Percorrer por autor "Martins, V."
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- Factors influencing recent benthic foraminifera distribution on the Guadiana shelf (Southwestern Iberia)Publication . Mendes, Isabel; Gonzalez, R.; Dias, João M. A.; Lobo, F.J.; Martins, V.Benthic foraminiferal assemblages in 24 sediment surface samples collected at water depths ranging from 9 to 103 m on the continental shelf off Guadiana River were analysed, leading to the identification of a total of 270 species. Cluster analyses performed on species with a relative abundance higher than 5% led to the identification of four assemblages. The shallowest assemblage, down to 12 m water depth, is represented by Ammonia beccarii, Asterigerinata mamila, Eggerelloides scaber, Mississipina concentrica, Planorbulina mediterranensis, Elphidium crispum and Quinqueloculina laevigata. A second assemblage between 12 and 40 m water depth is characterised by Bulimina elongata, Cribrononion gerthi and Nonion fabum. The assemblage between 40 and 95 m water depth is characterised by Bolivina dilatata, Epistominella vitrea, Bulimina aculeata, Bolivina ordinaria, Spiroloxostoma croarae and Nonionella iridea. Finally, below a depth of 95 m on the upper outer shelf, an assemblage exists characterised by Brizalina spathulata, Bulimina marginata, Cassidulina minuta, Brizalina subaenariensis, Cassidulina laevigata and Uvigerina peregrina. The spatial distribution of assemblages is closely associated with sea-bottom sedimentary environments and bathymetry. The number of benthic foraminiferal tests, and the distribution of several nearshore species within the two shallowest assemblages are clearly influenced by the outflow of the Guadiana Estuary and by local hydrodynamic conditions. The deeper water assemblages, on the other hand, were found to be more related to low levels of tidal energy, low oxygen environments associated to fine-grained sediments, and cold-water filaments related to seasonal upwelling.
- Genomic variability of prune dwarf virus as affected by agricultural practicePublication . Fonseca, Filomena; Neto, J. D.; Martins, V.; Nolasco, GustavoTwelve new sequences of the coat protein gene of Prune dwarf virus (PDV) variants, obtained from almond trees, are presented. Comparison with previously reported sequences of the same region, obtained from other hosts (plum, cherry and peach) revealed not only the existence of a wider range of variants of PDV than formerly predicted, but also the frequent presence of a mixture of variants in each sample. In spite of the heterogeneity found in almond, the amino acid composition of the domain at the N terminus of the coat protein maintained the potential to form an amphipathic helix, and hence the capacity to serve the previously suggested function of binding the viral RNA during particle formation. Except for synonymous substitutions, measures of nucleotide diversity calculated for the two groups, respectively 13 sequences from almond and 14 sequences from other hosts, were found to be significantly different, with the almond group showing a much higher variability. Analysis of the dendrogram constructed based in all 27 PDV CP sequences did not reveal host specificity, in agreement with previous findings. However, a clear divergence between almond and other hosts sequences could be found. It is discussed that the observed differences between almond and other hosts variants may derive from differences in agricultural practices.
- Occurrence of stem-pitting strains of Citrus tristeza virus in CroatiaPublication . Cerni, S.; Skoric, D.; Krajacic, M.; Gatin, Z.; Santos, C.; Martins, V.; Nolasco, GustavoCitrus is grown in Croatia (approximately 1,500 ha of citrus groves) on the Dalmatian Coast and Islands between 42 and 43°30'N. The major species, Citrus unshiu Marc. (Satsuma mandarin), is grafted on trifoliate rootstock. The presence of Citrus tristeza virus (CTV) in Satsumas in the Neretva Valley Region was previously reported (3). During the course of a biomolecular characterization of isolates from Croatia, 15 budsticks were collected from field- infected, enzyme-linked immunosorbent assay (ELISA)-positive sources during the autumn of 2003 near Kaštela, Split, Metković (Neretva Valley), and on the island of Vis. Isolates were propagated by graft transmission to Madam Vinous sweet orange (SwO) and maintained in an insect-proof greenhouse at 21 to 33° C.
- The response of benthic foraminifera to pollution and environmental stress in Ria de Aveiro (N Portugal)Publication . Martins, V.; Yamashita, C.; Sousa, S. H. M.; Martins, P.; Laut, L. L. M.; Figueira, R. C. L.; Mahiques, M. M.; Ferreira da Silva, E.; Dias, J. M. Alveirinho; Rocha, F.This work evaluates the quality of the sediment in Ria de Aveiro, a coastal lagoon located at N of Portugal that is under strong anthropic influence, and the effects of the contamination on benthic foraminifera. The initial approach for measuring pollution was done through the load pollution index (LPI), based on As, Cd, Cr, Cu, Ni, Pb and Zn concentrations, and determined by total digestion of the sediments (TDS). This information was complemented by conducting a metal fractionation technique (sequential chemical extraction - SCE) in some of the most contaminated samples in order to define the relevance of different metal bearing- phases (exchangeable cations adsorbed by clay and co-precipitated with carbonates, absorbed by organic matter and retained in the mineralogical phase) and to evaluate the toxic heavy metal availability. Multivariable statistical analyses were carried out taking into consideration the geochemical results, as well as the biotic (percentage of species/groups of species; foraminifer abundance and diversity) and abiotic variables, such as sediment content in mud, total organic carbon (TOC) and Eh. SCE results show that most of the element concentration in the sediments is retained in the resistant mineralogical phase. However, the higher bioavailability of some toxic elements, such as As, Cd, Cu, Hg, Ni, Pb and Zn, found in Laranjo Bay, Aveiro City, Aveiro Harbours and Espinheiro Channel, have a generic negative impact on benthic foraminifera of the Aveiro lagoon. Differential sensitivity of benthic foraminifera to high concentrations of heavy metals may exist. quinqueloculina seminulum, for instance, seems to be more tolerant to higher bioavailable concentrations of Pb and Cu than Ammonia tepida or Haynesina germanica. Both species were previously considered to be the most heavy metal-tolerant foraminifer species. This study confirmed the use of benthic foraminifera as an important tool for the evaluation of the environmental quality of an ecosystem and for monitoring and restoring it.