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)     

The diatoms ingested by freshwater snails: temporal,spatial, and interspecific variation

Seventeen species of diatoms, representing a broad range of sizes, shapes, and growth habits, were collected from rocks in rapidly-flowing sections of the Mitchell River, North Carolina. The diatoms ingested by adult Goniobasis proxima, juvenile Leptoxis carinata, and adult Physa sp. co-occurring in this habitat were indistinguishable from one another, in spite of great differences in radular morphology. All snails sampled the diatom flora almost randomly, with only one or two of the larger diatom species under-represented in the gut contents. Some snails also seemed to selectively ingest the smaller individuals of the larger diatom taxa, and larger individuals of the smaller diatom taxa. The diatoms identifiable in juvenile Goniobasis guts were somewhat more distinctive, although this seemed to be due at least partly to more mechanical breakage. The diatom flora of quiet, muddy pools was much different from that of shallow, rocky areas, but once again, Goniobasis seemed to sample the available flora randomly. Seasonal variation was also apparent in the diatom diet of Goniobasis. We suggest that in some cases, it may be reasonable to use snails to sample the diatom assemblage present in a particular habitat, if more direct methods are impractical.     

SILICEOUS SCALE PRODUCTION IN CHRYSOPHYTE AND SYNUROPHYTE ALGAE. I. EFFECTS OF SILICA-LIMITED GROWTH ON CELL SILICA CONTENT,SCALE MORPHOLOGY,AND THE CONSTRUCTION OF THE SCALE LAYER OF SYNURA PETERSENII1

The cells of synurophyte flagellates (algal class Synurophyceae, formerly included in the Chrysophyceae) are enclosed within a regularly imbricate layer of ornamented siliceous scales. Scale morphology is of critical taxonomic importance within this group of algae, and the scales are valuable indicator microfossils in paleolimnological studies. The data presented here demonstrate that scale morphology and the integrity of the scale layer can exhibit extreme variability in culture as a function of the cellular quota of silica under silica-limited growth. Silica-limited, steady-state populations of the colonial flagellate Synura petersenii Korsh. were maintained over a range of specific growth rates (μ= 0.11–0.69 days^?1) and silica cell quotas (Q_si= 0.13–2.40 pmoles Si · cell¹). Scale morphology and the organization of the scale layer became increasingly aberrant as silica stress increased. Under severe stress, scale deposition was completely suppressed so that cells appeared scale-free. This depression of scale deposition was reversible; populations of silica-starved, scale-free cells rapidly regenerated new scale layers when placed in batch culture and spiked with dissolved silica. During recovery from silica stress, cell division was repressed for 24 h while mean cell silica quota increased 25-fold. The first new scales appeared within 2 h after the silica addition, and development of the new scale layer proceeded in an approximately synchronous manner, residting in normal scale layers on virtually all cells after 48 h of recovery in Sirich medium. Silica content of silica-replete Synura cells is comparable to freshwater diatoms of siynilar size, but Synura has much greater potential quota variability than diatoms and no apparent threshold silica requirement. Silica-limited growth kinetics and competition between diatoms and Synura for silica are discussed. The results suggest that morphological variability of siliceous scales in natural populations of synurophyte flagellates may result from silica stress and that the experimental approach developed here has great potential value as a means for circumscribing ecotypic variation in scale morphology. Results also demonstrate that scale production can be uncoupled from cell division, suggesting that cell cycle regulation of silica biomineralization in the Synurophyceae may be fundamentally different from that of diatoms (algal class Bacillariophyceae). This experimental system has application in the future study of the intracellular membrane systems and the regulatory processes involved in silica biomineralization.     

