The effect of current on the distribution of diatoms settling on submerged glass slides

Glass microscope slides were submerged for two to six week periods at selected sites in a small, spring-fed stream near Lennoxville, Quebec. Slides were oriented parallel and perpendicular to the current. Qualitative and quantitative data from transects across slides show that diatoms are randomly distributed on slides perpendicular to the current but not on slides oriented parallel to the current. In the later case, most individuals first settled near the upstream or downstream edge of the slide. Non-random distribution is most pronounced on slides containing Cocconeis placentula. This species and two others, Achnanthes linearis and A. minutissima, are abundant and determine most distribution patterns found on slides. Preference of diatoms for the edges of slides appears to be affected by current. We propose a model, based upon water flow, to explain the preferential distribution of diatoms on slides oriented parallel to the current. Light appears not to affect settling patterns to a great extent in this study.     

SEM observations of some noteworthy diatoms from the Ikpoba reservoir,Nigeria

ABSTRACT

Eighteen taxa of diatoms from the Ikpoba reservoir, southern Nigeria are listed in this report. They belong to the genera Cymbella, Stenopterobia, Eunotia, Brachysira, Frustulia, Navicula, Pinnularia, Stauroneis and Surirella. The occurrences and distribution of the algae are indicated. Two of these taxa occurred very frequently, six frequently and four occasionally. Five taxa had rare occurrences while one was very rare. They were compared with national as well as regional records.     

A review of diatoms found in highly acidic environments

A review is presented of 28 studies in the literature of diatoms in environments at pH 3.5, including natural and anthropogenic acid sources. A total of 124 diatom taxa have been reported, but many are likely to have been accidental occurrences, because only a few specimens were found. Approximately 19 taxa abundant in at least one study or common in several studies are considered true inhabitants of highly acidic waters. These include: Achnanthes minutissima, Eunotia exigua, E. tenella, E. septentrionalis, E. osoresanensis, E. arcus, E. glacialis, E. pectinalis, Frustulia rhomboides, F. rhomboides var. saxonica, Nitzschia capitellata/subcapitellata, Nitzschia communis, Nitzschia pusilla, Nitzschia vasta, Pinnularia acoricola, P. obscura, P. braunii var. amphicephala, P. subcapitata and P. terminitina. There are inconsistencies in the taxonomy of several of these species and possible synonymies could lower the number of taxa to less than 9. Compared to diatom species richness in environments at pH 4.5–5.0, there are many fewer taxa in environments pH 3.5, suggesting a threshold between pH 4.5 and 3.5 below which many species are unable to maintain a population.     

SEA ICE MICROBIAL COMMUNITIES. V. THE VERTICAL ZONATION OF DIATOMS IN AN ANTARCTIC FAST ICE COMMUNITY1

A distinct vertical zonation was observed among diatoms in a bottom congelation ice community at McMurdo Sound, Antarctica during the 1981 spring bloom. The bottom 20 cm of ice collected in December from four stations with variable snow cover was subdivided into 5 cm sections for analysis of algal distribution. Algal abundance was inversely related to the depth of snow cover, and generally decreased with increasing distance above the ice-water interface. Most diatoms, including the dominant species Nitzschia stellata Manguin, Amphiprora kufferathii Manguin and Fragilaria islandica var. adeliae Manguin showed peak abundance in the bottom 10 cm of the ice, where the proportion of living to empty cells was also highest. Two species, however, an Auricula Castracane sp. and Navicula glaciei van Heurck, reached highest concentrations at depths 10–20 cm above the ice-water interface. We considered two factors as contributing to the observed vertical zonation: (1) successive blooms at the ice-water interface become spatially stratified within the ice by further accretion below; (2) a differential growth of species occurs along physicochemical gradients within the ice column. A comparison of early versus late season profiles suggests the latter mechanism may prevail once ice accretion has ceased.     

