Diatom, chrysophyte and protozoan distributions along a latitudinal transect in Fennoscandia

Diatoms, chrysophyte scales and cysts, and the siliceous plates of thecoamoebae were studied from the surface sediments of 20 freshwater habitats in Fennoscandia The study sites are distributed along a latitudinal transect extending from southern Finland to northern Norway, spanning boreal forest through arctic tundra vegetational zones Diatom assemblages were usually dominated by acidophilic, periphytic members of the genera Achnanthe, Fragilaria and Navicula Marked shifts in diatom assemblage composition were recorded along the latitudinal transect, whereas scaled chrysophytes were rare in all study sites Meanwhile, siliceous protozoa were common, but did not exhibit any noticeable trends in assemblage composition with changing latitude A comparison of the Fennoscandian diatom assemblages with those recorded from freshwater sites near Yellowknife (central Northwest Territories, Canada) revealed similar trends in diatom assemblage composition with changing ecoclimatic zones in both regions Moreover, canonical correspondence analysis showed that diatom assemblages in cold, dilute tundra sites were effectively separated from sites with forested catchments from both the Fennoscandian and Canadian transects The general similarity between the two regions suggests that autecological data and the resulting environmental transfer functions based on diatom assemblages may eventually be joined from North American and European regions     

Consistent patterns in diatom assemblages and diversity measures across water‐depth gradients from eight Boreal lakes from north‐western Ontario (Canada)

1. Until recently, the distribution of diatom species assemblages and their attributes (e.g. species richness and evenness) in relation to water depth have been identified but not quantified, especially across several lakes in a region. Here, we examined diatom assemblages in the surface sediment across a water‐depth gradient in eight small, boreal lakes in north‐western Ontario, minimally disturbed by human activities. 2. Surface‐sediment diatom assemblages were collected within each lake along a gentle slope from near‐shore to the centre deep basin of the lake, at a resolution of ～1 m water depth. Analysis of sedimentary samples provided an integrated view of assemblages that were living in the lake over several years and enabled a high‐resolution analysis of many lakes. The study lakes ranged in water chemistry, morphology and size and are located along an east–west transect approximately 250 km long in north‐western Ontario (Canada). 3. The majority of diatom species were distributed along a continuum of depth, with those taxa having similar habitat requirements forming distinct, though overlapping, assemblages. Three major zones of diatom assemblages in each lake were consistently identified: (i) a near‐shore assemblage of Achnanthes (sensu lato), Nitzschia, Cymbella (sensu lato) and other benthic species; (ii) a mid‐depth assemblage of small Fragilaria (sensu lato)/small Aulacoseira and various Navicula taxa; and (iii) a deep‐water assemblage of planktonic origin (mainly Discotella spp.). 4. The depth of the transition between assemblage zones varied between the eight lakes. The boundary between the deep‐water planktonic zone and the mid‐depth benthic zone varied according to water chemistry and was probably related to light attenuation. The boundary was deeper in lakes with the lower dissolved organic carbon and total phosphorus (TP) (i.e. less light attenuation) and vice versa. 5. Generally, species richness, species evenness and turnover rate of species as a function of depth were significantly lower in the planktonic assemblage zone in comparison with the two zones nearer the shore. Reproducibility of species and assemblage distributions across the depth gradient of the lakes illustrated that, despite potential for sediment transport, detailed ecological characterisation of diatom species can be gleaned from sedimentary data. Such data are often lacking, particularly for near‐shore benthic species.     

