Zooplankton Feeding Ecology: Grazing by Marine Copepods and Cladocerans upon Phytoplankton and Cyanobacteria from Kingston Harbour, Jamaica     

Jefferson T.  Turner  Russell R.  Hopcroft  Jean A.  Lincoln  Cameran Sassman  Huestis  Patricia A.  Tester John c.  Roff 《Marine Ecology》1998,19(3):195-208

Abstract. Grazing by the copepods Temora turbinata and Acartia lilljeborgii and the marine cladoceran Penilia avirostris on natural phytoplankton and cyanobacteria assemblages from Kingston Harbour. Jamaica, was examined in summer 1992. Food assemblages were often dominated by an unidentified filamentous cyanobacterium. with abundances of up to 1.16 × 10⁴ filaments. ml^-1. Other abundant phytoplankters included microflagellates and diatoms of the genus Niteschia. Mean clearance rates for the entire food assemblage ranged from 0.10 to 2.41 ml animal^-1. h^-1, although most mean clearance rates were between 0.5 and 1.5 ml. animal^-1 h^-1. Patterns of selection of different food items by various grazers on different dates were variable and inconsistent. Microscopic measurements revealed that cyanobacterial filament lengths were shorter in grazed than initial aliquots during a cyanobacterium bloom in August. This suggests that grazers reduced lengths of many filaments by biting off portions, in addition to consuming entire filaments. Such ‘filament clipping’ of cyanobacteria filaments has been recorded previously in freshwater studies and suggests that grazers impact a larger portion of the phytoplankton assemblage than is accounted for by ingestion and clearance rates based only upon removal of filaments. Grazers exhibited no adverse effects from consuming cyanobacteria. Cyanobacterkd are often considered to be toxic or of poor food quality for planktonic grazers. but due to the high abundance and dominance of filamentous cyanobacteria in Kingston Harbour. if these cyanobacteria were ungrazed. there would at times be little alternative phytoplankton food for copepods and cladocerans. Our results suggest that the trophic role of tilamentous cyanobacteria in pelagic food webs of the tropical ocean should be further investigated and possibly reconsidered.  相似文献   

Study of the effect of temperature, irradiance and salinity on growth and yessotoxin production by the dinoflagellate Protoceratium reticulatum in culture by using a kinetic and factorial approach     

Paz B  Vázquez JA  Riobó P  Franco JM 《Marine environmental research》2006,62(4):286-300

A complete first order orthogonal plan was used to optimize the growth and the production of yessotoxin (YTX) by the dinoflagellate Protoceratium reticulatum in culture by controlling salinity, temperature and irradiance. Initially, an approach to the kinetic data of cellular density and YTX production for each one of the experimental design conditions was performed. The P. reticulatum growth and YTX production were fitted to logistical equations and to a first-order kinetic model, respectively. The parameters obtained from this adjustment were used as dependent variables for the formulation of the empirical equations of the factorial design tested. The results showed that in practically all the cases for both, P. reticulatum growth and YTX production, irradiance is the primary independent variable and has a positive effect in the range 50-90 micromol photons m(-2) s(-1). Additionally, in certain specific cases, temperature reveals significant positive effects when maintained between 15 and 23 degrees C and salinity in the range of 20-34 displays negative effects. Despite the narrow ranges used in the work, results showed the suitability of factorial analysis to evaluate the optimal conditions for growth and yessotoxin production by the dinoflagellate P. reticulatum.  相似文献   

Time variant analysis of geomagnetic signals describes the volcanic activity of Mt. Etna between early 2000 and late 2002     

Maurizio Fedi  Lorenzo Cascone  Ciro Del Negro  Mauro La Manna 《Earth and Planetary Science Letters》2008,269(1-2):155-163

Volcanomagnetic anomalies have been mostly observed during strong eruptions. Our aim is to improve the geomagnetic data analysis to evidence the anomalies occurring in a larger time span, especially in the phases preceding the eruptive events. We developed a time variant statistical approach and applied it to the 2000–2002 Etna geomagnetic temporal series. It is based on an algorithm that statistically predicts the geomagnetic field at the station on the volcanic edifice by that recorded at the remote one. In such a way a number of significant changes in the time series (called statistical innovations), marking the local magnetic field change, were detected. The distribution of such statistical innovations accurately describes the Etna volcanic evolution: we note a progressive increase of the innovation occurrence as the eruptive cycles were approaching and only few and weak innovations at times between the various eruptive cycles. The significance of this analysis is further confirmed by the close agreement among the mean square prediction error, strain release and the volcanic activity behavior. On the contrary, the geomagnetic field at a single station or its difference at two stations do not have any clear correlation with other measured physical quantities. The complex pattern of the prediction error was also investigated by a multifractal analysis. We found that the Holder regularity increases with the intensification of the volcanic activity, implying that innovations tend to be less sporadic and correlated during the major volcanic phases.  相似文献   

The selection of filters for reduction of optical contamination in astronomical CCD X-ray images     

