Moss diatom communities from Ile de la Possession (Crozet,Subantarctica) and their relationship with moisture

More than 190 taxa, belonging to 33 genera, were observed on mosses collected on Ile de la Possession, Crozet Archipelago, Antarctica. Six assemblages could be identified. Habitat type and moisture content of the samples appeared to be the major factors in separating the communities. It was clear that diatom communities growing on mosses found in rivers and brooks are different from assemblages on rocks and in stagnant pools. The Diadesmis contenta assemblage was bound to dry mosses growing on rocks whereas the Eunotia paludosa var. paludosa community preferred acid stagnant pools, situated in the larger valleys. The other four assemblages are typical for circumneutral waterbodies, with the Fragilaria maillardii and the Fragilaria vaucheriae-Fragilaria germainii assemblages found in running water and the Fragilaria pinnata var. pinnata and the Achnanthes confusa-Achnanthes aueri assemblages in more stagnant water. Weighted averaging and calibration were used to develop a statistical transfer function to infer the moisture content of moss samples from the diatom assemblages. Accepted: 29 March 1999     

Freshwater diatoms from Ile de la Possession (Crozet Archipelago, sub-Antarctica): an ecological assessment

An ecological study of freshwater waterbodies on Ile de la Possession (Crozet Archipelago, Antarctica) was undertaken during the austral summer of 1997/1998. Both diatom and chemistry data were collected. A highly diverse diatom flora of 210 taxa, belonging to 32 genera, was identified from 127 samples. The most abundant genera were Fragilaria, Achnanthes and Navicula. Principal Component Analysis was used to classify the samples on the basis of their chemical characteristics. The analysis revealed that pH and chloride were the main factors dividing the samples into three categories: rivers, more acid lakes, and lakes with higher chloride content. Species assemblages correspond well with this division. Forward selection with Monte Carlo permutations selected pH, chloride, habitat and hardness. Based on the analysis, four groups of samples can be made: rivers, acid lakes, circumneutral lakes with low chloride concentrations and coastal pools with relatively high chloride levels. The results also indicate that a specific diatom flora exists on the island, which is comparable to that of other islands in the same area (Kerguelen and Macquarie). Accepted: 29 March 1999     

Water quality assessment using diatom assemblages and advanced modelling techniques

1. Two types of artificial neural networks procedures were used to define and predict diatom assemblage structures in Luxembourg streams using environmental data. 2. Self‐organising maps (SOM) were used to classify samples according to their diatom composition, and multilayer perceptron with a backpropagation learning algorithm (BPN) was used to predict these assemblages using environmental characteristics of each sample as input and spatial coordinates (X and Y) of the cell centres of the SOM map identified as diatom assemblages as output. Classical methods (correspondence analysis and clustering analysis) were then used to identify the relations between diatom assemblages and the SOM cell number. A canonical correspondence analysis was also used to define the relationship between these assemblages and the environmental conditions. 3. The diatom‐SOM training set resulted in 12 representative assemblages (12 clusters) having different species compositions. Comparison of observed and estimated sample positions on the SOM map were used to evaluate the performance of the BPN (correlation coefficients were 0.93 for X and 0.94 for Y). Mean square errors of 12 cells varied from 0.47 to 1.77 and the proportion of well predicted samples ranged from 37.5 to 92.9%. This study showed the high predictability of diatom assemblages using physical and chemical parameters for a small number of river types within a restricted geographical area.     

Ecology of the Major Periphytic Diatom Communities from the Mesta River,Bulgaria

Epilithon, epiphyton, epipelon, epipsammon and plocon diatom samples and water chemistry samples were collected bimonthly from 11 stations along the Mesta River, Bulgaria between December 1989 and April 1991. Principal component analysis (PCA), correlation, and dominance analysis were employed for describing the seasonal dynamics of diatom assemblages and estimating the correlation between diatom distribution and the physico-chemical parameters. All periphytic communities were compared by PCA, MANOVA and Fisher's LSD multiple comparison test. Ionic strength and eutrophication were the major abiotic factors affecting diatom distribution in the epilithon, epiphyton, epipelon and epipsammon. Current velocity had an important influence on the diatom assemblages from the epilithon and epiphyton. Epilithon showed the lowest correlation with most of the environmental factors and had significantly lower species diversity than epiphyton, epipelon and epipsammon. Multivariate analysis of the diatom data suggested that in all benthic habitats of the Mesta River seasonal replacement of diatom assemblages was controlled by the water chemistry rather than substratum, current velocity or discharge. The oligotrophic, mesotrophic and eutrophic diatom communities in the Mesta River comprised early-, mid- and late-successional colonizers respectively. Multiple comparisons of all periphytic communities showed that habitat specificity was positively correlated with current velocity.     

