120 research outputs found
Loss of surficial sedimentary carbon stocks in seagrass meadows subjected to intensive clam harvesting
Seagrass carbon stocks are vulnerable to physical disturbance. We assessed the effect of clam harvesting on the
organic carbon (Corg) stocks in surface sediments in four intertidal Zostera noltei meadows on the Iberian Atlantic
coast (Spain and Portugal), by comparing undisturbed and harvested areas. We also monitored the spatial cover
of the meadows throughout the growing season. Sedimentary Corg content and Corg stocks were about four times
lower in intensively harvested areas than in control areas, but there were not differences between areas with low
harvesting pressure and control areas. Reductions of 53–85% in sedimentary Corg stocks of Z. noltei meadows
were caused by intensive clam harvesting. The effect of intensive clam harvesting on Corg stocks increased
throughout the growing season, but the area covered by the seagrass increased from 21 to 37%, suggesting rapid
recovery of seagrass canopies and potential recovery of sedimentary Corg stocks.info:eu-repo/semantics/publishedVersio
Effects of warming on biological interactions between clams and the seagrass Zostera noltei: A case study using open top chambers
Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGBivalves and seagrasses can interact through diverse environmentally-modulated mechanisms. To assess the
effects of climate warming on bivalve-seagrass interactions, we carried out a pioneering field experiment in
which open top chambers (OTCs) were used to increase air and sediment temperature in a shellfish bed in NW
Spain during two consecutive spring tides (16 days of exposure to OTCs). The temperature increase produced by
OTCs was significant, as observed in the daily maximum and mean temperature and in degree hours, although
the difference was greater in air and at the sediment surface (up to 8 ◦C and 3 ◦C, respectively) than at 5 cm depth
(up to 1 ◦C). Warming was less acute in boxes with the seagrass Zostera noltei, which acted as a thermal buffer,
reducing the mean temperature by 1 ◦C at the sediment surface in OTC boxes and control boxes (without OTCs).
Although the short-term increase in temperature did not greatly affect physiological responses of Z. noltei, the
carbohydrate reserves and nutrient content increased in the presence of clams. Growth of the native clam
Ruditapes decussatus was significantly slower in OTC boxes with bare sediment, and the seagrass thus buffered the
negative effect of warming on growth. The presence of Z. noltei may save clams from having to spend energy to
burrow deeper to encounter cooler conditions, leaving more energy available for growth. Conversely, growth of
the introduced clam R. philippinarum did not differ between habitats or treatments. Our findings confirm a twoway
facilitative interaction that may be particularly important in relation to the resilience of both species in the
current context of global warming.Ministerio de Ciencia e Innovación | Ref. RTI2018-095583-B-I00Xunta de Galicia-FEDER | Ref. ED431C 2021/42Xunta de Galicia | Ref. ED481A- 2020/199NASA | Ref. 80NSSC20K007
Hierarchical Stellar Structures in the Local Group Dwarf Galaxy NGC 6822
We present a comprehensive study of the star cluster population and the
hierarchical structure in the clustering of blue stars with ages <~ 500 Myr in
the Local Group dwarf irregular galaxy NGC 6822. Our observational material
comprises the most complete optical stellar catalog of the galaxy from imaging
with the Suprime-Cam at the 8.2-m SUBARU Telescope. We identify 47 distinct
star clusters with the application of the nearest-neighbor density method to
this catalog for a detection threshold of 3sigma above the average stellar
density. The size distribution of the detected clusters can be very well
approximated by a Gaussian with a peak at ~ 68 pc. Their cluster mass function
is fitted very well by a power-law with index alpha ~ 1.5 +/- 0.7, consistent
with other Local Group galaxies and the cluster initial mass function. The
application of the nearest-neighbor density method for various density
thresholds, other than 3sigma, enabled the identification of stellar
concentrations in various length-scales. The stellar density maps constructed
with this technique provide a direct proof of hierarchically structured stellar
concentrations in NGC 6822. We illustrate this hierarchy by the so-called
"dendrogram" of the detected stellar structures, which demonstrates that most
of the detected structures split up into several substructures over at least
three levels. We quantify the hierarchy of these structures with the use of the
minimum spanning tree method. The morphological hierarchy in stellar
clustering, which we observe in NGC 6822 resembles that of the turbulent
interstellar matter, suggesting that turbulence on pc- and kpc-scales has been
probably the major agent that regulated clustered star formation in NGC 6822.Comment: 18 pages in ApJ two-column format, 13 figure
Waist circumference percentiles for Hispanic-American children and comparison with other international references
Introduction Waist circumference (WC) constitutes an indirect measurement of central obesity in children and adolescents. Objective To provide percentiles of WC for Hispanic-American children and adolescents, and compare them with other international references. Materials and methods The sample comprised 13 289 healthy children between 6 and 18 years coming from public schools of middle and low socioeconomic levels in different parts of Argentina, Cuba, Spain, Mexico, and Venezuela. The LMS method to calculate WC percentiles was applied. Sex and age differences were assessed using Student'sttest and ANOVA (SPSS v.21.0). Comparisons were established with references from the United States, Colombia, India, China, Australia, Kuwait, Germany, Tunisia, Greece, and Portugal. Results WC increases with age in both sexes. Boys show higher WC in P3, P50, and P97. Comparison of 50th and 90th percentiles among populations from diverse sociocultural and geographical contexts shows high variability, not all justified by the measurement method. Discussion and conclusions Specific WC percentiles for sex and age, and P90 cut-off points are provided; these values are potentially useful to assess central obesity in Hispanic-American adolescent children
Cluster-formation in the Rosette molecular cloud at the junctions of filaments
For many years feedback processes generated by OB-stars in molecular clouds,
including expanding ionization fronts, stellar winds, or UV-radiation, have
been proposed to trigger subsequent star formation. However, hydrodynamic
models including radiation and gravity show that UV-illumination has little or
no impact on the global dynamical evolution of the cloud. The Rosette molecular
cloud, irradiated by the NGC2244 cluster, is a template region for triggered
star-formation, and we investigated its spatial and density structure by
applying a curvelet analysis, a filament-tracing algorithm (DisPerSE), and
probability density functions (PDFs) on Herschel column density maps, obtained
within the HOBYS key program. The analysis reveals not only the filamentary
structure of the cloud but also that all known infrared clusters except one lie
at junctions of filaments, as predicted by turbulence simulations. The PDFs of
sub-regions in the cloud show systematic differences. The two UV-exposed
regions have a double-peaked PDF we interprete as caused by shock compression.