N. La Palombara  A. J. Court  G. F. Bignami 《Experimental Astronomy》1994,5(3-4):221-246

The European Photon Imaging Camera(EPIC), is the X-ray imaging and medium spectroscopy instrument for theESA X-ray Multi Mirror telescope(XMM) mission. TheCCD detectors to be used in the three focal plane cameras will provide images in the energy band from 0.1 to 10 keV. However, spectral studies may be compromised by low energy, optical photon contamination. In order to reduce this effect, a number of filters will be incorporated onto a rotating mechanism in the camera head. The filters will be chosen to provide a significant reduction in the optical contamination from a source whilst minimising the attenuation of the X-ray flux. Four commercial filters are described here and their effects on calculated typical source fluxes evaluated. In addition, two alternative filter designs are described and their effects on a simulated source spectra are debated. In both cases, particular attention is given to the problem of maintaining high sensitivity at soft X-ray energies (less than 2 keV).  相似文献   

Distribution, abundance, and growth of larval tautog, Tautoga onitis, in Buzzards Bay, Massachusetts, USA     

David A. Gauthier  Jean A. Lincoln  & Jefferson T. Turner 《Marine Ecology》2008,29(1):76-88

Tautog, Tautoga onitis, is an abundant species of fish in estuaries of the northeastern United States. Planktonic tautog larvae are abundant in summer in these estuaries, but there is little information on rates of growth of tautog larvae feeding on natural assemblages of food in the plankton. We examined abundance and growth of larval tautog and environmental factors during weekly sampling at three sites along a nearshore‐to‐offshore transect in Buzzards Bay, Massachusetts, USA during summer 1994. This is the first study of a robust sample size (336 larvae) to estimate growth rates of field‐caught planktonic tautog larvae feeding on natural diets, using the otolith daily‐growth‐increment method. The study was over the entire summer period when tautog larvae were in the plankton. The sampling sites contrasted in several environmental variables including temperature, dissolved oxygen (DO), and chlorophyll a concentration. There was a temporal progression in the abundance of tautog larvae over the summer, in relation to location and temperature. Tautog larvae were first present nearshore, with a pronounced peak in abundance occurring at the nearshore sites during the last 2 weeks in June. Larvae were absent at this time further offshore. From late June through August, larval abundance progressively decreased nearshore, but increased offshore although never approaching the abundance levels observed at the nearshore sites. The distribution and abundance of tautog larvae appeared to be related to a nearshore‐to‐offshore seasonal warming trend and a nearshore decrease in DO. Otoliths from 336 larvae ranging from 2.3 to 7.7 mm standard length had otolith increment counts ranging from 0 to 19 increments. Growth of larval tautog was estimated at 0.23 mm·day^?1, and length of larvae prior to first increment formation was estimated at 2.8 mm indicating that first increment formation occurs 3–4 days after hatching at 2.2 mm. Despite spatial and temporal differences in environmental factors, there were no significant differences in growth rates at any of three given sites over time, or between sites. Because larval presence only occurred at a narrow range of temperature (17–23.5 °C) and DO (6.5–9.3 mg·l^?1), in situ differences in growth did not appear to be because of differences in larval distribution and abundance patterns relative to these parameters.  相似文献   

Variability and spectral energy distributions of low-luminosity active galactic nuclei: a simultaneous X-ray/UV look with Swift     

E. Pian  P. Romano  D. Maoz  A. Cucchiara  C. Pagani  V. La Parola 《Monthly notices of the Royal Astronomical Society》2010,401(1):677-686

We have observed four low-luminosity active galactic nuclei (AGNs) classified as type 1 Low-Ionization Nuclear Emission-Line Regions (LINERs) with the X-Ray Telescope (XRT) and the Ultraviolet–Optical Telescope (UVOT) onboard Swift , in an attempt to clarify the main powering mechanism of this class of nearby sources. Among our targets, we detect X-ray variability in NGC 3998 for the first time. The light curves of this object reveal variations of up to 30 per cent amplitude in half a day, with no significant spectral variability on this time-scale. We also observe a decrease of ∼30 per cent over 9 d, with significant spectral softening. Moreover, the X-ray flux is ∼40 per cent lower than observed in previous years. Variability is detected in M81 as well, at levels comparable to those reported previously: a flux increase in the hard X-rays (1–10 keV) of 30 per cent in ∼3 h and variations by up to a factor of 2 within a few years. This X-ray behaviour is similar to that of higher luminosity, Seyfert-type objects. Using previous high-angular-resolution imaging data from the Hubble Space Telescope ( HST ), we evaluate the diffuse UV emission due to the host galaxy and isolate the nuclear flux in our UVOT observations. All sources are detected in the UV band, at levels similar to those of the previous observations with HST . The XRT (0.2–10 keV) spectra are well described by single power laws and the UV-to-X-ray flux ratios are again consistent with those of Seyferts and radio-loud AGNs of higher luminosity. The similarity in X-ray variability and broad-band energy distributions suggests the presence of similar accretion and radiation processes in low- and high-luminosity AGNs.  相似文献   