Ecology of terrestrial testate amoebae assemblages from coastal Lowlands on Devon Island (NWT,Canadian Arctic)

Summary Fifty-seven taxa belonging to 17 genera of testate rhizopods were recorded in samples of mosses, soils and lichens, collected from the Truelove and Sparbo Hardy Lowlands on the high arctic Devon Island (NWT, Canada). Different groups of habitats are characterized by particular assemblages of Testacea species, with the quantity and quality of the available water as important ecological parameters. The Assulina muscorum-Corythion dubium assemblage characterizes the most dry and acidic moss habitats, while the Paraquadrula irregularis assemblage is to be found in wet and rather neutral habitats. The sedge moss meadows with their more moderately coarse textured and poorly drained soils, bear a Plagiopyxis callida-Plagiopyxis declivis soil-dwelling testate amoebae assemblage. The Centropyxis minuta assemblage lives in the most coarsely textured soils. pH seems to play a subordinate role, not only in the mosses but also in the soils. Multivariate methods (cluster analysis and CANOCO) have been used to separate these different assemblages.     

Raid process, activity pattern and influence of abiotic conditions in the slave-making ant Rossomyrmex minuchae (Hymenoptera, Formicidae)

Summary: In the present work, we present the results of a study on the seasonal and daily activity, as well as on the raid process in Rossomyrmex minuchae. A comparative study of the annual and daily activity of the host species, Proformica longiseta, has also been made in parasitized and non-parasitized colonies. R. minuchae is an obligate slave-maker, in which the annual activity is strongly related to abiotic conditions, especially temperature and moisture of the soil. The raid process is comprised of three phases: scouting, assault of the host nest and robbing of the host brood. Recruitment of nestmates by mean of adult transport, concentration close to and invasion of the host nest, are the three tasks carried out by R. minuchae workers during the assault phase. Major differences between Rossomyrmex and Polyergus (the other obligate dulotic genus of the tribe Formicini) in terms of behaviour, both in nestmate recruitment and in the host-nest invasion, reflect different parasitic strategies in the two genera, supporting the assignment of these two genera to different phylogenetic groups.     

PERIPHYTIC DIATOM ASSEMBLAGES FROM HIGH ARCTIC PONDS1

Epiphytic, epilithic, and surface sediment diatom assemblages were identified and enumerated from 35 study ponds on CapeHerschel (78°37″N, 74°42″W), east-central Ellesmere Island, Canada. All the sites are shallow (maximum depth <2 m), clear, oligotrophic, and freshwater. The ponds freeze completely for 10 months of the year. Major ion concentrations are relatively similar among the 35 sites, although environmental gradients exist. Over 130 diatom taxa from 28 genera were identified in the periphyton samples. Marked differences in species composition were evident among the ponds. Moreover, many of the diatoms exhibited varying degrees of microhabitat specificity. Variance partitioning by canonical correspondence analysis showed that 26% of the total variance exhibited by diatom species composition could be accounted for by the measured environmental variables (i.e. 10.2% by habitat and 15.8% by water chemistry). Pondwater alkalinity best explained the distribution of taxa, and weighted averaging regression and calibration were used to develop a transfer function to infer pondwater alkalinity from the diatom assemblages. Other important environmental variables included [Na⁺] for the epilithic and [SiO₂] for the epiphytic assemblages.     

Geographical and seasonal patterns of epiphytic diatoms on a subtropical mangrove (Kandelia candel) in southern China

Geographical and seasonal patterns of epiphytic diatoms on a subtropical mangrove (Kandelia candel (L.) Druce) were examined at four sites in southern China. A total of one hundred and three epiphytic diatom species and varieties belonging to 40 genera were identified. Dominant species included Nitzschia fasciculata, Luticola mutica and Achnanthes javanica var. subcontricta. Further analysis using canonical correspondence analysis revealed three diatom associations which could be closely related to environmental variables such as salinity and nutrients resources of nitrogen and phosphate. Epiphytic diatom assemblages on roots would be a good indicator for the evaluation of water quality in mangroves.     

