chlorite zones.An experimental study of a metasomatic system was undertaken in an attempt to clarify diffusion relationships during the metasomatic event. To simulate the natural event, ultramafic and quartzofeldspathic natural starting materials were tightly packed in a gold tube with a graphite layer between to allow later identification of the original lithological interface. Run conditions were 450° C at 2 kb for 40 days. Phase dissolution and formation were analysed petrographically and component migration was examined with the electron-microprobe. The following hierarchical scheme of component migration, phase dissolution and phase formation is delineated: CO₂ migrates from the schist into the ultramafite forming first the antigorite-magnesite zone and then the magnesite-talc zone at higher values of CO₂. These zones are then partially overprinted by the formation of talc due to SiO₂ metasomatism. The SiO₂ is supplied from the schist by the dissolution of quartz and albite in the region adjacent to the ultramafite. The tremolite zone forms at the expense of the metasomatic talc zone upon the introduction of CaO from the schist into the ultramafite. Concurrent with tremolite formation, MgO migrates from the ultramafite into the schist to form the chlorite metasomatic zone. The growth of the chlorite zone causes dissolution of the pre-metasomatic micas and displaces K₂O from the chlorite zone further into the schist. Displaced K₂O and Na₂O are responsible for the formation of the muscovite zone and the albitite pods.     

Late Vistulian insect assemblages from Zabinko, western Poland

Insect analysis was carried out in deposits from a Late Vistulian site at Zabinko, western Poland. Geomorphological, lithostratigraphical and palaeobotanical investigations have been carried out earlier at the same section and published elsewhere. The analysed samples are dated from c. 12,600 to 12,200 BP. A total of 54 insect taxa were determined, the majority being Coleoptera. No major change in the insect fauna during this 400 years period could be detected from the study. The presence of specific phytophagus beetles suggests the same local vegetational environment as reconstructed from the plant macrofossil record, namely a shallow pool with a well-developed reed vegetation. The pool was situated in an open landscape with scattered trees and herb vegetation. The climatic reconstruction from the insect assemblages suggests a cool temperate climate with an average July temperature of 14–15C, During the same time period arctic/ksubarctic conditionsd, with mean July temperatures of c. 10–12C, prevailed in southernmost Scandinavia. The climatic amelioration in western Poland seems to have started possibl 500 years earlier than in southern Sweden.     

Chemographic analysis of metabasite assemblages from c central Scottish Highlands

From the observed textures and mineral associations, chemographic relations have been derived in isobaric T-X_CO2 space for the minerals actinolite, ankerite, calcite, chlorine, epidote, and hornblende in Scottish Dalradian metabasites from Central Perthshire. Mineralogical variations in the carbonate-bearing metabasites within the distances of 0.5-1 km or so, are attributed to varying partial pressures of CO₂ operating during metamorphism.     

Early cretaceous radiolarian assemblages from the East Sakhalin Mountains

Three-dimensional radiolarian skeletons isolated from rock matrix in HF solution and then studied under scanning electron microscope substantiate the Early Cretaceous age of volcanogenic-cherty deposits sampled from fragmentary rock successions of the East Sakhalin Mountains. Accordingly the Berriasian age is established for jasper packets formerly attributed to the Upper Paleozoic-Mesozoic Daldagan Group; the Valanginian radiolarians are identified in cherty rock intercalations in the Upper Paleozoic (?) Ivashkino Formation; the Berriasian-Barremian assemblage is macerated from cherty tuffites of the Jurassic-Cretaceous Ostraya Formation; and the Aptian-early Albian radiolarians are characteristic of tuffaceous cherty rocks sampled from the Cretaceous Khoe Formation of the Nabil Group. Photographic documentation of radiolarian skeletons specifies taxonomic composition and age of the Berriasian, Valanginian, Berriasian-Valanginian, Barremian, and Aptian-Albian radiolarian assemblages from the East Sakhalin Mountains, and their evolution as related to abiotic events is considered. Coexistence of Tethyan and Pacific species in the same rock samples evidence origin of radiolarian assemblages in an ecotone. Consequently, the assemblages are applicable for intra- and interregional correlations and paleogeographic reconstructions.     

Significance of the pyroxene chemistry from leucite-bearing and related assemblages

Summary The mineral chemistry of the pyroxene from representative suites of leucite-bearing and related assemblages occurring in south-west Uganda, Roman Region, Australia and Antarctica is considered in terms of some serial characteristics of the host rocks. The pyroxene compositions show distinct and systematic chemical variations, which are evaluated in terms of the ratios Ti/Al and (2–Si)/Al=Td, calculated from the structural formula. Both ratios generally increase from early- to late-crystallized pyroxene compositions but the variations are typical of individual rock series and depend on the level of alkalinity of the host rocks, i.e. (Na+K)/Al and the pressure under which the pyroxene crystallized. Low Ti/Al and Td values result largely from the influence of pressure, while Ti/Al>0.5 and Td>1.0 reflect the chemistry of the host rock, particulary in terms of high (Na+K)/Al ratio. Some experimental data bearing on the genetic interpretation of the pyroxene chemistry from the above assemblages are reappraised.

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Zur Bedeutung des Pyroxen-Chemismus in Leuzit-führenden und verwandten Gesteinen

Zusammenfassung Die Mineralchemie des Pyroxens aus repräsentativen Leuzit-führenden und verwandten Gesteinen in Südwest-Uganda, in der Romana, in Australien und in der Antarktis steht in Beziehung zur Charakteristik der Muttergesteine. Die Zusammensetzungen der Pyroxene zeigen klare und systematische chemische Variationen, die auf der Basis der aus der Strukturformel berechneten Verhältniszahlen Ti/Al und (2-Si)/Al=Td bewertet werden. Beide Verhältniszahlen nehmen grundsätzlich von früh- zu spätkristallisierten Pyroxenen zu, jedoch sind diese Variationen typisch für bestimmte Gesteinsserien und abhängig vom Grad der Alkalinität des Muttergesteins, d.h. (Na+K)/Al und vom Druck unter dem der Pyroxen kristallisierte. Niedrige Ti/Al und Td-Werte resultieren vor allem aus dem Einfluß des Druckes, während Ti/Al>0,5 und Td>1,0 die chemische Zusammensetzung des Muttergesteins reflektieren, besonders im Hinblick auf hohe Na+K/Al-Verhältnisse. Einige experimentelle Daten zur genetischen Interpretation des Pyroxen-Chemismus aus den oben genannten Vorkommen werden im Lichte dieser neuen Ergebnisse betrachtet.

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