Phylogenetic diversity,trait diversity and niches: species assembly of ferns along a tropical elevational gradient

Aim To analyse the structure of pteridophyte assemblages, based on phylogenetic relatedness and trait properties, along an elevational gradient. Ecological theory predicts that co‐occurring species may be: randomly selected from a regional pool; ecologically sorted so that they are functionally different hence resulting in reduced competition (overdispersion); or functionally similar as an adaptation to specific ecological conditions (clustering). Location Braulio Carrillo National Park and Cerro de la Muerte, Costa Rica, Central America. Methods We used an empirical dataset of the quantitative pattern of species occurrences and individual numbers of ferns within 156 plots along a tropical elevational gradient to test whether directed ecological sorting might cause deviations in patterns of trait and phylogenetic diversity. Mean pairwise distances of species based on phylogenetic and trait properties were compared with two different sets of null assemblages, one maintaining species frequency distributions (constrained) and one not (unconstrained). Results Applying different null models resulted in varying degrees of overdispersion and clustering, but overall patterns of deviation from random expectations remained the same. Contrary to theoretical predictions, phylogenetic and trait diversity were relatively independent from one another. Phylogenetic diversity showed no patterns along the elevational gradient, whereas trait diversity showed significant trends for epiphytes. Main conclusions Under stressful environmental conditions (drought at low elevations and frost at high elevations), epiphytic fern assemblages tended to be clustered with respect to trait characteristics, which suggests environmental filtering. Conversely, under less extreme environmental conditions (middle of the transect), the sorting was biased towards high differentiation (overdispersion), presumably because of interspecific competition and trait shifts among closely related species (character displacement).     

Distribution and Flowering Ecology of Bromeliads along Two Climatically Contrasting Elevational Transects in the Bolivian Andes1

We compared the diversity, taxonomic composition, and pollination syndromes of bromeliad assemblages and the diversity and abundance of hummingbirds along two climatically contrasting elevational gradients in Bolivia. Elevational patterns of bromeliad species richness differed noticeably between transects. Along the continuously wet Carrasco transect, species richness peaked at mid‐elevations, whereas at Masicurí most species were found in the hot, semiarid lowlands. Bromeliad assemblages were dominated by large epiphytic tank bromeliads at Carrasco and by small epiphytic, atmospheric tillandsias at Masicurí. In contrast to the epiphytic taxa, terrestrial bromeliads showed similar distributions across both transects. At Carrasco, hummingbird‐pollination was the most common pollination mode, whereas at Masicurí most species were entomophilous. The proportion of ornithophilous species increased with elevation on both transects, whereas entomophily showed the opposite pattern. At Carrasco, the percentage of ornithophilous bromeliad species was significantly correlated with hummingbird abundance but not with hummingbird species richness. Bat‐pollination was linked to humid, tropical conditions in accordance with the high species richness of bats in tropical lowlands. At Carrasco, mixed hummingbird/bat‐pollination was found especially at mid‐elevations, i.e., on the transition between preferential bat‐pollination in the lowlands and preferential hummingbird‐pollination in the highlands. In conclusion, both richness patterns and pollination syndromes of bromeliad assemblages varied in distinct and readily interpretable ways in relation to environmental humidity and temperature, and bromeliad pollination syndromes appear to follow the elevational gradients exhibited by their pollinators.     

Diatom (Bacillariophyceae) assemblages in salt marshes of south‐central Chile: Relations with tidal inundation time and salinity

To reconstruct sea‐level history from changes in tidal environments using diatom assemblages, we need to better understand the relations among brackish diatom assemblages and changing environments along elevational gradients from diverse coastal sites. Our statistical analysis reveals relations between environmental variables and brackish benthic diatom assemblages in the little studied region of south‐central Chile. Along four transects across salt marshes at two sites, we identified 224 diatom taxa in 112 samples. Detrended canonical correspondence analysis showed that tidal exposure time index and salinity were appropriately regressed against the abundance of diatom species using unimodal‐based methods. Our tests of classical and inverse regressions of weighted average and weighted averaging partial least squares (WA‐PLS) showed that WA‐PLS resulted in the highest coefficient of determination and the lowest root‐mean square of the error of prediction. Our regression will be useful in reconstructing environmental variables from fossil diatom assemblages in Chile.     

