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The ecological significance of benthic diatom taxocoenoses in marine ecosystems renders them a suitable reference when making decisions on conservation, as well as ecological and biogeographical issues. This study focuses on floristics of epiphytic diatoms of macroalgae from the central region of the Gulf of California and their biogeographical affinities. Based on current floristics for benthic diatoms of the Mexican NW, it was hypothesized that species richness would be higher for the central gulf (transitional) than for the tropical Revillagigedo Archipelago. Additionally, it was hypothesized that it would be composed mainly of common taxa of the region, with tropical and temperate components. Likewise, it was hypothesized that Mastogloia (tropical) would include less taxa and Lyrella would include more taxa in the transitional central gulf. The diatom flora yielded 333 taxa and 101 genera, and out of which the best represented were Navicula with 29 taxa, Amphora (27), Cocconeis (25), Nitzschia (24), Diploneis (19), Achnanthes (13), Halamphora (14), Fallacia (10), Lyrella (9), and Mastogloia (8), adding up to 53% of the total. The inspected diatom taxocoenosis included mostly taxa commonly distributed in the Mexican NW, albeit with 16 new records. This, plus the high species richness, as well as the proportions of selected taxa depicting this diatom taxocoenosis as being of transitional biogeographical affinity, back the posed hypotheses.

Background Diatoms in genus Licmophora are found as epiphytes on marine shores and are members of fouling communities. They can be abundant on natural coral reef substrates such as filamentous algae and as fringes on Halimeda. Biodiversity of benthic tropical diatoms is generally poorly known. Several new species of Licmophora have been reported from Guam but many are still undescribed. Methods Samples of seaweeds with evident diatom coatings were collected during scuba dives, examined live, preserved in formalin, and processed with nitric acid cleaning following standard practice. Cleaned samples were examined in LM and SEM. Results We describe two species unusual in having an axial wave in the valve, and a further long, straight species. L. repanda n. sp. and L. undulata n. sp. were of similar lengths (ca. 200 μm long) and both had axial waves but L. undulata was more slender with an inflated basal pole, had colonies on mucilage pads vs. long, single-stranded mucilage stalks. In addition, L. undulata had one apical rimoportula vs. two, elongated areolae along the midrib vs. uniform areolae, and the valvocopular advalvar striae ended halfway along, whereas in L. repanda they continued to the end. L. joymaciae n. sp. grew on long, single-stranded mucilage stalks with valves 300–400 μm long, with two apical rimoportulae, and basal pole not inflated. As in L. undulata its valvocopular advalvar striae ended halfway along the band. Stria densities were different at apex vs. base in L. joymaciae but not in the two wavy species. In all species, the 4th pleura had an apical cap and a narrow band with a single row of pores but it was larger in L. joymaciae. The other three girdle bands did not present any major differences among the three species but are documented for future comparisons with other species. Conclusions Although the morphometric differences are small among the new species and between them and similar known species, the combinations of character states clearly shows that they are different.

We applied DNA metabarcoding to evaluate the ecology of genetic variants within several diatom species that are important for biomonitoring. Benthic diatoms are widely used as bioindicators for biomonitoring programmes, including those for European rivers demanded by Water Framework Directive (WFD). Morphological identification of diatoms at species level is required for assessing the ecological status in biomonitoring programmes. However, this is a time-consuming task and requires expert knowledge. In addition, closely related species, which sometimes are scarcely distinguishable on the basis of their morphology, can show different ecological preferences; these may even vary within a single diatom species. Not being able to identify the different ecological preferences shown by the genetic variants of a single species or closely related species, might have consequences for biomonitoring programmes, especially if such differences occur within common species. The key diatom species that we studied were: Fistulifera saprophila (FSAP), widely regarded as a marker for elevated nutrient levels, organic pollution and hence poor ecological status; Achnanthidium minutissimum (ADMI), which usually indicates good ecological status; and Nitzschia inconspicua (NINC) and N. soratensis (NSTS), two species that are widely separated phylogenetically but almost impossible to distinguish in the light microscope. Our dataset was based on high-throughput sequencing using a 312-bp rbcL marker. We used the denoising pipeline DADA2 to infer amplicon sequence variants (ASVs) from 554 environmental samples from river biomonitoring campaigns in Catalonia (NE Spain) and France. Ecological groupings of ASVs were distinguished according to their environmental responses given by Threshold Indicator Taxa ANalysis (TITAN); the environmental parameters that most influenced the occurrence of these groupings were tested using boosted regression trees. We could distinguish three different ecological groupings of ASVs within ADMI and three within FSAP. In each species two of the groupings were clearly separated by their opposite responses to calcium and conductivity and boosted regression trees showed that for three out of four of these groupings, these two variables were among the most important variables for explaining the ASV distributions. The third grouping in FSAP had a negative response to total organic carbon and a positive response to altitude and hence was better represented in less organically polluted waters and higher ecological status than is generally assumed for FSAP. Our analyses did not identify ecological groupings of ASVs within NINC and NSTS but confirmed earlier studies, based on more limited sampling, that indicated different preferences of these species. Conductivity and calcium were the variables that most influenced the occurrence of NINC and NSTS, NINC being better distributed in waters with higher levels of calcium and conductivity than NSTS. Our findings indicate the potential use of DNA metabarcoding for distinguishing the ecological preferences of genetic variants within a single species or closely related species. This information, coupled with the broad knowledge generated over many years using traditional microscope-based identifications, will facilitate the development of more accurate biological indexes for the biomonitoring programmes of the future.

Benthic diatoms are well known bioindicators of water quality, used in many aquatic ecosystems. Since diatom-based monitoring of water quality is required by European legislation, the search for methods that facilitate this task has become more relevant. The aim of this study was to test the reliability of DNA metabarcoding combined with high-throughput sequencing (HTS) techniques in the bioassessment of 22 Mediterranean shallow ponds in Spain. For each pond, Trophic Diatom Index (TDI) was calculated from inventories obtained by using light microscopy, and then molecular (HTS) methods. Ponds were subsequently classified into five water quality classes. Our results showed a good correspondence between both methods, especially after applying a correction factor depending on the biovolume of the cells. This correspondence led to the assignment to the same quality class in 59% of the ponds. The determination and quantification of valves or DNA sequences was one of the main pitfalls, mainly those related to the variability in the relative abundances of some species. Accordingly, ponds with similar relative abundances for the dominant species were assigned to the same quality class. Moreover, other difficulties leading the discrepancies were the misidentification of some species due to the presence of semi-cryptic taxa, the incompleteness of the reference database and the bioinformatic protocol. Therefore, the validation of DNA-based methods for the identification of freshwater diatoms represents an important goal, as an alternative to traditional ones in Mediterranean shallow ponds.

