Diatom Taxonomy and Ecology

The sediments of shallow basins formed on along the coast of the Baltic Ice Lake in the Late Glacial are a valuable source of information for reconstructing the paleoenvironment. A detailed diatom analysis, along with chronological and lithological studies, was performed for the sediments of one of these paleoreservoirs, uncovered in the Kulikovo
section (Sambian Peninsula, Kaliningrad Region of the Russian Federation) and dated to 14,000–12,500 calBP. As a result of this study, the essential diversity of Late Glacial diatoms was revealed and 204 species were found. Among them, benthic and epiphytic species belonging to the group of oligohalobous indifferents predominate. The most typical species
are Pseudostaurosira brevistriata, Staurosirella ovata, Gyrosigma attenuatum, G. acuminatum, Amphora affinis, Epithemia adnata and Cymbopleura inaequalis. A comparison with available regional data showed that the mass development of pioneer epiphytic diatoms of the Fragilariaceae in the Allerød is common to most of the paleoaquatic ecosystems. A local feature of the Kulikovo paleoreservoir, along with a wide range of ecological diatom groups, is the episode of massive development of Gyrosigma spp., benthic diatoms capable of living
in streaming water, in the first half of the Allerød. The Kulikovo diatom assemblages reacted sensitively, not only to the main environmental shifts of the Allerød and Younger Dryas, but also to smaller-scale climatic events, such as Herzensee Oscillation (GI-1b) and changes in hydrological regimes (water level fluctuations, flow rate) caused by local
environmental transformations.

Temporary ponds are peculiar and vulnerable habitats widespread in different biogeographical regions, which ecological and social importance was historically neglected. Among all the life forms supported by ponds, diatoms represent a key tool for assessing the conservation status of temporary waters. In this perspective, this study investigates patterns of diatom α and β diversity across an elevation gradient in low-elevation (LP) and high-elevation (HP) temporary ponds, assessing the influence of environmental, local, and seasonal factors. Samplings were performed throughout the entire year in six temporary ponds located along an altitudinal gradient. Species richness did not differ significantly between LP and HP sites, but Shannon diversity was lower in LP, indicating fewer even communities. Species richness, as predicted by our models, was influenced by pH and electrical conductivity (EC), while elevation was the main driver of both Shannon and Simpson diversity. EC consistently had the strongest influence on α diversity indices. Community similarity declined with increasing elevation, halving every ~1059 m, demonstrating rapid species turnover along elevational gradients. Both elevation and environmental factors independently shaped community structure, whereas seasonal effects contributed little to community variation. Ecologically, these results suggest that diatom communities in temporary ponds are strongly structured by elevational and physicochemical gradients, making them sensitive to environmental changes such as climate shifts or pollution. Conservation efforts should prioritize protecting a range of habitats across elevations to preserve regional biodiversity, as loss of specific habitats could lead to significant declines in diversity.

Çanakkale is located in Western Anatolia, a region known for extensive mining in the country. In this study, three new species: Nitzschia arslaniana sp. nov., Nitzschia efeiana sp. nov., and Nitzschia szaboiana sp. nov. are described from highly acidic environments in Çanakkale. In morphology, Nitzschia arslaniana is similar to Nitzschia inconspicua but Nitzschia inconspicua is broader, with a lower fibulae density. Nitzschia efeiana is similar to Nitzschia. bremensis, Nitzschia capitellata, Nitzschia homburgiensis, Nitzschia hybrida, Nitzschia palustris, and Nitzschia pellucida. However, Nitzschia efeiana has variable fibulae widths, thickened virgae on its external valve face, and an elevated ridge on the valve margin opposite the keel. Nitzschia szaboiana is similar to Nitzschia pusilla, but the later taxon has a higher striae density. This study highlights the unique species diversity of extreme environments, including anthropogenic extreme environments, by describing three new ...

