Some factors affecting distribution of diatom assemblages in Pyrenean springs

SUMMARY.

• 1 The composition and abundance of diatom assemblages were studied together with physiographical and physicochemical variables in twenty-eight springs in the Central Pyrenees during the period 1987–88.
• 2 Characteristic groupings of diatom taxa are revealed by Principal Components Analysis. One group, made up of assemblages of the taxa Navicula cincta, Caloncis spp. and Niizschia elliptica, is characteristic of springs with waters of high ionic strength. Certain diatom taxa are characteristic of hard water springs, either in quiet waters (Denticula tenuis, Achnanthes minutissima, Eunotia spp.) or fast flowing ones (Fragilaria spp., Diatoma hiemale). Other taxa are representative of relatively quiet, softwater springs: Anomoeoneis bracfiysira, Tabellaria flocculosa, Aulacoseira distans and Fragilaria vaucheriae.
• 3 Five different spring types were identified, with respect to diatom assemblages, using discriminant analysis. The first consisted of high mountain springs with cold, fast waters and low ionic strength. The second group, distributed throughout the Pyrenees, had similar environmental characteristics to the first group but with intermediate water velocity and slightly higher mineral content. The third contained springs in calcareous regions of the Pyrenees, mainly slow-flowing and with hard waters. The fourth was composed of softwater springs, whilst the fifth consisted of two springs which were subject to stressful conditions (limitation of light, abundance of nitrates or high salinity).
• 4 Ionic strength and current velocity appeared to be the dominant environmental factors affecting diatom distribution in Pyrenean springs. These factors also seem to determine diatom communities in some other geographical areas. In some springs, however, peculiar environmental factors (dim light, salinity, and high temperature) affect the structure of diatom assemblages.

     

ACHNANTHIDIUM DOLOMITICUM SP. NOV. (BACILLARIOPHYTA) FROM OLIGOTROPHIC MOUNTAIN SPRINGS AND LAKES FED BY DOLOMITE AQUIFERS1

A new benthic freshwater diatom, Achnanthidium dolomiticum sp. nov., was identified from light and scanning electron micrographs. The most characteristic morphological features are a narrow, but distinctive fascia; a filiform raphe with narrowly spaced central ends and a very narrow and straight axial area on the raphe valve; a convex‐shaped rapheless valve; the length/width ratio; and valve outline. The new species, has been found so far to be mainly epiphytic on bryophytes and aquatic vascular plants in carbonate springs and lakes of the Italian Alps. The environmental preferences of the new species, as assessed by the comparative analysis of these sites, appear to be quite distinctive. These freshwater habitats are fed by drainage basins dominated by dolomite lithology with medium mineralization, are oligotrophic, and are affected by seasonal desiccation.     

MICROFISSURATA GEN. NOV. (BACILLARIOPHYTA), A NEW DIATOM GENUS FROM DYSTROPHIC AND INTERMITTENTLY WET TERRESTRIAL HABITATS1

A new freshwater benthic diatom genus, Microfissurata gen. nov., was identified from light and scanning electron micrographs. The most characteristic morphological feature (referred to also by the name of the new genus) is the structure of the striae/alveoli, which are simple, mostly uninterrupted, transapical slits. The combination of characteristics of the new genus is unique. It includes two new species: Microfissurata paludosa Cantonati et Lange‐Bert. sp. nov. and M. australis Van de Vijver et Lange‐Bert. sp. nov., distributed in Europe and on an austral island, respectively. The new genus occurs in freshwater dystrophic lakes, pools, seepage springs, mires, and in intermittently wet terrestrial habitats. It is not abundant but widespread wherever these habitat types are well developed, in Nordic‐alpine and sub‐Antarctic areas. Overall, the new genus appears to be mostly epiphytic (bryophilous) and capable of tolerating a wide range of moisture conditions (xerotolerant). The finding of the type species (M. paludosa) in a well‐investigated area like central Europe highlights the diatom species richness of dystrophic habitats and their importance for diatom biodiversity conservation.     

