Home About us Contact
|
Home About us Contact | ||
|
|
||
Diatoms
Kinds of Diatoms Terms modified by Diatoms Selected AbstractsCOMPARISON OF SIMPLE AND MULTIMETRIC DIATOM-BASED INDICES FOR GREAT LAKES COASTLINE DISTURBANCE,JOURNAL OF PHYCOLOGY, Issue 3 2008Euan D. Reavie Because diatom communities are subject to the prevailing water quality in the Great Lakes coastal environment, diatom-based indices can be used to support coastal-monitoring programs and paleoecological studies. Diatom samples were collected from Great Lakes coastal wetlands, embayments, and high-energy sites (155 sites), and assemblages were characterized to the species level. We defined 42 metrics on the basis of autecological and functional properties of species assemblages, including species diversity, motile species, planktonic species, proportion dominant taxon, taxonomic metrics (e.g., proportion Stephanodiscoid taxa), and diatom-inferred (DI) water quality (e.g., DI chloride [Cl]). Redundant metrics were eliminated, and a diatom-based multimetric index (MMDI) to infer coastline disturbance was developed. Anthropogenic stresses in adjacent coastal watersheds were characterized using geographic information system (GIS) data related to agricultural and urban land cover and atmospheric deposition. Fourteen independent diatom metrics had significant regressions with watershed stressor data; these metrics were selected for inclusion in the MMDI. The final MMDI was developed as the weighted sum of the selected metric scores with weights based on a metric's ability to reflect anthropogenic stressors in the adjacent watersheds. Despite careful development of the multimetric approach, verification using a test set of sites indicated that the MMDI was not able to predict watershed stressors better than some of the component metrics. From this investigation, it was determined that simpler, more traditional diatom-based metrics (e.g., DI Cl, proportion Cl-tolerant species, and DI total phosphorus [TP]) provide superior prediction of overall stressor influence at coastal locales. [source] USING QUANTITATIVE PCR TO DETERMINE THE DISTRIBUTION OF A SEMICRYPTIC BENTHIC DIATOM, NAVICULA PHYLLEPTA (BACILLARIOPHYCEAE),JOURNAL OF PHYCOLOGY, Issue 5 2006Véronique Créach Evidence has accumulated during the last decade showing that many established diatom morpho-species actually consist of several semicryptic or truly cryptic species. As these species are difficult or even impossible to differentiate by microscopic analysis, there is virtually no information on how they behave in natural environments. In this study, we developed a quantitative real-time PCR (qPCR) assay using TaqMan probes® targeted to the internal transcribed spacer 1 (ITS1) to assess the spatial distribution and seasonal dynamics of an important component of the microphytobenthos of intertidal sediments. Navicula phyllepta Kützing is a brackish-marine morpho-species with a cosmopolitan distribution. Axenic clones of this species were isolated from natural assemblages of benthic diatoms at different intertidal stations in the Westerschelde estuary (The Netherlands). At least two distinct semicryptic species of N. phyllepta were present, as shown by differences in the quantity of DNA per cell, the ITS1 sequences and the copy number of ITS per cell. DNA and chl a concentrations extracted from sediment surface samples were closely correlated, showing that the DNA used for subsequent analysis mostly belonged to the microalgal community. The results of real-time qPCR from sites throughout the estuary and over several seasons agreed well with microscopic counts. Additionally, the seasonal pattern of the two forms of N. phyllepta showed an overlapping, but unique distribution along the estuary. [source] BEYOND SEQUENCE HOMOLOGY: REDUNDANT AMMONIUM TRANSPORTERS IN A MARINE DIATOM ARE NOT FUNCTIONALLY EQUIVALENTJOURNAL OF PHYCOLOGY, Issue 1 2005Andrew E. Allen No abstract is available for this article. [source] THE TYCHOPELAGIC DIATOM, PARALIA SULCATA, AS PALEOINDICATOR SPECIES IN COASTAL MARINE ENVIRONMENTSJOURNAL OF PHYCOLOGY, Issue 2000M.R. McQuoid Paralia sulcata is a diatom commonly found in both the plankton and benthos of coastal environments. This species is heavily silicified and, thus preserves well in sedimentary records making it a potentially useful paleoindicator species. However, its tychopelagic nature and its association with a wide range of environmental conditions have made detailed paleoecological interpretations complicated. High-resolution sediment records from coastal fjords in both Canada and Sweden show variations in the abundance and morphology of P. sulcata that provide evidence of changes in benthic habitat distribution and surface water properties in the fjords on timescales of decades to centuries. These studies suggest that P. sulcata can be an important paleoindicator species when interpretations are made in the context of its complex ecology. [source] Novel Monocyclic Sester- and Triterpenoids from the Marine Diatom, Rhizosolenia setigera.CHEMINFORM, Issue 13 2004Simon T. Belt No abstract is available for this article. [source] The nature of calcareous deposits along pan margins in eastern central NamibiaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2002Florias MeesArticle first published online: 13 JUN 200 Abstract In a region along the western margin of the Kalahari in eastern Namibia and western Botswana, many pan basins have mainly calcareous deposits along part of their margins. These are typically lined by low vertical scarps. In Namibia, these pans are mainly located in dry river beds. The petrographical study of these deposits demonstrates that they consist of lacustrine sediments that have to a varying extent been affected by early-diagenetic processes and by the formation of late-diagenetic features. The original composition of the deposits ranges from highly calcareous sediments, typically with ostracod, diatom and charophyte remains, to entirely non-calcareous diatomites. The deposits generally show an upward increase in total carbonate content, which is mainly a synsedimentary feature. The early-diagenetic processes that affected the deposits include the formation of orthic siliceous nodules. At a later stage, secondary calcite enrichment occurred, leaving only the silica-impregnated