Fragilaria gracilis is one of the most reported Fragilaria species in Europe, observed in a broad range of water bodies, ranging from (ultra)oligotrophic rivers to even eutrophic lakes. A revision of this important taxon based on the analysis of the morphology of a large number of historic and recent populations was highly needed. In the present study, type material of Fragilaria gracilis and several related taxa such as Synedra radians, Fragilaria pseudolaevissima, S. utermoehlii, F. aquaplus, F. boreomongolica and F. tridentina together with more than 10 modern populations were investigated using LM and SEM observations. The results based on these comparisons show that Fragilaria (Synedra) radians is the name for the taxon formerly known as F. gracilis. Moreover, detailed analysis demonstrated that F. pseudolaevissima and Synedra utermoehlii are conspecific with F. radians and should be considered as heterotypic synonyms. The observations made in this study also resulted in the description of several new species, often with distinct ecologies and distribution areas:

Background and aims – An increased interest in the diatom flora from subaerial habitats in the Republic of North Macedonia has revealed the presence of a large number of interesting and often unknown, species. During a recent biodiversity survey, seven Muelleria species were recorded, several of which could not be identified based on the available literature. Methods – Using both Light Microscopy and Scanning Electron Microscopy techniques, the morphology of several Muelleria species has been analysed. The morphology of all taxa is described, illustrated and compared with other possible similar Muelleria taxa, known worldwide. Key results – Four already documented Muelleria species, M. gibbula, M. islandica, M. terrestris and M. undulata (= Navicula gibbula f. undulata) were identified, while two distinct species are described as new. These new species belong to the M. gibbula complex, and can be differentiated by valve size, stria density, shape of the proximal raphe ends and the s...

Two new freshwater species of Achnanthidium Kützing are described from Eastern Ghats Mountain range of Peninsular India based on light and scanning electron microscopy observations. Achnanthidium initium sp. nov. belongs to the group of Achnanthidium taxa that have terminal raphe fissures curved to opposite sides of the valve. This taxon is characterized by distinctive fascia, raphe endings extending to the valve margin, lineate distal raphe endings and 2-5 linear areola per striae. Achnanthidium linannulum sp. nov. belongs to the group of Achnanthidium taxa with terminal raphe fissures curved to the same side of the valve. This species is characterized by the presence of occluded areolae near the margin, striae orientation and the weakly bent internal distal ends of the raphe. These new species are known only from their type locality, oligotrophic Masilla Waterfalls from Kolli Hills, Eastern Ghats.

Contaminant-related stress on aquatic biota is difficult to assess when lethal impacts are not observed. Diatoms, by displaying deformities (teratologies) in their valves, have the potential to reflect sub-lethal responses to environmental stressors such as metals and organic compounds. For this reason, there is great interest in using diatom morphological aberrations in biomonitoring. However, the detection and mostly the quantification of teratologies is still a challenge; not all studies have succeeded in showing a relationship between the proportion of abnormal valves and contamination level along a gradient of exposure. This limitation in part reflects the loss of ecological information from diatom teratologies during analyses when all deformities are considered. The type of deformity, the severity of aberration, species proneness to deformity formation, and propagation of deformities throughout the population are key components and constraints in quantifying teratologies. Before a metric based on diatom deformities can be used as an indicator of contamination, it is important to better understand the "ecological signal" provided by this biomarker. Using the overall abundance of teratologies has proved to be an excellent tool for identifying contaminated and non-contaminated environments (presence/absence), but refining this biomonitoring approach may bring additional insights allowing for a better assessment of contamination level along a gradient. The dilemma: are all teratologies significant, equal and/or meaningful in assessing changing levels of contamination? This viewpoint article examines numerous interrogations relative to the use of diatom teratologies in water quality monitoring, provides selected examples of differential responses to contamination, and proposes solutions that may refine our understanding and quantification of the stress. Hopefully, this paper highlights the logistical problems associated with accurately evaluating and interpreting teratologies and stimulates more discussion and research on the subject to enhance the sensitivity of this metric in bioassessments.

Intermittent rivers (IR) are among the most widespread watercourses globally, characterized by alternating dry and wet phases. Despite these fluctuations, IRs support diverse ecosystems and considerable biodiversity. Among their biotic communities found in these rivers, diatoms serve as key primary producers and bioindicators. Due to the limited knowledge of how droughts affect IR biodiversity, this study investigates diatom responses to seasonal hydrological changes and water flow. Specifically, it focuses on taxonomic and functional composition and community structure of diatoms in a naturally occurring Mediterranean IR. Overall, species richness appeared to be unaffected by droughts and water flow, with similar values observed at both lentic and lotic sites. Taxonomic and functional α-diversity were generally higher in lotic waters (TRic = 12.9; Fric = 9.79) compared to lentic (TRic = 8.7; Fric = 3.23) sites across all diversity indices, though no significant differences were found in α-diversity between sites. While the environmental variables considered did not significantly affect variability between sampling sites, permutational analysis identified temperature (F = 1.49, p = 0.09) and dissolved oxygen (F = 2.11, p = 0.01) as important predictors for taxonomic and functional α-diversity. However, seasonality significantly influenced taxonomic (F = 2.28, p = 0.009) and functional (F = 8.86, p < 0.01) β-diversity, with greater variability (1.33 times) observed in August. Findings also indicate significant differences in taxonomic dispersion between site types (F = 2.21, p = 0.04) but no significant differences in functional dispersion. These results suggest that whereas IR conditions may not definitely influence diatom α-diversity, seasonal changes play a key role for community turnover, highlighting the importance of the hydroperiod for shaping IR biodiversity. In the context of ongoing climate change, these findings are particularly relevant, as shifts in hydrological regimes may increasingly affect ecological dynamics and community structure in IR systems.