EVIDENCE OF DARK AVOIDANCE BY PHOTOTROPHIC PERIPHYTIC DIATOMS IN LOTIC SYSTEMS1

Short-term (24–48 h) colonization dynamics of periphytic diatoms on artificial (styrofoam) substrata were examined using fast-flushing, continuous-flow troughs located on the North Thompson River, British Columbia. Two parallel troughs, one exposed to natural light and the other completely darkened, showed significant differences in periphyton biomass, chlorophyll a, and algal taxonomic composition with 24 h. Experiments which commenced at the onset of natural darkness demonstrated that rates of algal immigration during the night were the same in both troughs. Within 2–3 h of sunrise, however, certain diatom species (most notably Hannaea arcus (Ehr.) Pair, and Diatoma tenue Ag.) selectively emigrated from the artificially darkened trough but remained in the trough exposed to natural light. More closely adhering species such as Achnanthes minutissima Kütz, also showed significant emigration from the darkened trough after light deprivation for two photoperiods. Data from adhesion, emigration, and sinking rate experiments indicate that differential egress of cells from the darkened versus the lighted environments is the result of cellular regulation of buoyancy or form resistance.     

Vertical distribution of Hymenophyllaceae species among host tree microhabitats in a temperate rain forest in Southern Chile

Question: Are differences in microhabitat preferences of co‐occurring epiphytic Hymenophyllaceae species (filmy ferns) correlated with differences in ecophysiological responses to light availability and humidity in the host tree? Location: The Andean foothills in south‐central Chile. Methods: We evaluated the distribution pattern of nine filmy fern species in microhabitats that differ in light availability and humidity in four host tree species. A DCA was developed to assess Hymenophyllaceae species microhabitat preference in terms of canopy openness (CO) and relative humidity. We assessed whether differences in chlorophyll content, maximum photochemical efficiency (Fv/Fm), photosynthetic capacity (A_max), evapotranspiration (E) and instantaneous water use efficiency (WUE) are consistent with any pattern. Results: CO and relative humidity differed significantly with height in the host trees. While CO increased with height in a host tree, relative humidity decreased. DCA analysis showed that filmy fern species distribution within and among trees was mainly explained by the relative humidity of the microhabitat. Chlorophyll content, chlorophyll a/b ratio, A_max and E differed significantly among filmy fern species. A_max and E were correlated with axis 1 scores from the DCA analysis. Conclusions: The vertical distribution and abundance of filmy fern species in Chilean temperate rain forest seems to be closely related to the different microhabitats offered by host trees. This pattern may reflect interspecific differences in ecophysiological traits related both to light availability and humidity. Our results suggest that humidity is the main environmental factor driving functional responses and habitat preferences of these filmy fern species.     

Characterization of the triacylglycerol profile in marine diatoms by ultra performance liquid chromatography coupled with electrospray ionization–quadrupole time-of-flight mass spectrometry

Diatoms are considered to have great potential as new biofuel sources because they can effectively accumulate triacylglycerols (TAGs). Detailed structure information of TAG in diatoms is much needed not only for the assessment of biofuel quality such as fatty acid chain length and unsaturation degree but also for the tracing of biosynthetic precursors because the biosynthesis of TAG is typically completed by utilizing the diacylglycerol acyltransferase in the cytoplasm. In this report, a comprehensive characterization of TAGs in marine diatoms was performed using ultra performance liquid chromatography–electrospray ionization–quadrupole time-of-flight mass spectrometry. Many types of major TAGs were identified for the first time in these diatoms: 12 TAGs in Chaetoceros debilis, 9 TAGs in Phaeodactylum tricornutum Bohlin, 16 TAGs in Nitzschia closterium f. minutissima, 16 TAGs in Thalassiosira weissflogii, 13 TAGs in Thalassiosira sp., 16 TAGs in Stephanodiscus asteaea and 7 TAGs in Skeletonema costatum. Semi-quantification of TAGs in these diatoms was also carried out, and it was found that the contents of individual TAGs ranged from 0.5?±?0.1 to 217.9?±?8.1 nmol mg^?1 total lipids. In addition, the total lipid contents in diatoms ranged from 143.6?±?16.3 to 201.1?±?16.3 mg g^?1 dry microalgae and the total TAG contents ranged from 36.8?±?9.5 to 793.2?±?54.4 nmol mg^?1 total lipids. By comparative analysis of the compositions and concentrations of major TAGs in the seven algal strains, N. closterium f. minutissima with high abundance of TAGs containing the most monounsaturated fatty acids (mainly palmitoleic acid) was considered as one of the most promising diatom strains for microalgal biofuel production. Additionally, based on the information of sn-2 fatty acid obtained (mainly C16 in the sn-2 position), we propose the hypothesis that TAGs in diatoms are mainly derived from lipids in chloroplasts through the prokaryotic biosynthesis pathway, including monogalactosyldiacylglycerol and digalactosyldiacylglycerol.     