sections unaffected. This enrichment partly accounts for the upward increase in total carbonate content in some profiles and often resulted in the development of a highly calcareous surface horizon. Sepiolite and amorphous silica that are part of the groundmass of the deposits may also partly have formed at this stage. Late-diagenetic features include various forms of secondary calcite and silica. This study of pan basins in eastern central Namibia indicates that a lacustrine rather than purely pedogenic origin should also be considered for calcareous deposits that commonly occur along pan margins in other parts of southern Africa. Copyright © 2002 John Wiley & Sons, Ltd. [source] Seasonal dynamics and toxicity of Cylindrospermopsis raciborskii in Lake Guiers (Senegal, West Africa)FEMS MICROBIOLOGY ECOLOGY, Issue 3 2006Céline Berger Abstract Cylindrospermopsis raciborskii is a toxic bloom-forming cyanobacterium that occurs at tropical and temperate latitudes. Despite several reports from Africa, no data were previously available about its dynamics or toxic potential there. We therefore carried out a 1-year survey of the dynamics of C. raciborskii in the main water reservoir in Senegal, Lake Guiers. Cylindrospermopsis raciborskii never formed a bloom in this lake during the period studied, but was dominant during the dry season. The only observed bloom-forming species was a diatom, Fragilaria sp., which displayed a seasonal pattern contrary to that exhibited by C. raciborskii. Principal component analysis applied to environmental and phytoplankton data showed that high C. raciborskii biomasses were mainly related to high temperature and water column stability. Tests for C. raciborskii species-related toxicity and/or toxin synthesis were performed on 21 isolated clones. All the strains isolated tested negative in mouse toxicity bioassays, toxin analysis (MS/MS) and tests for known cylindrospermopsin genes (ps, pks). The limited number of isolates studied, and the occurrence of toxic and nontoxic clones in natural cyanobacterial populations, mean that we cannot conclude that there is no C. raciborskii- associated health risk in this drinking water reservoir. [source] Winter diatom blooms in a regulated river in South Korea: explanations based on evolutionary computationFRESHWATER BIOLOGY, Issue 10 2007DONG-KYUN KIM Summary 1. An ecological model was developed using genetic programming (GP) to predict the time-series dynamics of the diatom, Stephanodiscus hantzschii for the lower Nakdong River, South Korea. Eight years of weekly data showed the river to be hypertrophic (chl. a, 45.1 ± 4.19 ,g L,1, mean ± SE, n = 427), and S. hantzschii annually formed blooms during the winter to spring flow period (late November to March). 2. A simple non-linear equation was created to produce a 3-day sequential forecast of the species biovolume, by means of time series optimization genetic programming (TSOGP). Training data were used in conjunction with a GP algorithm utilizing 7 years of limnological variables (1995,2001). The model was validated by comparing its output with measurements for a specific year with severe blooms (1994). The model accurately predicted timing of the blooms although it slightly underestimated biovolume (training r2 = 0.70, test r2 = 0.78). The model consisted of the following variables: dam discharge and storage, water temperature, Secchi transparency, dissolved oxygen (DO), pH, evaporation and silica concentration. 3. The application of a five-way cross-validation test suggested that GP was capable of developing models whose input variables were similar, although the data are randomly used for training. The similarity of input variable selection was approximately 51% between the best model and the top 20 candidate models out of 150 in total (based on both Root Mean Squared Error and the determination coefficients for the test data). 4. Genetic programming was able to determine the ecological importance of different environmental variables affecting the diatoms. A series of sensitivity analyses showed that water temperature was the most sensitive parameter. In addition, the optimal equation was sensitive to DO, Secchi transparency, dam discharge and silica concentration. The analyses thus identified likely causes of the proliferation of diatoms in ,river-reservoir hybrids' (i.e. rivers which have the characteristics of a reservoir during the dry season). This result provides specific information about the bloom of S. hantzschii in river systems, as well as the applicability of inductive methods, such as evolutionary computation to river-reservoir hybrid systems. [source] Contiguous multi-proxy analyses (X-radiography, diatom, pollen, and microcharcoal) of Holocene archaeological features at Kuk Swamp, Upper Wahgi Valley, Papua New GuineaGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 6 2009Tim Denham Contiguous multi-proxy analyses (X-radiography, diatom, pollen, and microcharcoal) have been conducted on the fills of early, mid-, and mid-late Holocene features at Kuk Swamp, Upper Wahgi Valley, Papua New Guinea. The features are associated with key periods of archaeological interest: plant exploitation (ca. 10,000 cal yr B.P.), earliest cultivation (6950,6440 cal yr B.P.), and earliest ditches (ca. 4000 cal yr B.P.). The analyses are designed to clarify uncertainties regarding the reliability and association of different samples within feature fills for the interpretation of human activities on the wetland in the past. Methodologically, these investigations have clarified site formation processes, including pedogenesis within feature fills, which enable a better determination of archaeological associations for different samples within those fills. Substantively, the results provide higher resolution interpretations of paleoenvironments and past human activities on the wetland margin. © 2009 Wiley Periodicals, Inc. [source] Hemispheric-scale patterns of climate-related shifts in planktonic diatoms from North American and European lakesGLOBAL CHANGE BIOLOGY, Issue 11 2008KATHLEEN RÜHLAND Abstract A synthesis of over 200 diatom-based paleolimnological records from nonacidified/nonenriched lakes reveals remarkably similar taxon-specific shifts across the Northern Hemisphere since the 19th century. Our data indicate that these diatom shifts