Coastal ponds are peculiar and threatened habitats, considered biodiversity hotspots. In many ecosystems ponds can be a valuable resource for the conservation of freshwater biodiversity. The Castelporziano Presidential Estate is a Mediterranean protected area hosting numerous ponds which are suffering severe droughts and a general decline in number and hydroperiod length. Hydroperiod changes can be particularly relevant for biodiversity inhabiting ponds, in particular diatom communities. Here, for the first time, we evaluate the conservation status of Mediterranean ponds inside the Castelporziano Reserve. The aims of this research are to i) investigate the influence of environmental variables on diatom communities of ponds; (ii) analyse diatom community structure in function of species richness and competitive interactions; (iii) highlight the potential and effectiveness of diatom ecological guilds in supporting the interpretation of the ecological status of threatened small waterbodies. Overall, 122 diatom taxa in the 29 ponds were described. Nitzschia (18 species) was the most species-rich genus, followed by Gomphonema (14) and Navicula (13). 17 species were included in the Red List of endangered species. Intra-pond distance and anthropogenic impacts didn't influence diatom assemblages. On the contrary, diatom communities were influenced by altitude and the distance from the sea. Furthermore, temporary ponds showed the lowest values for Shannon, evenness and Simpson indexes Considering Beta-diversity, both Bray-Curtis and Jaccard dissimilarity matrices highlighted a large dissimilarity between sampling sites. Inter-variability between sites and intra-variability within the sites resulted both very low. Our results highlight that diatom species are not influenced by hydroperiod length. Moreover, a structured diatom community emerged, where segregation processes predominating over aggregation ones. Finally, the average water quality of the ponds, calculated using the EPI-D index, was described as "good". This study represents the most complete checklist of diatom communities inside coastal ponds of Castelporziano, providing valuable insights into the effects of natural and anthropogenic influences on ponds conservation and management activities. However, spatial-temporal changes and anthropogenic impacts should be deeply investigated.

Ephemeral waters (EW) are sensitive and vulnerable ecosystems that, although the numerous ecosystem services provided, are poorly investigated and properly managed. Diatoms represent an important biological model largely used in aquatic permanent habitats but underused in ephemeral waters. The aim of this review is to address the knowledge gap, examining the current state of knowledge regarding the health of EW, with a focus on diatoms as bioindicators, specially (i) presenting research trends on EW ecosystem types investigated (ii) analysing the methodological approach, (iii) providing the influence of abiotic factors on the diatom assemblages in EW. A bibliographic search yielded a total of 512 papers. After removing duplicate records, 118 were eliminated. The screening of abstracts resulted in the selection of 48 articles on diatoms and EW since 1982. To avoid discrepancy between terminology we decided to classify the EW found in 3 different categories: Intermittent Running Waters (IRW: rivers, streams, creek, springs), Temporary Large Wetlands (TLW: wetlands, lakes, lagoons) and Temporary Small Waters (TSW: ponds, pools, ventaroles, ditches, thermal waters, troughs, pans). Studies are reported in all continents including Antarctic. IRW are the most investigated ecosystem (n = 683), followed by TSW (2 3 9) and TLW (96). Furthermore, studies were mainly conducted on sites located below 1000 m a.s.l. of altitude (n = 27). Studies mainly focus on epilithic diatoms (52 %). Electrical conductivity (80 %), pH (77 %) and water temperature (75 %) are the principal physical-chemical parameters considered. Moreover, electrical conductivity, pH, temperature, nitrate and nitrite resulted the best diatom community drivers. Future research is encouraged (1) to achieve a standardised protocol for monitoring EW using diatoms, (2) to focus on conservation projects for high-altitude temporary waters, and (3) to investigate the main driving forces influencing diatom diversity on EW.