Diatoms, eukaryotic algae with silica cell wall have been proved to be reliable bioindicators and are applied in ecological status assessment of aquatic ecosystems using indices calculated from pollution sensitivity and indicator values of species. Traditional method of identification of diatom species is based on morphological features of frustule that requires in-depth taxonomical knowledge and expertise. Metabarcoding that combines barcodes and high-throughput sequencing offers a promising alternative. In this pilot study we tested the applicability of metabarcoding of benthic diatom assemblages for ecological status assessment of water bodies in Hungary comparing its performance to that of morphology-based identification of species. Samples from 78 rivers and streams arranged along a trophic gradient and 14 soda pans representing unique types of habitats were investigated. Sequences of the barcode region of rbcL gene suggested by Vasselon et al. (2017) were acquired revealing 1135 diatom amplicon sequence variants (ASVs) of which 54% could be assigned at species level using Diat.barcode (Rimet et al. 2019) as reference database. Morphological investigation detected more species and intraspecific taxa in the lotic and lentic samples (413 and 78, respectively) than metabarcoding (190 and 75). Correspondence between taxa detected based on morphology and DNA sequences was relatively low (on average 24% in lotic and 26% in lentic samples) but considerably increased (on average 66% and 56%, respectively) when taking into account only the taxa reaching higher than 5% relative abundance in microscopy counting. The differences mainly derived from that a considerable portion (59% and 32%, respectively) of the morphologically identified taxa were not recorded in the reference database. Community structure of samples from both running and standing waters based on microscopy and DNA sequence analysis showed significant correlation as revealed using Mantel test. For rivers and streams diatom index IPS (Specific Pollution Sensitivity Index, (Coste in Cemagref, 1982) for soda pans indices H (Ziemann et al., 2001) and IBD (Indice Biologique Diatomées, Lenoir and Coste, 1996) were calculated from the results of the two aspects. Strong correlation was found between morphology- and sequence-based indices and in about half of the samples, the ecological status class obtained with the two methods coincided. Our results suggest that metabarcoding inheres a great opportunity and could be successfully applied in benthic diatom-based ecological status assessment of Hungarian waters after the reference database is supplemented with taxa frequently occurring in these habitats. References Cemagref, 1982. Etude des méthodes biologiques quantitativesd’appréciation de la qualité des eaux, Rapport Division Qualité des Eaux Lyon. Agence financière de Bassin Rhône-Méditerranée-Corse, Pierre-Bénite, France. Lenoir, A., Coste, M., 1996. Development of a practical diatom index of overall water quality applicable to the French National Water Board Network. Presented at the International symposium, Volksbildungsheim Grilhof Vill, AUT, 17-19 September 1995, Universität Innsbruck, pp. 29–43. Rimet, F., Gusev, E., Kahlert, M., Kelly, M.G., Kulikovskiy, M., Maltsev, Y., Mann, D.G., Pfannkuchen, M., Trobajo, R., Vasselon, V., Zimmermann, J., Bouchez, A., 2019. Diat.barcode, an open-access curated barcode library for diatoms. Sci. Rep. 9, 15116. Vasselon, V., Rimet, F., Tapolczai, K., Bouchez, A., 2017. Assessing ecological status with diatoms DNA metabarcoding: Scaling-up on a WFD monitoring network (Mayotte island, France). Ecol. Indic. 82, 1–12. Ziemann, H., Kies, L., Schulz, C.-J., 2001. Desalinization of running waters: III. Changes in the structure of diatom assemblages caused by a decreasing salt load and changing ion spectra in the river Wipper (Thuringia, Germany). Limnologica 31, 257–280.

Ongoing climatic change and anthropogenic pressure highlight the importance of reliable assessment of the ecological status of freshwaters. Bioindicators are used widely in ecological assessments as biotic assemblages reflect the environmental conditions in current ecosystems. However, the robustness of bioindicators relies on the transferability of indices and models outside the regions they were derived from. We tested the reliability of stream diatom assemblages as indicators of water chemistry and climatic factors in a cross-regional assessment by developing a predictive model with diatom assemblage data from Sweden and using it to model stream conditions in Finland. The inference models and predictions were performed using the Boosted Regression Trees (BRT) method, separately in species and genus levels. The predictive performance of the calibration models in Sweden were good or moderate for both water chemistry and climatic variables, both at species and genus levels. The most important climatic (growing degree days, r2 = 0.57) and water chemistry variables (pH, r2 = 0.65; and total phosphorus (TP), r2 = 0.52) could be inferred from diatom assemblages relatively well. However, predictive performances of the cross-regional models were low (r2 ≤ 0.13). Nevertheless, water chemistry variables, conductivity (r2 = 0.13) and TP (r2 = 0.12), were predicted the best. The most important diatom indicators for climatic and environmental variables varied between Sweden and Finland. The study showed that diatom assemblages can be robust indicators of water chemistry and climatic variables within the region where the inference models are calibrated. However, their indicator ability may be weak between regions. The reason for the low transferability of the diatom inference models may stem from between-region differences in species realized niches, species pools and/or ecosystems, local adaptation or species identification. Hence, models should only be used with caution in geographical contexts other than the one where they were developed. The calibration data should cover as large geographical area as possible to give reliable predictions when applied in smaller regions.

Changes in land use, climate and flow diversion are key drivers of river flow regime change that may eventually affect freshwater biodiversity and ecosystem functions. However, our knowledge is limited on how the functional features of stream organisms vary along the gradient of hydrological disturbance (i.e. flow regime changes) and how flow regimes mediate the functional features in lowland streams. We analyzed the functional traits of benthic diatoms (unicellular siliceous algae) that are most sensitive and tolerant to flow regime changes along a nationwide scale of 246 sites in Denmark. We combined RLQ and fourth-corner analyses to explore the co-variation between hydrological variables (R table) and species traits (Q table), constrained by the relative abundance of each species (L table) as observed in each of the sampling sites. Further, we examine the relationships between functional features (i.e., functional redundancy and diversity) and hydrological variables by multivariate statistical analyses. Results show that species turnover with displacement of sensitive species by tolerant species was the dominating process in benthic diatom communities during high flow disturbances. Functional features, as indicated by functional diversity and redundancy indices, were mediated mainly by high and low flow magnitude. Median daily flow magnitude shows a consistent positive relationship with functional redundancy and richness indices indicating that larger streams are more resilient to flow perturbations. In addition flow regime changes are less important than median daily flow magnitude and show inconsistent correlation to functional features likely due to the interaction of multiple environmental stressors. Our study highlights the robustness of trait-based approaches for identifying flow regime changes in streams, and strongly suggests that biodiversity conservation and water resource management should focus on protecting natural base flow in headwater streams and generally reduce flow regulation for sustaining stream ecosystems under future global changes.