occurred in conjunction with changes in freshwater habitat structure and quality, which, in turn, we link to hemispheric warming trends. Significant increases in the relative abundances of planktonic Cyclotella taxa (P<0.01) were concurrent with sharp declines in both heavily silicified Aulacoseira taxa (P<0.01) and benthic Fragilaria taxa (P<0.01). We demonstrate that this trend is not limited to Arctic and alpine environments, but that lakes at temperate latitudes are now showing similar ecological changes. As expected, the onset of biological responses to warming occurred significantly earlier (P<0.05) in climatically sensitive Arctic regions (median age=ad 1870) compared with temperate regions (median age=ad 1970). In a detailed paleolimnological case study, we report strong relationships (P<0.005) between sedimentary diatom data from Whitefish Bay, Lake of the Woods (Ontario, Canada), and long-term changes in air temperature and ice-out records. Other potential environmental factors, such as atmospheric nitrogen deposition, could not explain our observations. These data provide clear evidence that unparalleled warming over the last few decades resulted in substantial increases in the length of the ice-free period that, similar to 19th century changes in high-latitude lakes, likely triggered a reorganization of diatom community composition. We show that many nonacidified, nutrient-poor, freshwater ecosystems throughout the Northern Hemisphere have crossed important climatically induced ecological thresholds. These findings are worrisome, as the ecological changes that we report at both mid- and high-latitude sites have occurred with increases in mean annual air temperature that are less than half of what is projected for these regions over the next half century. [source] Organic facies and geochemical aspects in Neogene neritic sediments of the Takafu syncline area of central Japan: Paleoenvironmental and sedimentological reconstructionsISLAND ARC, Issue 4 2006Ken Sawada Abstract Organic petrological observations of kerogen macerals and organic geochemical analyses of carbon isotopes of kerogen macerals and biomarkers were conducted on Neogene neritic sediments of the Takafu syncline area of central Japan. The Senmi, Sakainomiya and Lower Shigarami Formations in that area were deposited at the neritic provinces on the southern edge of the paleo-Japan Sea during the Late Miocene to Early Pliocene. Sedimentary organic matter in these formations was almost terrigenous in origin. Changes in kerogen maceral compositions reflect sedimentological and tectonic histories evaluated in previous studies from sedimentary facies and paleontology. It was found that carbon isotope ratios (,13C) of kerogen macerals increased from ,28, to ,25, from the Sakainomiya to the lower part of the Lower Shigarami Formations. The cause of that increase was presumably the expansion of C4 plants into southwest Japan. The timing was concordant with that of the expansion of C4 plant grasslands in East Asia. The oxicity (oxic to anoxic) conditions of sea bottoms evaluated from pristane/phytane ratios varied. Particularly, in the lower part of the Senmi Formation, layers in which no steroid biomarkers could be detected were found, and had presumably formed under oxic conditions when strong biodegradation had occurred. Concentrations of regular (C27,C29) steranes and dinosteranes were higher in the Sakainomiya and Lower Shigarami Formations. This indicates that dinoflagellates-dominant primary productions were higher at those stages. In addition, concentrations of diatomaceous biomarkers such as C26 norsterane increased from the Lower Shigarami Formation, thus adding diatoms to the major producers. Furthermore, similar associations between the increases of ,13C values of kerogen macerals and concentrations of diatomaceous biomarkers were observed in the Takafu syncline area. Thus, the expansion of C4 plants was possibly associated with the high production of diatom in the shallow-marine areas of the paleo-Japan Sea during the Neogene Period. [source] SEASONAL VARIABILITY OF THE ORGANIC-WALLED DINOFLAGELLATE CYST PRODUCTION IN THE COASTAL UPWELLING REGION OFF CAPE BLANC (MAURITANIA): A FIVE-YEAR SURVEY,JOURNAL OF PHYCOLOGY, Issue 1 2010Karin A. F. Zonneveld A 5-year sediment trap survey in the upwelling area off Cape Blanc (NW Africa) provides information on the seasonal and annual resting cyst production of dinoflagellates, their sinking characteristics and preservation potential. Strong annual variation in cyst production characterizes the region. Cyst production of generally all investigated species, including Alexandrium pseudogonyaulax (Biecheler) T. Horig. ex T. Kita et Fukuyo (cyst genus Impagidinium) and Gonyaulax spinifera (Clap. et J. Lachm.) Diesing (cyst genus Nematosphaeropsis) was enhanced with increasing upper water nutrient and trace-element concentrations. Cyst production of Lingulodinium polyedrum (F. Stein) J. D. Dodge was the highest at the transition between upwelling and upwelling-relaxation. Cyst production of Protoperidinium americanum (Gran et Braarud) Balech, Protoperidinium monospinum (Paulsen) K. A. F. Zonn. et B. Dale, and Protoperidinium stellatum (D. Wall) Balech, and heterotrophic dinoflagellates forming Brigantedinium spp. and Echinidinium aculeatum Zonn., increased most pronouncedly during upwelling episodes. Production of Protoperidinium conicum (Gran) Balech and Protoperidinium pentagonum (Gran) Balech cysts and total diatom valves were related, providing evidence of a predator,prey relationship. The export cyst-flux of E. aculeatum, P. americanum, P. monospinum, and P. stellatum was strongly linked to the flux of total diatom valves and CaCO3, whereas the export production of Echinidinium granulatum Zonn. and Protoperidinium subinerme (Paulsen) A. R. Loebl. correlated with total organic carbon, suggesting potential consumption of diatoms, prymnesiophytes, and organic matter, respectively. Sinking velocities were at least 274 m · d,1, which is in range of the diatom- and coccolith-based phytoplankton aggregates and "slower" fecal pellets. Species-selective degradation did not occur in the water column, but on the ocean floor. [source] DIEL VARIATIONS IN OPTICAL PROPERTIES OF IMANTONIA ROTUNDA (HAPTOPHYCEAE) AND THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE) EXPOSED TO DIFFERENT IRRADIANCE LEVELS,JOURNAL OF PHYCOLOGY, Issue 3 2008Sébastien Mas Diel variations of cellular optical properties were examined for cultures of the haptophyte Imantonia rotunda N. Reynolds and the diatom Thalassiosira pseudonana (Hust.) Hasle et Heimdal grown under a 14:10 light:dark (L:D) cycle and transferred from 100 ,mol photons · m,2 · s,1 to higher irradiances of 250 and 500 ,mol photons · m,2 · s,1. Cell volume and abundance, phytoplankton absorption coefficients, flow-cytometric light scattering and chl fluorescence, and pigment composition were measured every 2 h over a 24 h period. Results showed that cell division was more synchronous for I. rotunda than for T. pseudonana. Several variables exhibited diel variability with an amplitude >100%, notably mean cell volume for the haptophyte and photoprotective carotenoids for both species, while optical properties such as flow-cytometric scattering and chl a,specific phytoplankton absorption generally showed <50% diel variability. Increased irradiance induced changes in pigments (both species) and mean cell volume (for the diatom) and amplified diel variability for most variables. This increase in amplitude is larger for pigments (factor of 2 or more, notably for cellular photoprotective carotenoid content in I. rotunda and for photosynthetic pigments in T. pseudonana) than for optical properties (a factor of 1.5 for chl a,specific absorption, at 440 nm, in I. rotunda and a factor of 2 for the absorption cross-section and the chl a,specific scattering in T. pseudonana). Consequently, diel changes in optical properties and pigmentation associated with the L:D cycle and amplified by concurrent changes in irradiance likely contribute significantly to the variability in optical properties observed in biooptical field studies. [source] COMPARISON OF SIMPLE AND MULTIMETRIC DIATOM-BASED INDICES FOR GREAT LAKES COASTLINE DISTURBANCE,JOURNAL OF PHYCOLOGY, Issue 3 2008Euan D. Reavie Because diatom communities are subject to the prevailing water quality in the Great Lakes coastal environment, diatom-based indices can be used to support coastal-monitoring programs and paleoecological studies. Diatom samples were collected from Great Lakes coastal wetlands, embayments, and high-energy sites (155 sites), and assemblages were characterized to the species level. We defined 42 metrics on the basis of autecological and functional properties of species assemblages, including species diversity, motile species, planktonic species, proportion dominant taxon, taxonomic metrics (e.g., proportion Stephanodiscoid taxa), and diatom-inferred (DI) water quality (e.g., DI chloride [Cl]). Redundant metrics were eliminated, and a diatom-based multimetric index (MMDI) to infer coastline disturbance was developed. Anthropogenic stresses in adjacent coastal watersheds were characterized using geographic information system (GIS) data related to agricultural and urban land cover and atmospheric deposition. Fourteen independent diatom metrics had significant regressions with watershed stressor data; these metrics were selected for inclusion in the MMDI. The final MMDI was developed as the weighted sum of the selected metric scores with weights based on a metric's ability to reflect anthropogenic stressors in the adjacent watersheds. Despite careful development of the multimetric approach, verification using a test set of sites indicated that the MMDI was not able to predict watershed stressors better than some of the component metrics. From this investigation, it was determined that simpler, more traditional diatom-based metrics (e.g., DI Cl, proportion Cl-tolerant species, and DI total phosphorus [TP]) provide superior prediction of overall stressor influence at coastal locales. [source] MOLECULAR GENETIC MANIPULATION OF THE DIATOM THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE),JOURNAL OF PHYCOLOGY, Issue 5 2006Nicole Poulsen Here, we describe the first system for genetic transformation of Thalassiosira pseudonana (Hustedt) Hasle et Heimdal, the only diatom for which a complete genome sequence is presently available. This method is based on microparticle bombardment followed by selection of transformants using the antibiotic nourseothricin. It exhibits the highest transformation efficiency compared with transformation systems for other diatom species. To achieve the high transformation efficiency, it is important to allow recovery of the bombarded T. pseudonana cells in non-selective suspension culture before spreading on nourseothricin containing agar plates. It is demonstrated that T. pseudonana is readily susceptible to co-transformation allowing for the simultaneous introduction of a non-selective gene together with the selection marker gene. Both introduced genes are stably inherited even in the absence of the antibiotic selection pressure. We have developed two T. pseudonana -specific expression vectors that can drive constitutive expression (vector pTpfcp) and inducible expression (vector pTpNR) of introduced genes. In combination with the available genome data the T. pseudonana transformation system is expected to provide a powerful tool for functional genomics in diatoms. [source] USING QUANTITATIVE PCR TO DETERMINE THE DISTRIBUTION OF A SEMICRYPTIC BENTHIC DIATOM, NAVICULA PHYLLEPTA (BACILLARIOPHYCEAE),JOURNAL OF PHYCOLOGY, Issue 5 2006Véronique Créach Evidence has accumulated during the last decade showing that many established diatom morpho-species actually consist of several semicryptic or truly cryptic species. As these species are difficult or even impossible to differentiate by microscopic analysis, there is virtually no information on how they behave in natural environments. In this study, we developed a quantitative real-time PCR (qPCR) assay using TaqMan probes® targeted to the internal transcribed spacer 1 (ITS1) to assess the spatial distribution and seasonal dynamics of an important component of the microphytobenthos of intertidal sediments. Navicula phyllepta Kützing is a brackish-marine morpho-species with a cosmopolitan distribution. Axenic clones of this species were isolated from natural assemblages of benthic diatoms at different intertidal stations in the Westerschelde estuary (The Netherlands). At least two distinct semicryptic species of