Terrestrial soil diatom assemblages from different vegetation types in Zackenberg (Northeast Greenland)

A total of 81 taxa were observed from 30 soil samples taken from 5 different vegetation types in Northeast Greenland. Most of the dominant diatoms are well-known cosmopolitan aerophilic taxa; only Caloneis aerophila and Pinnularia lagerstedtii are less widespread species. The valve lengths of P. borealis and Hantzschia amphioxys are correlated with the moisture content of the soils. Average cell number/g dry weight of soil amounts to 1,120,000 ± 740,000. In a TWINSPAN classification, the soils of the different vegetation types are separated, with the exception of the Vaccinium soils, which are grouped partly with the Cassiope samples and partly with the Salix soils. In a CCA ordination diagram, the Navicula atomus–Fragilaria elliptica assemblage shows a positive correlation with organic content and pH and a negative one with permafrost depth. The Pinnularia divergentissima var. martinii–P. obscura assemblage is positively correlated with moisture. The Pinnularia lagerstedtii–Caloneis aerophila assemblage is positively correlated with permafrost depth and negatively with pH and moisture. Accepted: 27 November 1999     

SPATIAL PARADIGMS OF LOTIC DIATOM DISTRIBUTION: A LANDSCAPE ECOLOGY PERSPECTIVE

Spatial distributional patterns of benthic diatoms and their relation to current velocity were investigated in an unshaded cobble-bottom reach of White Creek (Washington County, NY). On 27 August 1999, diatoms were sampled and current velocity and depth were measured on a regular square sampling grid with a grain size of 0.01 m², interval of 0.5 m, and extent of 16 m². The relative abundance of the 18 common diatom species enumerated in the 81 samples was subjected to detrended correspondence analysis (DCA). The first axis (DCA1) explained 51% of the variance in diatom data and separated the samples according to current regimes. The spatial autocorrelation of DCA1 sample scores in deposition and erosion regions of White Creek was determined by Moran's I statistic to indicate patch size. In White Creek the patch length of all diatom communities was more than 3.1 m, whereas the patch width was 1 m in the deposition region and 0.5 m in the erosion region. There were 5 dominant diatom taxa, Achnanthes minutissima Kütz. et vars, Fragilaria capucina Dezmazières et vars, F. crotonensis Kitt., Diatoma vulgaris Bory, and Synedra ulna (Nitz.) Ehr. et vars. The patch length of the dominant species varied from 1 to more than 4.1 m, whereas the patch width, if defined, was 0.5 m. Achnanthes minutissima and F. capucina, the two diatom species with the highest relative abundance, displayed spatially structured patches of low abundance and comparatively random patches of high abundance, suggesting broad scale abiotic control of species performance in low abundance regions and finer scale biotic control of high abundance areas. Another objective of this study was to test the hypothesis that higher current velocities, which generally impede immigration, would increase randomness and complexity (i.e. homogeneity of diatom distributional patterns). The spatial complexity in low versus high velocity transects was determined by calculating the respective fractal dimension (D) of DCA1 scores. D of DCA1 was higher in the higher current velocity transects, suggesting that spatial complexity and homogeneity of diatom communities increased in faster currents. Partial canonical correspondence analysis was conducted on diatom, environmental, and spatial data to assess how much of the variance in species distribution could be attributed to environmental (current velocity and depth) versus spatial factors. The variance of species data, explained by the environment (exclusively current velocity), was 38%; whereas space alone contributed only 10%, indicating that 1) current velocity was the major factor that controlled diatom distribution in streams and 2) there were other spatially dependent variables, most likely biotic, but their role in shaping diatom communities was minor.     

