Fine-scale mapping of vector habitats using very high resolution satellite imagery : a liver fluke case-study

The visualization of vector occurrence in space and time is an important aspect of studying vector-borne diseases. Detailed maps of possible vector habitats provide valuable information for the prediction of infection risk zones but are currently lacking for most parts of the world. Nonetheless, monitoring vector habitats from the finest scales up to farm level is of key importance to refine currently existing broad-scale infection risk models. Using Fasciola hepatica, a parasite liver fluke as a case in point, this study illustrates the potential of very high resolution (VHR) optical satellite imagery to efficiently and semi-automatically detect detailed vector habitats. A WorldView2 satellite image capable of <5m resolution was acquired in the spring of 2013 for the area around Bruges, Belgium, a region where dairy farms suffer from liver fluke infections transmitted by freshwater snails. The vector thrives in small water bodies (SWBs), such as ponds, ditches and other humid areas consisting of open water, aquatic vegetation and/or inundated grass. These water bodies can be as small as a few m(2) and are most often not present on existing land cover maps because of their small size. We present a classification procedure based on object-based image analysis (OBIA) that proved valuable to detect SWBs at a fine scale in an operational and semi-automated way. The classification results were compared to field and other reference data such as existing broad-scale maps and expert knowledge. Overall, the SWB detection accuracy reached up to 87%. The resulting fine-scale SWB map can be used as input for spatial distribution modelling of the liver fluke snail vector to enable development of improved infection risk mapping and management advice adapted to specific, local farm situations

Conservation status of large branchiopods in the Western Cape, South Africa

Temporary wetlands are an ecologically and economically important habitat in South Africa. They harbor large branchiopods, known to be flagship species of nonpermanent aquatic habitats, and sensitive to land use changes. In this study we review the current status of large branchiopods in the Western Cape, a South African province subject to increasing agriculture and urbanization. We studied the species diversity and distribution of large branchiopods by sampling 58 temporary wetlands in an area covering about 30% of the Western Cape. Information obtained from field samples was supplemented by incubating resting egg banks from the sampled wetlands. Our data were compared with all known distribution records for large branchiopods in the target region. Based on this combined information, the International Union for the Conservation of Nature and Natural Resources (IUCN) Red List category was assessed for each species. Four of the eight large branchiopod species known to occur in the sampling area were collected. Of all wetlands sampled, 40% harbored large branchiopods. Most anostracan populations were small, and species co-occurred in only one wetland. From the entire Western Cape, 14 species have been recorded in the past. Two of these are already included in the IUCN Red List. Insufficient data are available to determine the IUCN Red Data Category of six other species. A large variation in the telsonic appendages of S. dendyi was found across the studied area. In view of possible ongoing speciation and subsequent radiation, individual populations need protection. Since little information is available, it is difficult to evaluate recent changes in the conservation status of large branchiopods. Their populations are currently very low and have probably diminished in the last few decades. More knowledge about the functioning of temporary systems is needed to manage these vulnerable habitats and conserve their threatened species.Web of Scienc

Remote sensing and wetland ecology: a South African case study

Remote sensing offers a cost efficient means for identifying and monitoring wetlands over a large area and at different moments in time. In this study, we aim at providing ecologically relevant information on characteristics of temporary and permanent isolated open water wetlands, obtained by standard techniques and relatively cheap imagery. The number, surface area, nearest distance, and dynamics of isolated temporary and permanent wetlands were determined for the Western Cape, South Africa. Open water bodies (wetlands) were mapped from seven Landsat images (acquired during 1987 – 2002) using supervised maximum likelihood classification. This study has indicated that ecologically relevant data can be generated for the larger wetlands through relatively cheap imagery and standard techniques, despite the relatively low resolution of Landsat and Envisat imagery. For the characterisation of very small wetlands, high spatial resolution optical or radar images are needed. This study exemplifies the benefits of integrating remote sensing and ecology and hence stimulates interdisciplinary research of isolated wetlands

Status en ecologie van tijdelijke wetlands in de Westelijke Kaap, Zuid-Afrika.