Biofilms were allowed to develop on ceramic tiles placed in closed containers on the shore of Potter Cove, 25 de Mayo (King George) Island. Water pumping from the cove inside the containers extended for 25 days. Diatoms were the dominant microalgae in these biofilms, which were removed from a set of tiles to a) characterize the extracellular mucilage, b) carry out floristic determination and c) perform grazing experiments with the limpet Nacella concinna. Biofilms mucilaginous matrix consisted of proteins and carbohydrates. Room temperature aqueous extraction of the freeze-dried material rendered a fraction enriched in the storage glucan chrysolaminarin, its identity confirmed by methylation structural analyses. Hot water extracted products showed greater heterogeneity in monosaccharide composition, including glucose, mannose, galactose, fucose, xylose and rhamnose. Diatom identification revealed that Pseudogomphonema kamtschaticum was the dominant species followed by several Navicula species, Nitzschia pellucida and Synedra kerguelensis. Photographical survey of colonized tiles placed in glass flasks together with a specimen of Nacella concinna exhibited between 5 and 30% removal of the biofilms coverage after 24 h of exposure to the limpet, suggesting that EPS and chrysolaminarin constitute a C-source for the gastropod., Yasmin Daglio, Hernán Sacristán, Martín Ansaldo, María C.Rodríguez南極キングジョージ島、Potter Coveの海岸に陶器のタイルを設置し、25日間でのバイオフィルムの発達実験を行った。バイオフィルム中では珪藻が優占したが、そこからa）細胞外粘液質の特徴、b）植物相の同定、c）カサガイの一種Nacella concinnaを用いた囓り取り実験を行った。バイオフィルムの粘液層は、タンパク質と炭水化物からなり、グルカノ-クリソラミナリンやグルコースなどの多様な単糖類が含まれていた。珪藻を同定したところ、Pseudogomphonema kamtschaticumが優占し、Naviculaなどがそれに続く事が明らかになった。カサガイによる囓り取りは、24時間で5～30%で、EPSとクリソラミナリンは彼らの炭素源となっていることが示唆された。

The Sava River Basin is a major drainage basin of southeastern Europe, significantly influenced by anthropogenic activities. Our study was focused on diatom communities as an indicator of the ecological status of running waters. We investigated over 937km of the Sava River at 19 sampling sites. Benthic diatom communities and 17 diatom indices were analyzed along with a large set of environmental parameters. CCA revealed that the most important elements along the spatial gradient were As and Si. Our results show that the species Navicula recens (Lange-Bert.) Lange-Bertalot and Eolimna minima (Grunow) Lange-Bertalot are very abundant at downstream localities where the highest concentrations of As were measured. The number of motile diatoms increased along the nutrient gradient, i.e. with Si availability. Correlations between diatom indices and selected environmental factors showed that temperature, As, Si and Fe are in significant negative correlation with most diatom indices. Analysis revealed the influence of As and metals in water on diatoms, although their concentrations did not exceed environmental standards. While our findings do not confirm that diatom indices reveal the intensity of pressures solely caused by nutrient and/or organic pollutants, they suggest that in moderately polluted large rivers benthic diatoms are good bioindicators of multiple pressures, and that diatom indices could serve as indicators of the level of overall degradation of an ecosystem.

The species richness and community composition of the diatom communities were studied in the Baltic Sea, Northern Europe, to enhance knowledge about the diversity of these organisms in a brackish water ecosystem. Many organisms in the Baltic Sea have been studied extensively, but studies investigating littoral diatoms are scarce. The goal of this study was to examine the importance of climatic, spatial and water physicochemical variables as drivers of epilithic diatoms in the Gulf of Finland and the Gulf of Bothnia. The variation in species richness was best explained by pH, total phosphorus and total nitrogen. Redundancy Analysis indicated that the most important factors correlating with species composition were air temperature, silicon, total phosphorus, water temperature, salinity and pH. Variation Partitioning showed that the species composition was mostly affected by climatic and spatial variables, whereas physicochemical variables had little impact. However, the strongest factor was the combined influence of climatic, spatial and physicochemical variables. The results suggest that diatom species richness in the northern Baltic Sea is primarily regulated by local factors, while climatic and spatial variables have little impact on richness. Species composition is mostly affected by climatic and spatial variables. We conclude that understanding the distribution patterns of Baltic Sea diatoms requires the inclusion of climatic, spatial and water chemistry variables.

The global biodiversity loss has raised interest in the different facets of diversity, and the importance of diversity for ecosystem functions has been recognized. However, our knowledge on seasonal and inter-annual variation in the composition and diversity of communities is still poor. Here, we investigated the seasonal and inter-annual changes in taxonomic and functional community composition and diversity of benthic diatoms in a coastal habitat of the northern Baltic Sea, where seasonal and inter-annual variation of climate is pronounced. We found that the taxonomic and functional alpha diversity remained stable at seasonal and inter-annual level despite strong changes in community composition. However, alpha diversity decreased during an exceptionally warm winter possibly due to disturbances induced by the lack of ice. This may suggest that climate warming and consequently limited ice cover will affect the diversity of benthic communities.

Our study of 164 diatom samples from Catalonia (NE Spain) is the first to evaluate the applicability of DNA metabarcoding, based on high throughput sequencing (HTS) using a 312-bp rbcL marker, for biomonitoring Mediterranean rivers. For this, we compared the values of a biotic index (IPS) and the ecological status classes derived from them, between light microscope-based (LM) and HTS methods. Very good correspondence between methods gives encouraging results concerning the applicability of DNA metabarcoding for Catalan rivers for the EU Water Framework Directive (WFD). However, in 10 sites, the ecological status class was downgraded from “Good”/“High” obtained by LM to “Moderate”/“Poor”/“Bad” by HTS; these “critical” sites are especially important, because the WFD requires remedial action by water managers for any river with Moderate or lower status. We investigated the contribution of each species to the IPS using a “leave-one-out” sensitivity analysis, paying special attention to critical sites. Discrepancies in IPS between LM and HTS were mainly due to the misidentification and overlooking in LM of a few species, which were better recovered by HTS. This bias was particularly important in the case of Fistulifera saprophila, whose clear underrepresentation in LM was important for explaining 8 out of the 10 critical sites and probably reflected destruction of weakly-silicified frustules during sample preparation. Differences between species in the rbcL copy number per cell affected the relative abundance obtained by HTS for Achnanthidium minutissimum, Nitzschia inconspicua and Ulnaria ulna, which were also identified by the sensitivity analysis as important for the WFD. Only minor IPS discrepancies were attributed to the incompleteness of the reference library, as most of the abundant and influential species (to the IPS) were well represented there. Finally, we propose that leave-one-out analysis is a good method for identifying priority species for isolation and barcoding. info:eu-repo/semantics/acceptedVersion

Diatoms are so important in ocean food-webs that any human induced changes in their abundance could have major effects on the ecology of our seas. The large chain-forming diatom Biddulphia biddulphiana greatly increases in abundance as pCO2 increases along natural seawater CO2 gradients in the north Pacific Ocean. In areas with reference levels of pCO2, it was hard to find, but as seawater carbon dioxide levels rose, it replaced seaweeds and became the main habitat-forming species on the seabed. This diatom algal turf supported a marine invertebrate community that was much less diverse and completely differed from the benthic communities found at present-day levels of pCO2. Seawater CO2 enrichment stimulated the growth and photosynthetic efficiency of benthic diatoms, but reduced the abundance of calcified grazers such as gastropods and sea urchins. These observations suggest that ocean acidification will shift photic zone community composition so that coastal food-web structure and ecosystem function are homogenised, simplified, and more strongly affected by seasonal algal blooms.

