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Mixed Assemblage (mixed + assemblage)

Distribution by Scientific Domains
Life Sciences60%
Earth and Environmental Science40%

Selected Abstracts

Ostracode faunas of bottom sediments from the continental shelf, south Marmara Sea, NW Turkey, and their comparison with other shelf environments in the Mediterranean and Aegean regions

GEOLOGICAL JOURNAL, Issue 2 2001
Atike Nazik
Abstract This study describes the ostracode faunal composition and distribution on the continental shelf of the southern Marmara Sea in Turkey. Twenty-three bottom samples were collected from the shelf. These samples are characterized by silt-clay (mud), sand and gravel in the studied area. A total of 46 species belonging to 32 genera were determined from these samples. Seven species were dominant from 46 ostracode species. Three assemblages were identified by their dominant species. These are characterized by: Costa edwardsii (Roemer); a mixed assemblage which consists of Cytheridea neapolitana Kollmann, Pterygocythereis ceratoptera (Bosquet), Tegmenia rugosa (Costa), Acanthocythereis hystrix (Reuss) and Xestoleberis communis (G.W. Müller); and Aurila convexa (Baird). The relations between the dominant species, lithology and CaCO3 concentration have been investigated, and the results are compared with other shelf environments within the Mediterranean and Aegean regions. Pterygocythereis, Costa, Tegmenia and Cytheridea are abundant in muddy substrates; Aurila and Acanthocythereis are abundant in sandy substrates. Acanthocythereis hystrix (Reuss), Aurila convexa (Baird), Buntonia subulata Ruggieri, Carinocythereis antiquata (Baird), Carinocythereis carinata (Roemer), Costa batei (Brady), Costa edwardsii (Roemer), Cytheridea neapolitana Kollmann, Celtia quadridentata (Baird), Loxoconcha rhomboidea (Fischer), Pterygocythereis jonesii (Baird) and Semicytherura acuticostata (Sars) are common, and similar species are recorded from other continental shelves of the Mediterranean. Copyright © 2001 John Wiley & Sons, Ltd. [source]

SHIFT FROM CHLOROPHYTES TO CYANOBACTERIA IN BENTHIC MACROALGAE ALONG A GRADIENT OF NITRATE DEPLETION,

JOURNAL OF PHYCOLOGY, Issue 1 2008
Chantal Vis
A survey of the spatial distribution of benthic macroalgae in a fluvial lake of the St. Lawrence River (Lake Saint-Pierre, Quebec, Canada) revealed a shift in composition from chlorophytes to cyanobacteria along the flow path of nutrient-rich waters originating from tributaries draining farmlands. The link between this shift and changes in water quality characteristics was investigated by sampling at 10 sites along a 15 km transect. Conductivity, current, light extinction, total phosphorus (TP; >25 ,g P · L,1), and ammonium (8,21 ,g N · L,1) remained fairly constant along the transect in contrast to nitrate concentrations, which fell sharply. Filamentous and colonial chlorophytes [Cladophora sp. and Hydrodictyon reticulatum (L.) Bory] dominated in the first 5 km where nitrate concentrations were >240 ,g N · L,1. A mixed assemblage of chlorophytes and cyanobacteria characterized a 1 km transition zone where nitrate decreased to 40,80 ,g N · L,1. In the last section of the transect, nitrate concentrations dropped below 10 ,g N · L,1, and cyanobacteria (benthic filamentous mats of Lyngbya wollei Farl. ex Gomont and epiphytic colonies of Gloeotrichia) dominated the benthic community. The predominance of nitrogen-fixing, potentially toxic cyanobacteria likely resulted from excessive nutrient loads and may affect nutrient and trophic dynamics in the river. [source]

Review of the El Soplao Amber Outcrop, Early Cretaceous of Cantabria, Spain

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 4 2010
Marķa NAJARRO
Abstract: El Soplao outcrop, an Early Cretaceous amber deposit recently discovered in northern Spain (Cantabria), has been shown to be the largest site of amber with arthropod inclusions that has been found in Spain so far. Relevant data provided herein for biogeochemistry of the amber, palynology, taphonomy and arthropod bioinclusions complement those previously published. This set of data suggests at least two botanical sources for the amber of El Soplao deposit. The ńrst (type A amber) strongly supports a source related to Cheirolepidiaceae, and the second (type B amber) shows non-specific conifer biomarkers. Comparison of molecular composition of type A amber with Frenelopsis leaves (Cheirolepidiaceae) strongly suggests a biochemical affinity and a common botanical origin. A preliminary palynologlcal study indicates a regional high taxonomical diversity, mainly of pteridophyte spores and gymnosperm pollen grains. According to the preliminary palynologlcal data, the region was inhabited by conifer forests adapted to a dry season under a subtropical climate. The abundant charcoalified wood associated with the amber in the same beds is evidence of paleofires that most likely promoted both the resin production and an intensive erosion of the litter, and subsequent great accumulation of amber plus plant cuticles. In addition, for the first time in the fossil record, charcoalified plant fibers as bioinclusions in amber are reported. Other relevant taphonomic data are the exceptional presence of serpulids and bryozoans on the surfaces of some amber pieces indicating both a long exposure on marine or brackish-water and a mixed assemblage of amber. Lastly, new findings of insect bioinclusions, some of them uncommon in the fossil record or showing remarkable adaptations, are reported. In conclusion, a documented scenario for the origin of the El Soplao amber outcrop is provided. [source]

Community heterogeneity and single-cell digestive activity of estuarine heterotrophic nanoflagellates assessed using lysotracker and flow cytometry

ENVIRONMENTAL MICROBIOLOGY, Issue 7 2010
Eva Sintes
Summary Heterotrophic nanoflagellates (HNFs) are an essential component of all aquatic microbial food webs, and yet the exploration of the numerical and single-cell responses of these organisms in mixed assemblages still represents a major technical challenge. LysoTracker Green staining combined with flow cytometry was recently proposed for the enumeration of aquatic HNFs. Here we show that LysoTracker Green not only allows the enumeration of HNFs in estuarine samples with a wide range of HNF abundances, but also allows the discrimination of distinct HNF populations in mixed assemblages. In addition, the resulting cytometric parameters can be used to characterize cell size and the level of activity of the cells in the different populations that are detected. LysoTracker Green accumulates preferentially in lysosomes, and we demonstrate that the green fluorescence emission from HNF cells stained with LysoTracker strongly correlates with cell-specific ,-glucosaminidase (,-Gam) activity, a key digestive enzyme of lysosomal origin in eukaryotic cells. Our results further show that different populations that develop in estuarine regrowth cultures are characterized by different intrinsic ranges of size and of feeding activity, and that there is a wide range of single-cell responses within these HNF populations. We found a large degree of uncoupling between cell size and feeding activity, both between and within HNF populations, and there appears to be no clear allometric scaling of feeding activity. We were able to reconstruct the succession of distinct HNF populations that developed during the regrowth experiments, and explore the complex interactions that occurred between numerical (change in abundance of the cytometric populations) and single-cell HNF responses. [source]

Evidence for bias in estimates of local genetic structure due to sampling scheme

ANIMAL CONSERVATION, Issue 3 2006
E. K. Latch
Abstract Traditional population genetic analyses typically seek to characterize the genetic substructure caused by the nonrandom distribution of individuals. However, the genetic structuring of adult populations often does not remain constant over time, and may vary relative to season or life-history stages. Estimates of genetic structure may be biased if samples are collected at a single point in time, and will reflect the social organization of the species at the time the samples were collected. The complex population structures exhibited by many migratory species, where temporal shifts in social organization correspond to a large-scale shift in geographic distribution, serve as examples of the importance that time of sampling can have on estimates of genetic structure. However, it is often fine-scale genetic structure that is crucial for defining practical units for conservation and management and it is at this scale that distributional shifts of organisms relative to the timing of sampling may have a profound yet unrecognized impact on our ability to interpret genetic data. In this study, we used the wild turkey to investigate the effects of sampling regime on estimates of genetic structure at local scales. Using mitochondrial sequence data, nuclear microsatellite data and allozyme data, we found significant genetic structuring among localized winter flocks of wild turkeys. Conversely, we found no evidence for genetic structure among sampling locations during the spring, when wild turkeys exist in mixed assemblages of genetically differentiated winter flocks. If the lack of detectable genetic structure among individuals is due to an admixture of social units as in the case of wild turkeys during the spring, then the FIS value rather than the FST value may be the more informative statistic in regard to the levels of genetic structure among population subunits. [source]