The deviations of the PDF from the log-normal shape typically associated with
low- and high-mass star-forming regions at Av~3-4m and 8-10m, respectively, are
found here within the very same cloud. This shows that there is no fundamental
difference in the density structure of low- and high-mass star-forming regions.
We conclude that star-formation in Rosette - and probably in high-mass
star-forming clouds in general - is not globally triggered by the impact of
UV-radiation. Moreover, star formation takes place in filaments that arose from
the primordial turbulent structure built up during the formation of the cloud.
Clusters form at filament mergers, but star formation can be locally induced in
the direct interaction zone between an expanding HII--region and the molecular
cloud.Comment: A&A Letter, in pres
A large‑scale comparison of reproduction and recruitment of the stalked barnacle Pollicipes pollicipes across Europe
Understanding large-scale spatial and temporal patterns of marine populations is a central goal in ecology, which has received
renewed attention under climate change. However, few studies explore the large-scale dynamics of populations using standardized
protocols and during the same time frames. We studied the phenology and intensity of reproduction and recruitment
for the intertidal stalked barnacle Pollicipes pollicipes over an European scale and described their potential linkages with
environmental variables. This species supports profitable fisheries in the Iberian Peninsula (Spain and Portugal). In Brittany
(France), we had observed a significant lower reproductive effort (long non-breeding season, short breeding period in summer)
and low values of recruitment intensity. This pattern may be related to the fact that Brittany corresponds to the northern
limit of the distribution of this species in continental Europe. On the Iberian Peninsula, the most different region was Galicia
(Spain), with Asturias (Spain) and SW Portugal being more similar. In Galicia, we have observed a contradictory pattern
characterized by the absence of a non-breeding period and by a shorter recruitment season than observed in other Iberian
regions. Our results suggest that air temperature, SST and chlorophyll-a might be related to the variability in reproduction
and recruitment patterns of P. pollicipes. Moreover, spring and early summer upwelling in SW Portugal and Galicia might
be inhibiting recruitment in this period. At the northern limit, the expected increase in performance under climate change
might facilitate the recovery of populations after exploitation, increasing the resilience of the resource to fishing pressure
Cerebrovascular events and outcomes in hospitalized patients with COVID-19: The SVIN COVID-19 Multinational Registry
© 2020 World Stroke Organization.[Background]: Severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) has been associated with a significant risk of thrombotic events in critically ill patients.
[Aim]: To summarize the findings of a multinational observational cohort of patients with SARS-CoV-2 and cerebrovascular disease.
[Methods]: Retrospective observational cohort of consecutive adults evaluated in the emergency department and/or admitted with coronavirus disease 2019 (COVID-19) across 31 hospitals in four countries (1 February 2020–16 June 2020). The primary outcome was the incidence rate of cerebrovascular events, inclusive of acute ischemic stroke, intracranial hemorrhages (ICH), and cortical vein and/or sinus thrombosis (CVST).
[Results]: Of the 14,483 patients with laboratory-confirmed SARS-CoV-2, 172 were diagnosed with an acute cerebrovascular event (1.13% of cohort; 1130/100,000 patients, 95%CI 970–1320/100,000), 68/171 (40.5%) were female and 96/172 (55.8%) were between the ages 60 and 79 years. Of these, 156 had acute ischemic stroke (1.08%; 1080/100,000 95%CI 920–1260/100,000), 28 ICH (0.19%; 190/100,000 95%CI 130–280/100,000), and 3 with CVST (0.02%; 20/100,000, 95%CI 4–60/100,000). The in-hospital mortality rate for SARS-CoV-2-associated stroke was 38.1% and for ICH 58.3%. After adjusting for clustering by site and age, baseline stroke severity, and all predictors of in-hospital mortality found in univariate regression (p < 0.1: male sex, tobacco use, arrival by emergency medical services, lower platelet and lymphocyte counts, and intracranial occlusion), cryptogenic stroke mechanism (aOR 5.01, 95%CI 1.63–15.44, p < 0.01), older age (aOR 1.78, 95%CI 1.07–2.94, p ¼ 0.03), and lower lymphocyte count on admission (aOR 0.58, 95%CI 0.34–0.98, p ¼ 0.04) were the only independent predictors of mortality among patients with stroke and COVID-19.
[Conclusions]: COVID-19 is associated with a small but significant risk of clinically relevant cerebrovascular events, particularly ischemic stroke. The mortality rate is high for COVID-19-associated cerebrovascular complications; therefore, aggressive monitoring and early intervention should be pursued to mitigate poor outcomes
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