Model-data comparisons for Titan's nightside ionosphere     

T.E. Cravens  I.P. Robertson  R.V. Yelle  A.J. Coates  K. Agren  V. De La Haye  F.M. Neubauer 《Icarus》2009,199(1):174-188

Solar and X-ray radiation and energetic plasma from Saturn's magnetosphere interact with the upper atmosphere producing an ionosphere at Titan. The highly coupled ionosphere and upper atmosphere system mediates the interaction between Titan and the external environment. A model of Titan's nightside ionosphere will be described and the results compared with data from the Ion and Neutral Mass Spectrometer (INMS) and the Langmuir probe (LP) part of the Radio and Plasma Wave (RPWS) experiment for the T5 and T21 nightside encounters of the Cassini Orbiter with Titan. Electron impact ionization associated with the precipitation of magnetospheric electrons into the upper atmosphere is assumed to be the source of the nightside ionosphere, at least for altitudes above 1000 km. Magnetospheric electron fluxes measured by the Cassini electron spectrometer (CAPS ELS) are used as an input for the model. The model is used to interpret the observed composition and structure of the T5 and T21 ionospheres. The densities of many ion species (e.g., CH⁺₅ and C₂H⁺₅) measured during T5 exhibit temporal and/or spatial variations apparently associated with variations in the fluxes of energetic electrons that precipitate into the atmosphere from Saturn's magnetosphere.  相似文献   

The Fountain Hills unique CB chondrite: Insights into thermal processes on the CB parent body     

Dante S. LAURETTA  Julia S. GOREVA  Dolores H. HILL  Marvin KILLGORE  Alyssa R. La BLUE  Andrew CAMPBELL  R. C. GREENWOOD  A. B. VERCHOVSKY  Ian A. FRANCHI 《Meteoritics & planetary science》2009,44(6):823-838

Abstract— We report the results of an extensive study of the Fountain Hills chondritic meteorite. This meteorite is closely related to the CB_a class. Mineral compositions and O‐isotopic ratios are indistinguishable from other members of this group. However, many features of Fountain Hills are distinct from the other CB chondrites. Fountain Hills contains 23 volume percent metal, significantly lower than other members of this class. In addition, Fountain Hills contains porphyritic chondrules, which are extremely rare in other CB_a chondrites. Fountain Hills does not appear to have experienced the extensive shock seen in other CB chondrites. The chondrule textures and lack of fine‐grained matrix suggests that Fountain Hills formed in a dust‐poor region of the early solar system by melting of solid precursors. Refractory siderophiles and lithophile elements are present in near‐CI abundances (within a factor of two, related to the enhancement of metal). Moderately volatile and highly volatile elements are significantly depleted in Fountain Hills. The abundances of refractory siderophile trace elements in metal grains are consistent with condensation from a gas that is reduced relative to solar composition and at relatively high pressures (10^?3bars). Fountain Hills experienced significant thermal metamorphism on its parent asteroid. Combining results from the chemical gradients in an isolated spinel grain with olivine‐spinel geothermometry suggests a peak temperature of metamorphism between 535 °C and 878 °C, similar to type‐4 ordinary chondrites.  相似文献   

Multiple flaring activity in the supergiant fast X-ray transient IGR J08408−4503 observed with Swift     

P. Romano  L. Sidoli  G. Cusumano  P. A. Evans  L. Ducci  H. A. Krimm  S. Vercellone  K. L. Page  A. P. Beardmore  D. N. Burrows  J. A. Kennea  N. Gehrels  V. La Parola  V. Mangano 《Monthly notices of the Royal Astronomical Society》2009,392(1):45-51

IGR  J08408−4503  is a supergiant fast X–ray transient discovered in 2006 with a confirmed association with a O8.5Ib(f) supergiant star, HD 74194. We report on the analysis of two outbursts caught by Swift /Burst Alert Telescope (BAT) on 2006 October 4 and 2008 July 5, and followed up at softer energies with Swift /X-ray Telescope (XRT). The 2008 XRT light curve shows a multiple-peaked structure with an initial bright flare that reached a flux of  ∼10⁻⁹ erg cm⁻² s⁻¹  (2–10 keV), followed by two equally bright flares within 75 ks. The spectral characteristics of the flares differ dramatically, with most of the difference, as derived via time-resolved spectroscopy, being due to absorbing column variations. We observe a gradual decrease in the N _H, derived with a fit using absorbed power-law model, as time passes. We interpret these N _H variations as due to an ionization effect produced by the first flare, resulting in a significant decrease in the measured column density towards the source. The durations of the flares as well as the times of the outbursts suggest that the orbital period is ∼35 d, if the flaring activity is interpreted within the framework of the Sidoli et al. model with the outbursts triggered by the neutron star passage inside an equatorial wind inclined with respect to the orbital plane.  相似文献   

On the origin of the scatter around the Fundamental Plane: correlations with stellar population parameters     

A. Gargiulo  C. P. Haines  P. Merluzzi  R. J. Smith  F. La Barbera  G. Busarello  J. R. Lucey  A. Mercurio  M. Capaccioli 《Monthly notices of the Royal Astronomical Society》2009,397(1):75-89

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