Benthic Diatoms as Indicators of Stream Sediment Concentrationin Hong Kong

Diatoms are photosynthetic unicellular, eukaryotic, microorganisms (algae) that are distinguished by their silicified (SiO₂‐nH₂O) cell walls. They have often been employed to assess salinity, pH, and nutrient conditions. Our data suggest that, they may also be used to assess suspended solid levels in streams. The ratio of motile to attached benthic diatoms from five different stream sites in Hong Kong was correlated with the level of suspended solids for each of these sites. Sites with high concentrations of suspended solids had a high percentage of motile diatoms on their rocks while sites with low concentrations of suspended solids had a high percentage of attached (non‐motile) diatoms on their rocks. When water carried by a stream has a high concentration of suspended solids, benthic diatoms in the stream are often covered in a layer of silt. Those diatoms that are motile are able to get on top of this silt layer while attached diatoms cannot. If the silt layer is not washed away, the attached diatoms perish and the percentage of motile diatoms increases. Thus, streams with high concentrations of suspended solids display a higher proportion of motile diatoms than do clear water streams with low concentrations of suspended solids. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Review--Interactions between diatoms and stainless steel: focus on biofouling and biocorrosion

There is a considerable body of information regarding bacterially enhanced corrosion, however, this review focuses on diatoms (unicellular algae) whose contribution to biocorrosion is less well studied. The reasons why diatoms have been neglected in studies of biocorrosion in natural waters are discussed and the question whether diatoms should be considered as inert with respect of electrochemical processes is considered. A particular focus is given to the case of stainless steels (SS), which are widely used in variety of applications in natural waters. Basic information on the cell biology of diatoms is included in the review, particularly with respect to their ability to 'sense' and adhere to surfaces. Investigations at the nanoscale are reviewed as these studies provide information about the behavior of cells at interfaces. Recent advances include the use of atomic force microscopy (AFM), although only a few studies have been applied to diatoms. Regarding the electrochemical behavior of SS, the mechanisms by which diatoms influence the potential ennoblement process is discussed. Such studies reveal the association of diatoms, in addition to bacteria, with biocorrosion processes.     

Induction of larval metamorphosis in the sea cucumber Stichopus japonicus by periphitic diatoms

The mass production of juvenile seeds of the sea cucumber,Stichopus japonicus has recently developed by the SeaFarming Center of Saga Prefecture. Methods for the culture ofperiphicic diatoms have been improved. There are three importantsteps in propagating the diatoms. The first step is theenrichment, with the addition of the nutrient salts, undercontrolled light intensity. The second step is washing withhigh pressure seawater and reversal of the plates. The laststep is elimination of copepods, which feed on diatoms, usinga pesticide. Small periphitic diatoms such as Navicula,Amphora, Achnanthes, and Nitzschia are easily culturedat a density of more than one million cells cm^–2, andthese diatoms are able to induce larval metamorphosis andserve as a food source for juvenile sea cucumbers.     

Review – Interactions between diatoms and stainless steel: focus on biofouling and biocorrosion

There is a considerable body of information regarding bacterially enhanced corrosion, however, this review focuses on diatoms (unicellular algae) whose contribution to biocorrosion is less well studied. The reasons why diatoms have been neglected in studies of biocorrosion in natural waters are discussed and the question whether diatoms should be considered as inert with respect of electrochemical processes is considered. A particular focus is given to the case of stainless steels (SS), which are widely used in variety of applications in natural waters. Basic information on the cell biology of diatoms is included in the review, particularly with respect to their ability to ‘sense’ and adhere to surfaces. Investigations at the nanoscale are reviewed as these studies provide information about the behavior of cells at interfaces. Recent advances include the use of atomic force microscopy (AFM), although only a few studies have been applied to diatoms. Regarding the electrochemical behavior of SS, the mechanisms by which diatoms influence the potential ennoblement process is discussed. Such studies reveal the association of diatoms, in addition to bacteria, with biocorrosion processes.     