Protists in the marine ice of the Amery Ice Shelf, East Antarctica

Samples of marine ice were collected from the Amery Ice Shelf, a large embayed ice shelf in East Antarctica, during the Austral summer of 2001–2002. The samples came from a site ∼90 km from the iceberg calving front of the shelf, where the ice is 479 m thick and the lower 203 m is composed of accreted marine ice. Protists identified within the marine ice layer of the Amery Ice Shelf include diatoms, chrysophytes, silicoflagellates and dinoflagellates. The numerical dominance of sea ice indicator diatoms such as Fragilariopsis curta, Fragilariopsis cylindrus, Fragilariopsis rhombica and Chaetoceros resting spores, and the presence of cold open water diatoms such as Fragilariopsis kerguelensis and species of Thalassiosira suggest the protist composition of the Amery marine ice is attributable to seeding from melting pack and/or fast ice protist communities in the highly productive waters of Prydz Bay to the north.     

GROWTH INHIBITION AND TOXICITY OF THE DIATOM ALDEHYDE 2‐TRANS, 4‐TRANS‐DECADIENAL ON THALASSIOSIRA WEISSFLOGII (BACILLARIOPHYCEAE)1

A common aldehyde present in marine and freshwater diatoms, 2‐trans, 4‐trans‐decadienal (A3), is involved in the wound‐activated response of diatoms to copepod grazing. Upon breakage of the diatom cell membrane, aldehydes are enzymatically produced by the rapid conversion of precursors and strongly impact copepod reproduction by impairing egg production and hatching success, inducing teratogenic embryos modifications. In this study, A3 was assayed with the marine diatom Thalassiosira weissflogii (Grunow) Fryxell et Hasle. The aldehyde concentration necessary to reduce 50% growth rate (EC₅₀) was 0.29 mg·L^?1. Decadienal was found to inhibit T. weissflogii cell growth in a dose‐ and time‐dependent manner, with irreversible effects after 24 h of exposure. Decadienal induced a degenerative process, through modifications of cell membrane characteristics, interference with cell cycle progression, and with cell metabolic activity, leading to cell death. A preferential action of A3 on dividing cells was observed. Photosynthetic efficiency significantly decreased upon exposure to the aldehyde, paralleled by an increase in diatoxanthin, suggesting a protective role of this xanthophyll, usually involved in photoprotection. Dying cells exhibited the morphological and biochemical features that bear close resemblance to apoptosis of mammalian cells, including cell shrinkage, chromatin condensation, and degradation of nuclear DNA to nucleosomal size fragments. These data are the first direct evidence to show aldehydes are toxic to diatoms. We suggest a possible nontoxic role of such compounds as chemical signals of unfavorable conditions within the phytoplankton communities, which may be relevant for the population dynamics of diatoms during blooms.     

Causation of reversal simultaneity for diatom biomass and density of <Emphasis Type="Italic">Phormidium tenue</Emphasis> during the warm season in eutrophic Lake Barato,Japan

The diatom biomass of Lake Barato, as measured from July to September, decreased simultaneously with an increase in filament density of Phormidium tenue after 1997. There was a high negative correlation between the diatom biomass and the densities of P. tenue (r² = 0.928). Although total nitrogen (TN) and total phosphorus (TP) concentrations decreased from 1996, TN:TP ratio increased from 1997 because the TP concentration became markedly lower. The decrease in diatom biomass might have been due to the loss in phosphorus available for algae. Because the increase in density of P. tenue might have been due to the decrease in diatom biomass, experiments using a growth inhibitor for diatoms were performed to examine whether the density of cyanobacteria increases without diatom growth. Samples of the lake water collected in three seasons (August and October 1998, May 1999) were incubated with and without germanium (Ge) as a growth inhibitor of diatoms. The increase in density of P. tenue was inhibited concurrent with the increase in diatom biomass in the first and middle stages of incubation without the addition of Ge in August 1998 and May 1999. In contrast, a higher density of P. tenue was observed in the incubation with diatom growth inhibited by Ge over the same period. These results suggest that diatoms have an effect in restraining the growth of P. tenue.     