River impoundment constitutes one of the most important anthropogenic impacts on the World’s rivers. An increasing number of studies have tried to quantify the effects of river impoundment on riverine ecosystems over the past two decades, often focusing on the effects of individual large reservoirs. This study is one of the first to use a large-scale, multi-year diatom dataset from a routine biomonitoring network to analyse sample sites downstream of a large number of water supply reservoirs (n = 77) and to compare them with paired unregulated control sites. We analysed benthic diatom assemblage structure and a set of derived indices, including ecological guilds, in tandem with multiple spatio-temporal variables to disclose patterns of ecological responses to reservoirs beyond the site-specific scale. Diatom assemblage structure at sites downstream of water supply reservoirs was significantly different to control sites, with the effect being most evident at the regional scale. We found that regional influences were important drivers of differences in assemblage structure at the national scale, although this effect was weaker at downstream sites, indicating the homogenising effect of river impoundment on diatom assemblages. Sites downstream of reservoirs typically exhibited a higher taxonomic richness, with the strongest increases found within the motile guild. In addition, Trophic Diatom Index (TDI) values were typically higher at downstream sites. Water quality gradients appeared to be an important driver of diatom assemblages, but the influence of other abiotic factors could not be ruled out and should be investigated further. Our results demonstrate the value of diatom assemblage data from national-scale biomonitoring networks to detect the effects of water supply reservoirs on instream communities at large spatial scales. This information may assist water resource managers with the future implementation of mitigation measures such as setting environmental flow targets.

The current decrease in biodiversity affects all ecosystems, and the impacts of diversity on ecosystem functioning need to be resolved. So far, marine studies about diversity?ecosystem productivity-relationships have concentrated on small-scale, controlled experiments, with often limited relevance to natural ecosystems. Here, we provide a real-world study on the effects of microorganismal diversity (measured as the diversity of benthic diatom communities) on ecosystem productivity (using chlorophyll a concentration as a surrogate) in a heterogeneous marine coastal archipelago. We collected 78 sediment cores at 17 sites in the northern Baltic Sea and found exceptionally high diatom diversity (328 observed species). We used structural equation models and quantile regression to explore relationships between diatom diversity and productivity. Previous studies have found contradictory results in the relationship between microorganismal diversity and ecosystem productivity, but we showed a linear and positive basal relationship between diatom diversity and productivity, which indicates that diatom diversity most likely forms the lowest boundary for productivity. Thus, although productivity can be high even when diatom diversity is low, high diatom diversity supports high productivity. The trait composition was more effective than taxonomical composition in showing such a relationship, which could be due to niche complementarity. Our results also indicated that environmental heterogeneity leads to substantial patchiness in the diversity of benthic diatom communities, mainly induced by the variation in sediment organic matter content. Therefore, future changes in precipitation and river runoff and associated changes in the quality and quantity of organic matter in the sea, will also affect diatom communities and, hence, ecosystem productivity. Our study suggests that benthic microorganisms are vital for ecosystem productivity, and together with the substantial heterogeneity of coastal ecosystems, they should be considered when evaluating the potential productivity of coastal areas.

Species occurrences are influenced by numerous factors whose effects may be context dependent. Thus, the magnitude of the effects and their relative importance to species distributions may vary among ecosystems due to anthropogenic stressors. To investigate context dependency in factors governing microbial bioindicators, we developed species distribution models (SDMs) for epilithic stream diatom species in human-impacted and pristine sites separately. We performed SDMs using boosted regression trees for 110 stream diatom species, which were common to both data sets, in 164 human-impacted and 164 pristine sites in Finland (covering similar to 1,000 km, 60 degrees to 68 degrees N). For each species and site group, two sets of models were conducted: climate model, comprising three climatic variables, and full model, comprising the climatic and six local environmental variables. No significant difference in model performance was found between the site groups. However, climatic variables had greater importance compared with local environmental variables in pristine sites, whereas local environmental variables had greater importance in human-impacted sites as hypothesized. Water balance and conductivity were the key variables in human-impacted sites. The relative importance of climatic and local environmental variables varied among individual species, but also between the site groups. We found a clear context dependency among the variables influencing stream diatom distributions as the most important factors varied both among species and between the site groups. In human-impacted streams, species distributions were mainly governed by water chemistry, whereas in pristine streams by climate. We suggest that climatic models may be suitable in pristine ecosystems, whereas the full models comprising both climatic and local environmental variables should be used in human-impacted ecosystems.

Benthic diatoms have traditionally been used as bioindicators of aquatic ecosystems. Because diatom-based monitoring of water quality is required by European legislation, molecular-based methods had emerged as useful alternatives to classical methods based on morphological identification using light microscopy. The aim of this study was to test the reliability of DNA metabarcoding combined with High-Throughput Sequencing (HTS) techniques in the bioassessment of the trophic status of 22 Mediterranean shallow ponds in NW Spain. For each pond, the Trophic Diatom Index (TDI) was calculated from inventories obtained by identification using light microscopy (LM) followed by high-throughput sequencing (HTS) at the molecular level. Ponds were subsequently classified into five water quality classes. The results showed a good correspondence between both methods, especially after applying a correction factor that depended on the biovolume of the cells. This correspondence led to the assignment to the same quality class in 59% of the ponds. The determination and quantification of valves or DNA sequences was one of the main pitfalls, which mainly included those related to the variability in the relative abundances of some species. Accordingly, ponds with similar relative abundances for the dominant species were assigned to the same quality class. Moreover, other difficulties leading the discrepancies were the misidentification of some species due to the presence of semi-cryptic taxa, the incompleteness of the reference database and the bioinformatic protocol. Thus, the validation of DNA-based methods for the identification of freshwater diatoms represents an important goal, as an alternative to using traditional methods in Mediterranean shallow ponds.