Background and aims – The samples on which this study is based were collected in two streams in Puerto Rico as part of a long-term monitoring program conducted by the National Ecological Observatory Network (NEON). Detailed study of the diatom assemblages revealed the occurrence of a new diatom species belonging to the genus Adlafia. Methods – The study considered 82 samples of epilithic diatoms from two streams in Puerto Rico (Rio Cupeyes and Rio Guilarte) subjected to different degrees of anthropogenic impacts. The new species description is based on high-quality Nomarski (DIC) LM micrographs which document the full spectrum of shape variability along the size diminution series (including girdle views), and SEM images documenting valve ultrastructure (including detailed internal views). In addition we provide information about ecological preferences with respect to trophic state / nutrients, habitat within the stream channel / microhabitat (riffle, run, pool), and season of maximu...

A study was conducted in the river Belan (156 km), a north central Indian river of Vindhyan ranges to determine diatom diversity from headwater to mouth. Samples were collected 5 different stations by scraping 3x3 cm . area of substratum (stones) during winter season 2 December 2021 to March 2023. The count data were computed diversity indices (Margalef D', Shannon diversity H') and evenness (E). Total of 119 diatom taxa belonging to 28 genera were identified. H and D indices ranged from 2.77 to 2.62 and 26.709 to 18.4979, respectively. Evenness value was 0.81 to 0.77. The gradual decline in diversity and evenness was recorded from S1 to S5 except at S3. The anthropogenic activities impact (agriculture) at S3 was responsible for extreme low of diversity and evenness.

A catalog of Bacillariophyceae for the rivers of NW of Spain is made for the first time. It includes a re-examination of the taxa reported in previous publications, taxa cited during the last years of the rivers of the Galicia-Costa Hydrographic Demarcation, and a revision of the taxonomy, in line with the systematic and nomenclature changes, which have occurred mainly in recent years. The epilethic diatoms of the river basins of Galicia-Costa were sampled during the years 2005, 2006, and 2007, in May-June and September. The study was carried out in 41 localities distributed along 31 rivers, samples were taken in upstream and downstream sections. Diatom communities were compared in all upstream sections of these rivers draining from siliceous substrates. We identified 141 taxa of diatoms from the coast of Galicia. In this paper we present 15 new citations for Galicia, two for Spain and three for the Iberian Peninsula, in addition to a new species recently described. The dominant tax...

We used light and electron microscopy to characterize a Late Miocene freshwater diatomite deposit in the Chalk Hills Formation, near Payette, Idaho, USA. The diatom assemblage from this sample was nearly monotypic, dominated by a single taxon with similarities to Lindavia bodanica (Thalassiosirales) but with several features uncharacteristic of the genus Lindavia, such as a rimoportula(e) on the valve mantle located on a costa, simple alveolar structure, and spines at the external valve face-mantle junction. A combination of other characters for this species complicate its placement into existing genera, including a lack of central fultoportulae, central area with loculate areolae with domed cribra, and a single ring of mantle fultoportulae with three satellite pores with well-developed cowlings and broad satellite pore covers. Based on this unique set of features, we have established a new genus, Fascinorbis, which appears to represent an important transitional form in the evolution of the Lindavia lineage.

Three new species of Navicula sensu stricto are described from samples deposited in the Montana Diatom Collection. Navicula galloae and N. sovereignii live in streams in the Cascade Mountains of Oregon. N. flatheadensis lives in lakes in the headwaters of the Flathead River Basin in western Montana. At present, 80 species and varieties of endemic diatoms in 20 genera define the Northwest as a distinct biogeographical region, and many endemic species remain to be described. Other diatom taxa in the region indicate floristic affinities with northeast Asian, Arctic, and European alpine floras. Factors contributing to the large number of endemic taxa and to observed floristic affinities are discussed.