Oligotrophic waters of the Northwest Atlantic support taxonomically diverse diatom communities that are distinct from coastal waters

Diatoms are important components of the marine food web and one of the most species-rich groups of phytoplankton. The diversity and composition of diatoms in eutrophic nearshore habitats have been well documented due to the outsized influence of diatoms on coastal ecosystem functioning. In contrast, patterns of both diatom diversity and community composition in offshore oligotrophic regions where diatom biomass is low have been poorly resolved. To compare the diatom diversity and community composition in oligotrophic and eutrophic waters, diatom communities were sampled along a 1,250 km transect from the oligotrophic Sargasso Sea to the coastal waters of the northeast US shelf. Diatom community composition was determined by amplifying and sequencing the 18S rDNA V4 region. Of the 301 amplicon sequence variants (ASVs) identified along the transect, the majority (70%) were sampled exclusively from oligotrophic waters of the Gulf Stream and Sargasso Sea and included the genera Bacteriastrum, Haslea, Hemiaulus, Pseudo-nitzschia, and Nitzschia. Diatom ASV richness did not vary along the transect, indicating that the oligotrophic Sargasso Sea and Gulf Stream are occupied by a diverse diatom community. Although ASV richness was similar between oligotrophic and coastal waters, diatom community composition in these regions differed significantly and was correlated with temperature and phosphate, two environmental variables known to influence diatom metabolism and geographic distribution. In sum, oligotrophic waters of the western North Atlantic harbor diverse diatom assemblages that are distinct from coastal regions, and these open ocean diatoms warrant additional study, as they may play critical roles in oligotrophic ecosystems.     

Spatial and temporal distributions of epiphytic diatoms growing on Thalassia testudinum Banks ex König: relationships to water quality

The spatial and temporal distributions of the epiphytic diatom flora on Thalassia testudinum was described within the Florida Bay estuary and at one Atlantic site east of the Florida Keys over a 1-year period. Species of the genus Mastogloia dominated the epiphytic diatom flora (82 out of 332 total species). Nonmetric Multidimensional Scaling (NMDS) and Analysis of Similarity (ANOSIM) revealed four distinct spatial assemblages and two temporal assemblages. Eastern and western Florida Bay assemblages were identified within the estuary. The eastern diatom assemblage was characterized by high relative abundances of Brachysira aponina and Nitzschia liebetruthii, while the western assemblage was characterized by the abundance of Reimerothrix floridensis, particularly during summer. Two diverse and distinct marine assemblages, one located in the Gulf of Mexico along the western edge of Florida Bay and the other behind the Florida reef tract in the Atlantic Ocean, were also identified. Analysis of the spatial distribution of diatoms and water quality characteristics within Florida Bay suggest that these assemblages may be structured by salinity and nutrient availability, particularly P. The Gulf of Mexico and the western Florida Bay assemblages were associated with higher water column salinities and TP concentrations and lower DIN concentrations and TN:TP ratios relative to the eastern Florida Bay assemblage. The temporal variation in diatom assemblages was associated with water temperature, though temporal indicator species were few relative to the number of spatial indicators. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Abundance of Diurnal Primates in Mwanihana Forest, Udzungwa Mountains, Tanzania

Many individual researchers have used line transect counts to estimate forest primate abundance. They have devoted less attention to the interpretation of line transect data obtained by several observers, as is often the case in long-term monitoring programs. We present primate relative abundance data that 5 observers collected over 6 yr (not continuous) along 4 different transects each 4 km long in the Mwanihana Forest, Udzungwa Mountains National Park, Tanzania. Total distance walked during transect repetitions is ca. 700 km. The species we saw most frequently was the endemic Udzungwa red colobus Procolobus gordonorum (mean 0.59 groups/km walked), followed by the Angolan black-and-white colobus Colobus angolensis (0.43 groups/km) and Sykes’s monkey Cercopithecus mitis (0.35 groups/km). We sighted the endemic Sanje mangabey Cercocebus galeritus sanjei and the yellow baboon Papio cynocephalus infrequently, the latter being confined to the deciduous forest parts of the transects. We analyzed sighting frequency by gross habitat type, transect, season, and observer. Interobserver differences in the relative abundance of each species were moderate and the few cases of significant variations were due to discordance of only 1 observer from the others. Estimated distances of primate group sightings differ significantly among observers, thus preventing us from deriving estimates of absolute density. Frequency distributions of distance-class intervals are not significantly different among observers, which may indicate gross interobserver consistency in the width of the area sampled. We conclude that unless consistency in data collection is checked, as we did for 2 observers who collected data simultaneously, potential interobserver differences remain an underlying source of variance in the results that cannot be separated from other sources of variance.     