The condition of New Zealand's remnant wetlands has been documented by landscape-scale assessments such as the Index of Ecological Integrity and Wetland Condition Index. We explored the potential for microscopic aquatic biota (epiphytic diatoms) to provide complementary information about wetland condition using data from 77 lowland sites (mainly palustrine swamps) with circumneutral pH. In the South Island, correspondence between diatoms and wetland indices or water quality was weak. In the North Island, conductivity and total dissolved nitrogen (TDN) together explained 49% of the variance in assemblage composition and several diatom genera were indicative of high or low conductivity, dissolved phosphorus and TDN. Changes in these water quality variables may trigger changes in wetland condition, which are eventually reflected by the landscape-scale indices. Diatoms respond rapidly to water quality changes suggesting potential for diatom indicator taxa to provide early warning of wetland degradation or to track restoration.

"The Mesa River (MR) in the Iberian Range (Spain) displays prominent, Pleistocene to present-day fluvial tufa deposits. Little of their associated microbiota has been studied to date despite the regional and historical relevan- ce of these calcareous buildups. Goals . This paper is a preliminary exploration of the diatom (Bacillariophyta) genera associated with actively-growing tufa from 10 benthic environments along 24 km of the Mesa River. Methods . Bright- field microscopy, as well as consultation with specialists and specialized literature was used for taxonomic classifi- cation of diatoms. Results . We identified 25 diatom genera in three different types of sedimentary facies (porous and moss-algae rich, dense-laminated, and tufa-free gravel). Most diatoms were raphid pennate (class Bacillariophyceae), while a few were centric (class Coscinodiscophyceae) or araphid pennate (class Fragilariophyceae). They appeared as integral components of the tufa structure along with cyanobacteria and other algae and mosses. Conclusions . Toge- ther with previous studies on the hydrochemistry and sedimentology of the MR, our interpretations suggest that HCO 3 - , pCO 2 , Ca 2+ , and TDIC negatively affect diatom richness and that their abundance is positively related to the presence of mosses and algae."

In this study we explored the use of less conventional diatom metrics (motility, nuclear abnormalities and ecological guilds) to measure changes in diatom assemblages related to the transfer of epipelic communities from urban impacted streams to less impacted sites. Three lowland streams in the Argentine Pampean plain were selected, and two sites were established per stream for a total of six sites. Three sites were referenced as low urban impact (LI), as they run through peri-urban areas, and three downstream sites were referenced as high impact sites (HI), since they run through a dense urban area. Six germination trays filled with stream sediment were placed at each HI site, and three at each LI site, and left to be colonized for 30 days before transferring three trays from the HI sites to their respective LI site upstream. Samples were collected at days 0, 15, 30 and 45 days from each tray, and diatom species were identified and classified into ecological guilds. Motility variables were measure per individual of the genera Nitzschia (path length, velocity and maximum velocity) through video recording. Also, the frequency of abnormal nuclear locations and nuclear membrane breakage were determined. Results showed that there were no significant differences in any motility metrics, while the nuclei variables exhibited higher proportion of abnormally positioned nuclei and nuclear membrane breakage at the HI sites. The proportion of nuclear membrane breakage decreased over time in the translocated assemblage, indicating that it could be a sensitive indicator of water quality improvement, while the ecological guilds showed significant differences on the proportion of high profile and motile diatoms. The improvement in water quality produced a significative increase in the proportion of the high profile guild in the translocated biofilm. Despite the motile forms being the dominant group, the water quality improvement allowed the high profile forms, to colonize the substrate. These results emphasize the possible use of the ecological guilds as a suitable indicator of water quality improvement in Pampean streams, especially in nutrient rich environment. These tools can provide a rapid assessment of diatom condition and could be considered supplementary to biomonitoring protocols in lowland streams. Fil: Nicolosi Gelis, María Mercedes. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Cochero, Joaquin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Donadelli, Jorge Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Gomez, Nora. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina

International audience; Meiofauna have a strong role in the functioning of coastal ecosystems but how their food sources affect their community structure remains unclear, likely due to the influence of abiotic parameters and the small size of these organisms. The meiofauna and their potential food sources were sampled in several intertidal habitats (i.e., mudflat, seagrass bed, sandflat) of the Marennes-Oléron Bay, France, and the Sylt-Rømø Bight, Germany, to assess the relationships between habitat characteristics and meiofauna community structure. Biomass and quality (carbon/chlorophyll a ratios) of food sources were estimated. Meiofauna community structure based on density and biomass was determined, as well as nematode diversity and feeding types. Meiofauna density and biomass varied highly within habitats and within ecosystems, ranging from 1.7 × 10⁵ to 3.4 × 10⁶ ind. m⁻² and from 0.057 to 1.541 gC m⁻², respectively. Benthic microalgae and sediment organic matter are important drivers in these food webs as the density of two important trophic groups of nematodes, non-selective deposit feeders and epigrowth feeders, varied in accordance with these food sources. No clear relationship was observed between bacterial biomass and selective deposit feeders (i.e., bacterivores) probably due to the high production rate of bacteria. Complementary information about production rates of food source as well as data from trophic markers would provide complimentary information to better understand flows of organic matter in intertidal habitats, particularly for opportunistic species such as non-selective deposit feeders.

Benthic diatoms are an indispensable link of the water ecological system in terms of energy flow and material cycling, and they directly or indirectly reflect the status of the water environment. We sampled benthic diatoms and environmental factors from April to May of 2013 from 53 sites along the Ying River to study their application in local water trophic status assessment, with a focus on the dominant benthic diatom species, their composition and distribution pattern, and the relationship between benthic diatoms and environmental factors. A total of 370 species and varieties were identified, belonging to 56 genera and six orders. The dominant species were as follows: Nitzschia inconspicua Grunow, Achnanthidium minutissimum (K&uuml, tzing) Czarnecki, Navicula aitchelbee L. L. Bahls, Nitzschia palea (K&uuml, tzing) Smith, Cyclotella meneghiniana K&uuml, tzing, Navicula submuralis Hustedt and Mayamaea atomus (K&uuml, tzing) Lange-Bertalot. The Ying River was divided into five orders using the Strahler method and three regions according to total nitrogen, total phosphorus and ammonia nitrogen. In region Y-1, which had the lowest nutrient level, the dominant species was Achnanthidium minutissimum. In region Y-2, which had the highest nutrient level, Navicula aitchelbee, Nitzschia palea, and Cyclotella meneghiniana were dominant, while in region Y-3, which had moderate nutrient levels, Nitzschia inconspicua was dominant. Pearson&rsquo, s correlation analysis and canonical correspondence analysis (CCA) revealed a significant correlation between the environmental factors with dominant species and diatom indices (especially the SPI). Our study indicates that dominant species and diatom indices can, to some extent, indicate the environment, especially nutrient distribution.