Lake Hovsgol (5 I oN, 10 IOE) is Mongolia's largest lake, over 1.6 million years old, and the southernmost extant lake in the 25 million years old Baikal Rift Zone. In spite of their proximity and geological relationship, Lake Baikal and Lake Hovsgol share no common offshore planktonic diatoms, though their planktonic communities are both characterized by species-poor richness and probable endemism. Lake Hovsgol's phytoplankton has been studied sparsely for nearly 100 years; however, a modern taxonomic and systematic treatment has not been undertaken. Vertical net-tow plankton samples collected in summer 1998 fr om throughout the lake showed that the phytoplankton is dominated by chlorococcalean green algae, nan oplanktonic cyanobacteria, and six predominant diatom species: a large-celled race of AsterioneLla fo rmosa, the epizooic Synedra cyclopum, two new Stephanodiscus species, Cy clotella sibirica, and a complex of fo rms identified as C. ocellata. Some taxa may be endemic to Lake Hovsgol or restricted in distribution to lakes in and near the Baikal Rift Zone. Stephanodiscus mongolicus Edlund, Soninkhishig & R.M. Williams sp. nov. is characterized by a spine and marginal fu ltoportula at each interfascicle, one rimoportula, and no central fu ltoportulae. Stephanodiscus jamsranii Edlund, Sonin khishig & R.M. Williams sp. nov. has a spine on each interfascicle, one rimoportula, and heterovalvy expressed in valve form and placement of central fu ltoportulae. Cyclotella ocellata contains a complex of forms. Evidence of near species level separation is a polymodal distribution of postsexual initial cell sizes, a larger size range of initial and vegetative cells than is known for C. ocellata, notably at the taxon's upper size spectrum, and persistence of these size distributions. The complex may represent a species flock that has developed reproductive separation but has not yet clearly separated along morphological lines. Alternatively, there may be a life history mechanism that allows stepwise auxosporulation or multiple vegetative cell sizes to enter sexuality and produce size-restored cell lines containing a wider range of cell sizes than previously reported for C. ocellata.

Se estudiaron las diatomeas epilíticas y las condiciones fisicoquímicas del agua en el río Tapartó Andes, Colombia. El perifiton se colectó en cuatro campañas de muestreo, en tres estaciones del río: parta alta, media y baja. El material fue tratado con peróxido caliente y se prepararon muestras en Naphrax para observación al microscopio óptico y al microscopio electrónico. Se identificaron 49 especies de diatomeas, se reportan por primera vez para Colombia las especies Amphipleura chiapasensis, Cymbella cf. ehrenbergii, Encyonema minutiforme, Encyonema silesiacum, Pseudostaurosira aff. americana, Pseudostaurosira medliniae, Surirella bryophila, además se registran las condiciones fisicoquímicas en las que se encuentran las diatomeas. Esta información es importante para incorporarla dentro de métodos de monitoreo biológico que emplean las diatomeas y sus valores de bioindicación. Con este trabajo se aumenta el conocimiento en la distribución de las diatomeas en el país y de las condiciones fisicoquímicas a las que se pueden asociar.

Anthropogenic activities more and more degrade wetlands. The management of these wetlands involves analyzing the ecological quality of the water. Diatoms constitute a biological marker widely used in the assessment of waters. The objective of the study was to determine the water quality of the Nkwen rivers by diatom index with a view to their sustainable management. The study took place in 3 rivers from July 2023 to June 2024. Periphytic diatoms were sampled in these rivers by scraping and taken to the laboratory for analysis. It emerged that river 1 was of average quality with an index of 5.11. River 2 was of poor ecological quality with an index of 5.62. River 3 was of very good ecological quality with an index of 2.17. Measures should be taken by public authorities and the council to restore the degraded river 2 and monitor these watercourses using ecological methods by Diatoms to maintain the balance of these hydro-systems.

In this work, the assessment of the ecological status of the Oum Er-rabie River basin was carried out by determining the physical-chemical, bacteriological and biological parameters. sampling Benthic macroinvertebrates and water were collected only once during the fourth seasons at the 31 stations upstream to downstream of the streams from spring 2018 to winter 2019. Physical-chemical quality was assessed from the Weighted Index (IP) based on 16 parameters (temperature, conductivity, dissolved oxygen, nitrate, nitrites, Ammonium, biochemical oxygen demand, chemical oxygen demand, turbidity, ortho phosphate, calcium, magnesium, chloride, sulphate) and revealed an average to very poor quality in most stations. The microbiological quality, based on the assessment of the three parameters: fecal coliforms, total coliforms and fecal streptococcus, varies between, good and bad. The values of the biotic indices, Iberian Biological Monitoring Working Group Index (IBMWP), River Habitat Index (IHF) and River Quality Index (QBR), classify the waters of the various prospected stations as good quality waters for upstream stations (S2, S10, S12, S14, S15, S16) and in the medium to very bad quality category for other localities except for two stations (S27, S30) which are downstream but have good qualities.