N. phyllepta were present, as shown by differences in the quantity of DNA per cell, the ITS1 sequences and the copy number of ITS per cell. DNA and chl a concentrations extracted from sediment surface samples were closely correlated, showing that the DNA used for subsequent analysis mostly belonged to the microalgal community. The results of real-time qPCR from sites throughout the estuary and over several seasons agreed well with microscopic counts. Additionally, the seasonal pattern of the two forms of N. phyllepta showed an overlapping, but unique distribution along the estuary. [source] EXTRACELLULAR MATRIX ASSEMBLY IN DIATOMS (BACILLARIOPHYCEAE).JOURNAL OF PHYCOLOGY, Issue 2 2006The effects of phosphate (P) limitation, varying salinity (5,65 psu), and solid media growth conditions on the polysaccharides produced by the model diatom, Phaeodactylum tricornutum Bohlin were determined. Sequential extraction was used to separate polymers into colloidal (CL), colloidal extracellular polymeric substances (cEPS), hot water soluble (HW), hot bicarbonate soluble (HB), and hot alkali (HA) soluble fractions. Media-soluble polymers (CL and cEPS) were enriched in 4-linked mannosyl, glucosyl, and galactosyl residues as well as terminal and 3-linked xylosyl residues, whereas HW polymers consisted mainly of 3-linked glucosyl as well as terminal and 2,4-linked glucuronosyl residues. The HB fraction was enriched in terminal and 2-linked rhamnosyl residues derived from the mucilage coating solubilized by this treatment. Hot alkali treatment resulted in the complete dissolution of the frustule releasing 2,3- and 3-linked mannosyl residues. The fusiform morphotype predominated in standard and P-limited cultures and cultures subjected to salinity variations, but growth on solid media resulted in an enrichment of the oval morphotype. The proportion and linkages of 15 residues, including neutral, uronic acid, and O -methylated sugars, varied with environmental conditions. P limitation and salinity changes resulted in 1.5- to 2.5,fold increase in carbohydrate production, with enrichment of highly branched/substituted and terminal rhamnose, xylose, and fucose as well as O -methylated sugars, uronic acids, and sulfate. The increased deoxy- and O -methylated sugar content under unfavorable environments enhances the hydrophobicity of the polymers, whereas the anionic components may play important roles in ionic cross-linking, suggesting that these changes could ameliorate the effects of salinity or P-stress and that these altered polysaccharide characteristics may be useful as bioindicators for environmental stress. [source] MOVEMENT MODALITIES AND RESPONSES TO ENVIRONMENTAL CHANGES OF THE MUDFLAT DIATOM CYLINDROTHECA CLOSTERIUM (BACILLARIOPHYCEAE),JOURNAL OF PHYCOLOGY, Issue 2 2006Melba D. Apoya-Horton Cylindrotheca closterium (Ehrenberg) Reiman et Lewin is a raphid diatom widely distributed in mudflat assemblages. Video microscopy showed various movement modalities defined as smooth and corkscrew gliding, pirouette, pivot, rock and roll, rollover, and simultaneous pirouette and gliding. Z -axis projection analysis of images revealed a unique gliding motif with corkscrew motions, which may have important ecological implications for C. closterium movement in muds. The general response to salinity alteration was a decrease in gliding movements with a concomitant increase in other modalities listed above. Short-term responses to salinity change include dramatic alteration in modalities in hypo-saline conditions and cessation of motility in extreme hyper-saline environments. Modality changes were rapid and occurred within 5 s in response to hyper-saline conditions. Hypo- or hyper-saline conditions resulted in decreased gliding speed in standard media. Five- and 15-day acclimation to salinity changes resulted in a progressive reduction in gliding movement, increased non-gliding modalities and increased cell aggregation. Aggregation in hypo-saline conditions was accompanied by a large increase in the polymer extracted by hot bicarbonate- and ethylenediamine tetraaceticacid- fractions of extracellular polymeric substance (EPS), the polymers of which have been implicated in cell attachment/motility phenomena. The monosaccharide profiles of these fractions were altered in response to hypo-saline conditions. In general, monosaccharide profiles showed increased diversity upon cessation of motility and aggregation of cultures. The movement responses of C. closterium in response to environmental changes, accompanied by modifications in EPS, may form part of an adaptive strategy to survive in mudflats and could be useful as bioindicators of environmental changes. [source] RELATING PHYTOPLANKTON DYNAMICS AND PRODUCTION TO SEDIMENT RESUSPENSION IN SOUTHERN LAKE MICHIGANJOURNAL OF PHYCOLOGY, Issue 2001Article first published online: 24 SEP 200 Millie, D. F.1, Fahnenstiel, G. L.2, Carrick, H. J.3, Lohrenz, S. E.4, & Schofield, O. M. E.5 1USDA-Agricultural Research Service, Sarasota, FL 34236, USA, 2NOAA-Lake Michigan Field Station, Muskegon, MI 49441, USA, 3Institute of Marine Science, University of Southern Mississippi, Stennis Space Center, MS 39529, USA, 4Department of Biological Sciences, State University of New York at Buffalo, Buffalo, NY 14060, USA; 5Isttitute of Marine and Coastal Sciences, Rutgers University, 71 Dudley Road New Brunswick NJ 08901 USA, Sediment resuspension is an annually recurrent feature during spring holomixis in southern Lake Michigan. Relationships between resuspension events and phyt-oplankton biomass, compositional dynamics, and pro-duction were evaluated during 1998 and 1999. Increased water-column light attenuation (KPAR) and suspended particulate matter (SPM) concentrations corresponded with resuspension events within nearshore regions. However, neither KPAR nor SPM corresponded with chlorophyll (Chl) a concentrations, indicating no impact of resuspension on instantaneous biomass accumulation. Diatoms and cryptophytes dominated phytoplankton assemblages and together typically comprised greater than 85% of the Chl a. The associations of SPM/KPAR with diatom Chl a, and the inverse relationship between relative diatom and crypto-phyte Chl a corresponded with the dominance of diatoms and cryptophytes in near- and offshore waters, respectively. Moreover, a