Understanding the drivers of community structure is an important topic in ecology. We examined whether different species trait groups of stream diatoms (ecological guilds and specialization groups) show divergent responses to spatial and environmental factors in a subarctic drainage basin. We used local- and catchment-scale environmental and spatial variables in redundancy analysis and variation partitioning to examine community structuring. Local and catchment conditions and spatial variables affected diatom community structure with different relative importance. Local-scale environmental variables explained most of the variation in the low-profile and motile guilds, whereas local and spatial variables explained the same amount of the variation in the high-profile guild. The variations in the planktic guild and the specialist species were best explained by spatial variables, and catchment variables explained most variation only in generalist species. Our study showed that diatom communities in subarctic streams are a result of both environmental filtering and spatial processes. Our findings also suggested that dividing whole community into different groups by species traits can increase understanding of metacommunity organization.

The first German intercalibration exercise for benthic diatoms was conducted to improve the application of the implementation of the European Water Framework Directive for running waters and lakes in Germany. The intercalibration exercise revealed several taxonomic problems. Among others, considerable problems occurred with identifying and differentiating species of the following four groups: (I) Amphora indistincta Levkov and A. pediculus (Kützing) Grunow, (II) Cocconeis placentula var. euglypta Ehrenberg and C. placentula var. lineata (Ehrenberg) Van Heurck, (III) Navicula cryptotenella Lange-Bertalot and N. cryptotenelloides Lange-Bertalot and (IV) N. reichardtiana Lange-Bertalot and N. caterva Hohn & Hellermann. The taxonomic problems that emerged occurred due to both insufficient use of given taxonomic details (by limnologists) and ambiguous species descriptions and documentation (by taxonomists). Thus, we recommend to the applied limnologist to use the mandatory identification literature and to document any ambiguous valves during routine counts. Also, it would be desirable to further investigate certain species by taxonomists and, in general, to provide more basic data with species descriptions or in identification manuals. These measures will improve the use of diatoms as bioindicators and consequently benefit both applied limnologists and taxonomists.

Biological activities in marine soft-sediments can modify the sedimentary environment through processes that change erosion rates. In low-energy environments, bioturbating macrofauna destabilizes sediments while microbes bind sediments and stabilize them. The degree to which these counter-acting processes influence sediment movement in a physically dynamic environment has not been well quantified. In a field experiment, we established 56 (1 m(2)) plots on an exposed intertidal sandflat. We used shade cloth and manipulated grazing pressure exerted by the deposit-feeding bivalve Macomona liliana (0-200 ind. m(-2)) to alter the microphytobenthic community. Three months post-manipulation, initiation of sediment transport (T-c) and change in sediment erosion rate with increasing bed shear stress (m(e)) were measured. Mean grain size, density of the spionid polychaete Aonides trifida, density of adult M. liliana, and bulk carbohydrate concentration could account for 54% of the variation in T-c (0.3-1.1 N m(-2) s(-1)). Mean grain size was the only significant predictor (p

Blanket peat catchments are important biodiversity refugia and are increasingly recognised for their role in regional carbon and water balances. A key pressure on these catchments is forest clearfelling which increases stream phosphorus potentially leading to eutrophication. However, these unique systems are underrepresented in the development of bioassessment monitoring programmes and so are at risk to impacts. In this study, a multiple before-after-control-impact (MBACI) study was designed in three neighbouring peatland catchments and provided a unique opportunity to assess the impact of forest clearfelling events on macroinvertebrate and phytobenthic assemblages. Statistical analysis revealed substantial differences in the macroinvertebrate assemblages after clearfelling with higher abundances of chironomids. Macroinvertebrate derived indices EPT, diversity and species richness were significantly reduced. This was accompanied by a shift in functional feeding group representation away from shredders and collector–filterers to a dominance of collector–gatherers after clearfelling. In contrast, forest clearfelling did not significantly impact the diatom assemblages and diatom derived indices remained static for the duration of the study period.

Biomonitoring is central to the European Union's Water Framework Directive (WFD) and to the French water and aquatic environmental law, but most diatom indices do not separate different anthropogenic impacts. To address this gap, the effect of water chemistry on diatom ecological guilds and life forms was assessed in order to indicate stream perturbations. Generalised additive models (GAMs) were built on a large-scale data set of 1571 samples from the French monitoring network. The relationships between diatom ecological guild and life form metrics were investigated by Principal components analysis and the results predicted by GAMs. The models characterised eight chemical parameters that modified adaptive strategies (ecological guilds) and growth morphology (life forms). Total phosphorus, conductivity, nitrate and pH are the main influencing factors, followed by temperature, dissolved oxygen and organic matter. The findings confirm three groups of diatoms with different adaptive strategies: 1 - fast moving species, 2 - species growing close to the substrate and 3 - species extending to the surface layers of the biofilm. Thirteen diatom metrics displayed a variety of responses to different ranges of the eight chemical parameters. These metrics could be used to help to identify and quantify which chemical alterations are caused by polluted effluents in rivers.

Benthic diatoms are widely used in Europe and worldwide to access ecological status of running waters. One of key goals of Water Framework Directive is to classify rivers and streams using biological quality elements and type specific reference conditions. According to system B which incorporates additional abiotic descriptors, there are 24 water types in Croatia. For biological analyses 92 rivers and streams with 140 sampling points were chosen and sampled for benthic diatoms and water chemistry simultaneously. Self organizing map (SOM) analysis was used to define biotypes from species composition and abundance of benthic diatoms. Grouping of samples in SOM resulted in 10 distinctive groups. Based on their geographical position and site characteristics, groups represent sites with similar properties (as waterbed, catchment size, altitude, size of stream) belonging to different ecoregions in Croatia. Analysis of variance revealed statistically significant differences (p

The aim of this study was to propose an index [Index of Biotic Integrity for the Rio de la Plata (IBIRP)] formulated from a minimum of information-rich metrics related to biological integrity for evaluation of the coastal freshwater tidal zone of the Rio de la Plata estuary. A total of 23 sites were selected along 170 km of shoreline (34°27′10″ S, 58°30′21″ W and 35°23′28″ S, 57°08′50″ W), being influenced by different land uses. We explored 36 biotic descriptors (designated candidate metrics), each of which is considered as an environmental indicator, and selected four metrics: two related to phytoplankton assemblage (planktonic cyanobacterial density and phytoplanktonic total density) and two linked to benthic assemblages, the diatoms (percent most tolerant taxa), and the invertebrates (percent Tanaidacea). The metrics that were chosen to integrate the IBIRP provide valuable information about the biotic integrity both in terms of time and space. The multimetric index can assume values between 0 (very bad status) and 10 (very good status). The IBIRP correlated significantly with the second (p < 0.001) and fourth (p < 0.01) factors of the factor analysis—those being related to variables indicative of eutrophication and organic pollution. This index constitutes an approach that is capable of reflecting the anthropogenic impacts produced along the coast of the Rio de la Plata, with the inherent flexibility of being subject to modification and ultimate validation for estuaries of similar characteristics.