Validation of diatoms as proxies for phytobenthos when assessing ecological status in lakes

Research to develop tools to assess the ecological status of phytobenthos, as required in Annex V of the European Union Water Framework Directive, has focussed largely on diatoms. Diatoms are often the most abundant and diverse group of algae within the phytobenthos and have been used widely for other monitoring purposes. However, there is little empirical justification for the use of diatoms as proxies for the wider phytobenthos. In this paper, we re-examine an existing dataset compiled largely from littoral samples from standing waters in the English Lake District and compared transfer functions for total phosphorus, dissolved inorganic carbon, conductivity and calcium concentration generated from diatoms and non-diatoms separately and together. The results show that transfer functions generated from diatoms alone are as powerful as transfer functions generated from diatoms and non-diatoms combined, while transfer functions generated from non-diatoms alone are less effective. These results provide support for the use of diatoms as proxies for phytobenthos when ecological status is being assessed. Handling editor: J. Saros     

Epidiatomic diatoms: An insight into interaction specificity

Little is known about direct interactions between diatoms. In this study, small diatoms attaching onto larger benthic and motile diatoms were considered. This phenomenon is commonly considered as epiphytism (with diatom epiphytes) although the exact nature of this interaction has not been investigated yet. The question that was addressed here is the specificity of the interaction, simply by observing species associations in their natural environment. A comparison of this special form of epiphytism was carried out between two sites, on a Mediterranean river and one of its tributaries. The results showed both host and epiphyte selection, but with some variability in species associations. This excludes the two alternative hypotheses that (i) large diatoms are a neutral substrate for smaller diatoms and that (ii) the interactions are strictly specific between two species.     

Diatoms as a tool for reconstructing sedimentary environments in coastal wetlands; methodological aspects

This paper presents a method for reconstructing sedimentary environments on the basis of diatoms in clastic deposits of coastal wetlands. The method includes improvements and updates of previously described approaches of coding ecological data on diatom species for computer utilization and of combining diatom species into ecological groups, which are related to specific environments.The assessment of autochthonous and allochthonous diatoms is the major problem in the palaeoenvironmental diatom research in tide-influenced coastal areas, because the allochthonous influx by tidal currents (mainly marine planktonic and tychoplanktonic diatoms) is significant. In tidal deposits, the allochthonous diatoms often outnumber the autochthonous assemblage. Criteria for the assessment regarding which diatoms are in or out of place are discussed.     

Recommendations for sampling littoral diatoms in lakes for ecological status assessments

This review summarises the existing literature and outlines the theoretical basis for using standard methods for sampling diatoms from rivers to sample littoral diatoms and other phytobenthos from standing waters. The European Union's Water Framework Directive has created a statutory obligation for EU Member States to monitor macrophytes and phytobenthos in lakes. Although there has been a considerable amount of work using phytobenthos (especially diatoms) to monitor river water quality in Europe, there are fewer studies on the use of phytobenthos for monitoring in lakes. European standard methods for sampling diatoms from rivers should be suitable, with only minor modifications, for sampling littoral diatoms from lakes and other standing water bodies. These recommendations should be applicable to all temperate regions.     

Centric diatom algae of the Selenga River and its delta branches

Different stages of the study of taxonomical composition of centric diatoms in the Selenga River are considered. A revision of the species composition and a general systematic list are made. New for the Selenga River diatom species are discovered. The role of small-sized centric diatoms in different years and vegetation periods is assessed. A comparison of the composition and the level of development of centric diatoms in 1958–1959 and 2002–2005 is made.     