Tijdelijke wetlands hebben een hoge ecologische waarde en oefenen belangrijke ecosysteem functies uit, maar zijn echter wereldwijd bedreigd. De status en structurerende processen van deze systemen zijn grotendeels ongekend, ondanks dat deze kennis nodig is voor het opstellen van goede beheersmaatregelen. Deze thesis tracht informatie in te winnen betreffende de huidige en vroegere status en de natuurwaarde van wetlands in de Westelijke Kaap (Zuid-Afrika), a.h.v. teledetectie technieken enerzijds en vlaggenschipgroepen anderzijds. Bovendien worden de ecologische processen die werkzaam zijn in deze systemen onderzocht. Om deze doelstellingen na te streven, werden satellietbeelden van de Westelijke Kaap geclassificeerd en het voorkomen en de evolutie van wetlands over de laatste twintig jaar bepaald. Vervolgens werden in de winter van 2004 tijdelijke wetlands bemonsterd afkomstig van zeven regio s in de Westelijke Kaap. Eén regio werd een tweede maal onderzocht in de winter van 2005. De status van grote branchiopoden werd bepaald a.h.v. een literatuurstudie en veldgegevens uit 2004. De belangrijkste omgevingsvariabelen (hydro-morfometrie, fysico-chemie en vegetatie) en diversiteitspatronen werden tevens onderzocht.Een relatief groot aantal tijdelijke en permanente wetlands werd gedetecteerd in de Westelijke Kaap (gemiddeld 0.23 wetlands per km&sup2; in de winter en gemiddeld 0.09 wetlands per km&sup2; in de zomer). Tegen de verwachtingen in werd geen daling in het aantal wetlands waargenomen over de jaren. Dit stemt immers niet overeen met het verlies aan wetlands over grote delen van de wereld. Dit afwijkend patroon kan het gevolg zijn van de relatief lage resolutie van de geclassificeerde satellietbeelden (ongeveer 30 bij 30 meter), de invloed van regenval op het vullingspatroon van de wetlands en het construeren van nieuwe wetlands. Hoge resolutie beelden, zoals IKONOS-beelden, zouden waarschijnlijk meer gedetailleerde resultaten kunnen aanreiken.Verscheidene grote branchiopoden soorten zijn waarschijnlijk sterk bedreigd of reeds uitgestorven in de Westelijke Kaap. De achteruitgaande status van deze vlaggenschipsoorten suggereert dat hoogstwaarschijnlijk ook hun habitat is bedreigd. Habitat vernieling, verandering in landgebruik en klimaatsveranderingen vormen waarschijnlijk de belangrijkste bedreigingen voor deze systemen.Hydro-morfometrie, fysico-chemie en vegetatie karakteristieken waren belangrijke factoren welke de invertebratengemeenschappen beïnvloedden en zouden dus best alledrie in rekening worden gebracht bij het opstellen van beheersmaatregelen. Ondanks de multicollineariteit van de hydro-morfometrische variabelen in onze studiesystemen, waren oppervlakte en volume nog steeds significant gerelateerd aan de macroinvertebraten- gemeenschapsstructuur na correctie voor maximale diepte (uniek of individueel effect). Hydroperiode zelf (geschat door maximale diepte) had echter geen uniek effect op de gemeenshappen. Vegetatie had wel een uniek effect op de invertebraten, na correctie voor de gecorreleerde variabelen lokale diepte, wetland oppervlakte en hydroperiode. De hydro-morfometrische variabelen hadden ook een indirect effect op de invertebraten gemeenschappen, via hun effect op fysico-chemische variabelen. Het is echter niet duidelijk welke ecologische processen aan de basis liggen van deze relaties met invertebratengemeenschappen. A.h.v. uitgebreide experimenten op nieuw gecreëerde wetlands of gerichte veld monitoring kunnen de eigenlijke oorzaken van de relaties worden onderzocht.Volgens de Water Act van 1998 moeten zuidafrikaanse waterbronnen worden beschermd, gebruikt, ontwikkeld, bewaard, beheerd en gecontroleerd zodanig dat ook bescherming van aquatische ecosystemen en hun biologische diversiteit wordt in rekening gebracht. De Resource Directed Measures (RDM) vormen een handig middel om deze Water Act toe te passen. Onze studie vergaarde algemene informatie over tijdelijke wetland ecosystemen in de Westelijke Kaap, die kan worden gebruikt om de Water Act toe te passen.We besluiten dat deze studie waardevolle kennis heeft vergaard betreffende de huidige en vroegere status van wetlands en hun bewoners in de Westelijke Kaap. Onze resultaten duiden bovendien op een structurerend effect van hydro-morfometrie, fysico-chemie en macrofieten op de invertebratengemeenschappen in tijdelijke wetlands. Deze resultaten kunnen worden gebruikt om betrouwbare beheersmaatregelen op te stellen voor deze kwetsbare systemen in de Westelijke Kaap.status: publishe

Integrating remote sensing and wetland ecology : a case study on South African wetlands

Remote sensing is a valuable tool for wetland ecology and conservation. With this study, we aimed at providing relevant information on wetland characteristics, obtained by standard techniques and relatively cheap optical imagery. The number, surface area, distance, and dynamics of temporary and permanent wetlands were determined for the Western Cape, South Africa. These characteristics are important for the metacommunity structure of amphibians and invertebrates. Isolated open water wetlands were classified by supervised maximum likelihood classification on seven Landsat images (1987 - 2002). Imagery acquired in summer contained fewer wetlands than those acquired in winter. The number of winter wetlands showed an increasing trend over time, which was not significantly correlated with yearly rainfall. Most classified wetlands were smaller than 1.5 ha. The distance to the nearest-wetland was longer in winter. In comparison to temporary wetlands, fewer, but on average larger permanent wetlands were classified. The relatively high number of wetlands is essential for local and migrating wading birds. The many small observed wetlands could also serve as stepping-stones, important for species conservation. We conclude that through relatively cheap imagery and standard Geographical Information System (GIS) techniques, basic ecological data can be generated. However, the resolution of Landsat imagery is too low to detect small wetlands. High accuracy images (such as IKONOS) would give more detailed results, but the high cost and the lack of long term data are at present restricting factors for their use by ecologists