Distribution of benthic diatoms in relation to environmental variables in lowland streams

The composition (% relative abundance) of diatom assemblages from soft bottom sediments was studied at 75 sites situated in 46 rivers, brooks, and ditches in the islands of Hiiumaa and Saaremaa and in the lowland of West Estonia. Although the total number of recorded taxa was 205, the studied diatom assemblages consisted of 54, 55, 48, and 50 constant species in the drainage basin of Moonsund, the Gulf of Riga, Hiiumaa, and Saaremaa, respectively. The habitats of the dominating taxa were heterogenous and the most widespread species were Achnanthidium minutissimum, Martyana martyi, Meridion circulare, Cocconeis placentula, Planothidium lanceolatum, and Amphora pediculus. The Shannon–Weaver diversity (H) index varied from 2.09 to 4.63. Multivariate analyses were used to identify the environmental variables governing the composition and structure of the benthic diatom assemblage. Principal Component Analysis (PCA) and Redundancy Analysis (RDA), based on 56 most abundant taxa, indicated differences in the composition and structure of diatom assemblages between different drainage basins as well as between the upper and lower stream courses. In the headwaters there prevailed small epipsammic diatoms (Martyana, Planothidium, Staurosira, Staurosirella). Different motile epipelic species from the genera Amphora, Navicula, Nitzschia, etc. were distributed abundantly in the lower courses of the streams. There was a positive correlation between order of the stream site and trophic level of water (R=0.35; p<0.05). Along a river system, the increasing order of the stream was accompanied by higher trophic level of water.     

COASTAL DIATOM‐ENVIRONMENT RELATIONSHIPS IN THE BRACKISH BALTIC SEA1

High‐quality calibration data sets are required when diatom assemblages are used for monitoring ecological change or reconstructing palaeo‐environments. The quality of such data sets can be validated, in addition to other criteria, by the percentage of significant unimodal species responses as a measure of the length of an environmental gradient. This study presents diatom‐environment relationships analyzed from a robust data set of diatom communities living on submerged stones along a 2,000 km long coastline in the Baltic Sea area, including 524 samples taken at 135 sites and covering a salinity gradient from 0.4 to 11.4. Altogether, 487 diatom taxa belonging to 102 genera were recorded. Detrended canonical correspondence analysis showed that salinity was the overriding environmental factor regulating diatom community composition, while exposure to wave action and nutrient concentrations were of secondary importance. Modeling the abundances of the 58 most common diatom taxa yielded significant relationships with salinity for 57 taxa. Twenty‐three taxa showing monotonic responses were species with optimum distributions in freshwater or marine waters. Thirty‐four taxa showing unimodal responses were brackish‐water species with maximum distributions at different salinities. Separate analyses for small (cell biovolume <1,000 μm³) and large (≥1,000 μm³) taxa yielded similar results. In previous studies along shorter salinity gradients, large and small epilithic diatom taxa responded differently. From our large data, we conclude that counts of large diatom taxa alone seem sufficient for indicating salinity changes in coastal environments with high precision.     

Comparison of contemporary and fossil diatom assemblages from the western Antarctic Peninsula shelf

During the past ten years, the Antarctic Peninsula has been identified as the most rapidly warming region of the Southern Hemisphere and it is important to place this warming in the context of the natural climate and oceanographic variability of the recent geological past. Many biological proxies, such as marine diatom assemblages, have been used to determine Southern Ocean palaeoceanographic conditions during the Late Quaternary, however, few investigations have attempted to link observations of modern floras with the fossil record. In this study we examine a suite of modern austral spring (December 2003) and summer (February 2002) surface water samples from along the western Antarctic Peninsula (WAP) continental shelf and compare these to core-top, surface sediment samples. Using detrended correspondence analysis (DCA) and principal component analysis (PCA) of diatom abundance data we investigate the relationship of contemporary diatom floras with the fossil record. This multivariate analysis reveals that our modern assemblages can be divided into three groups: summer southern WAP sites, summer northern WAP sites, and spring WAP sites. Sea surface temperature (SST) is an important environmental variable for explaining seasonal differences in diatom assemblages between spring and summer, but sea surface salinity (SSS) is more important for understanding temporally-equivalent regional variations in assemblage. Our summer diatom samples are more reminiscent of early season assemblages, reflecting the unusually late sea ice retreat from the region that year. When the modern assemblages are compared to the fossil record, it is clear that most of the important diatoms from the summer assemblage are not preserved into the sediments, and that the fossil record more closely reflects spring assemblages. This observation is important for any future attempts to quantitatively reconstruct palaeoceanographic conditions along the WAP during the Late Quaternary and highlights the need for many more such studies in order to address longer timescales, such as interannual variability, in the context of the fossil record.     

