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Hindcast and near real-time monitoring of green macroalgae blooms in shallow coral reef lagoons using Sentinel-2 : a New-Caledonia case study
No full textDespite the necessary trade-offs between spatial and temporal resolution, remote sensing is an effective approach to monitor macroalgae blooms, understand their origins and anticipate their developments. Monitoring of small tropical lagoons is challenging because they require high resolutions. Since 2017, the Sentinel-2 satellites has provided new perspectives, and the feasibility of monitoring green algae blooms was investigated in this study. In the Poe-Gouaro-Deva lagoon, New Caledonia, recent Ulva blooms are the cause of significant nuisances when beaching. Spectral indices using the blue and green spectral bands were confronted with field observations of algal abundances using images concurrent with fieldwork. Depending on seabed compositions and types of correction applied to reflectance data, the spectral indices explained between 1 and 64.9% of variance. The models providing the best statistical fit were used to revisit the algal dynamics using Sentinel-2 data from January 2017 to December 2019, through two image segmentation approaches: unsupervised and supervised. The latter accurately reproduced the two algal blooms that occurred in the area in 2018. This paper demonstrates that Sentinel-2 data can be an effective source to hindcast and monitor the dynamics of green algae in shallow lagoons
Bottom trawling on a carbonate shelf : do we get what we see ?
No full textBottom trawling is a common fisheries method and also a widespread scientific sampling method for benthic and demersal species. Selectivity and catchability are usually estimated using different meshes and studies with alternative methods are rare. In this study, to improve the estimation of trawl selectivity, we compare bottom trawl catches and recordings made by a camera fitted on the top of the net. Scientific trawling was conducted along the Northeast Brazilian shelf, a typical carbonate shelf with presence of sponges, coralline bottoms and a high water visibility. In total, 23 taxa (19 species and four genera) were identified in the videos and 30 taxa (25 species and five genera) in the trawls, indicating a higher potential of trawling to record species richness. Overall, no significant differences were observed in the assemblage structure identified by trawling and underwater footages. However, divergences were observed in fish catchability between trawls and videos. Net sampling was more selective for fish with low swimming capacity, while species with shelter and fast swimming capacity seemed to be underestimated. Furthermore, underwater footages allowed for an assessment of the trawling impacts on erect sponges with the observation of the damage on large branching and tubular sponges. The vulnerability of those habitats that concentrate higher fish diversity to mechanical impact raise the need for creation of preventive measures to protect these sensitive areas from commercial fishing operations. The use of less destructive methods is an important survey alternative under special conditions, particularly in conservation areas. In this study the videos could not be used as a complete alternative for the trawls, which presented higher efficiency, however, videos had shown to be a useful complement. Possibly, the speed and height determined by the trawling operation affected the performance of video sampling, being performed in suboptimal conditions. Using dedicated video sampling, such as towed video, could significantly improve its efficiency and compensate the disadvantages observed from the videos
Temperature and soil management effects on carbon fluxes and priming effect intensity
No full textAny change in the intensity and sign of CO2 flux between soil and atmosphere is expected to have a significant impact on climate. The net emission of CO2 by soils depends on antagonistic processes: the persistence of dead plant matter and the mineralization of soil organic matter. These two processes are partly interdependent: their interaction is known as the "priming effect" (PE), i.e. the stimulation of the mineralization of stable soil organic matter by more labile fresh organic matter. Documenting the response of PE to global change is needed for predicting long term dynamics of ecosystems and climate change. We have tested the effects on PE of temperature, nutrient availability, biodegradibility of added organic matter (fresh vs. decomposed), soil cover (agricultural vs. forest soil) and interactions. Our results suggest that the biodegradability of plant debris (wheat straw, fresh or pre-decomposed) is the first determinant of the intensity of PE, far ahead of temperature and nutrients: fresh wheat straw addition induced up to 800% more CO2 emission than pre-decomposed one. The raise of temperature from 15 to 20 degrees C, increased basal soil organic matter mineralization by 38%, but had little effect on PE. Interactions between biodegradability of straw and the other factors showed that the agricultural soil was more responsive to all factors than the forest soil. We have shown in our study that the intensity of PE could be more dependent on soil cover and plant residue management than on other drivers of global change, particularly temperature and nutrients. There is an urgent need to assess the genericity of our results by testing other soil types and plant debris for a better integration of PE in models, and for identifying alternative land carbon management strategies for climate change mitigation
Genome skimming resolves the giant clam (Bivalvia : Cardiidae : Tridacninae) tree of life