Modelling of coupled water transport and large deformation during dehydration of apple tissue

Water loss of fruit during storage has a large impact on fruit quality and shelf life and is essential to fruit drying. Dehydration of fruit tissues is often accompanied by large deformations. One-dimensional water transport and large deformation of cylindrical samples of apple tissue during dehydration were modeled by coupled mass transfer and mechanics and validated by calibrated X-ray CT measurements. Uni-axial compression-relaxation tests were carried out to determine the nonlinear viscoelastic properties of apple tissue. The Mooney-Rivlin and Yeoh hyperelastic potentials with three parameters were effective to reproduce the nonlinear behavior during the loading region. Maxwell model was successful to quantify the viscoelastic behavior of the tissue during stress relaxation. The nonlinear models were superior to linear elastic and viscoelastic models to predict deformation and water loss. The sensitivity of different model parameters using the nonlinear viscoelastic model using Yeoh hyperelastic potentials was studied. The model predictions proved to be more sensitive to water transport parameters than to the mechanical parameters. The large effect of relative humidity and temperature on the deformation of apple tissue was confirmed by this study. The validated model can be employed to better understand postharvest storage and drying processes of apple fruit and thus improve product quality in the cold chain. © 2012 Springer Science+Business Media, LLC.status: publishe

Longitudinal study on the temporal and micro-spatial distribution of Galba truncatula

Background: The trematode parasite Fasciola hepatica causes important economic losses in ruminants worldwide. Current spatial distribution models do not provide sufficient detail to support farm-specific control strategies. A technology to reliably assess the spatial distribution of intermediate host snail habitats on farms would be a major step forward to this respect. The aim of this study was to conduct a longitudinal field survey in Flanders (Belgium) to (i) characterise suitable small water bodies (SWB) for Galba truncatula and (ii) describe the population dynamics of G. truncatula. Methods: Four F. hepatica-infected farms from two distinct agricultural regions were examined for the abundance of G. truncatula from the beginning (April 2012) until the end (November 2012) of the grazing season. Per farm, 12 to 18 SWB were selected for monthly examination, using a 10 m transect analysis. Observations on G. truncatula abundance were coupled with meteorological and (micro-) environmental factors and the within-herd prevalence of F. hepatica using simple comparison or negative binomial regression models. Results: A total of 54 examined SWB were classified as a pond, ditch, trench, furrow or moist area. G. truncatula abundance was significantly associated with SWB-type, region and total monthly precipitation, but not with monthly temperature. The clear differences in G. truncatula abundance between the 2 studied regions did not result in comparable differences in F. hepatica prevalence in the cattle. Exploration of the relationship of G. truncatula abundance with (micro)-environmental variables revealed a positive association with soil and water pH and the occurrence of Ranunculus sp. and a negative association with mowed pastures, water temperature and presence of reed-like plant species. Conclusions: Farm-level predictions of G. truncatula risk and subsequent risk for F. hepatica occurrence would require a rainfall, soil type (representing the agricultural region) and SWB layer in a geographic information system. While rainfall and soil type information is easily accessible, the recent advances in very high spatial resolution cameras carried on board of satellites, planes or drones should allow the delineation of SWBs in the future

The 5S ribosomal RNA sequences of a red algal rhodoplast and a gymnosperm chloroplast : implications for the evolution of plastids and cyanobacteria

The 5S ribosomal RNA sequences have been determined for the rhodoplast of the red algaPorphyra umbilicalis and the chloroplast of the coniferJuniperus media. The 5S RNA sequence of theVicia faba chloroplast is corrected with respect to a previous report. A survey of the known sequences and secondary structures of 5S RNAs from plastids and cyanobacteria shows a close structural similarity between all 5S RNAs from land plant chloroplasts. The algal plastid 5S RNAs on the other hand show much more structural diversity and have certain structural features in common with bacterial 5S RNAs. A dendrogram constructed from the aligned sequences by a clustering algorithm points to a common ancestor for the present-living cyanobacteria and the land plant plastids. However, the algal plastids branch off at an early stage within the plastid-cyanobacteria cluster, before the divergence between cyanobacteria and land plant chloroplasts. This evolutionary picture points to the occurrence of multiple endosymbiotic events, with the ancestors of the present algal plastids already established as photosynthetic endosymbionts at a time when the ancestors of the present land plant chloroplasts were still free-living cells