Clinal differentiation during invasion: <Emphasis Type="Italic">Senecio inaequidens</Emphasis> (Asteraceae) along altitudinal gradients in Europe

The dynamics of plant population differentiation may be integral in predicting aspects of introduced species invasion. In the present study, we tested the hypothesis that European populations of Senecio inaequidens (Asteraceae), an invasive species with South African origins, differentiated during migration from two independent introduction sites into divergent altitudinal and climatic zones. We carried out 2 years of common garden experiments with eight populations sampled from Belgian and ten populations from French altitudinal transects. The Belgian transect followed a temperature and precipitation gradient. A temperature and summer drought gradient characterized the French transect. We evaluated differentiation and clinal variation in plants germinated from field-collected seed using the following traits: days to germination, days to flowering, height at maturity, final plant height and aboveground biomass. Results showed that S. inaequidens populations differentiated in growth traits during invasion. During the 1st year of sampling, the results indicated clinal variation for growth traits along both the Belgium and French altitudinal transects. Data from the 2nd year of study demonstrated that with increasing altitude, a reduction in three growth traits, including plant height at maturity, final plant height and aboveground biomass, was detected along the French transect, but no longer along the Belgian one. Phenological traits did not exhibit a clear clinal variation along altitudinal transects. The possible evolutionary causes for the observed differentiation are discussed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The modality of nine Triturus newt hybrid zones assessed with nuclear,mitochondrial and morphological data

The shape of hybrid zones provides insight into genetic isolation between the evolutionary lineages involved: the greater the limitation to gene flow, the farther along the unimodal to bimodal continuum. We study hybrid zone modality in a group of closely related species at a variety of levels of genetic divergence. We explore the degree and the geography of hybridization in 12 transects of Triturus newts, for nine of the ten secondary contact zones in Europe, using nuclear and mitochondrial encoded genetic data and morphological characteristics. Species status is verified by examining the correlation between the three marker systems in a geographical context. At 40 allozyme loci, two transects classify as unimodal, three as bimodal and two as intermediate, while the signal for hybridization is weak or absent in five transects. One zone studied in duplicate was classified as intermediate in one region and as bimodal in another region. mtDNA introgression is frequent and extends beyond nuclear introgression in two transects. Morphology provides additional evidence for hybridity, including one transect for which the signal of nuclear gene flow is weak. Compared to simulations allowing panmixia, the observed allozyme transitions at contact zones show a deficit of backcrossing to various degrees. Over all transects, there is a weak negative relationship between the level of hybridization and allozyme genetic distance for species pairs, consistent with Bateson–Dobzhansky–Muller effects. This observation, based upon highly comparable data for a single genus, supports conclusions derived from analyses over a wide variety of other taxa. © 2014 The Authors. Biological Journal of the Linnean Society published by John Wiley & Sons Ltd on behalf of The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 604–622.     