Shifting N and P limitation along a north-south gradient of mangrove estuaries in South Florida

The heterotrophic utilization of organic substrates by diatoms is likely an important survival strategy when light levels are too low for photosynthesis. The objectives of this study were: (1) to determine if heterotrophic utilization of a large array of organic compounds by eight common freshwater benthic diatom taxa was light-dependent, and (2) to determine if organic substrate utilization patterns differed between dark-grown diatoms and bacteria as a possible means of reducing competition by niche separation. Eight light- and dark-grown diatom taxa and five bacterial species were incubated in 96-well Biolog^® Microtiter plates with each well containing 1 of 95 different organic substrates. Oxidation rates of each organic substrate were measured through time. There was a substantial increase in the number of organic substrates oxidized by diatoms grown in the dark compared to their light-grown counterparts, indicating that the transport systems for these molecules may be light activated. Therefore, diatoms likely only utilize these metabolically expensive uptake mechanisms when they are necessary for survival, or when substrates are plentiful. A principal components analysis indicated discernible differences in the types of organic-C substrates utilized by dark-grown diatoms and bacteria. Although bacteria were able to oxidize a more diverse array of organic substrates including carboxylic acids and large polymers, diatoms appeared to more readily utilize the complex carbohydrates. By oxidizing different organic substrates than bacteria, heterotrophically metabolizing diatoms may be reducing direct competition and enhancing coexistence with bacteria.     

Use of benthic vs planktonic organic matter by sandy-beach organisms: A food tracing experiment with C labelled diatoms

Benthic diatoms are assumed to be of minor importance as food sources in sandy-beach food webs, since they are typically scarce in sandy-beach sediments; whereas organic matter derived from land and sea is known to be more important in sandy-beach food webs. In order to test if benthic and planktonic diatoms play a minor or major role, respectively, in sandy-beach food webs, a laboratory experiment was conducted. Labelled planktonic and benthic diatoms, enriched in the stable carbon ¹³C isotope, were offered as food sources to sandy-beach macrofauna and meiofauna communities. Uptake of both types of diatoms occurred with most of the species, but benthic diatoms were preferentially consumed by two macrofaunal species and all meiofaunal species. This result reveals the importance of benthic carbon sources in both macrofaunal and interstitial food webs, and suggests a link between both food webs through the common use of benthic diatoms.     

Biology of epiphytic Chironomidae (Diptera:Nematocera) in chalk streams

Submerged macrophytes are a conspicuous feature of chalk stream ecosystems, supporting large populations of diatoms and invertebrates, including larvae of the nematocerous family Chironomidae. Close temporal and spatial association is evident between chironomid larvae and diatoms, and diatoms are frequently a major component of the food of midge larvae. Larvae provided with food that is rich in diatoms survive better and grow and develop more quickly than larvae that are supplied with food that is predominantly fine organic detritus. First instar larvae selectively feed on diatoms but it is likely that selection is on the basis of particle size, rather than for diatoms per se. Three species of epiphytic larvae (2 Cricotopus spp. and Eukiefferiella ilkleyensis) transfer to a diet that is predominantly of fresh plant material (Ranunculus calcareus leaves) in the third and fourth instar. The life cycle strategies of many species of Orthocladiinae equip them to exploit temporarily favourable environmental conditions very rapidly and effectively. This fact helps to explain the coexistence of species with similar strategies of resource utilization, as part of the normal epiphytic fauna of chalk streams.     

Diatom assemblages in superficial sediments from the Gulf of Riga,eastern Baltic Sea

Twenty one superficial sediment samples from areas of high and moderate eutrophication in the Gulf of Riga were studied with respect to siliceous microfossils, mainly diatoms.The results seem to imply that the number of taxa and the abundance of the frustules are affected by runoff from rivers and the degree of eutrophication in different parts of the Gulf. Areas with high eutrophication, e.g. the river estuaries, have diatom assemblages of varying composition, while in areas with moderate eutrophication the composition is almost constant and the influx of freshwater diatoms and littoral periphyton small. The high abundance and low diversity of brackish-marine and brackish, planktonic diatoms seem to be a result of an influx of nutrients and pollutants in the water and bottom sediments. The sea ice diatoms occurring in the Baltic waters and also in the Gulf of Riga tend to be resistant to eutrophication or are even favoured by it.     