COMPARISON OF ATTACHED DIATOM COMMUNITIES ON NATURAL AND ARTIFICIAL SUBSTRATES1

A study of attached diatom communities on artificial and natural substrates was conducted in Wheelwright Pond, New Hampshire, during 1975. There were differences in the species composition growing on artificial glass slides and natural substrates. The slides favored the accumulation of Achnanthes minutissima Kütz. and decreased the relative abundance of Eunotia incisa W. Sm. ex. Greg. and Cocconeis placentula v. euglypta (Ehr.) Cleve. Large growths of planktonic species were also noted on the slides. Compositional differences between slides positioned at 15–30 cm (upper) and 1 m (lower) from the surface of the water were minimal. A similar community composition of periphytic diatoms was found on five aquatic macrophytes.     

THE STRUCTURE AND NANOMECHANICAL PROPERTIES OF THE ADHESIVE MUCILAGE THAT MEDIATES DIATOM‐SUBSTRATUM ADHESION AND MOTILITY1

We investigated the adhesive mucilage and mechanism of cell‐substratum adhesion of two benthic raphid diatoms, the marine species Craspedostauros australis E. J. Cox and the freshwater species Pinnularia viridis (Nitzsch) Ehrenberg. SEM images of P. viridis and C. australis cells revealed the presence of multistranded tethers that appear to arise along the raphe openings and extend for a considerable distance from the cell before forming a “holdfast‐like” attachment with the substratum. We propose that the tethers result from the elongation/stretching of composite adhesive mucilage strands secreted from raphes during the onset of cell adhesion and reorientation. Atomic force microscopy (AFM) force measurements reveal that the adhesive strands originating from the nondriving raphe of live C. australis and P. viridis are highly extensible and accumulate to form tethers. During force measurements tethers can be chemically stained and are seen to extend between the cantilever tip and a cell during elongation and relaxation. In most cases, AFM force measurements recorded an interaction with a number of adhesive strands that are secreted from the raphe. The force curves of C. australis and P. viridis revealed a sawtooth pattern, suggesting the successive unbinding of modular domains when the adhesive strands were placed under stress. In addition, we applied the “fly‐fishing” technique that allowed the cantilever, suspended a distance above the cell, to interact with single adhesive strands protruding from the raphe. These force curves revealed sawtooth patterns, although the binding forces recorded were in the range for single molecule interactions.     

广东鉴江水系底栖硅藻多样性与时空分布特征

为了解广东省鉴江水系底栖硅藻多样性和时空分布特征,对全流域进行了底栖硅藻采样调查。结果表明,从19个采样点4次采样中共检出底栖硅藻10科52属242种,其中舟形藻属(Navicula)、菱形藻属(Nitzschia)和异极藻属(Gomphonema)是优势类群,出现频次和相对丰度较高。硅藻多样性指数(丰富度、真香农多样性指数和真辛普森多样性指数)随河流等级呈现一定的空间分布特征,但它们季节变化不明显。底栖硅藻群落相异性在上游和下游河段较高,从一级到三级河流递减,四级河流又增加。底栖硅藻群落结构空间变化明显,季节变化显著。群落丰富度的稀疏曲线表明,热带河流底栖硅藻群落以400个体计数,不能完整反映底栖硅藻多样性。这些为鉴江水系河流健康监测和水生态保护奠定了基础。     

Cypris Habitat Selection Facilitated by Microbial Films Influences the Vertical Distribution of Subtidal Barnacle Balanus trigonus

The potential driving force(s) of the vertical distribution of subtidal barnacle Balanus trigonus Darwin were investigated using both field and laboratory experiments. Early juveniles (∼24 h old) placed in intertidal [∼0.5 m above mean low water level (MLWL)] and subtidal (∼3 m below MLWL) habitats survived equally well, indicating that the intertidal absence of B. trigonus in Hong Kong waters was not determined by differential mortality. However, enhanced attachment of cyprids in subtidal habitats indicated the importance of differential larval choice in determining their vertical distribution. In the laboratory, cyprids preferred to attach in response to subtidal microbial films, which may implicate microbial films as a primary cue in driving the adult vertical distribution. Microbial films developed in these two habitats differed in their biomass (=total organic carbon), abundance of bacteria and diatoms (determined by fluorescence microscopy), and bacterial diversity (determined by DNA fingerprinting analysis). For example, 6-day films in subtidal habitat had a significantly higher biomass than in films from intertidal habitat (P<0.05). There was no difference in the biomass of films from these two habitats in 9-day films (P>0.05); however, bacterial abundance was greater in subtidal films than in intertidal films, irrespective of the age of the film, although there was no difference in diatom abundance in films from these two habitats. Neither the abundance of bacteria and diatoms nor the biomass correlated with the attachment preferences of cyprids. This study has not provided any data to prove the existence of inductive and inhibitive (to cyprid attachment) bacterial species in subtidal and intertidal films, respectively; however, results indicate that bacterial community provided qualitative information that might explain the preferential attachment of B. trigonus cyprids in subtidal habitat.     