Alpine freshwater ecosystems in a protected area: a source of diatom diversity

The “All Taxa Biodiversity Inventories” (ATBIs) project coordinated by the European Distributed Institute of Taxonomy (EDIT) aims to achieve a baseline biodiversity assessment of flora and fauna in those regions characterized by a lack of knowledge and a high potential for biodiversity. Within the framework of the ATBIs, the aim of this study was to analyse the diatom flora and ecology of a complex of freshwater ecosystems in the Maritime Alps Natural Park (Italy), designated as a Special area of Conservation under the European Habitat Directive. We sampled epilithic and epiphytic diatoms in different habitats in 24 sites: shallow lake, springs, and streams. Our analysis resulted in a list of 138 diatom taxa, highlighting the great biodiversity and the complex structure of the investigated diatom communities. The taxa list included a wide range of uncommon species, including some recorded for the first time in North-Western Italy. Among the different habitats the highest level of diversity was found in the more lentic waters, in particular in limnocrene springs. These results show that the diatom communities of pristine and undisturbed high-mountain environments are rich and complex, despite the severe environmental conditions.     

Mediterranean karst springs: diatom biodiversity hotspots under the pressure of hydrological fluctuation and nutrient enrichment

Abstract

Mediterranean karst springs are affected by strong climatic seasonality, with long, dry and hot summers and are increasingly threatened by anthropogenic pressures. In Sardinia (western Mediterranean Sea, Italy), they are largely unexplored and their biocoenoses are mostly unknown. The diatom flora from two substrates (cobbles and macrophytes) in eight springs of different areas of the island was investigated in summer 2016 and winter 2017. A total of 162 diatom taxa (58 genera) were found of which 27 (17 genera) only on cobbles and 26 (18 genera) only on macrophytes. The most abundant species from both substrates were Achnanthidium minutissimum, Amphora indistincta, Amphora pediculus, Cocconeis euglypta, Planothidium frequentissimum and P. lanceolatum. Overall, 67 taxa (40 genera) were recorded in single sites and some of these taxa showed high affinity with specific environmental conditions. Hydrological stability (water flow permanence), discharge and nutrients were the main environmental factors influencing diatom assemblages. Our results suggest that diatoms can reflect important local factors related to the vulnerability of these spring ecosystems and underline the importance of their preservation both for biodiversity and water quality maintenance.     

The influence of substrates and physicochemical factors on the composition of diatom assemblages in karst springs and their applicability in water-quality assessment

The methodological standards of monitoring programs recommend collecting material from stones, but this community is often absent in slow-flowing waters, whereas a great number of localities do offer bryophytic material for sampling. In order to investigate whether the kind of substrate (epilithic or bryophytic) influences the diatom-based biomonitoring results the structure of diatom assemblages from 13 anthropogenically altered springs were investigated. To examine differences between diatom assemblages, the species richness of diatom assemblages, H′ (Shannon-Wiener diversity index), Trophic Diatom Index (TDI) and Specific Pollution sensitivity Index (SPI) were compared. The TDI and SPI differed significantly (P = 0.002 and P = 0.004) between springs located in villages and springs away from villages, and did not differ significantly between epilithic and bryophytic samples (P > 0.05). No significant differences in species richness or the diversity index (H′) (P > 0.05) were found between the epilithic and bryophytic diatom assemblages. This study suggests that both the kinds of substrates can be successfully used for diatom-based water-quality biomonitoring in mesotrophic and eutrophic environments.     

High-throughput pyrosequencing of the chloroplast genome of a highly neutral-lipid-producing marine pennate diatom, Fistulifera sp. strain JPCC DA0580

The chloroplast genome of the highly neutral-lipid-producing marine pennate diatom Fistulifera sp. strain JPCC DA0580 was fully sequenced using high-throughput pyrosequencing. The general features and gene content were compared with three other complete diatom chloroplast genomes. The chloroplast genome is 134,918 bp with an inverted repeat of 13,330 bp and is slightly larger than the other diatom chloroplast genomes due to several low gene-density regions lacking similarity to the other diatom chloroplast genomes. Protein-coding genes were nearly identical to those from Phaeodactylum tricornutum. On the other hand, we found unique sequence variations in genes of photosystem II which differ from the consensus in other diatom chloroplasts. Furthermore, five functional unknown ORFs and a putative serine recombinase gene, serC2, are located in the low gene-density regions. SerC2 was also identified in the plasmids of another pennate diatom, Cylindrotheca fusiformis, and in the plastid genome of the diatom endosymbiont of Kryptoperidinium foliaceum. Exogenous plasmids might have been incorporated into the chloroplast genome of Fistulifera sp. by lateral gene transfer. Chloroplast genome sequencing analysis of this novel diatom provides many important insights into diatom evolution.     