The use of periphytic diatoms as a means of assessing impacts of point source inorganic nutrient pollution in south-eastern Australia

1. Periphytic diatoms are used as indicators of water quality because their ecological tolerances or preferences to environmental variables are thought to be predictable. However, much of the present autecological information for periphytic diatoms has been derived from studies conducted in the northern hemisphere. In this present study we used periphytic diatoms to determine the impacts of inorganic nutrient pollution in a tidal river system in the temperate latitudes of south‐east Australia. In so doing, we assess the suitability of the use of the ‘northern hemisphere’ ecological tolerance/preference data for periphytic diatoms. 2. Artificial substrates were used to collect periphytic diatoms at 35 sites, which were positioned along the riverbanks and the middle of the river at various distances upstream and downstream of the sewage outfall. The sampling design took into account tidal excursions and the observed sewage plume dynamics. Periphytic diatoms were collected during the austral winter month of August and the austral spring months of September and October. We deployed the artificial substrates for 4 weeks to allow the periphytic diatoms to recruit and colonise, before identifying and enumerating the assemblages. 3. Data analysis included two approaches: multivariate visualisations of combinations of environmental and biological data to investigate shifts in species structure of the periphytic diatom assemblage and multimetric indices based on ecological tolerance/preference data. 4. We found that the spatial patterns inferred from multivariate and multimetric analyses were consistent. Temporal variation in the composition of the periphytic diatom assemblage was greater than the spatial variation along horizontal sections of the river (in any one deployment) due mainly to shifts between winter and spring species. 5. Outfall effects were most apparent in winter, possibly because subsequent deployments were swamped by growth of spring periphytic diatoms. The outfall effects included a shift towards pollutant tolerant species and a reduction in the variability of the periphytic diatom assemblage across the river. 6. We conclude that the use of periphytic diatoms and associated ecological tolerance/preference data as a means of assessing impacts of point source inorganic nutrient pollution is effective. An understanding of river and sewage flow patterns is essential to the design of appropriate monitoring programmes and to the interpretation of results, especially as periphytic diatoms are sensitive to many environmental variables.     

东海南部陆缘(莆、泉段)全新世沉积硅藻

对东海南部陆缘莆田、泉州地区两口钻井岩芯系统的沉积硅藻研究,共发现33属117种（或变种）硅藻化石,根据剖面硅藻组合特征的变化,结合计算机的对应分析结果划分了硅藻带,建立该区全新世的7个硅藻组合序列,恢复当时古环境演变的7个阶段,填补该区沉积硅藻系统研究的空白,丰富了海陆过渡沉积硅藻的研究。     

Revisiting Ross and Sims (1971): toward a molecular phylogeny of the Biddulphiaceae and Eupodiscaceae (Bacillariophyceae)

The ocellate and pseudocellate diatoms in the Eupodiscaceae and Biddulphiaceae (respectively) are common inhabitants of the marine littoral (and plankton zone) with a rich fossil history making them important components of marine stratigraphic studies and good candidates for molecular dating work. These diatoms are important for un‐derstanding the phylogeny of the diatoms as a whole, as molecular phylogenies have blurred the traditional distinction between the pennate and multipolar non‐pennate diatoms. However, the convoluted taxonomic history of these groups has the potential to disrupt both stratigraphic and molecular dating studies. Although efforts have been made to examine frustule morphology of several ocellate and pseudocellate diatoms and develop a morphological scheme to define genera, very little work has been done to determine how these groups are interrelated. In this study, we use nuclear and chloroplast molecular markers to construct a phylogeny of a diverse sampling of Eupodiscaceae and Biddulphiaceae taxa. The ocellus‐bearing taxa (Eupodiscaceae) are monophyletic, and thus the ocellus may be a useful character in delimiting the Eupodiscaceae, the Biddulphiaceae are polyphyletic and scattered across a number of lineages of multipolar non‐pennate diatoms. Hypothesis testing aimed at assessing the likeliness of several morphology based hypotheses against the molecular data highlights uncertainty in both types of data. We present evidence that there are monophyletic genera within both the Biddulphiaceae and Eupodiscaceae, and recommend the taxa within the Odontella mobilensis/sinensis/regia clade be transferred to a new genus: Trieres Ashworth & Theriot.     