spatial variation in species composition occurred during resuspension events; small, centric diatoms exhibiting meroplanktonic life histories and large, pennate diatoms considered benthic in origin were associated with sediment resuspension whereas large, net diatoms and cryptophytes typically comprising phytoplankton of the annual spring bloom and of optically-clear, offshore waters were not. The presence of viable diatom photopigments and the abundance of small centric diatoms within the surficial sediments, established this layer as the source of meroplankton. Integral production was dramatically reduced within sediment-impacted waters; however, nearshore assemblages appeared to have greater photosynthetic capacities than offshore assemblages. Although resuspension dramatically influenced near-shore phytoplankton assemblages, it appeared to have little, if any relationship with the compositional development of the annual spring bloom. [source] PLASTID FATTY ACID BIOSYNTHESIS IN THE DIATOMS NITZSCHIA ALBA AND NITZSCHIA LAEVISJOURNAL OF PHYCOLOGY, Issue 2000K.M. McGinnis The role of the plastid in fatty acid biosynthesis in the non-photosynthetic diatom Nitzschia alba was studied and compared to that in the photosynthetic, closely related Nitzschia laevis. Transmission electron microscopy was used to analyze structural features of the plastid that may be relevant to biochemical function. Typical of a photosynthetic diatom, N. laevis had a chloroplast envelope composed of four membranes, and had abundant chloroplast ribosomes. The leucoplast of N. alba also had a multi-membrane envelope, chloroplast ribosomes, and a genome that encodes plastid specific proteins. This suggested that the plastid of N. alba may still possess the biochemical functions of the chloroplast, aside from photosynthesis. To determine whether plastidial fatty acid biosynthesis occurred in N. alba, the response of the two diatoms to the compound thiolactomycin was compared. Thiolactomycin has been shown to effect keto-acyl-ACP-synthases, and specifically inhibits the plastidial fatty acid biosynthetic pathway. While growth of N. alba was not impacted by thiolactomycin as in N. laevis, neutral lipid accumulation and fatty acid composition was impacted by thiolactomycin in both organisms. These findings suggest that the plastidial fatty acid biosynthetic pathway does exist in the leucoplast of N. alba, although it lacks photosynthetic capacity. [source] THE TYCHOPELAGIC DIATOM, PARALIA SULCATA, AS PALEOINDICATOR SPECIES IN COASTAL MARINE ENVIRONMENTSJOURNAL OF PHYCOLOGY, Issue 2000M.R. McQuoid Paralia sulcata is a diatom commonly found in both the plankton and benthos of coastal environments. This species is heavily silicified and, thus preserves well in sedimentary records making it a potentially useful paleoindicator species. However, its tychopelagic nature and its association with a wide range of environmental conditions have made detailed paleoecological interpretations complicated. High-resolution sediment records from coastal fjords in both Canada and Sweden show variations in the abundance and morphology of P. sulcata that provide evidence of changes in benthic habitat distribution and surface water properties in the fjords on timescales of decades to centuries. These studies suggest that P. sulcata can be an important paleoindicator species when interpretations are made in the context of its complex ecology. [source] INTRACELLULAR CYANOBACTERIAL SYMBIONTS IN THE MARINE DIATOM CLIMACODIUM FRAUENFELDIANUM (BACILLARIOPHYCEAE)JOURNAL OF PHYCOLOGY, Issue 3 2000Edward J. Carpenter The diatom Climacodium frauenfeldianum Grunow was collected in the tropical Atlantic and Pacific Oceans. Observations with epifluorescence microscopy revealed that this diatom contained coccoid symbionts (2.5,3.5 ,m) with a typical cyanobacterial fluorescence in addition to that of their own chloroplasts. Mean concentration of C. frauenfeldianum for 28 stations in the SW tropical Pacific Ocean was 530 x 103 (SE = 1372) cells·m,2, with highest concentration (mean 17.5 cells·L,1) at 40-m depth. The symbiosis was only observed at water temperatures between 26.3 and 28.9° C, with highest concentrations at 27.7° C. Three almost complete 16S rDNA sequences from one sample were determined, and they were identical. The phylogenetic analysis of this 16S rDNA sequence and those from other cyanobacteria and plastids revealed that it was closely related to the 16S rDNA sequence from Cyanothece sp. ATCC 51142. Cyanothece sp. ATCC 51142 is a unicellular nitrogen-fixing cyanobacterium isolated from a coastal marine environment and has ultrastructural features similar to the symbionts of C. frauenfeldianum. The close relationship between Cyanothece sp. and the cyanobacterial symbiont in C. frauenfeldianum suggests the potential for nitrogen fixation in the symbiosis. [source] Oxidative metabolism by Thalassiosira weissflogii (Bacillariophyceae) of a diol-ester of okadaic acid, the diarrhetic shellfish poisoningJOURNAL OF PHYCOLOGY, Issue 2 2000Anthony J. Windust Previous investigations into the comparative toxicity of the diarrhetic shellfish poisoning (DSP) toxins to Thalassiosira weissflogii (Grun.) Fryxell et Hasle found that this diatom oxidatively metabolized okadaic acid diol-ester (OA diol-ester) to a more water-soluble product. This oxidative transformation of OA diol-ester by the diatom is significant for two reasons. First, it is known that dinophysistoxin-4 (DTX-4), the primary DSP toxin produced by the dinoflagellate Exuviaella lima (Ehr.) Butschli, will be hydrolyzed to the diol-ester following cell rupture (e.g. ingestion by a predator). Second, it implies that the ester, an uncharged, lipophilic intermediate, can easily enter cells and therefore may play an important role in the uptake and transfer of DSP toxins through the food web. It has been suggested that the water soluble DTX-4 may also be the form in which DSP toxins are excreted from the producing cell. Therefore, the stability of DTX-4 was examined when incubated either in fresh seawater medium into which washed cells of E. lima were introduced or in seawater medium conditioned by E. lima cells. Rapid hydrolysis of DTX-4 to the diol-ester took place in both cases. Thus, regardless of the route by which DTX-4 is liberated from the cell, either