The anarchic and rampant human impact in the city of Douala is the cause of the deterioration of its wetlands. The overall objective of the study is to determine the water quality of Kambo and Longmayagui rivers of Douala located in periurban and urban center respectively from Diatoms indexes. Organic materials and stones were sampled in each river. A total of 43 species belonging to 9 families and 22 genera were identified. The Diatom index is 4.0 to Kambo river (site 1) and 6.9 to Longmayagui river (site 2). These indexes show that Kambo river is less polluted, while Longmayagui river is polluted. The most frequent and abundant Diatoms in the samples of the two streams, Batika river characteristics (control) and Kambo can be used as indicators of unpolluted environment. These are :

Algal assemblages were evaluated at two Southeastern U.S. streams with reduced human impact, Upper Three Runs Creek and Tobbler Creek. The two sites were collected using standard protocols for stream samplings. The algal community was dominated by diatoms. Community attributes were found to be similar between the two sites, while indicator species varied as determined by Trophic Diatom Index values and the percentage of tolerant taxa to pollutants. Low pH tolerant Eunotia species were dominant in Upper Three Runs Creek while pH neutral, mesotrophic species were dominant in Tobbler Creek. This is the first report on primary producers from both sites and a taxonomic evaluation of the more common taxa is given for future reference.

Three new needle-shaped Fragilaria species from freshwater lake Apastepeque in El Salvador (Fragilaria salvadoriana sp. nov., F. maarensis sp. nov.) and subsaline lake Nam Co on the Tibetan Plateau (F. huebeneri sp. nov.) are described and compared based on light and scanning electron microscopy observations and morphometric analyses. Fragilaria salvadoriana sp. nov. is characterized by narrowly linear-lanceolate, sometimes centrally constricted valves, subcapitate to rarely capitate apices, and a distinct, dented appearing central area. Striae are composed of 2−5 occluded areolae. It can be differentiated from similar needle-shaped species by the valve outline, relatively low striae density, and shark fin-shaped spines. Characteristic of F. maarensis sp. nov. are a very narrowly lanceolate valve outline and subcapitate apices. The apical pore field is composed of 2–3 rows of poroids and acute, irregularly oriented spines are present at the junction between valve face and mantle. Th...

Actions to monitor, restore, protect, and utilize water ecosystems require adequate understanding and knowledge of the freshwater body's biological community structure and water quality . As such, biological components alongside physicochemical parameters are used to assess water quality and give insights to ecological status . Biological components such as diatoms are great tools to utilize to reach water quality assessment and monitoring goals. Diatoms are algae that have quick generation times and are sensitive to environmental changes. This allows them to become indicators of pollution in freshwater bodies and be used for freshwater biomonitoring . Diatom-based indices were developed to utilize the diatom's generally cosmopolitan distribution and robust relationship to nutrient and environmental variables

Actions to monitor, restore, protect, and utilize water ecosystems require adequate understanding and knowledge of the freshwater body's biological community structure and water quality . As such, biological components alongside physicochemical parameters are used to assess water quality and give insights to ecological status . Biological components such as diatoms are great tools to utilize to reach water quality assessment and monitoring goals. Diatoms are algae that have quick generation times and are sensitive to environmental changes. This allows them to become indicators of pollution in freshwater bodies and be used for freshwater biomonitoring . Diatom-based indices were developed to utilize the diatom's generally cosmopolitan distribution and robust relationship to nutrient and environmental variables

The marine mucilaginous tube-forming benthic diatoms Berkeleya hyalina (Round et Brooks) Cox and Parlibellus berkeleyi (Kütz.) Cox are reported for the fist time for the Caribbean coast of Colombian, in Santa Marta area. These two species were found infrequently growing as macroscopic colonies inhabiting shallow rocky substrata. The report of P. berkeleyi species is the fist for the Caribbean Sea.

We investigated the structure and diversity of diatoms in communities of metaphyton and periphyton from the wetland of El Edén Ecological Reserve, Quintana Roo, Mexico. In spite of the close association and communication between these communities, our comparisons reveal that the 2 communities have distinct species assemblages, with the periphyton being more diverse overall. We fi t abundance curves for periphyton and metaphyton, and argue that our results are consistent with communities where environmental conditions play a more important role than competition in structuring diatom species assemblages.