Species-richness patterns of vascular plants along seven altitudinal transects in Norway

Altitudinal richness patterns were investigated along altitudinal gradients located in northern Norway (two transects) and along a west–east gradient in southern Norway (five transects). The transects were sampled for vascular plant species richness using a uniform sampling method. Each transect consisted of 38–48 5×5 m sample plots regularly spaced from sea level or valley bottom to a local mountain top. In five transects species richness peaked at mid-altitudes, whereas in the two northern transects species richness decreased with altitude. The observations were qualitatively evaluated in relation to the influence of the area of the species pool, hard boundaries, temperature and precipitation, and mass effect. The observed patterns cannot be fully accounted for by any of these factors. However, the altitude of the peak in species richness was above the forest-limit for all the humped relationships, which may suggest that species richness above the forest-limit might be enhanced by a mass effect from forest taxa. The two monotonic relationships found in the north may be caused by the relatively low number of alpine species at these sites. The monotonic pattern may result from a decrease in "forest species" towards the mountain tops.     

Spatial patterns of plant diversity and communities in Alpine ecosystems of the Hengduan Mountains,Northwest Yunnan,China

Aims Conduct a quantitative, but rapid, regional-level assessment of the alpine flora across northwest Yunnan (NWY) to provide a broad-based understanding of local and regional patterns of the composition, diversity and health of alpine ecosystems across NWY.Methods A stratified random sampling design was employed to select sites across the different mountain ranges of NWY. Vegetation was sampled by stratifying each site by the three major alpine vegetation community types: meadow, dwarf shrub and scree. Two 50-m transects were randomly located within each community type at each sampling site with 10 1-m 2 subplots systematically placed along each transect. Environmental variables were recorded at each transect. Multivariate analyses were used to classify the major plant community assemblages and link community patterns to environmental and habitat variables.Important findings Forb species richness varied from 19 to 105 species per site (21 sites total) with an average of 59 species per site (60 m 2 sampled per site). Most species were patchily distributed with narrow distributions and/or small population sizes; over half the species occurred at only one or two sites. Distinct species assemblages were identified in the meadow vegetation that was strongly aggregated by geographic location suggesting the presence of distinct phytogeographic zones of the meadow alpine flora. Elevation and geographic location were the dominant environmental gradients underlying the variations in species composition. Jaccard's coefficient of similarity averaged only 10% among sites indicating there was little similarity in the alpine flora across the region. The alpine vegetation is highly heterogeneous across the complex landscape of the Hengduan Mountains of NWY. Conservation strategies need to take into account the large geographic differences in the flora to maximize protection of biodiversity.     

Changes in algal assemblages along observed and experimental phosphorus gradients in a subtropical wetland, U.S.A.

• 1 We wanted to determine if changes in algae in the Everglades were due to increased phosphorus (P) loading. Epiphytic algae, water chemistry, and surface sediment chemistry were characterized from 32 sloughs along a P gradient in the Everglades and changes in the algal assemblages along the P gradient were compared with those along an experimental P gradient of in situ mesocosms. The sloughs are the wettest open water habitats characterized by floating and submerged aquatic plants in the Everglades.
• 2 Algal species composition was much more sensitive to P concentration than algal biomass. The diatom species variance among sloughs, captured by 1st ordination axis, was more highly correlated with total P (TP) in surface sediments (r = ‐ 0.79), than soluble reactive P (SRP) (r = ‐ 0.08) and TP (r = ‐ 0.48) in the water column. Algal biomass (µg chl a cm^‐2) was not significantly correlated with P (SRP: r = 0.22, TP: r = 0.19, sediment TP: r = 0.07) along the P gradient in the Everglades. Cluster analysis classified diatom species assemblages in 32 sloughs into three groups (TWIN I, II, III), which corresponded to three zones along the P gradient. Dominant diatom species shifted from Mastogloia smithii (40.3%), Cymbella scotica (22.3%), and Fragilaria synegrotesca (21.8%) in TWIN I to Nitzschia amphibia (22.4%) and C. microcephala (12.4%) in TWIN III. TP in surface sediments and TP in epiphyton assemblages increased 4‐ and 5‐fold from TWIN I to TWIN III, respectively.
• 3 Patterns in epiphytic assemblages along the experimental P gradient in the mesocosms were very similar to those along the Everglades P gradient. Shannon diversity indices and species richness significantly increased along both P gradients. TN : TP ratio in epiphyton assemblages significantly decreased as sediment TP increased along both P gradient. Ordination analysis showed that diatom assemblages in the impacted zone (TWIN III) were ordinated closely to the assemblages from the highest P treatments in the mesocosms. The assemblages from the less impacted zone (TWIN I) were ordinated closely to the assemblages from controls in the mesocosms.
• 4 Concurrence between results of our survey and experiments suggest that changes in epiphytic assemblages along the P gradient in the Everglades are caused by increases in P concentrations.