Long-term interannual variations in the mean microphytobenthos chlorophyll a (chl a) of the Ems estuary were investigated. Concentrations in the 1990s were on average 1.5 times higher than during the period from 1976 to 1978, but a trend in chl a over the entire period (1976 to 1999) was not found. In agreement with findings from the late 1970s, the mean chl a concentrations over the post 1990 period correlated significantly with the station elevation related exposure time. Over the entire 1976 to 1999 study period, the estuary mean annual chl a concen- trations correlated strongly and significantly with the mean annual air temperature. Although the range of the variation in the mean annual air temperature of the studied years was only 7.5 to 10.2°C, it surprisingly corresponded with a ca. 2.5-fold variation in the mean annual microphyto- benthos chl a. In addition to chl a, mean monthly C:chl a ratios from 1976 to 1977 also correlated positively with changes in temperature. Microphytobenthos carbon biomass (chl a × (C:chl a)) may, therefore, respond even stronger to air temperature than chl a does. The correlations are most likely a combination of direct temperature effects on microphytobenthos and stronger, prob- ably complex, indirect temperature effects on the seasonal development and standing stock of young and adult grazers (bivalves) and their carnivores like the brown shrimp Crangon crangon.

It has been proved that littoral diatoms provide a useful marker for detecting localised changes resulting from uneven anthropogenic disturbances or intermittent releases of sewage along the shorelines of lakes. This study tested the spatial resolution at which this general observation occurs, by selecting areas with different anthropogenic pressures (urbanization) along a latitudinal gradient in Lake Garda, a deep and wide peri-Alpine lake. The sampling design aimed to detect differences in diatom distribution in terms of species diversity, quality indices, proportion of Red List taxa, assemblages, and individual species. Because the extent to which diatom assemblages respond to these gradients was unknown, we used assemblage metrics of different sensitivities. Results showed that the most important environmental factor was the latitudinal gradient, which was revealed by almost all the assemblage metrics. This dominant trend was explained by two co-occurring environmental gradients: concentration of nutrients and thermal gradient. The importance of different levels of urbanization was unevenly partitioned among locations and latitudes because of the different intensities of urbanization pressure. Only the species Brachysira neglectissima, the quality index (Trophic Index), and to a lesser extent, the metric at assemblage level revealed significant effects. Overall, this study comes to two main conclusions: (1) different metrics are needed to detect the multifaceted effects of anthropogenic disturbances, which by their very nature are unevenly distributed and of different intensities, and therefore affect assemblages to different degrees; (2) for any monitoring program in this lake to be effective, the various gradients revealed in this work should be taken into account. Failing to include these sources of variability might lessen the benefits of monitoring.

Freshwater diatoms are considered to be reliable indicators of the trophic status of rivers and lakes. In the past 30 years, a number of indicator indices have been developed and used for the assessment of trophic conditions all over Europe. It is however still not clear whether the ecologic signature of diatoms differs between these indicator indices. The present study assessed a large number of published European indices on the response of freshwater diatoms to trophic conditions by evaluating the consistency in the use of taxa and their trophic score from seven European indicator indices. The STAR (Standardisations of River Classifications) diatom database, a large set of samples from European running waters, was used to test the application of trophic classifications in water quality assessment. The analysis of taxa in common within the trophic indices showed that there are considerable differences between the indices, for example in the score of trophic values. There was more agreement in classification of taxa within the oligotrophic and the hypertrophic preferences than within the mesotrophic range. Based on these results, a list of diatom taxa, that are consistently used in different trophic indices, was composed. It included 159 reliable taxa that are not sensitive to regional setting, water type and taxonomic uncertainty. The list was further accompanied by a description of the taxa's trophic preferences. The large deviation in trophic scores for a number of diatom taxa could most probably be explained by taxonomic uncertainties. Application of these taxa for trophic assessment was questionable. The test set of the 359 STAR samples showed that differences between the trophic indices also lead to a significant variation in the water quality assessment results. Although trophic indices provide an excellent biomonitoring tool, they should be applied with caution, considering the recommendations provided in this paper.

Diatoms are highly abundant unicellular algae that often dominate pelagic as well as benthic primary production in the oceans and inland waters. Being strictly dependent on silica to build their biomineralized cell walls, marine diatoms precipitate 240 × 1012 mol Si per year, which makes them the major sink in the global Si cycle. Dissolved silicic acid (dSi) availability frequently limits diatom productivity and influences species composition of communities. We show that benthic diatoms selectively perceive and behaviourally react to gradients of dSi. Cell speed increases under dSi-limited conditions in a chemokinetic response and, if gradients of this resource are present, increased directionality of cell movement promotes chemotaxis. The ability to exploit local and short-lived dSi hotspots using a specific search behaviour likely contributes to micro-scale patch dynamics in biofilm communities. On a global scale this behaviour might affect sediment–water dSi fluxes and biogeochemical cycling., Diatoms often dominate production in aquatic communities, but the amount of available dissolved silicic acid (dSi) limits their growth. Here, Bondoc et al., show that diatoms perceive gradients in dSi, and can increase the encounter with this resource by chemotaxis toward high concentrations under resource-limited conditions.

International audience; Species sensitivity distributions (SSDs) are an important predictive tool in risk assessment. Usually, literature data are used to build SSDs that are mostly based on planktonic species. But, to get adequate protective thresholds for environmental communities, one could argue that SSD should be built on ecotoxicological data obtained from species found in the ecosystem that should be protected. This is particularly true when benthic algae are of concern. Due to the lack of literature data, building SSD on benthic microalgae is difficult. This paper aims in comparing SSDs, and thus protective thresholds (hazardous concentration that affects 5 % of the species of a community, HC5), built on ecotoxicological data obtained (1) from literature and (2) with specific bioassays on benthic diatoms from a lake. Thresholds were derived for protection against four herbicides separately and for a mixture of them. Sensitivity data obtained from literature were statistically lower than the specific data for all herbicides: Species tested in the literature were usually more sensitive (mainly chlorophytes), leading to more protective lower HC5. The HC5 thresholds (literature or specific) derived for protection against the mixture were also compared to the observed sensitivity of an assemblage of benthic diatom species exposed to an increasing range of herbicide mixture concentrations. We observed that one species within the assemblage (Fragilaria rumpens) was affected at a concentration below both the literature and the specific HC5 thresholds.

