77 research outputs found
Microzooplankton grazing and phytoplankton growth in marine mesocosms with increased CO2 levels
Microzooplankton grazing and algae growth responses to increasing pCO2 levels (350, 700 and 1050 μatm) were investigated in nitrate and phosphate fertilized mesocosms during the PeECE III experiment 2005. Grazing and growth rates were estimated by the dilution technique combined with taxon specific HPLC pigment analysis. Microzooplankton composition was determined by light microscopy. Despite a range of up to 3 times the present CO2 levels, there were no clear differences in any measured parameter between the different CO2 treatments. During days 3–9 of the experiment the algae community standing stock, measured as chlorophyll a (Chl-a), showed the highest instantaneous grow rates (k=0.37–0.99 d−1) and increased from ca. 2–3 to 6–12 μg l−1, in all mesocosms. Afterwards the phytoplankton standing stock decreased in all mesocosms until the end of the experiment. The microzooplankton standing stock, that was mainly constituted by dinoflagellates and ciliates, varied between 23 and 130 μg C l−1 (corresponding to 1.9 and 10.8 μmol C l−1), peaking on day 13–15, apparently responding to the phytoplankton development. Instantaneous Chl-a growth rates were generally higher than the grazing rates, indicating only a limited overall effect of microzooplankton grazing on the most dominant phytoplankton. Diatoms and prymnesiophytes were significantly grazed (12–43% of the standing stock d−1) only in the pre-bloom phase when they were in low numbers, and in the post-bloom phase when they were already affected by low nutrients and/or viral lysis. The cyanobacteria populations appeared more affected by microzooplankton grazing which generally removed 20–65% of the standing stock per day
Dissolution of coccolithophorid calcite by microzooplankton and copepod grazing
International audienceIndependent of the ongoing acidification of surface seawater, the majority of the calcium carbonate produced in the pelagial is dissolved by natural processes above the lysocline. We investigate to what extent grazing and passage of coccolithophorids through the guts of copepods and the food vacuoles of microzooplankton contribute to calcite dissolution. In laboratory experiments where the coccolithophorid Emiliania huxleyi was fed to the rotifer Brachionus plicatilis, the heterotrophic flagellate Oxyrrhis marina and the copepod Acartia tonsa, calcite dissolution rates of 45?55%, 37?53% and 5?22% of ingested calcite were found. We ascribe higher loss rates in microzooplankton food vacuoles as compared to copepod guts to the strongly acidic digestion and the individual packaging of algal cells. In further experiments, specific rates of calcification and calcite dissolution were also measured in natural populations during the PeECE III mesocosm study under differing ambient pCO2 concentrations. Microzooplankton grazing accounted for between 27 and 70% of the dynamic calcite stock being lost per day, with no measurable effect of CO2 treatment. These measured calcite dissolution rates indicate that dissolution of calcite in the guts of microzooplankton and copepods can account for the calcite losses calculated for the global ocean using budget and model estimates
Copepod feeding and reproduction in relation to phytoplankton development during the PeECE III mesocosm experiment
International audienceWithin the frame of the Pelagic Ecosystem CO2 Enrichment (PeECE III) experiment, reproduction and feeding of the copepod Calanus finmarchicus was monitored in relation to phytoplankton development in two mesocosms, at present 1× (350 ?atm) and ca 3× present (1050 ?atm) CO2 concentrations, respectively. Both mesocosms showed rapid phytoplankton growth after the initial nutrient additions and reached maximum chlorophyll (Chl) a concentrations around day 10. Flow-cytometry and specific pigment analysis (HPLC-CHEMTAX), showed that diatoms and prymnesiophyceae (Emiliania huxleyi (Ehux) and other nanoplankton) dominated the biomass. Feeding and egg production rates of C. finmarchicus developed similarly in both mesocosms, and were positively correlated with Chla, Ehux, diatom and prymnesiophyceae concentrations. Although the total number of copepod nauplii recruited during the experiment was similar in 1× and 3×, significantly less nauplii were recruited in 3× during the peak of the bloom compared to in 1×. We conclude that the algae responsible for the higher biomass in 3× during the peak of the bloom (diatoms and Ehux), may have been relatively inferior food for C. finmarchicus naupliar recruitment, possibly due to a high C:N ratio (>8). Nevertheless, the 3 fold increase in CO2 concentration did not show any clear overall effect on bulk phytoplankton or zooplankton development over the whole experiment, suggesting a more complex coupling between increased CO2 and the nutritional status of the system
Zooplankton Biomass Depletion Event Reveals the Importance of Small Pelagic Fish Top-Down Control in the Western Mediterranean Coastal Waters
The influence of hydrochemistry and trophic conditions on the coastal zooplankton community’s biomass and metabolic activities was investigated along the Spanish Mediterranean coastal waters, from Algeciras Bay to Barcelona, from autumn 2011 to autumn 2012. Two hydrographic regions were differentiated: NW Alboran (ALB) and W Mediterranean (MED). Zooplankton metabolism was assessed from measurements of the electron transport system (ETS) and aminoacyl-tRNA synthetases (AARS) activities, as proxies for potential respiration and somatic growth, respectively. Zooplankton showed three to fivefold higher biomass in ALB than in MED during autumn 2011 and spring 2012. However, in autumn 2012, a drastic decrease in biomass standing stock was observed in ALB, with no significant differences between the two regions. This biomass depletion event was not associated with environmental variables, food availability or zooplankton metabolic rates, but coincided with a twofold peak of Sardina pilchardus landings in ALB. A reduced standing stock coupled with high zooplankton growth rates suggests mortality by predation as the main cause for the low zooplankton biomass typically observed in MED, and in ALB during autumn 2012.Versión del edito