     

长江安庆段江豚主要栖息地鱼类群落结构

长江皖河交汇处(皖河口)是安庆江段江豚主要的栖息地之一。为了解江豚主要栖息地鱼类群落结构,于2013年9月—2014年8月对皖河口及其附近4个断面逐月进行了鱼类调查。研究结果表明,共采集鱼类35种,与历史资料相比,鱼类物种多样性已经严重下降,并且小型化趋势明显。5个断面当中,皖河口鱼类种数最多,为27种,且以中上层鱼类餐和油餐为主要优势种;其余4个断面分别为16、20、19和14种,且多数断面以底层鱼类黄颡鱼和长须黄颡鱼为主要优势种。方差分析结果表明,皖河口渔获物的总数量和总重量与其他断面无显著差异,但总种数却显著高于断面1和5。对中上层、中下层和底层鱼类的进一步分析发现,5个断面的显著差异仅存在于中上层鱼类,且皖河口中上层渔获物的数量和重量均显著高于其他断面。由此推断,江豚选择皖河口作为主要栖息地可能主要由于其更加丰富的中上层鱼类资源。研究结果不仅有助于了解鱼类资源的变化,还对江豚的原地和迁地保护具有重要意义。     

Summer distribution of netphytoplankton in the Atlantic sector of the Southern Ocean

The surface distribution of netphytoplankton (>20 m) in the Atlantic sector of the Southern Ocean was investigated along two transects during early and late austral summer 1990/91. Sampling was under-taken at intervals of 60 of latitude between 34° and 70°S for the analysis of nutrients and for the identification and enumeration of netphytoplankton. Peaks in total diatom abundances were recorded at the Antarctic Polar Front (APF), in the vicinity of the South Sand wich Islands, in the marginal ice zone and in the neritic waters of the Atlantic sector of Antarctica. Cluster analysis indicates the existence of two major zones between Southern Africa and Antarctica. Diatom abundance increased south of the Antarctic Polar From along both transects, which can be partially explained by gradients of silicate concentration. Small chain-forming species (e.g. Fragilariopsis kerguelensis and Nitzschia lineata) dominated the diatom assemblages in early summer, while larger species, such as Rhizosolenia hebetata f. semispina and Corethron criophilum, dominated late summer diatom assemblages. The predominance of typically ice-associated forms in early summer suggests that the release of epontic cells during ice melt provides the initial inoculum for the netphytoplankton biomass. These small diatoms are subsequently replaced by larger species.     

Using Diatom Assemblages to Assess Urban Stream Conditions

We characterized changes in diatom assemblages along an urban-to-rural gradient to assess impacts of urbanization on stream conditions. Diatoms, water chemistry, and physical variables of riffles at 19 urban and 28 rural stream sites were sampled and assessed during the summer base flow period. Near stream land use was characterized using GIS. In addition, one urban and one rural site were sampled monthly throughout a year to assess temporal variation of diatom assemblages between the urban and rural stream sites. Canonical correspondence analysis (CCA) showed that the 1st ordination axis distinctly separated rural and urban sites. This axis was correlated with conductivity (r = 0.75) and % near-stream commercial/industrial land use (r = 0.55). TWINSPAN classified all sites into four groups based on diatom assemblages. These diatom-based site groups were significantly different in water chemistry (e.g., conductivity, dissolved nutrients), physical habitat (e.g., % stream substrate as fines), and near-stream land use. CCA on the temporal diatom data set showed that diatom assemblages had high seasonal variation along the 2nd axis in both urban and rural sites, however, rural and urban sites were well separated along the 1st ordination axis. Our results suggest that changes in diatom assemblages respond to urban impacts on stream conditions.     