No full textGiant clams are conspicuous bivalves inhabiting Indo-Pacific reefs. Since Rosewater’s seminal paper in 1965, the number of giant clam species described or resurrected has exactly doubled. The increased number of species reported and accessibility to genetic material of rare or uncommon species therefore call for a reappraisal of the phylogenetic relationships within the Tridacninae subfamily. Here, we aim to reconstruct the evolutionary relationships among all 12 extant species by performing a comprehensive phylogenetic analysis of mitochondrial genome and nuclear 18S rRNA data from a combination of genome skimming, Sanger sequencing and previously published sequences. Comparing the mitogenomes among Tridacninae species, we report two new findings: (1) the T. crocea mitogenome length obtained here (18,266 bp) is shorter than previously known, and (2) the mitochondrial gene order in T. crocea and T. squamosa differs from the other species. Our phylogeny based on a concatenated 16-gene dataset (15 mitochondrial markers and nuclear 18S rRNA) reveals highly supported relationships within and between the three subgenera, Tridacna (Tridacna), Tridacna (Persikima) and Tridacna (Chametrachea). Overall, the inclusion of new molecular markers greatly improves the confidence and support for the subfamily’s phylogeny. The availability of this comprehensive phylogenetic dataset serves as the foremost baseline of Tridacninae relationships to support future studies examining giant clam systematics, ecology and conservation
Plasmodium falciparum gametocyte carriage in symptomatic patients shows significant association with genetically diverse infections, anaemia, and asexual stage density
No full textBackgroundMulti-genotype malaria infections are frequent in endemic area, and people commonly harbour several genetically distinct Plasmodium falciparum variants. The influence of genetic multiplicity and whether some specific genetic variants are more or less likely to invest into gametocyte production is not clearly understood. This study explored host and parasite-related risk factors for gametocyte carriage, and the extent to which some specific P. falciparum genetic variants are associated with gametocyte carriage.MethodsGametocytes and asexual forms were detected by light microscopy on thick smears collected between 2010 and 2012 in Nanoro, Burkina Faso. Merozoite surface protein 1 and 2 were genotyped by nested PCR on clinical samples. Associations between gametocyte carriage and factors, including multiplicity of infection, parasite density, patient age, gender, haemoglobin (Hb) level, and body temperature were assessed. The relationship between the presence of a particular msp1 and msp2 genetic variants and gametocyte carriage was also explored.ResultsOf the 724 samples positive to P. falciparum and successfully genotyped, gametocytes were found in 48 samples (6.63%). There was no effect of patient gender, age and body temperature on gametocyte carriage. However, the probability of gametocyte carriage significantly increased with increasing values of multiplicity of infection (MOI). Furthermore, there was a negative association between parasite density and gametocyte carriage. MOI decreased with parasite density in gametocyte-negative patients, but increased in gametocyte carriers. The probability of gametocyte carriage decreased with Hb level. Finally, the genetic composition of the infection influenced gametocyte carriage. In particular, the presence of RO33 increased the odds of developing gametocytes by 2 while the other allelic families K1, MAD20, FC27, and 3D7 had no significant impact on the occurrence of gametocytes in infected patients.ConclusionThis study provides insight into potential factors influencing gametocyte production in symptomatic patients. The findings contribute to enhance understanding of risk factors associated with gametocyte carriage in humans.Trial registration NCT01232530
Insecticide resistance status of malaria vectors Anopheles gambiae (s.l.) of southwest Burkina Faso and residual efficacy of indoor residual spraying with microencapsulated pirimiphos-methyl insecticide
No full textBackgroundThe rapid spread of insecticide resistance in malaria vectors and the rebound in malaria cases observed recently in some endemic areas underscore the urgent need to evaluate and deploy new effective control interventions. A randomized control trial (RCT) was conducted with the aim to investigate the benefit of deploying complementary strategies, including indoor residual spraying (IRS) with pirimiphos-methyl in addition to long-lasting insecticidal nets (LLINs) in Diebougou, southwest Burkina Faso.MethodsWe measured the susceptibility of the Anopheles gambiae (s.l.) population from Diebougou to conventional insecticides. We further monitored the efficacy and residual activity of pirimiphos-methyl on both cement and mud walls using a laboratory susceptible strain (Kisumu) and the local An. gambiae (s.l.) population.ResultsAn. gambiae (s.l.) from Diebougou was resistant to DDT, pyrethroids (deltamethrin, permethrin and alphacypermethrin) and bendiocarb but showed susceptibility to organophosphates (pirimiphos-methyl and chlorpyrimiphos-methyl). A mixed-effect generalized linear model predicted that pirimiphos-methyl applied on cement or mud walls was effective for 210 days against the laboratory susceptible strain and 247 days against the local population. The residual efficacy of pirimiphos-methyl against the local population on walls made of mud was similar to that of cement (OR=0.792, [0.55-1.12], Tukey's test p-value=0.19).ConclusionsIf data on malaria transmission and malaria cases (as measured trough the RCT) are consistent with data on residual activity of pirimiphos-methyl regardless of the type of wall, one round of IRS with pirimiphos-methyl would have the potential to control malaria in a context of multi-resistant An. gambiae (s.l.) for at least 7 months
In the era of humanitarian crisis, young women continue to die in childbirth in Mali