Contemporary distributions of saltmarsh diatoms in the Seymour–Belize Inlet Complex, British Columbia, Canada: Implications for studies of sea-level change

Surface diatom samples were collected from two saltmarshes in the Seymour–Belize Inlet Complex on the mainland coast of British Columbia to examine the controls on diatom distribution and provide training sets for regional studies of sea-level change. Cluster analysis and detrended correspondence analysis (DCA) were used to examine diatom distributions within and between the two marshes whilst canonical correspondence analysis (CCA) and partial canonical correspondence analysis (pCCA) were used to analyse species–environment relationships. The diatom assemblages were shown to be quite different between the two marshes, Waump and Wawwat'l. Q-mode cluster analysis separated the diatom assemblages from Waump into three zones corresponding to recognized vegetation zones; diatom zone C corresponds to the high marsh and is dominated by Pinnularia obscura, Caloneis bacillum and Diploneis ovalis, zone B spans the high- and mid marsh and is characterised by Fragilaria exigua, Nitzchia palea and D. ovalis, whilst zone A from the low marsh/tidal flat includes high frequencies of Diploneis smithii, Ctenophora pulchella and F. exigua. Three different diatom zones were recognised at Wawwat'l; two upper zones, E and F, corresponding to the mid-marsh which are dominated by mixed abundances of N. palea and Fragilaria construens var. venter, Navicula peregrina and Navicula clementis and zone D from the low marsh/tidal flat with increased frequencies of F. exigua and Achnanthes delicatula. At Waump, the major controls on diatom distribution were found to be elevation and to a lesser extent pH, whilst at Wawwat'l, the primary controls were grain size/organic content, conductivity and elevation. The results confirm that saltmarsh diatoms may have potential for future sea-level studies in this region. However, caution must be exercised as the significant difference in the diatom assemblages between the two marshes suggests that the diatoms are responding to a number of environmental variables on a local scale. Some of this variation may reflect highly seasonal changes in sedimentation and salinity resulting from the proximity of the marshes to adjacent streams which are subject to spring freshet. Local differences in elevation between the collected samples may also account for some of the assemblage variability. The results emphasize the great diversity and high sensitivity of intertidal diatom species to environmental controls.     

THE INFLUENCE OF SUBMERGED MACROPHYTES ON SEDIMENTARY DIATOM ASSEMBLAGES1

Submerged macrophytes are a central component of lake ecosystems; however, little is known regarding their long‐term response to environmental change. We have examined the potential of diatoms as indicators of past macrophyte biomass. We first sampled periphyton to determine whether habitat was a predictor of diatom assemblage. We then sampled 41 lakes in Quebec, Canada, to evaluate whether whole‐lake submerged macrophyte biomass (BiomEpiV) influenced surface sediment diatom assemblages. A multivariate regression tree (MRT) was used to construct a semiquantitative model to reconstruct past macrophyte biomass. We determined that periphytic diatom assemblages on macrophytes were significantly different from those on wood and rocks (ANOSIM R = 0.63, P < 0.01). A redundancy analysis (RDA) of the 41‐lake data set identified BiomEpiV as a significant (P < 0.05) variable in structuring sedimentary diatom assemblages. The MRT analysis classified the lakes into three groups. These groups were (A) high‐macrophyte, nutrient‐limited lakes (BiomEpiV ≥525 μg · L^?1; total phosphorus [TP] <35 μg · L^?1; 23 lakes); (B) low‐macrophyte, nutrient‐limited lakes (BiomEpiV <525 μg · L^?1; TP <35 μg · L^?1; 12 lakes); and (C) eutrophic lakes (TP ≥35 μg · L^?1; six lakes). A semiquantitative model correctly predicted the MRT group of the lake 71% of the time (P < 0.001). These results suggest that submerged macrophytes have a significant influence on diatom community structure and that sedimentary diatom assemblages can be used to infer past macrophyte abundance.     