Evaluating diatom community composition in the absence of marked limnological gradients in the high Arctic: a surface sediment calibration set from Cornwallis Island (Nunavut,Canada)

Fossil diatom assemblages preserved within the sedimentary record in Arctic lakes provide the potential to reconstruct past changes in important limnological variables. During the summers of 1992 and 1993, we examined previously unstudied freshwater ecosystems on Cornwallis Island, Arctic Canada, with the specific objectives of (1) documenting the limnology and modern diatom assemblages from this region, and (2) determining which environmental variables most influence diatom species distributions. The Cornwallis Island study sites displayed the least amount of variance in measured water chemistry variables in comparison to nearly all of our labs’ previous freshwater surveys in the Arctic. The small limnological gradients precluded the development of a statistically robust diatom inference model, but perhaps more importantly, allowed us to explore variations in diatom composition in the absence of marked variations in water chemistry. Diatom species turnover was minimal, with the most common diatom taxa being Achnanthidium minutissima, Nitzschia perminuta, N. frustulum, with lesser percent abundances of Chaemaepinnularia soehrensis, Navicula chiarae, Psammothidium marginulata, and A. kryophila. A small number of study sites differed from the majority with respect to water chemistry (e.g., coastal sites with high specific conductivities) and habitat availability (e.g., ephemeral ponds with extensive moss habitats), and these sites had markedly different diatom assemblages. These data reinforce previous observations that water chemistry and other climate-related factors are the primary environmental controls influencing diatom distributions at high latitudes. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Diatoms from Indonesian mangroves and their suitability as sea-level indicators for tropical environments

We collected modern diatom samples from two mangrove environments of Sulawesi, Indonesia to provide a much needed dataset for the reconstruction of sea level from tropical environments. The diatom assemblages are dominated by mesohalobous species (e.g. Amphora coffeaeformis, Amphora turgida, Achnanthes delicatula, Nitzschia sigma and Tryblionella balatonis) and oligohalobous (e.g. Amphora veneta, Diploneis ovalis and Progonoia didiomatia) taxa. Both study sites show strong vertical zonations, which suggests that duration and frequency of intertidal exposure are important factors in controlling the relative abundance of diatoms. The assemblages can be generally divided into a mixed assemblage of mesohalobous, oligohalobous–halophilous and oligohalobous-indifferent diatoms that are found from the dense mangrove vegetation towards the landward edge of the transects, and mesohalobous diatom assemblages that are located within the fringing Rhizophora and tidal flat environments. We subsequently developed a diatom-based transfer function, which is a quantitative approach to sea-level reconstruction. The relationship between observed and diatom-predicted elevations suggests accurate and precise reconstructions are possible. The error estimate (± 0.15 m) is comparable to diatom-based transfer functions from temperate marshes.     

The occurrence of sub-ice algal aggregations off northeast Greenland

Massive growth of sub-ice algal assemblages was recorded at two stations under first-year ice off northeast Greenland using a Remotely Operated Vehicle equipped with cameras. The assemblages mainly consisted of the diatom Melosira arctica (Ehr.) Dickie. A station sampled at the beginning of June 1993 revealed two forms of growth, curtain-like and rope-like, but with many intermediate types along the entire 150 m transect. The algal distribution was patchy. No significant sympagic fauna was found close to the algal masses. At a station sampled in the middle of July, similar algal concentrations seemed to be disturbed by ice-melting processes. Two casts under multi-year ice flows failed to show any algal aggregations. The observation of algal assemblages under first-year ice is in contrast to earlier reports from the Barents Sea where they have been recorded exclusively under multi-year ice.     

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.