An approach to the recent environmental history of Pilica Piaski spring (southern Poland) using diatoms

Diatom floras from springs have received little attention until recently, despite the fact that springs provide specific conditions that cannot be found in any other aquatic system, and remain of great importance in terms of general environmental changes. Due to pollution of the Kraków-Częstochowska upland aquifers, the chemical composition of spring waters in the area is anthropogenically modified, and far from the natural state. In order to generate a baseline diatom flora for springs, a paleolimnological study was applied as one of the best recognized and applied methods used to track long-term environmental changes worldwide. Little is known, however, about the direction and nature of such changes in aquatic environments fed by springs. The present article focuses on shifts in diatom assemblages preserved in sediments collected from a small pond, situated close to several spring outlets. They were interpreted as a record of environmental changes that had taken place during the last century. For most of the history of the pond—as recorded in this 84 cm long core—the diatom assemblage was dominated by small Fragilaria spp. The major shifts in species composition began in a core depth of 65 cm with a decline in Fragilaria construens var. venter (Ehrenberg) Grunow and Fragilaria pinnata Ehrenberg complexes, and a concurrent increase in Achnanthidium minutissimum (Kützing) Czarnecki. The second change was recorded at the depth of 45 cm with a sharp decline of A. minutissimum, which again was replaced by the small Fragilaria spp. In recent years, further changes in the diatom assemblage occurred, with a notable increase in Cyclotella delicatula Hustedt. The assemblage shifts recorded at this site appear to be consistent with environmental changes triggered by land use (e.g. agriculture intensity) and/or possible changes in spring water discharge. Guest editors: K. Buczkó, J. Korponai, J. Padisák & S. W. Starratt Palaeolimnological Proxies as Tools of Environmental Reconstruction in Fresh Water     

Microbial diversity and autotrophic activity in Kamchatka hot springs

Microbial communities of Kamchatka Peninsula terrestrial hot springs were studied using molecular, radioisotopic and cultural approaches. Analysis of 16S rRNA gene fragments performed by means of high-throughput sequencing revealed that aerobic autotrophic sulfur-oxidizing bacteria of the genus Sulfurihydrogenibium (phylum Aquificae) dominated in a majority of streamers. Another widely distributed and abundant group was that of anaerobic bacteria of the genus Caldimicrobium (phylum Thermodesulfobacteria). Archaea of the genus Vulcanisaeta were abundant in a high-temperature, slightly acidic hot spring, where they were accompanied by numerous Nanoarchaeota, while the domination of uncultured Thermoplasmataceae A10 was characteristic for moderately thermophilic acidic habitats. The highest rates of inorganic carbon assimilation determined by the in situ incubation of samples in the presence of ¹⁴C-labeled bicarbonate were found in oxygen-dependent streamers; in two sediment samples taken from the hottest springs this process, though much weaker, was found to be not dependent on oxygen. The isolation of anaerobic lithoautotrophic prokaryotes from Kamchatka hot springs revealed a wide distribution of the ability for sulfur disproportionation, a new lithoautotrophic process capable to fuel autonomous anaerobic ecosystems.

     

Haslea salstonica sp. nov. and Haslea pseudostrearia sp. nov. (Bacillariophyta), two new epibenthic diatoms from the Kingsbridge estuary, United Kingdom

Two new diatom species, Haslea salstonica and Haslea pseudostrearia are described in light and electron microscopy and compared with two well-known members of Haslea. Scanning electron microscope observations confirm that the new species belong to the genus Haslea. This study extends previous observations on the genus, particularly with respect to the development of a pseudostauros. The characteristic features of the genus are discussed briefly.     