A new Amphora species, Amphora soninkhishigae sp. nov. is described from the saline lakes, Oigon Nuur and Uvs Nuur, in western Mongolia. Amphora soninkhishigae is characterized by its small size (valves 12-28 mm long, 2.9-3.8 mm wide), fine ornamentation, and a broad, internally thickened central area on the dorsal side of the valve (dorsal stauros) that branches along the dorsal margin. Among the amphoroid diatoms, Amphora soninkhishigae belongs in the subgenus Oxyamphora Cleve, where it is allied with other small Amphora taxa bearing a dorsal stauros including Amphora staurophora Juhlin--Dannfelt, Amphora abludans Simonsen, Amphora laevissima var. perminuta Grunow, and Amphora laevis var. minuta Cleve.

The present paper deals with 10 taxa belonging to 5 genera of Bacillariophycean algae first time from Maipokhari Lake of Ilam district. Out of these, 8 taxa viz., Eunotia diodon Ehr., E. gracilis (Ehr.) Rabenh., E. monodon Ehr. var. bidens (Greg.) Sm., E. monodon Ehr. var. tropica Hust., Navicula placenta Ehr., Pinnularia conica Gandhi, P. sundaensis Hust. and Hantzschia amphioxys (Ehr.) Grun. var. capitata Muell. are being reported for the first time from Nepal. Key words: Algae, Bacillariophyceae, Diatom, Ilam, Maipokhari Lake, Nepaldoi:10.3126/on.v3i1.331Our Nature (2005) 3: 26-30

In this work, the assessment of the ecological status of the Oum Er-rabie River basin was carried out by determining the physical-chemical, bacteriological and biological parameters. sampling Benthic macroinvertebrates and water were collected only once during the fourth seasons at the 31 stations upstream to downstream of the streams from spring 2018 to winter 2019. Physical-chemical quality was assessed from the Weighted Index (IP) based on 16 parameters (temperature, conductivity, dissolved oxygen, nitrate, nitrites, Ammonium, biochemical oxygen demand, chemical oxygen demand, turbidity, ortho phosphate, calcium, magnesium, chloride, sulphate) and revealed an average to very poor quality in most stations. The microbiological quality, based on the assessment of the three parameters: fecal coliforms, total coliforms and fecal streptococcus, varies between, good and bad. The values of the biotic indices, Iberian Biological Monitoring Working Group Index (IBMWP), River Habitat Index (IHF) and River Quality Index (QBR), classify the waters of the various prospected stations as good quality waters for upstream stations (S2, S10, S12, S14, S15, S16) and in the medium to very bad quality category for other localities except for two stations (S27, S30) which are downstream but have good qualities.

We used light and scanning electron microscope analyses to quantify morphometric features (valve length, width, stria density, lineola density and valve curvature) from the observation of valves representing Seminavis pusilla. Cluster analysis based on Gaussian mixture models and the expectation-maximization algorithm was used for delineating two species, Seminavis pusilla sensu stricto and Seminavis lata (Krammer) Rioual comb. et stat. nov. By comparison with S. pusilla, S. lata is characterized by wider valves and lower stria density. The two species have also markedly different ecology. S. pusilla is most abundant in the most saline lakes of the dataset, while S. lata is most abundant in the less saline lakes. Our results indicate that combining the two species into S. pusilla sensu lato would lead to a loss of ecological information and a decrease of the performance of transfer functions developed for quantitative reconstruction of past salinity from fossil diatom assemblages in sediment cores.

Diatoms (Bacillariophyceae) are widely used as bioindicators of present and past water quality because they inhabit the vast majority of aquatic ecosystems, are very diverse, highly sensitive to a variety of environmental conditions, and are characterized by silicified cell walls that favor their long-term preservation in sediments. Alongside with traditional morphological analyses, metabarcoding has become a valuable tool to study the community structures of various organisms, including diatoms. Here, we aimed to test whether the quantity of sediment sample used for DNA extraction is affecting the results obtained from high-throughput sequencing (metabarcoding) of the diatom rbcL region by isolating DNA from 10 g and 0.5 g (wet weight) of lake surface sediment samples. Because bioinformatics processing of metabarcoding data may affect the outcome, we also tested the consistency of the results from three different pipelines. Additionally, the agreement between metabarcoding data and morphological inventories of corresponding samples were compared. Our results demonstrate highly uniform patterns between the diatom rbcL amplicons from 10 g and 0.5 g of DNA extracts (HTS 10 and HTS 0.5, respectively). Furthermore, metabarcoding results were highly consistent among the data sets produced by different bioinformatics pipelines. Comparing results from metabarcoding and microscopy, we identified some taxonomic mismatches, which are related to the common issue of incompleteness of the sequence databases, but also to inconsistencies in diatom taxonomy in general and potential dissolution effects of diatom valves caused by high alkalinity of the investigated lake waters. Nevertheless, multivariate community analysis demonstrated highly similar results between data sets identified by microscopy and metabarcoding, further confirming that metabarcoding is a viable alternative for identifying diatom-environment relationships.