Vertical zonation and production rates of epiphytic algae on Phragmites australis

1. The vertical distribution of chlorophyll in epiphyton on Phragmites australis showed a peak in the middle sections of the submerged parts. Just below the water surface and above the sediment, chlorophyll concentrations were much less. 2. During winter and early spring, loosely attached diatoms were predominant just below the water surface and on the middle sections of the Phragmites plants. Near the bottom, adnate diatoms, parenchymatous thalli of chlorophytes and cyanobacteria were abundant. 3. At high photosynthetic active radiation (PAR) during May, filamentous species of Ulpthricophyceae and Zygophyceae developed dense populations on the middle sections of the stems. 4. Primary production rate was proportional to chlorophyll concentration although production maxima were recorded above the biomass maxima. 5. Where illumination was low, the chlorophyll-specific rate of photosynthesis (P^B rate) decreased proportionally with the vertical decrease of PAR in the littoral zone, independent of the chlorophyll concentration on the stems. 6. When illumination was high, the P^B rate decreased as biomass increased, and was independent of surface radiation. 7. The dependence of primary production rate on chlorophyll concentration produced a saturation curve with a maximum production at 4.6 μgC cm^?2h^?1.     

Changing nutrient levels in Grasmere, English Lake District, during recent centuries

1. Historical nutrient changes in Grasmere were investigated using a 300‐year record derived from six sediment cores. One core was investigated at high resolution for diatoms, total sedimentary phosphorus, and loss‐on‐ignition (LOI), and was dated using ²¹⁰Pb and ¹³⁷Cs. Six other cores were scanned for magnetic susceptibility, diatoms and LOI to confirm the stratigraphic integrity of the primary record. 2. A rise in nutrient levels occurred after 1855 AD. This event was marked by a shift away from benthic diatom assemblages and a rise in Asterionella formosa. The onset of eutrophication from 1855 corresponds to the expansion of the local and tourist population in the area. 3. The replacement of A. formosa with Cyclotella spp. ca 1945–65 indicates reduced nutrient loads, possibly because of enhanced flushing brought about by the seasonal rainfall distribution. 4. After 1965 a step‐wise increase in both absolute and relative amounts of Asterionella was found. High sedimentary P and diatom inferred TP confirmed the high nutrient loading of the lake. Nutrient increase is attributable to problems with the Grasmere village sewage system and the installation of a wastewater treatment works (WwTW) on the River Rothay in 1971. Modifications to the WwTW in 1982 caused an initial improvement, but have not led to a full recovery to pre‐1965 ecological conditions. 5. The diatom record indicates a further improvement after 1990 by a return toward Achnanthes minutissima. 6. The sedimentary archive of sensitive sites provides important benchmarks against which to judge the attainment of water quality targets.     

Scanning electron microscope evidence for diatom uptake by two Antarctic sponges

Scanning electron microscopy (SEM) investigation of two Antarctic sponges, Phorbas glaberrima and Tedania charcoti, showed that the exopinacoderm effects a direct uptake of benthic diatoms which settle on the sponge surface. In P. glaberrima, planktonic diatoms were also observed penetrating through the inhalant system, the primary way of feeding in sponges. Benthic diatoms which accumulate in the mesohyl underneath the exopinacoderm help to strengthen the sponge cortex and may be an alimentary source during oligotrophic periods in the Antarctic environment.     