MOLECULAR EVIDENCE CONFIRMS SISTER RELATIONSHIP OF ARDISSONEA,CLIMACOSPHENIA, AND TOXARIUM WITHIN THE BIPOLAR CENTRIC DIATOMS (BACILLARIOPHYTA,MEDIOPHYCEAE), AND CLADISTIC ANALYSES CONFIRM THAT EXTREMELY ELONGATED SHAPE HAS ARISEN TWICE IN THE DIATOMS1

With the use of a new kit from Qiagen to amplify total genome quantity, DNA was bulked up from two diatoms that are difficult to grow (Ardissonea and Climacosphenia), and the nuclear SSU rRNA gene was successfully amplified. Results of Bayesian analyses showed that these diatoms are sister to Toxarium and belong to the bi‐ and multipolar centric diatoms. The results indicate that extremely elongate shape has arisen at least twice in diatoms, in the true pennates, and in the bipolar centrics. The two lateral pattern centers of Ardissonea and Climacosphenia likely represent a modified annulus that subtends ribs internally as well as externally. Studies of sexual reproduction are needed to determine whether Ardissonea, Climacosphenia, and Toxarium achieve their elongate shape by similar means to each other and to true pennates, that is, by controlling the expansion of the auxospores by sequential addition of silicified bands (to form a properizonium or perizonium).     

A discovery of the genus <Emphasis Type="Italic">Cabrieroceras</Emphasis> (Werneroceratidae,Ammonoidea) in Salair

The ammonoid genus Cabrieroceras Bogoslovsky is recorded for the first time from the Eifelian of Salair (from the Safonovo Horizon). These ammonoids date the host rocks as the Cabrieroceras crispiforme Zone, recognized in many sections in Western Europe, North America, and North Africa. The taxonomy of the genus Cabrieroceras is discussed, and a new species, C. salairicum Nikolaeva, is described.     

Unusual trophic strategies of Hydractinia angusta (Cnidaria, Hydrozoa) from Terra Nova Bay, Antarctica

Hydractinia angusta Hartlaub, 1904 has been recorded at Terra Nova Bay (Ross Sea, Antarctica) as epizoic on shells of the Antarctic scallop Adamussium colbecki. The species can exploit different trophic resources: first, polyps are able to detach and ingest tube feet and pedicellariae from the sea urchins Sterechinus neumayeri, grazing on the scallop shell, and second, they also eat masses of benthic diatoms settled among the hydrorhiza of the colony. The particular relationship observed between the hydroid and one of the most common Antarctic sea urchins may prevent or reduce the damage to A. colbecki shells, otherwise caused by the grazing of sea urchins on the algal film of the upper valve of the scallops. H. angusta is the first known species of hydroid that exploits prey several times its own size and the second that does not ingest entire prey but portions of them. The use of benthic diatoms as a food resource has previously been documented for the sub-Antarctic marine hydroid Silicularia rosea. Accepted: 20 December 1999     

DIATOMS AS HOSTS FOR OTHER DIATOMS: OBSERVATIONS FROM SOUTHERN CALIFORNIA

Large epiphytic and epilithic diatom species hosting other diatoms were observed in several fresh‐ and brackish water sites in Southern California. The most commonly encountered hosts were species forming long filaments attached to rocks or macroalgae, Hydrosera whampoensis (Schwarz) Hendey, Melosira varians Agardh, Pleurosira laevis (Ehrenberg) Compere and Terpsinoe musica Ehrenberg. These large diatoms often had smaller diatoms attached, usually to the girdle bands and occasionally to the mucilage pads connecting the cells. For example, cells of T. musica were observed supporting growth of a diverse diatom assemblage composed of species of the genera Achnanthes, Achnanthidium, Amphora, Cocconeis and Tabularia; Synedra sp. was attached to M. varians and B. paxillifer; and Cocconeis placentula was seen on H. whampoensis. Thus, large epiphytic and epilithic diatoms seem to provide suitable sites for attachment of small epiphytic diatom species, and it appears that this phenomenon is more common than previously thought.     