Oldest known non-marine diatoms (Aulacoseira) from the uppermost Cretaceous Deccan Intertrappean beds and Lameta Formation of India

Non-marine diatoms occur in the Deccan Intertrappean beds (Upper Cretaceous) of Mohgaon-Kalan, Chhindwara District, Madhya Pradesh and Pisdura, Lameta Formation (Upper Cretaceous), Maharashtra, India. This represents the oldest record of non-marine diatoms yet reported and the oldest from the Indian subcontinent. The diatoms were recovered from thin sections of chert and dinosaur coprolites by random fracturing. Solitary forms are the most common but colonial filaments up to five cells were also observed. Based on the morphological characters, the diatoms are identified as Aulacoseira Thwaites. The Lower Cretaceous marine diatom genus Archepyrgus Gersonde and Harwood also resembles Aulacoseira in general morphological characters and it seems that Aulacoseira evolved from Archepyrgus and migrated to the non-marine realm.     

Quantification of diatoms in biofilms: Standardisation of methods

Abstract

Benthic diatoms, which often dominate marine biofilms are mostly pennate along with a few centric species that have an attached mode of life. Even though the range of diatoms in biofilms is diverse, their ecology is poorly understood because of the difficulty in sampling and enumeration. Scraping or brushing are the traditional methods used for removal of diatoms from biofilms developed on solid substrata. The method of removal is the most critical step in enumerating the biofilm diatom community structure. In this study, a nylon brush and ceramic scraper were used as tools for the removal of diatoms from 1 – 4-day-old biofilms developed on fibreglass coupons and glass microscope slides. Standardisation of methods showed that the sample volume used in the analyses had the least influence on the quantification, whereas the method of removal was critical. The nylon brush was more efficient at recovering diatoms compared to a ceramic scraper. Direct microscopic enumeration of the community in the case of glass slides indicated that scraping resulted in between 30–50% underestimation. Heterogeneity in diatom community structure between replicate samples is one possible reason for such underestimation.     

Quantification of diatoms in biofilms: standardisation of methods

Benthic diatoms, which often dominate marine biofilms are mostly pennate along with a few centric species that have an attached mode of life. Even though the range of diatoms in biofilms is diverse, their ecology is poorly understood because of the difficulty in sampling and enumeration. Scraping or brushing are the traditional methods used for removal of diatoms from biofilms developed on solid substrata. The method of removal is the most critical step in enumerating the biofilm diatom community structure. In this study, a nylon brush and ceramic scraper were used as tools for the removal of diatoms from 1 - 4-day-old biofilms developed on fibreglass coupons and glass microscope slides. Standardisation of methods showed that the sample volume used in the analyses had the least influence on the quantification, whereas the method of removal was critical. The nylon brush was more efficient at recovering diatoms compared to a ceramic scraper. Direct microscopic enumeration of the community in the case of glass slides indicated that scraping resulted in between 30-50% underestimation. Heterogeneity in diatom community structure between replicate samples is one possible reason for such underestimation.     

Patterns of sexual reproduction in diatoms

Sexual reproduction takes many forms within the diatoms. The variation has been classified by several authors, but in most cases the distinctions between their main categories have depended on the number of gametes produced per gametangium (and thus on how many zygotes per pair of copulating cells), and upon whether fusion is oogamous, anisogamous or isogamous. These classifications are not themselves an adequate basis for taxonomic comparison, which should be based on individual characteristics of the sexual process. Diatoms seem to be primitively oogamous. In araphid pennate diatoms and some raphid diatoms the gametes and gametangia are morphologically alike but physiologically distinct; one gametangium produces active gametes and the other passive ones. This may be the primitive condition in pennate diatoms, providing a link to the oogamy of centrics via the morphological anisogamy of Rhabdonema Kütz.