Influence of groundwater depth on the seasonal sources of water accessed by <Emphasis Type="Italic">Banksia</Emphasis> tree species on a shallow,sandy coastal aquifer

In Mediterranean ecosystems vegetation overlying shallow, transient aquifers is often dominated by woody phreatophytes, trees and shrubs that have been shown to be dependent on groundwater for their water requirements. Natural and anthropogenic alterations of groundwater tables (abstraction) are of clear importance to phreatophytic vegetation as reduction of water tables may sever these plants from their natural water sources. Seasonal water sources were determined for species growing on a coastal dune system that overlies a shallow sandy aquifer in south-western Australia. The plants studied grew over groundwater that ranged in depth from 2.5 to 30 m. The naturally occurring stable isotope of hydrogen (deuterium, '²H) was used to distinguish potential water sources. Isotopic ratios from vascular water of the dominant species of the study area (Banksia ilicifolia R. Br. and Banksia attenuata R. Br. trees) were compared with those of potential sources of precipitation, soil moisture and groundwater. A relatively shallow-rooted perennial shrub, Hibbertia hypericoides Benth., was also included as an isotopic reference. The results suggest that both B. attenuata and B. ilicifolia are phreatophytic as they derived some of their water from groundwater throughout the dry-wet cycle, with the exception of B. attenuata at the site of greatest depth to groundwater (30 m) which did not use groundwater. A high proportion (>50%) of groundwater use was not maintained throughout all seasons. With the onset of the hot Mediterranean summer, progressive drying of the surface soils resulted in increased use of groundwater and deep soil moisture. During the wet winter plants used proportionately more water from the upper layers of the soil profile. The degree to which groundwater was utilised by the study species was dependent on the proximity of groundwater, availability of moisture in shallower horizons of the soil profile, root system distribution and maximum root depth.     

Characterization of diatom assemblages in mid-altitude streams of NW Italy

Following the European Water Framework Directive, this study aims to be the first step to (i) identify diatom type assemblages in unpolluted streams in NW Italy, and (ii) find which ecological factors explain most of the variation. To achieve this, we collected physical, chemical and benthic community data from four streams in NW Italy from 2001 to 2004, for a total of 72 samples. All sampling sites were between 200 m a.s.l. and 800 m a.s.l., but differed in the dominant lithological substrate, i.e. alluvial or siliceous. Relationships between diatom communities and environmental factors were examined using canonical correspondence analysis (CCA), while Indicator Species Analysis was used to define characterizing species and accompanying species of three environmental groups identified by CCA: (1) high water quality and medium saline content, (2) high water quality and low saline content, (3) poor water quality. The diatom assemblages of the three groups of sites differed significantly, as shown by the Multi-Response Permutation Procedure. There were strong correlations between diatoms and environmental factors, especially chlorides (also highly correlated with sulphates and carbonate hardness), nitrate concentration and conductivity. The group 1 assemblage was typical of the alluvial Alpine streams with medium saline content and was characterized by mostly oligosaprobic/β-mesosaprobic taxa such as Cymbella affinis, Diatoma ehrenbergii and Staurosira pinnata. The species assemblage found in the siliceous Alpine rivers with good water quality make them suitable reference sites for a benthic diatom community. Electronic Supplementary Material Supplementary material is available for this article at and accessible for authorised users Handling editor: K. Martens     

Effects of oil spills on microbial heterotrophs in Antarctic soils

Oil spillage on the moist coastal soils of the Ross Sea region of Antarctica can impact on populations of microbial heterotrophs in these soils, as determined by viable plate counts and a most probable number technique. Elevated numbers of culturable hydrocarbon degraders, bacteria and fungi were detected in surface and subsurface soils from oil-contaminated sites, compared with nearby control sites. Culturable yeasts were not detected in soil from coastal control sites, yet reached >10⁵ organisms g^-1 dry weight in contaminated soils. The presence of hydrocarbons in soils resulted in a shift in the genera of culturable filamentous fungi. Chrysosporium dominated control soils, yet Phialophora was more abundant in oil-contaminated soils. Hydrocarbon degraders are most likely bacteria; however, fungi could play a role in degradation of hydrocarbons or their metabolites. Depleted levels of nitrate detected in some contaminated soils and decreased pH may be the result of growth of hydrocarbon degraders. Numbers and diversity of culturable microbes from Antarctic soil varied depending on whether a pristine site or a human-impacted (in this case, by fuel spills) site is studied.     

Importance of scalar and riparian habitat effects for assessment of ecological status using littoral diatoms

The classification of waterbodies under the Water Framework Directive is dependent on the ability of monitoring programmes to reflect habitat quality using biotic elements including benthic diatom communities. This study investigated the influence of specific riparian habitats, of mixed woodland, grassland and lake artificial structures such as jetties and slipways, on benthic diatom assemblages in nine lakes across gradients of total phosphorus, alkalinity and in the presence or absence of Dreissena polymorpha. The heterogeneity of the benthic diatom assemblages at riparian and lake scale was assessed by taking three replicates per site category per lake, following standard European Union protocols. Canonical correspondence analysis (CCA) and mixed effect modelling was used to investigate the main environmental controls on assemblage structure. Non-metric Multidimensional Scaling (NMDS) was used to examine patterns in assemblage structure. No single environmental gradient was found to control benthic diatom composition, with differences among assemblages influenced both by riparian habitat type within lakes and interaction of multiple environment gradients, including presence of D. polymorpha. Greater control was exerted on community structure at the lake than local riparian scale. The influence of scalar factors on diatom assemblages increased with increasing scale. We recommend that for effective monitoring and assessment of ecological status, standard sampling protocols should include localised littoral habitats with individual samples pooled across riparian habitat types, thereby accounting for both multiple environmental and spatial controls on community structure.     