Diatoms of Dindifelou fall (upper Basin of the Gambia River,Senegal): floristic inventory

The Dindifelou fall, located in south‐eastern Senegal, receives its water from discharging springs located in Dande plate‐land. These waters form, at the foot of the cliff, a pond that drains into the Thiokoye, a tributary of the Gambia River. The water quality of the pond and the stream is very good based on physicochemical analyses. Around the pond region, a microclimate characterized by a higher humidity and a lower temperature compared with the surrounding area is present. Diatoms study is carried out in different habitat types associated with this fall. The samples were taken by scraping the surface of rocks and rinsing fern leaves with sparkling water. Dande plate‐land is made of Upper Proterozoic sandstones whose gravity accumulations litter the bottom of the pond and the stream. This study allowed us to inventory 61 species and varieties of diatoms belonging to 28 genera. The most represented genera are Achnanthidium (ten species), Eunotia and Pinnularia (eight species each). Twelve species and varieties are reported for the first time in Senegambia including five of the genera Achnanthidium. The microflora is dominated by Achnantidium minutissimum and Achnanthidium catenatum, followed by Ulnaria ulna and various species of the genera Eunotia and Brachysira. Aerial habitats are more diversified here than the epilithic samples.     

Antidiatom and antibacterial activity of epiphytic bacteria isolated from <Emphasis Type="Italic">Ulva</Emphasis><Emphasis Type="Italic">lactuca</Emphasis> in tropical waters

Bacteria and diatoms are primary colonizers of marine surfaces and hence play a crucial role in the attachment and subsequent growth of macroorganisms. It has been suggested that the temperate green alga Ulva lactuca relies on the defence provided by the epiphytic bacterial community to regulate surface fouling of colonising organisms. In this study, ten resident bacterial isolates from tropical U. lactuca were tested for their antibacterial and antidiatom properties that may regulate surface colonization on the algae. Sixty percent of the epiphytic isolates expressed antibacterial properties against other resident bacteria and 80% had antidiatom activity against the pennate diatom, Cylindrotheca fusiformis. Isolates of the Pseudoalteromonas genus showed both- antibacterial and antidiatom activities, while members of the genus Bacillus, Vibrio and Shewanella mostly possessed antidiatom activity. Our results show that a high proportion of bacterial isolates from tropical U. lactuca, like that of their temperate counterparts contain antibiotic properties that might impact on the bacterial community composition and prevent fouling by diatoms.     

Seasonal variations of diatoms and dinoflagellates in a shallow,temperate estuary,with emphasis on neritic assemblages

Seasonal changes in the diatom and dinoflagellate assemblages were examined in the neritic zone of the Urdaibai estuary (north Spain) with regard to some major physical and chemical variables during an annual cycle. A total of 81 diatoms and 38 dinoflagellates were identified and quantified during the study period. Both groups displayed a distinctive pattern of seasonal succession. The seasonal distribution of the Shannon index showed a trend of increasing values from the upper estuary to the lower neritic segment. The diatom diversity maxima were observed in February, April and September, and dinoflagellate maxima in April–May, July and October. Diatoms dominated the assemblages, reaching 1×10⁶ cells l^–1 from April to September. A shift from large diatoms and dinoflagellates to small bloom-forming taxa was observed during winter–early spring. A spring diatom bloom composed of Rhizosolenia spp. was observed in April, while small chain-forming taxa (chiefly Chaetoceros spp.) dominated from June to September. Cell maxima for both groups in late summer were produced by the diatoms Chaetoceros salsugineum and Skeletonema costatum, and by the dinoflagellates Heterocapsa pygmaea and Peridinium quinquecorne. Silicate availability by river supply and strong tidal-mixing of the water column seem to determine the year-round dominance of diatoms over dinoflagellates.     

Carbon:chlorophyll <Emphasis Type="Italic">a</Emphasis> ratio,assimilation numbers and turnover times of Lake Kinneret phytoplankton

Carbon to chlorophyll a (C:Chl) ratios, assimilation numbers (A.N.) and turnover times of natural populations of individual species and taxonomic groups were extracted from a long-term database of phytoplankton wet-weight biomass, chlorophyll a concentrations, and primary production in Lake Kinneret, Israel. From a database spanning more than a decade, we selected data for samples dominated by a single species or taxonomic group. The overall average of C:Chl was highest for cyanophytes and lowest for diatoms, while chlorophytes and dinoflagellates showed intermediate values. When converting chlorophyll a to algal cellular carbon this variability should be taken into account. The variability in C:Chl within each phylum and species (when data were available) was high and the variability at any particular sampling date tended to be greater than the temporal variability. The average chlorophyll a-normalized rate of photosynthetic activity of cyanophytes was higher and that of the dinoflagellates lower than that of other phyla. Turnover time of phytoplankton, calculated using primary productivity data at the depth of maximal photosynthetic rate, was longest in dinoflagellates and shortest in cyanophytes, with diatoms and chlorophytes showing intermediate values. The more extreme C:Chl and turnover times of dinoflagellates and cyanobacteria in comparison with chlorophytes and diatoms should be taken into consideration when employed in ecological modeling.     