by cell disruption or excretion, the diol-ester will be the dominant form of the toxin to challenge associated organisms. To examine the metabolism of OA diol-ester by T. weissflogii in more detail, serial cultures of the diatom were challenged with OA diol-ester at a concentration of 2.0 ,g·mL,1. The metabolism and fate of the diol-ester in both cellular and medium fractions were monitored over 3 days using liquid chromatography with either ultraviolet (LC-UV) or mass spectrometric (LC-MS) detection. During the course of the experiment, all of the diol-ester was metabolized. LC-MS analysis revealed the presence of multiple oxidative products of OA diol-ester in the medium fraction, including a carboxylic acid derivative. The major metabolites were isolated in sufficient quantity to permit structural elucidation by NMR and MS. All the metabolites identified resulted from oxidation of the diol-ester side chain with the primary sites of attack at the terminal, subterminal, and unsaturated carbons. OA was found in both cellular and medium fractions, and its production was directly correlated with the metabolism of the diol-ester. The relative partitioning of both OA diol-ester and its oxidation products between cells and medium supports the contention that OA diol-ester can readily enter cells, be metabolized, and then excreted in more water-soluble forms. [source] Relative sea-level observations in western Scotland since the Last Glacial Maximum for testing models of glacial isostatic land movements and ice-sheet reconstructions,JOURNAL OF QUATERNARY SCIENCE, Issue 6 2006Ian Shennan Abstract Observations of relative sea-level change and local deglaciation in western Scotland provide critical constraints for modelling glacio-isostatic rebound in northern Britain over the last 18,000 years. The longest records come from Skye, Arisaig and Knapdale with a shorter, Holocene, record from Kintail. Biostratigraphic (diatom, pollen, dinoflagellate, foraminifera and thecamoebian), lithological and radiocarbon analyses provide age and elevation parameters for each sea-level index point. All four sites reveal relative sea-level change that is highly non-monotonic in time as the local vertical component of glacio-isostatic rebound and eustasy (or global meltwater influx) dominate at different periods. Copyright © 2006 John Wiley & Sons, Ltd. [source] A multi-proxy study of Holocene lake development, lake settlement and vegetation history in central Ireland,JOURNAL OF QUATERNARY SCIENCE, Issue 2 2005K. A. Selby Abstract Stratigraphical investigations, geomorphological mapping, and diatom, plant macrofossil and pollen analyses were undertaken in and around two lakes in central Ireland to establish correlations between changes in lake conditions and catchment vegetation throughout the Holocene. Similar investigations of an adjacent mire reveal early Holocene changes in lake level and area. The palaeoecological data show high correlations related to variations in lake depth and area, catchment vegetation type, organic inputs and trophic status. Catchment-scale deforestation is gradual and occurs through the Bronze and the Iron Ages, and the construction of a crannog in the early Medieval period (seventh century AD) appears to be associated with a widespread increase in deforestation and mixed agriculture in the catchment. Both pollen and plant macrofossils suggest that one of the crannogs was used for crop storage in addition to domestic and any other activities. In the early to middle Holocene similarities in the proxy-data appear to be climatically driven through changing lake levels and areal extent whereas the later Holocene record is clearly dominated by anthropogenic changes within the catchment and the construction of crannogs in the lakes. The advantages of combining multi-proxy indicators of lake hydroecology with the vegetation record are illustrated. Copyright © 2005 John Wiley & Sons, Ltd. [source] Pollen- and diatom based environmental history since the Last Glacial Maximum from the Andean core Fúquene-7, ColombiaJOURNAL OF QUATERNARY SCIENCE, Issue 1 2003Maria Isabel Vélez Abstract The late Pleistocene,Holocene ecological and limnological history of Lake Fúquene (2580 m a.s.l.), in the Colombian Andes, is reconstructed on the basis of diatom, pollen and sediment analyses of the upper 7 m of the core Fúquene-7. Time control is provided by 11 accelerator mass spectrometry (AMS) 14C dates ranging from 19 670 ± 240 to 6040 ± 60 yr BP. In this paper we present the evolution of the lake and its surroundings. Glacial times were cold and dry, lake-levels were low and the area was surrounded by paramo and subparamo vegetation. Late-glacial conditions were warm and humid. The El Abra Stadial, a Younger Dryas equivalent, is reflected by a gap in the sedimentary record, a consequence of the cessation of deposition owing to a drop in lake-level. The early Holocene was warm and humid; at this time the lake reached its maximum extension and was surrounded by Andean forest. The onset of the drier climate prevailing today took place in the middle Holocene, a process that is reflected earlier in the diatom and sediment records than in the pollen records. In the late Holocene human activity reduced the forest and transformed the landscape. Climate patterns from the Late-glacial and throughout the Holocene, as represented in our record, are similar to other records from Colombia and northern South America (the Caribbean, Venezuela and Panama) and suggest that the changes in lake-level were the result of precipitation variations driven by latitudinal shifts of the Intertropical Convergence Zone. Copyright © 2003 John Wiley & Sons, Ltd. [source] Fluctuations in relative sea-level during the past 3000 yr in the Onnetoh estuary, Hokkaido, northern JapanJOURNAL OF QUATERNARY SCIENCE, Issue 5-6 2002Yuki Sawai Abstract This paper presents the results of a litho-, bio- and chronostratigraphical study of the evidence for late Holocene sea-level change, palaeoseismicity and coastal evolution at the Onnetoh estuary, northwest Japan. Alternating peat and mud couplets record evidence for four falls in relative sea-level since ca. 2500 cal. yr BP. In the latest instance, intertidal mud with a salt-tolerant diatom and plant macrofossil flora is abruptly overlain by a freshwater peat