No full textMaternal mortality occurs mostly in contexts of poverty and health system collapse. Mali has a very high maternal mortality rate and this extremely high mortality rate is due in part to longstanding constraints in maternal health services. The central region has been particularly affected by the humanitarian crisis in recent years, and maternal health has been aggravated by the conflict. Somine Dolo Hospital is located in Mopti, central region. In the last decade, a high number of pregnant or delivering women have died in this hospital. We conducted a retrospective and exhaustive study of maternal deaths occurring in Mopti hospital. Between 2007 and 2019, 420 women died, with an average of 32 deaths per year. The years 2014-2015 and the last 2 years have been particularly deadly, with 40 and 50 deaths in 2018 and 2019, respectively. The main causes were hypertensive disorders/eclampsia and haemorrhage. 80% of these women's deaths were preventable. Two major explanations result in these maternal deaths in Somine Dolo's hospital: first, a lack of accessible and safe blood, and second, the absence of a reference and evacuation referral system, all of which are aggravated by security issues in and around Mopti. Access to quality hospital care is in dire need in the Mopti region. There is an urgent need for a safe blood collection system and free of charge for pregnant women. We also strongly recommend that the referral/evacuation system be reinvigorated, and that universal health coverage be strengthened
Trace metal dynamics in an industrialized Brazilian river : a combined application of Zn isotopes, geochemical partitioning, and multivariate statistics
No full textThe Paraiba do Sul (PSR) and Guandu Rivers (GR) water diversion system (120 km long) is located in the main industrial pole of Brazil and supplies drinking water for 9.4 million people in the metropolitan region of Rio de Janeiro. This study aims to discern the trace metals dynamics in this complex aquatic system. We used a combined approach of geochemical tools such as geochemical partitioning, Zn isotopes signatures, and multivariate statistics. Zinc and Pb concentrations in Suspended Particulate Matter (SPM) and sediments were considerably higher in some sites. The sediment partition of As, Cr, and Cu revealed the residual fraction (F4) as the main fraction for these elements, indicating low mobility. Zinc and Pb were mostly associated with the exchangeable/carbonate (F1) and the reducible (F2) fractions, respectively, implying a higher susceptibility of these elements to being released from sediments. Zinc isotopic compositions of sediments and SPM fell in a binary mixing source process between lithogenic (delta Zn-66/64(JMC) approximate to + 0.30 parts per thousand) and anthropogenic (delta Zn-66/64(JMC) approximate to + 0.15 parts per thousand) end members. The lighter delta Zn-66/64(JMC) values accompanied by high Zn concentrations in exchangeable/carbonate fraction (ZnF1) enable the tracking of Zn anthropogenic sources in the studied rivers. Overall, the results indicated that Hg, Pb, and Zn had a dominant anthropogenic origin linked to the industrial activities, while As, Cr, and Cu were mainly associated with lithogenic sources. This work demonstrates how integrating geochemical tools is valuable for assessing geochemical processes and mixing source effects in anthropized river watersheds
Comparable canopy and soil free-living nitrogen fixation rates in a lowland tropical forest
No full textBiological nitrogen fixation (BNF) isa fundamental part of nitrogen cycling in tropical forests, yet little is known about the contribution made by free-living nitrogen fixers inhabiting the often-extensive forest canopy. We used the acetylene reduction assay, calibrated with N-15(2), to measure free-living BNF on forest canopy leaves, vascular epiphytes, bryophytes and canopy soil, as well as on the forest floor in leaf litter and soil. We used a combination of calculated and published component densities to upscale free-living BNF rates to the forest level. We found that bryophytes and leaves situated in the canopy in particular displayed high mass-based rates of freeliving BNF. Additionally, we calculated that nearly 2 kg of nitrogen enters the forest ecosystem through free-living BNF every year, 40% of which was fixed by the various canopy components. Our results reveal that in the studied tropical lowland forest a large part of the nitrogen input through free-living BNF stems from the canopy, but also that the total nitrogen inputs by free-living BNF are lower than previously thought and comparable to the inputs of reactive nitrogen by atmospheric deposition
Mid-infrared spectroscopy to trace biogeochemical changes of earthworm casts during ageing under field conditions
No full textEarthworm cast ageing controls soil ecosystem services such as carbon storage and nutrient availability. To test the hypothesis that biogeochemical changes during casts ageing can be traced by infrared spectroscopy, we collected topsoil aggregates and earthworm casts produced by the anecic earthworm Amynthas khami belonging to five distinct degradation stages in woodland in northern Vietnam. We analysed mid-infrared (MIR) spectra of both sample types using two approaches: (1) calculation of the proportion of aliphatic compounds and the humification index of organic matter (OM) using specific wavenumbers and (2) linear discriminant analysis (LDA) of the most important peaks and shoulders of the entire spectrum. Our results showed that aliphatic compound contribution to OM was similar and the humification index of OM lower (2-fold) in casts as compared to topsoil aggregates independent of their degradation stage. In contrast, LDA showed a continuous shift from fresh casts to aged casts and topsoil aggregates in agreement with biogeochemical changes of cast properties. We thus conclude that MIR analysis of bulk samples and LDA taking into account the absorbance intensity of most important wavenumbers is a promising tool to capture biogeochemical alterations of organic and mineral earthworm cast properties during ageing