Photosynthetic Activity of Dominant Algal Species in Eutrophic Shallow Lake (Großer Müggelsee,Berlin) Investigated by Microautoradiography

The photosynthetic activity of dominant phytoplankton in eutrophic shallow lake was investigated by the autoradiographic method in 1979 and 1980. It was shown by light and dark field microscopy that all species of Cyanophyta (Oscillatoria redekei, Oscillatoria agardhii, Aphanizomenon flos-aquae) were characterized by a continuously high uptake of NaH¹⁴CO₃. Similarly high photosynthetic activity was observed during the occurrence of Cryptomonas sp. and nanoplankton. Contrary to these observations, diatoms showed remarkably high portions of photosynthetically inactive biomass when their development was abundant. The reasons for this discrepancy between high biomass of diatoms and relatively low primary production (measured by the ¹⁴C-method and autoradiography) are discussed.     

福建敖江口表层沉积硅藻空间分布特征

为探讨福建敖江口表层沉积硅藻空间分布特征,2019年7月对敖江口进行表层沉积硅藻的采样调查,并研究了硅藻与环境因子的关系。结果表明,从13个站点共检出硅藻114种,隶属于39属。硅藻丰度具有从河口向外海先减少后增加的变化特征。聚类分析表明,主要硅藻属种可划分为淡水种组合带和半咸水-咸水种组合带。典型对应分析（CCA）表明,表层海水温度和盐度是影响硅藻分布的主要环境变量。河口区盐度相对较低,主要分布淡水种双面曲壳藻、优美曲壳藻和颗粒沟链藻;外海区北部盐度相对较高,主要分布咸水种流水双菱藻;外海区南部盐度相对较低,主要分布淡水种优美曲壳藻和颗粒沟链藻;滩涂的沉积物较粗,主要分布优美曲壳藻。此外,河口区和外海区南部可能存在一定的水体污染。     

Regulation of phosphoribulokinase and glyceraldehyde 3‐phosphate dehydrogenase in a freshwater diatom,Asterionella formosa1

The regulation of phosphoribulokinase (PRK) and glyceraldehyde 3‐phosphate dehydrogenase (GAPDH) was investigated in a freshwater pennate diatom, Asterionella formosa Hassall, and compared to the well‐studied chlorophyte Chlamydomonas reinhardtii P. A. Dang. As has been reported for a marine centric diatom, in A. formosa, PRK was not regulated by reduction with dithiothreitol (DTT) apart from a weak induction in the presence of NADPH and DTT. However, NADPH‐GAPDH was strongly activated when reduced, in contrast to a previous report on a diatom. Surprisingly, it was inhibited by NADPH, unlike in C. reinhardtii, while NADH‐GAPDH was not affected. NADH‐GAPDH was also strongly activated by DTT in contrast to most other photosynthetic cells. In A. formosa, unlike C. reinhardtii, 1,3‐bisphosphoglycerate, the substrate of GAPDH, activated this enzyme, even in the absence of DTT, when using both NADH and NADPH as cofactors. Some of these kinetic behaviors are consistent with regulation by protein–protein interactions involving CP12, a small protein that links PRK and GAPDH in cyanobacteria, green algae, and higher plants. This conclusion was supported by immunodetection of CP12 in crude extracts of A. formosa, using antibodies raised against CP12 from C. reinhardtii. This is the first report of the existence of CP12 in a diatom, but CP12 may be a common feature of diatoms since a bioinformatic search suggested that it was also present in the Thalassiosira pseudonana Hasle et Heimdal genome v3.0. Despite the presence of CP12, this work provides further support for the differential regulation of Calvin cycle enzymes in diatoms compared to green algae.     