containing abundant macrofossil remains of the conifer Picea glehnii. These stratigraphical changes record an abrupt change from tidal flat to upland, with no intermediate transition through saltmarsh. In the other three instances, the stratigraphy records a more gradual fall in relative sea-level, as shown by gradational stratigraphical contacts and transitional diatom and plant macrofossil assemblages. Once established, these freshwater peat communities are gradually submerged and become overlain by saltmarsh and then intertidal muds. Radiocarbon ages and tephra date the emergence events to 2700,1750 (gradual), 1350,950 (gradual), 650,300 (gradual) and ca. 400 cal. yr BP (abrupt). These ages are similar to a sequence of emergence events recorded at the Akkeshi estuary, 70 km to the west of the present study site. The three falls in relative sea-level may record coseismic, or swift post-seismic, uplift caused by plate boundary subduction earthquakes on the Kurile subduction zone. The oldest relative sea-level fall is correlated with the so-called ,Yayoi regression', dated to 1500,3000 cal yr BP in other parts of Japan. Copyright © 2002 John Wiley & Sons, Ltd. [source] A multiproxy record of Holocene environmental changes in the central Kola Peninsula, northwest RussiaJOURNAL OF QUATERNARY SCIENCE, Issue 4 2002Nadia Solovieva Abstract A sediment core from Chuna Lake (Kola Peninsula, northwest Russia) was studied for pollen, diatoms and sediment chemistry in order to infer post-glacial environmental changes and to investigate responses of the lake ecosystem to these changes. The past pH and dissolved organic carbon (DOC) of the lake were inferred using diatom-based transfer functions. Between 9000 and 4200 cal. yr BP, slow natural acidification and major changes in the diatom flora occurred in Chuna Lake. These correlated with changes in regional pollen, the arrival of trees in the catchment, changes in erosion, sediment organic content and DOC. During the past 4200 yr diatom-based proxies showed no clear response to changes in vegetation and erosion, as autochthonous ecological processes became more important than external climate influences during the late Holocene. The pollen stratigraphy reflects the major climate patterns of the central Kola Peninsula during the Holocene, i.e. a climate optimum between 9000 and 5400/5000 cal. yr BP when climate was warm and dry, and gradual climate cooling and an increase in moisture during the past 5400/5000 yr. This agrees with the occurrence of the north,south humidity gradient in Fennoscandia during the Holocene. Copyright © 2002 John Wiley & Sons, Ltd. [source] Low reproductive success for copepods during a bloom of the non-aldehyde-producing diatom Cerataulina pelagica in the North Adriatic SeaMARINE ECOLOGY, Issue 3 2008Adrianna Ianora Abstract Egg production rates and/or hatching success in the copepods Acartia clausi, Calanus helgolandicus and Temora longicornis were negatively affected by a late spring (May,June 2003) phytoplankton bloom in the North Adriatic Sea, dominated mainly by the large diatom Cerataulina pelagica. Highest total concentrations of 3.3·104 cells·ml,1 were located in the vicinity of the Po River, which also corresponded to the area where the highest numbers of phaeophorbides were measured (0.779, 0.528 and 0.419 ,g·l,1, respectively, compared to an average of the remaining stations of 0.183 ± 0.049 SD), suggesting some grazing on the bloom. Phytoplankton biomass in terms of carbon was dominated by diatoms, representing on average 42% of total phytoplankton carbon and more than 80% at several stations. Cerataulina pelagica, Cyclotella spp., Chaetoceros spp. and small unidentified centric diatoms dominated the diatom community numerically but C. pelagica was by far the dominant diatom in terms of carbon due to its large cell size. This species represented more than 60% of the diatom biomass at nine of the 14 stations sampled, and was absent only at one station, which was the most offshore station sampled during the cruise. Although polyunsaturated aldehydes (PUAs) were not detected, other oxylipins which are hydroxy and keto derivatives of eicosapentaenoic and docosahexaenoic acids that affect copepod reproduction were found in these samples. Hence, we can attribute the negative impact of diatoms not only to PUAs, as previously believed, but also to these compounds. This is the first direct evidence of the presence of oxylipins other than PUAs in marine blooms dominated by diatoms. [source] Linking the planktonic and benthic habitat: genetic structure of the marine diatom Skeletonema marinoiMOLECULAR ECOLOGY, Issue 20 2010ANNA GODHE Abstract Dormant life stages are important strategies for many aquatic organisms. The formation of resting stages will provide a refuge from unfavourable conditions in the water column, and their successive accumulation in the benthos will constitute a genetic reservoir for future planktonic populations. We have determined the genetic structure of a common bloom-forming diatom, Skeletonema marinoi, in the sediment and the plankton during spring, summer and autumn two subsequent years (2007,2009) in Gullmar Fjord on the Swedish west coast. Eight polymorphic microsatellite loci were used to assess the level of genetic differentiation and the respective gene diversity of the two different habitats. We also determined the degree of genetic differentiation between the seed banks inside the fjord and the open sea. The results indicate that Gullmar Fjord has one dominant endogenous population of S. marinoi, which is genetically differentiated from the open sea population. The fjord population is encountered in the plankton and in the sediment. Shifts from the dominant population can happen, and in our study, two genetically differentiated plankton populations, displaying reduced genetic diversity, occurred in September 2007 and 2008. Based on our results, we suggest that sill fjords maintain local long-lived and well-adapted protist populations, which continuously shift between the planktonic and benthic habitats. Intermittently, short-lived and mainly asexually reproducing populations can replace the dominant population in the water column, without influencing the genetic structure of the benthic seed bank. [source] | |||||||||||||||||||||||||||||||||||||||||||