Diatoms in northeast Pacific surface sediments as paleoceanographic proxies

Fossil diatom total abundances (# valves/g) in 54 surface-sediment samples from the northeast (NE) Pacific Ocean reflect the position of high primary production associated with coastal upwelling and that possible biases associated with dilution or dissolution are small. Diatom species assemblages, defined by Q-mode factor analysis in 30 samples with abundant diatoms, are related to modern oceanographic properties. Five statistical assemblages, given by five specific diatom species and/or groups, are related to upwelling (Chaetoceros spores), subtropical (Thalassionema nitzschioides), subarctic (Rhizosolenia hebetata), transitional (Neodenticula seminae) and freshwater (freshwater diatoms) ecological environments. These factors are significantly correlated with primary productivity, temperature, nutrient concentrations and salinity, although the strongest relationship is that between diatom assemblages and productivity. However, it is not possible to distinguish between coastal and open-ocean (curl-driven) upwelling based on Chaetoceros spores relative percentages by themselves or on the floral factors.     

Analysis of diversity of chromophytic phytoplankton in a mangrove ecosystem using rbcL gene sequencing

Phytoplankton forms the basis of primary production in mangrove environments. The phylogeny and diversity based on the amplification and sequencing of rbcL, the large subunit encoding the key enzyme ribulose‐1, 5‐bisphosphate carboxylase/oxygenase was investigated for improved understanding of the community structure and temporal trends of chromophytic eukaryotic phytoplankton assemblages in Sundarbans, the world's largest continuous mangrove. Diatoms (Bacillariophyceae) were by far the most frequently detected group in clone libraries (485 out of 525 clones), consistent with their importance as a major bloom‐forming group. Other major chromophytic algal groups including Cryptophyceae, Haptophyceae, Pelagophyceae, Eustigmatophyceae, and Raphidophyceae which are important component of the assemblages were detected for the first time from Sundarbans based on rbcL approach. Many of the sequences from Sundarbans rbcL clone libraries showed identity with key bloom forming diatom genera namely Thalassiosira, Skeletonema and Nitzschia. Similarly, several rbcL sequences which were diatom‐like were also detected highlighting the need to explore diatom communities from the study area. Some of the rbcL sequences detected from Sundarbans were ubiquitous in distribution showing 100% identities with uncultured rbcL sequences targeted previously from the Gulf of Mexico and California upwelling system that are geographically separated from study area. Novel rbcL lineages were also detected highlighting the need to culture and sequence phytoplankton from the ecoregion. Principal component analysis revealed that nitrate is an important variable that is associated with observed variation in phytoplankton assemblages (operational taxonomic units). This study applied molecular tools to highlight the ecological significance of diatoms, in addition to other chromophytic algal groups in Sundarbans.     

Spatial and temporal variations in moss-inhabiting summer diatom communities from Potter Peninsula (King George Island, Antarctica)

This work represents the first analysis of the spatial and temporal variations in the diversity and community structure of diatoms associated with mosses, either dry or wet, sampled during the summer season from the littoral zone of three ponds in Potter Peninsula (King George Island, South Shetland Islands). It also seeks to explore the effect moisture content in the mosses can have on the structure of the diatom assemblages. The ponds approximately had the same number of species, and differences were found between the dry and wet sampling points. The same 4 species were predominant in the three ponds (Nitzschia alpina, N. perminuta, Staurosira oldenburgiana, and Pinnularia subantarctica var. elongata), but not in the same proportions. The first three species differed from those which were found to be dominant in other basins covered by mosses in southern South America and in the sub-Antarctic region. The latter, P. subantarctica var. elongata, had only been found to be abundant in a moss sample from another South Shetland Island. The diatom assemblages were found to be more strongly related to habitat traits (e.g. distance to the sea, ponds’ areas, and the vegetation’s moisture levels) than to the physical–chemical variables measured in the water.