Valve morphogenesis in Diploneis smithii (Bacillariophyta)

Diploneis species have perhaps the most complex valve structure among pennate diatoms. The development of this structure was studied in Diploneis smithii and begins with the formation of a primary band, which then develops secondary arms at both poles and the center, as in the classic Chiappino–Volcani model of raphid diatom ontogeny. Spine‐like projections grow out from the primary band and secondary arms to establish the transapical ribs (virgae) of the mature valve and themselves develop spines, which are spaced first oppositely and then alternately and fuse with each other to delimit the stria pores. Subsequently, new pattern and structures develop both externally (formation of bifurcating projections that fuse to delimit the outer, sieve‐like layer of the valve) and internally (growth and fusion of flanges from the first‐formed ribs to create the longitudinal canals and deposition of a hymenate strip over the internal face of each stria). Comparisons are made with morphogenesis in other diatoms. Diploneis smithii ontogeny suggests how very slight developmental changes might have created the very variable external morphology of Diploneis species. It also indicates that the longitudinal canals of Diploneis and Fallacia have different origins, since the porous external wall is not formed as a unilaterally attached flap in Diploneis and the canal is internal to the first‐formed rib–stria system in Diploneis, but external to it in Fallacia.     

Diatoms from two macro-tidal mudflats in Chignecto Bay,Upper Bay of Fundy,New Brunswick,Canada

Mudflat research is dispersed among several fields (ecology, sedimentology), each with its own focus and methodology. Consequently, although the volume of mudflat literature is considerable, our understanding of mudflat ecology remains fragmented. For example, little is known about the structure of microbial communities outside Western Europe. Here we present the first North American specific composition and densities of live mudflat diatoms and relate them to properties of their environment on two closely located flats. The two flats (Daniel’s and Buck’s) were similar until the mid–1980s. After this time the biological and sedimentary environment on Buck’s Flats began to change and resulted in a precipitous decline of the keystone invertebrate Corophium volutator (Pallas). The specific diatom composition on each of the two flats examined was still very similar. Tychoplanktonic diatoms were numerically dominant on both flats. The flats differed significantly in the relative contribution of epipelic diatoms, which were about an order of magnitude greater on Buck’s Flats. CCA analysis suggests that very few of these species exist within their optimal habitat. Some of the differences appeared small, but were statistically and biologically significant. Daniel’s Flats sediments had a 30% larger mean grain size, less water and organic carbon compared to Buck’s Flats sediments. Buck’s Flats had more variable depths of the oxygenated layer, often with anoxic inclusions throughout. Daniel’s Flats supported more C. volutator, while Buck’s Flats contained greater densities of diatoms. The importance of preserving environmental conditions (sedimentary and biotic) prevailing on flats such as Danielȁ9s Flat in order to foster populations of Corophium at a level necessary to support foraging migratory shorebirds is also discussed.     

The invasive New Zealand mudsnail, <Emphasis Type="Italic">Potamopyrgus antipodarum</Emphasis>, is an effective grazer of algae and altered the assemblage of diatoms more than native grazers

Exploitation of shared resources often mediates the impacts of invasive species on native species. In a field experiment, we compared the ability to graze periphyton and the genera of diatoms removed by the invasive New Zealand mudsnail, Potamopyrgus antipodarum, a native caddisfly larva (Brachycentrus sp.), and a native mayfly nymph (Ephemerella sp.) over 1 week. P. antipodarum removed as much or slightly more periphyton than the native grazers, depending on whether chlorophyll a or ash-free dry mass was used to measure periphyton biomass. When we examined the diatoms in the periphyton, P. antipodarum altered the diatom assemblage more than the native grazers. Effective grazing of periphyton by P. antipodarum may impact native grazers by consuming shared algal resources. In particular, because Ephemerella sp. were also effective grazers, these mayflies may compete for periphyton with P. antipodarum in the western United States. Taken together, these results suggest that ability to procure food resources may contribute to the invasion success of P. antipodarum.