A new diatom (Bacillariophyceae) genus with two new species from New Mexico,USA

A new diatom (Bacillariophyceae) genus and two new species are described from the arid region of the North American southwest. The new genus, Playaensis, and new species, P. circumfimbria and P. furtiva, are distinguished by frustule morphology and autecology. Playaensis possesses unique, narrowly lunate longitudinal ribs bordering the raphe and spathulate spines, but their evolutionary relationship to known genera is unclear. In Payton Lake, New Mexico, P. circumfimbria and P. furtiva are rare in the diatom community, and their geographic and geological extent are not known, but they may be restricted to alkaline, slightly saline lakes of the region.     

Genome properties of the diatom Phaeodactylum tricornutum

Diatoms are a ubiquitous class of microalgae of extreme importance for global primary productivity and for the biogeochemical cycling of minerals such as silica. However, very little is known about diatom cell biology or about their genome structure. For diatom researchers to take advantage of genomics and post-genomics technologies, it is necessary to establish a model diatom species. Phaeodactylum tricornutum is an obvious candidate because of its ease of culture and because it can be genetically transformed. Therefore, we have examined its genome composition by the generation of approximately 1,000 expressed sequence tags. Although more than 60% of the sequences could not be unequivocally identified by similarity to sequences in the databases, approximately 20% had high similarity with a range of genes defined functionally at the protein level. It is interesting that many of these sequences are more similar to animal rather than plant counterparts. Base composition at each codon position and GC content of the genome were compared with Arabidopsis, maize (Zea mays), and Chlamydomonas reinhardtii. It was found that distribution of GC within the coding sequences is as homogeneous in P. tricornutum as in Arabidopsis, but with a slightly higher GC content. Furthermore, we present evidence that the P. tricornutum genome is likely to be small (less than 20 Mb). Therefore, this combined information supports the development of this species as a model system for molecular-based studies of diatom biology. The nucleotide sequence data reported has been deposited in GenBank Nucleotide Sequence Database (dbEST section) under accession nos. BI306757 through BI307753.     

Diatom communities along pH and hydrological gradients in three montane mires,central China

The distribution patterns of epiphytic diatom assemblages in three montane mires in central China were investigated to examine their relationships with selected environmental variables (pH and depth to water table, DWT). Two of the mires are considered to be in good ecological condition (Dajiuhu and Qizimeishan Mires) while Erxianyan Mire is extensively affected by acid deposition and human activities. A total of 206 taxa belonging to 56 genera were found in 44 Sphagnum samples. Multivariate analysis revealed that pH and DWT were significantly correlated with diatom distribution. In Erxianyan Mire, the characteristic taxa (Eunotia minor and Eunotia intermedia) had lower pH optima and may therefore be useful indicators of highly-acidic conditions. In Dajiuhu Mire, the dominant species had higher pH optima, and abundant xerotolerant taxa (Hantzschia amphioxys, Pinnularia borealis, Luticola mutica and Diadesmis contenta) were observed. In the partial canonical correspondence analyses with mire location as a covariable, the correlation between diatom data and pH was insignificant, likely because pH differences between mires were greater than those within mires. In contrast, diatom data were significantly correlated with DWT, suggesting that diatoms are good sensors of hydrological variability along the hollow to hummock gradient. Together, these data can expand current autecological information for these potential diatom indicator species, which is critical for refining our interpretations of bio-monitoring and palaeolimnological studies in montane mires.     

The palaeolimnological potential of diatom assemblages in floodplain lakes of the Danube Delta, Romania: a pilot study

Within the framework of a palaeolimnological pilot study, the potential of sedimentary diatom assemblages for the reconstruction of the eutrophication history was studied in short sediment cores from five shallow lakes located in the Romanian Danube Delta. A total of 234 diatom taxa representing 57 genera could be identified but diatom assemblages are generally predominated by a few species only. Loss on ignition percentages, total diatom abundances and diatom downcore successions largely vary within the single sediment cores and between all five lakes. This suggests the presence of various lake environments within the Danube Delta, each characterized by lake-specific geomorphological, sedimentological, hydrological, and biological conditions. Highly variable depositional conditions are also confirmed by radiocesium measurements in two of the five cores suggesting distinct inter-lake differences in the sedimentation rate. Causes for the great intra-lake and inter-lake variability in diatom downcore successions are difficult to specify and may include changes in the physico-chemical conditions, aquatic vegetation cover, water depth, river influence, turbidity and inter-biotic interactions. However, based on this pilot study, it is likely that the spatial and temporal distribution of sedimentary diatom assemblages in Danube Delta lakes were not triggered by the trophic state. The delta lakes likely became meso- to eutrophic long before 1950, possibly during late-Holocene times.     