Aquatic ecosystem biomonitoring tools are largely lacking for many developing countries, resulting in adoption of tools developed from other countries/regions. In many instances, however, the applicability of adopted tools to the new system has not been explicitly evaluated. The objective of this study was to test the applicability of foreign diatom-based water quality assessment indices to urban streams in Zimbabwe, with the view of stimulating research to develop improved approaches for assessing ecological integrity of lotic systems in the country. The study evaluated the relationship between measured water quality variables and diatom index scores. The study found a high degree of concordance between water quality variables and diatom index scores. Thus, the indices proved useful in providing an indication of the quality of the investigated waters. This could be attributed to the occurrence of many widely distributed diatom species that have similar environmental tolerances to those recorded elsewhere. Diatom indices which exhibited consistent classifications and strong correlations with water quality variables such as Trophic Index, Saprobic Index, Pampean Diatom Index, Biological Index of Water Quality and Leclercq Index are recommended for use in the country. However, ecological requirements of some diatom species from Zimbabwe need to be clarified and incorporated in a diatom-based water quality assessment protocol unique to the country. Keywords : biological monitoring, pollution, benthic diatoms, biotic indices

Stable carbon and nitrogen isotopic composition (delta C-13 and delta N-15) of benthic organisms was investigated to understand the effects of a gregarious tubicolous amphipod species (Haploops nirae) on benthic food web structures and test whether drastic changes in species composition cause changes in food web structure. The habitat engineered by this species was sampled and compared with the adjacent uncolonized Amphiura filiformis muddy habitat in winter and summer. The isotopic signatures of macrofaunal and megafaunal species associated with both habitats were analysed along with potential food sources at each sampling period. Similar food web structures for each habitat (and each season), with high delta N-15 ranges spanning over 3 trophic levels, were reported although omnivory was less frequent in the H. nirae habitat. The amphipod H. nirae appears to play a baseline role, with the lowest delta N-15 values and delta C-13 values indicating that it primarily feeds on phytoplankton. Bayesian mixing models were used to estimate the contributions of potential food sources to the diet of the species accounting for most of the biomass in each habitat and showed that the epibionts covering tube mats are a key contribution to the food webs of both habitats. Identified as benthic diatoms, they may minimize interspecific food competition between dominant suspension feeders such as Polititapes virgineus or H. nirae within a habitat. This finding highlights the contribution of microphytobenthic producers to subtidal (similar to 30 m deep) muddy habitat food webs, suggesting that the mucopolysaccharides composing the H. nirae tubes support the growth of a heterotrophic diatom population. As an engineer species, H. nirae acts as a facilitator for diatoms which ultimately sustain the secondary production of the H. nirae habitat as well as the immediate surrounding habitats.

International audience; Tools that may be used to characterize the state of aquatic ecosystems and the impacts associated to pesticides are currently requested for the monitoring of ecosystems. Chemical analysis alone is not sufficient for such purposes and biomonitoring is essential. Many bioindicators based on diatoms are commonly used to assess the quality of aquatic environments but have not been developed to specifically address the impacts of pesticides. It is therefore crucial to develop dedicated tools. Our research aimed at performing a field study (analysis of monitoring network data) in order to evaluate the responses of different metrics towards pesticide pressure. For diatom communities, toxic pressure associated to pesticides, especially herbicides, had a weak effect on species composition and on the various tested metrics. Nutrient and organic matter concentrations (and also typology) are the main influencing factors. When trophic and saprobic levels are controlled, it is possible to identify the effects of herbicides on some metrics. The only responding metric is the abundance of the "high profile" guild, which corresponds to taxa presenting an important contact surface with water flow. Its abundance decreases when herbicide toxic pressure increases. It could therefore be used to assess the impact of herbicides on diatom communities, but in a framework where confounding factors variability (e.g., nutrients, organic matter, river order) is reduced.

Key-words: Bacillariophyta, biomonitoring, check-list, metric, river Diatoms are a very diverse group of microalgae that encompass about 100000 taxa. This makes an excellent bioindicator especially of rivers. The majority of biotic indices based on diatoms are constructed on species pollution-sensitivities. Nevertheless, recent studies showed the interest to use complementary metrics for biomonitoring: life-forms, cell-sizes and ecological guilds. Unfortunately, taxa memberships to such metrics are scattered in numerous floras and papers. Therefore, studies using such metrics often referred to grey literature or home-made checklists. The objective of this paper is to make available to the scientific community an important check-list of taxa frequently observed in European rivers with their memberships to these metrics. After defining these metrics, 1115 taxa were codified using Biofresh and Omnidia codes in an Excel file. Metrics memberships were then explored in a taxonomical framework. It clearly appears that metrics memberships are determined by taxonomy. Lifeforms and cell sizes taxa memberships and their study in the framework of evolutionary history of diatoms is a field that is worth studying for a better understanding of diatoms ecology. Such inputs should be beneficial for the future improvement of diatom-based monitoring tools.

International audience; Intertidal flats of the estuarine macro-intertidal Baie des Veys (France) were investigated to identify spatial features of sediment and microphytobenthos (MPB) in April 2003. Gradients occurred within the domain, and patches were identified close to vegetated areas or within the oyster-farming areas where calm physical conditions and biodeposition altered the sediment and MPB landscapes. Spatial patterns of chl a content were explained primarily by the influence of sediment features, while bed elevation and compaction brought only minor insights into MPB distribution regulation. The smaller size of MPB patches compared to silt patches revealed the interplay between physical structure defining the sediment landscape, the biotic patches that they contain, and that median grain-size is the most important parameter in explaining the spatial pattern of MPB. Small-scale temporal dynamics of sediment chl a content and grain-size distribution were surveyed in parallel during 2 periods of 14 d to detect tidal and seasonal variations. Our results showed a weak relationship between mud fraction and MPB biomass in March, and this relationship fully disappeared in July. Tidal exposure was the most important parameter in explaining the summer temporal dynamics of MPB. This study reveals the general importance of bed elevation and tidal exposure in muddy habitats and that silt content was a prime governing physical factor in winter. Biostabilisation processes seemed to behave only as secondary factors that could only amplify the initial silt accumulation in summer rather than primary factors explaining spatial or long-term trends of sediment changes.

In order to characterize and analyze the distribution of species of the genus Navicula sensu stricto in the Lerma River and its tributaries, biannual samplings (wet and dry seasons) for the period 2003 to 2005 were made at eleven locations in the Upper Lerma basin, central-western Mexico. Twenty-one species of Navicula Bory, were identified, of which fourteen represent new records for Mexico and five were new to the study area. Most of the species of Navicula s. str. observed in the study area are tolerant to high contents of organic matter, which is incorporated into the aquatic ecosystems as a product of agricultural and industrial activities and from deficiently treated municipal discharges of cities and towns present in the study area at the sites most affected by these activities. Cosmopolitan species with broad tolerances to organic pollution and eutrophic conditions, such as Navicula antonii, N. germainii, N. perminuta, N. rostellata and N. erifuga were present throughout the year. N. tripunctata and N. veneta, widely reported as tolerant to pollution from industrial activities in other regions of the world, were present at the sites most affected by these activities. Fil: Segura García, Virginia. Universidad Michoacana de San Nicolás de Hidalgo; México Fil: Israde Alcántara, Isabel. Universidad Michoacana de San Nicolás de Hidalgo; México Fil: Maidana, Nora Irene. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina