OBSERVATIONS ON NAVICULA THALLODES (BACILLARIOPHYCEAE), A BLADE‐FORMING DIATOM FROM THE BERING SEA1
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ABSTRACT A thallus‐forming diatom, Navicula thallodes Proschkina‐Lavrenko, previously known only from the original collection at Bering Island (U.S.S.R.), has been found at Amchitka Island in the Aleutians, Alaska. The most remarkable observation of the present report is that N. thallodes may form blades up to 50 cm long, which to our knowledge is the greatest length reported for a colonial diatom. SEM observations of this diatom are presented for the first time.Keywords:
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Low temperature scanning electron microscopy (LTSEM) was superior to freeze-drying and ambient SEM in preserving the fine structure of diatom assemblages inhabiting cohesive sediments. The accumulation of diatoms at the surface of the sediment, maintained in a tidal micro-ecosystem, was examined for the first time using LTSEM techniques. LTSEM revealed a low standing assemblage present on the sediment surface when exposed before dawn. There was a linear increase in the numbers of diatoms at the surface when photon flux densities increased above 0.5 μEm−2s−1. The first diatoms to migrate to the surface were species of Navicula and Nitzschia. After 4h there was a synchronous appearance of large numbers of Scoliopleura tumida at the surface. Data on the depth distribution of diatoms in the sediment, derived from sediment samples that had been frozen and then fractured, support the hypothesis that light is the factor controlling the onset of diatom migration and that different diatoms have different thresholds triggering their movement.
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This paper presents the epilithic diatom flora from rivers Vit and Osum. Twenty-eight sampling sites were chosen along the river catchments, from the springs to the inflows (the Danube River). A total of 114 diatom taxa (103 species and 11 varieties) from 36 genera were identified in the epilithon of the studied rivers. The epilithic diatom floras from rivers Vit and Osum had high floristic similarity, Cs = 0.737 (with 66 common spesies). To characterize the diatom distributional patterns, nonmetric multidimensional scaling was used Two types of diatom assemblages were found throughout the studied rivers. The diatom assemblages from the upper reaches of the studied rivers were dominated by Achnanthidium pyrenaicum, A. minutissimum, Encyonema minutum, E. silesiacum, Gomphonema olivaceum, G. pumilum, Reimeria sinuata, Amphora pediculus, and Cocconeis pediculus. The diatom assemblages found in the lower reaches of the studied rivers were dominated by Navicula cryptotenella, N. lanceolata, Eolimna subminuscula, Mayamaea atomus, M. atomus var. permitis, Amphora pediculus, Cocconeis placentula and varieties, Nitzschia capitellata, N. dissipata, N. palea, N. incospicua, and Surirella brebissonii.
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As High Arctic environments are particularly sensitive to global and regional climate changes, a growing number of studies have focused on that region. It has been shown that living and fossil diatoms can be successfully used to track environmental changes in polar habitats. Nevertheless, the diatom flora of many Arctic areas remains unknown. The present study set out to examine the diatom flora in the rarely visited and near-pristine zone of northern Spitsbergen. Examination by light and scanning electron microscopy of 25 sediment samples, collected in fjords, tidal plains and lakes, indicated significant differences between the diatom assemblages identified in lakes located within different fjord watersheds. Altogether, 96 diatom taxa (46 genera) were found. The most abundant species (Achnanthidium minutissimum, Staurosirella pinnata and Nitzschia alpina) occurred in at least eight of the 11 investigated lakes. Assemblages from the Woodfjorden region were characterized by the presence of Cavinula pseudoscutiformis and Encyonema reichardtii, along with Navicula spp., which coincided with relatively low conductivity (34-58.7 µS cm-1) and near-neutral pH (7.2-7.5). Diatom assemblages found in the Wijdefjorden area were typically characterized by Denticula kuetzingii and Nitzschia inconspicua, with these lakes generally having higher water conductivity (>184 µS cm-1) and pH (7.5-8.1) conditions. Conductivity, biogenic silica concentration and water temperature were indicated as significant predictors of diatom community species composition and structure. No diatom frustules were found in fjord and tidal plain sediments. The effects of selected environmental factors on diatom assemblage formation are discussed.
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This review aimed to survey diatom composition in Iraqi waters. The facts were taken from surveys of phytoplankton in Iraq, covering freshwater and saline waters in diverse cities. A total of 454 taxa of the diatom group belonging to Bacillophycaea class have been verified in the review. These taxa varied among 107 genera. The genus Nitzschia had a higher number of taxa followed via Navicula, Cymbella, Fragilaria, and Gomphonema, respectively. This study proposes to present a checklist of diatom composition in Iraq, built on the compilation of preceding investigations
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The diatom test is the most reliable approach that provides scientific support for diagnosis of drowning. However, there are limitations, which, made forensic scientists stop using the test, such as the fact that it is time-consuming and lack of domain knowledge of the diatom identification. This study aims to find different types of diatoms that are commonly present in water bodies in China for a possible application of an automatic forensic diatom test. In total, 119 different water samples were obtained from different locations of the Yellow River, the Yangtze River and the Pearl River (China) and were analysed. About 50 ml of water of each sampling site was digested and then observed by a scanning electron microscopy. The diatom genera found in samples were recorded. Twenty-four diatom genera were found in all samples. Among them, Navicula, Nitzschia, Cyclotella, Synedra and Gomphonema were commonly presented (>70%) across the broad geographic regions. Navicula, Nitzschia, Cyclotella, Synedra and Gomphonema would be the main diatoms used in designing an automatic diatom identification system for forensic diatom test.
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The main objectives of this study were to assess the diversity of diatom species and explain how physico-chemical factors and trophic levels interact with diatom assemblages. An assemblage of diatom communities in a riverine environment was assessed through forthright sampling for a period of 7 months from September 2019 to March 2020. Three sampling sites from the upstream, midstream and downstream parts of a river located in the northwest part of Bangladesh were selected for water quality analysis. A variety of multivariate data analyses were done to evaluate the environmental and biological data as well as to observe their interrelationships. A total of 7 genera of Diatom namely Nitzschia, Diatoma, Melosira, Synedra, Tabillaria, Navicula, and Fragillaria were recorded. Nitzschia was the most dominant genus compared to the other genus at downstream with an abundance of 1.92×103 cells/L while Tabillaria sp. was noted as a rare one with the lowest abundance of 0.37×103 cells/L at the midstream site. The interrelationship analysis clarified that water temperature positively altered the distribution of Melosira, Navicula, and Tabillaria while its abundance was less dependent on dissolved oxygen and pH. The results from a 2-dimensional Nonmetric Multidimensional Scaling (NMS) revealed the abundance of diatom at downstream was statistically higher than upstream and midstream. Hence, the study concluded that the diatom composition was very sensitive to the physico-chemical parameters according to water direction and could be used as a bio-indicator to assess the surface water quality. HIGHLIGHTS Diatom species composition was very sensitive to water quality indicators Diatom assemblages can be used as a bio-indicator to assess the water quality Diatom concentration was statistically higher at downstream compared to upstream and midstream GRAPHICAL ABSTRACT
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Seasonality and composition of epipelic diatom community were studied for two years in two wetlands of Bangladesh namely, Joysagar and Sitlai Beel. A total 73 diatom taxa were recorded. The average density of epipelic diatom was higher in Sitlai Beel (52.97 × 104/g sediment) than in the Joysagar (3.92 × 104/g sediment). The epipelic diatom community of Joysagar was dominated by the species of Melosira, Synedra, Navicula, Pinnularia, Gomphonema, and Nitzschia, whereas Melosira, Navicula, Pinnularia, Cymbella and Gomphonema dominated in Sitlai Beel. Melosira granulata, Navicula americana, Pinnularia major, and Gomphonema lanceolatum were dominant and expressed distinct seasonality in both wetlands. The concentration of soluble reactive silicate of water and the average density of epipelic diatom did not express any significant relation in both of the water bodies. The concentration of phytoplankton chl a had a positive relationship with epipelic diatoms and was significant in Sitlai Beel. Key words: Epipelic diatoms; Sitlai Beel; Wetlands; Melosira; Bangladesh DOI: 10.3329/bjb.v39i1.5523Bangladesh J. Bot. 39(1): 29-36, 2010 (June)
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