DIATOMS (BACILLARIOPHYTA) OF ISOLATED ISLANDS: NEW TAXA IN THE GENUS NAVICULA SENSU STRICTO FROM THE GALáPAGOS ISLANDS1

The diatoms (Bacillariophyta) from a coastal lagoon from the Diablas wetlands (Isla Isabela, the Galápagos Islands) were studied in material from surface samples and a sediment core spanning the past 2,700 years in order to examine evidence of diatom evolution under geographic isolation. The total number of taxa found was ～100. Ultrastructural variation in valve morphology between members of Galápagos taxa was used to describe 10 species from the genus Navicula sensu stricto, which are new to science. Four taxa: N. isabelensis, N. isabelensoides, N. isabelensiformis, and N. isabelensiminor, shared several key characteristics that may be indicative of a common evolutionary heritage; these species therefore provide possible evidence for the in situ evolution of diatoms in the Galápagos coastal lagoons. Shared morphological characteristics include: (i) stria patterning in the central area, (ii) an elevated and thickened external raphe‐sternum, (iii) external central raphe endings that are slightly deflected toward the valve primary side, and (iv) an arched valve surface. To explain these findings, two models were proposed. The first suggested limited lateral diatomaceous transport of Navicula species between the Galápagos and continental South America. Alternatively, these new species may be ecological specialists arising from the unique environmental conditions of the Galápagos coastal lagoons, which restrict the colonization of common diatom taxa and enable the establishment of novel, rare species. The Diablas wetlands are an important site for diatom research, where local‐scale environmental changes have combined with global‐scale biogeographic processes resulting in unique diatom assemblages.     

Thermus aquaticus gen. n. and sp. n., a Nonsporulating Extreme Thermophile

The isolation of a new thermophilic bacterium, Thermus aquaticus gen. n. and sp. n., is described. Successful enrichment requires incubation at 70 to 75 C, and the use of nutrient media relatively dilute with respect to the organic components. Strains of T. aquaticus have been isolated from a variety of thermal springs in Yellowstone National Park and from a thermal spring in California. The organism has also been isolated from man-made thermal habitats, such as hot tap water, in geographical locations quite distant from thermal springs. Isolates of T. aquaticus are gram-negative nonsporulating nonmotile rods which frequently form long filaments at supraoptimal temperatures or in the stationary phase. All isolates form a yellow cellular pigment, probably a carotenoid. A characteristic structure formed by all isolates is a large sphere, considerably larger than a spheroplast. These large spheres, as well as lysozyme-induced spheroplasts, are resistant to osmotic lysis. Deoxyribonucleic acid base compositions of four strains were determined by CsCl density gradient ultracentrifugation and found to be between 65.4 and 67.4 moles per cent guanine plus cytosine. The growth of all isolates tested is inhibited by fairly low concentrations of cycloserine, streptomycin, penicillin, novobiocin, tetracycline, and chloramphenicol. Nutritional studies on one strain showed that it did not require vitamins or amino acids, although growth was considerably faster in enriched than in synthetic medium. Several sugars and organic acids served as carbon sources, and either NH(4) (+) or glutamate could serve as nitrogen source. The organism is an obligate aerobe and has a pH optimum of 7.5 to 7.8. The optimum temperature for growth is 70 C, the maximum 79 C, and the minimum about 40 C. The generation time at the optimum is about 50 min. The possible relationships of this new genus to the myxobacteria, flexibacteria, and flavobacteria are discussed.     