Distribution of Epilithic Diatoms in Response to Environmental Conditions in an Urban Tropical Stream, Central Kenya

Use of diatoms in monitoring water quality is well acknowledged in developed countries, but only recently has the assessment started gaining importance in developing countries. Diatoms can be obtained from natural and artificial substrates. Appreciating the differences and similarities of diatom assemblages on both substrates may contribute to a better understanding and standardization particularly during monitoring of water quality. During this study we assessed diatom assemblages, biodiversity and trophic indices in relation to water quality along the Nairobi River. Fifteen sites were sampled in September 2000 during the dry season. Diatoms were collected from natural substrates (stones, pebbles) and artificial substrates (100% acrylic wool). On artificial and natural substrates, a total of 190 and 151 taxa were found, respectively, the majority of these taxa (80%) have cosmopolitan distribution and are also widespread throughout tropical African. Species composition changed downstream, five taxa dominated upper and mid stream sites whereas lower stream sites were dominated by one or two taxa. Species richness, diversity, dominance and evenness were positively correlated with NO₃, O₂ and altitude but decreased markedly downstream with a simultaneous increase in total dissolved solids, alkalinity, chemical oxygen demand and PO₄. Ordination and classification (CANOCO and TWINSPAN) showed that diatom assemblages in the Nairobi River responded strongly to water quality changes with respect to concentrations of NO₃, NO₂, total dissolved solids and temperature. Taxa common at less impacted upstream sites included Gomphonema gracilis, Anomoeoneis brachysira and Fragilaria biceps; while common taxa at midstream sites with agricultural catchments were Gomphonema parvulum, Navicula cryptocephala, N. schroeteri, N. bryophila, N. halophila, Nitzschia linearis var. linearis and Cymbella silesica. Achnanthes minutissima var. saprophila, Gomphonema angustum, Navicula subminuscula, N. arvensis, Nitzschia palea and N. umbonata were most common at urban sites, which were polluted by residential and industrial effluents. Trophic diatom indices suggested that water quality was poor at most sites in the Nairobi River. Most sites along the river had low Generic Diatom Index values, GDI (<12) and high Trophic Diatom Index values, TDI 73–78 (median = 76) and 75–84 (median = 77) for artificial and natural substrates, respectively. This study showed that diatoms' response on natural and artificial substrates were similar and reflected environmental conditions correctly.     

Comparing the responses of diatoms and macro- invertebrates to metals in upland streams of Wales and Cornwall

SUMMARY 1. Surprisingly few data compare the apparent responses of diatoms and macroinvertebrates to metals in streams. We examined variation in metals, diatoms and macroinvertebrates between 51 streams in metal‐mining areas of Wales and Cornwall, U.K., using a survey design with multiple reference and polluted sites. 2. To quantify variations in metals between sites, we calculated cumulative criterion unit (CCU) scores, a recently defined measure of total stream metal concentration and toxicity, to account for additive effects of each metal relative to putative toxic thresholds. We compared assemblage responses among epilithic diatoms and macroinvertebrates to CCU scores or individual metal concentrations using correlation and detrended correspondence analysis (DCA). 3. Macroinvertebrate diversity, richness and total abundance declined and evenness increased with increasing copper concentrations. Trends with CCU scores were significant but less pronounced. Some individual macroinvertebrate taxa varied significantly in abundance with CCU scores, copper or zinc, but overall assemblage composition correlated only with manganese, pH and nitrate. 4. Among diatoms, pH and conductivity explained the major variations in assemblage composition, and neither diversity, richness nor evenness varied with metal concentration. Nevertheless, the single strongest predictor of diatom assemblages on ordination axis 2 was the CCU score. The abundances of some macroinvertebrate taxa, particularly grazers, also explained significant variations in diatom assemblages that were linked to both metals and acid–base status. 5. Diatom species apparently tolerant of high metal concentrations included Psammothidium helveticum, Eunotia subarcuatoides, Pinnularia subcapitata and Sellaphora seminulum. Of these, P. helveticum, E. subarcuatoides and P. subcapitata were abundant at lower pH than S.seminulum and might indicate metal enrichment over different pH ranges. Sensitive species included Fragilaria capucina var. rumpens, Achnanthes oblongella and Tabellaria flocculosa. 6. We conclude that macroinvertebrates at these sites reflected metal pollution most strongly through variations in diversity while effects on diatoms were best reflected by changes in assemblage composition. We suggest that, with further refinement, CCU scores might be useful in evaluating the possible effects of metal pollution on benthic organisms in European rivers.