The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory
The Photodetector Array Camera and Spectrometer (PACS) is one of the three
science instruments on ESA's far infrared and submillimetre observatory. It
employs two Ge:Ga photoconductor arrays (stressed and unstressed) with 16x25
pixels, each, and two filled silicon bolometer arrays with 16x32 and 32x64
pixels, respectively, to perform integral-field spectroscopy and imaging
photometry in the 60-210\mu\ m wavelength regime. In photometry mode, it
simultaneously images two bands, 60-85\mu\ m or 85-125\mu\m and 125-210\mu\ m,
over a field of view of ~1.75'x3.5', with close to Nyquist beam sampling in
each band. In spectroscopy mode, it images a field of 47"x47", resolved into
5x5 pixels, with an instantaneous spectral coverage of ~1500km/s and a spectral
resolution of ~175km/s. We summarise the design of the instrument, describe
observing modes, calibration, and data analysis methods, and present our
current assessment of the in-orbit performance of the instrument based on the
Performance Verification tests. PACS is fully operational, and the achieved
performance is close to or better than the pre-launch predictions
Intensive enteral nutrition is ineffective for individuals with severe alcoholic hepatitis treated with corticosteroids.
peer reviewedBACKGROUND & AIMS: Severe alcoholic hepatitis (AH) is a lifethreatening
disease for which adequate oral nutritional support
is recommended. We performed a randomized controlled trial to
determine whether the combination of corticosteroid and
intensive enteral nutrition therapy is more effective than corticosteroid
therapy alone in patients with severe AH. METHODS:
We enrolled 136 heavy consumers of alcohol (age, 18–75 y)
with recent onset of jaundice and biopsy-proven severe AH in
our study, performed at 18 hospitals in Belgium and 2 in
France, from February 2010 through February 2013. Subjects
were assigned randomly (1:1) to groups that received either
intensive enteral nutrition plus methylprednisolone or conventional
nutrition plus methylprednisolone (controls). In the
intensive enteral nutrition group, enteral nutrition was given
via feeding tube for 14 days. The primary end point was patient
survival for 6 months. RESULTS: In an intention-to-treat analysis,
we found no significant difference between groups in
6-month cumulative mortality: 44.4% of patients died in the
intensive enteral nutrition group (95% confidence interval [CI],
32.2%–55.9%) and 52.1% of controls died (95% CI, 39.4%–
63.4%) (P ¼ .406). The enteral feeding tube was withdrawn
prematurely from 48.5% of patients, and serious adverse
events considered to be related to enteral nutrition occurred in
5 patients. Regardless of group, a greater proportion of patients
with a daily calorie intake less than 21.5 kcal/kg/day died
(65.8%; 95% CI, 48.8–78.4) than patients with a higher intake
of calories (33.1%; 95% CI, 23.1%–43.4%) (P < .001).
CONCLUSIONS: In a randomized trial of patients with severe AH
treated with corticosteroids, we found that intensive enteral
nutrition was difficult to implement and did not increase survival.
However, low daily energy intake was associated with greater
mortality, so adequate nutritional intake should be a main goal for
treatment
A New Perceptual Bias Reveals Suboptimal Population Decoding of Sensory Responses
Several studies have reported optimal population decoding of sensory responses in two-alternative visual discrimination tasks. Such decoding involves integrating noisy neural responses into a more reliable representation of the likelihood that the stimuli under consideration evoked the observed responses. Importantly, an ideal observer must be able to evaluate likelihood with high precision and only consider the likelihood of the two relevant stimuli involved in the discrimination task. We report a new perceptual bias suggesting that observers read out the likelihood representation with remarkably low precision when discriminating grating spatial frequencies. Using spectrally filtered noise, we induced an asymmetry in the likelihood function of spatial frequency. This manipulation mainly affects the likelihood of spatial frequencies that are irrelevant to the task at hand. Nevertheless, we find a significant shift in perceived grating frequency, indicating that observers evaluate likelihoods of a broad range of irrelevant frequencies and discard prior knowledge of stimulus alternatives when performing two-alternative discrimination
Neuropixels 2.0: A miniaturized high-density probe for stable, long-term brain recordings
Measuring the dynamics of neural processing across time scales requires following the spiking of thousands of individual neurons over milliseconds and months. To address this need, we introduce the Neuropixels 2.0 probe together with newly designed analysis algorithms. The probe has more than 5000 sites and is miniaturized to facilitate chronic implants in small mammals and recording during unrestrained behavior. High-quality recordings over long time scales were reliably obtained in mice and rats in six laboratories. Improved site density and arrangement combined with newly created data processing methods enable automatic post hoc correction for brain movements, allowing recording from the same neurons for more than 2 months. These probes and algorithms enable stable recordings from thousands of sites during free behavior, even in small animals such as mice
Influence of the late winter bloom on migrant zooplankton metabolism and its implications on export fluxes.
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