Tissue changes in the rabbit periodontal ligament during orthodontic tooth movement

In this (semi) quantitative animal study the reaction of the periodontal ligament (PDL) to experimental tooth movement is described. To this end, rabbit first incisors were moved sideways with helical torsion springs for periods varying from 3-24 hours. The initial force of the springs was 50 gf. The histomorphology of the PDL was studied in 5 microns thick plastic sections. Comparison with control animals and animals wearing passive springs showed that tooth movement leads to an increased trauma in the PDL within only a few hours. This trauma is characterized by hyalinization, tears and ruptures in the fibres and blood vessels, and by the presence of extravascular erythrocytes and pyknosis. Tissue damage significantly increased with time. After 24 hours of tooth movement, the PDL fibers are compressed or stretched in 68% of the sections and the blood vessels in the PDL are compressed or stretched in 62% of the sections. Even in the controls, more than 15% of the sections displayed slightly stretched or compressed fibers, and about 10% showed slightly compressed or stretched blood vessels. This indicates that some damage is regularly present in a normally functioning PDL. Increases in the percentage of sections with blood vessel compression are found in all groups wearing passive springs, especially after 6 hours. A high concordancy in compression and tension patterns of blood vessels and fibers is present in 83% of the sections. Pyknotic cells are practically confined to areas with compressed PDL fibers in rabbits wearing active springs. Extravascular erythrocytes were found in sections with all types of fiber patterns. A significant majority of extravascular erythrocytes, however, was found in areas with compressed fibers.     

Seasonality of macroalgae and epilithic diatoms in spring-fed streams in Texas, USA

A seasonal study of two spring-fed stream systems in south-central Texas was undertaken over a 15-month period from June 1996 to September 1997. Relative abundance of the epilithic diatom flora, percent cover of macroalgae, and several physical and chemical conditions were monitored in one 20-m stretch in each of the streams at approximately two-month intervals. Six additional spring-fed stream segments were sampled in May 1996 for macroalgae and measured for the same conditions, in order to determine how representative the macroalgal floras of the study sites were of south-central and western Texas. Conditions in the two stream segments were relatively constant over the 15 months, except for maximum depth; this finding is similar those reported for other spring-fed systems worldwide. Sixty-eight diatom taxa and nine macroalgae taxa were identified from the San Marcos River, which compares to 46 diatom taxa and six macroalgae taxa from the Comal River. Several diatom and macroalgae species were significantly correlated to stream conditions (e.g. Dichotomosiphon tuberosus and Hildenbrandia angolensis with daylength, and Amphora pediculus with maximum depth). Twenty-one macroalgal taxa were identified from the six additional spring-fed steam segments. Conditions in these streams were very similar to those measured in the San Marcos River and Comal River, except that they had a higher average pH _x= 8.1 versus _x= 7.6). The epilithic diatom flora of the San Marcos River and the Comal River contains many of the diatom and some macroalgal taxa commonly reported from springs globally. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Diatoms,Productivity and Morphometry of 43 Lakes in New York State,U.S.A

Diatoms were examined in surface sediments collected from 43 lakes throughout New York State to determine the interrelationships among the abundances of various diatom taxa,' lake productivity and lake morphometry. Diatom ratios, including the A/C, C/P and five new quotients, were not well correlated with lake productivity, probably because of the diversity of the taxa which they employ. The abundance of individual genera or combinations of genera were better indicators of productivity. Cyclotella was the best single indicator of productivity being most abundant in low productivity lakes. Several fairly distinct diatom associations were identified by correlations between all possible pairs of diatom taxa. Finally, lake productivity was found to be significantly correlated with morphometry, being highest in small/shallow lakes.     

Paleolimnology and diatom flora of the Miocene Quincy Diatomite,Washington, USA

The Quincy Diatomite, central Washington, USA, is a middle Miocene (∼ 15 Ma) lacustrine deposit located between flows of the Columbia River Basalt Group. Two primary localities along the western margin of the deposit are examined for stratigraphic and geographic variation. Three lithologic units are recognized in the deposit and are distinguished by distinct diatom floras and subtle lithologic differences. Diatom assemblages vary geographically along the western margin of the basin. Distinctions between these assemblages are confirmed through analysis of point count data using nonMetric Multidimensional Scaling and cluster analyses. Three stages of lake development, directly influenced by the regional geology and geography, are recognized. The earliest stage was likely deposited in a series of small-interconnected pocket lakes that were eutrophic and slightly alkaline. This lake stage was succeeded by a period of shallower water depth, and dominated by benthic species. The latest stage of the lake is interpreted as representing a deepening and expansion of the lake, based on the dominance of planktonic diatom species. Tectonic uplift of the western Frenchman Hills Anticline combined with overall subsidence of the Quincy Basin during intermediate and late stages of lake development is interpreted to be the driver for relative changes in lake bathymetry.