Taxonomic analysis of fresh water phytoplankton based on bright field microscopy and SEM studies is yet to be done in depth that may elucidate a number of new taxa. The present study on the assemblage of fresh water phytoplankton is focused to interpret the ecological condition of the studied water body of Bankura District in West Bengal. hytoplankton samples were collected from water bodies of Bankura District, West Bengal during the winter season. Planktonic algal taxa were analyzed using Scanning Electron Microscopy after preliminary observations made under Bright Field Microscopy. Qualitative and quantitative analyses of the phytoplankton were done for accurate taxonomic assignment of the taxa and interpretation of ecological perspectives. The qualitative analysis revealed an assemblage of phytoplankton that includes ten taxa. In the present assemblage, euglenophytes are represented by only one species, whereas, five species of desmids belonging to three genera and four species of diatoms belonging to four genera have been identified and illustrated. Quantitatively amongst the different groups of phytoplankton, desmids are dominant (57%) followed by diatoms (40%) with a minor representation of euglenophytes (3%). The qualitative and quantitative analyses of the phytoplankton assemblage indicate an oligotrophic condition.

A new benthic freshwater diatom, Fragilaria rinoi Almeida & C.Delgado sp. nov., is described from river periphyton samples in Portugal. Fragilaria rinoi sp. nov. is illustrated and discussed based on populations collected from the Vouga, Mondego and Lis river basins in central Portugal and compared with the type material of Fragilaria vaucheriae (Kütz.) J.B.Petersen. The morphological features of the new diatom species are documented through light and scanning electron micrographs, including a comparative analysis with related species of the genus (F. candidagilae Almeida, C.Delgado, Novais & S.Blanco, F. intermedia Grunow in Van Heurck, F. neointermedia Tuji & D.M.Williams, F. recapitellata Lange-Bert. & Metzeltin, F. perminuta (Grunow) Lange-Bert., F. vaucheriae and F. microvaucheriae C.E.Wetzel & Ector). Fragilaria rinoi sp. nov. is characterized by solitary cells without spines, lanceolate valves with slightly rostrate apices, a narrow, linear axial area, and a large, unilateral...

Coscinodiscus dispar Héribaud described by Héribaud in 1893 has been reported from Miocène, Pliocène sites of France. A detailed light and scanning électron microscope study was undertaken to détermine a description of the species. Coscinodiscus dispar Héribaud does not fit in any of the known fossil gênera and this is discussed. RÉSUMÉ -Coscinodiscus dispar Héribaud, décrit par F. Héribaud en 1893, a été trouvé dans le Miocène et le Pliocène de France. Une étude détaillée en microscopie optique et en microscopie électronique à balayage a mis en évidence les caractères ultrastructuraux de l'espèce. Une discussion basée sur les caractères ultrastructuraux de Coscinodiscus dispar Héribaud montre pourquoi cette espèce n'appartient pas aux genres fossiles connus.

Diatoms are commonly used in environmental assessments to detect pollution and eutrophication. The specific pollution sensitivity index (SPI) is one of the most frequently used indices, which assigns scores to diatom taxa based on their sensitivity to pollution. The study analyzed diatom communities in the Duero River basin in Spain to examine the relationship between SPI scores and various limnological variables. A GLM model showed that phosphates, nitrites, and water temperature were the main factors explaining SPI variability. The study also reviews previous results using SPI for water quality monitoring in different world regions, highlighting the role of nutrients in general as major drivers of SPI values worldwide. Overall, the findings reinforce the reliability of SPI as a metric for biological monitoring in various watercourses.

The objective of this study was to explore the environmental factors having the greatest influence on the distribution and abundance of epipelic diatom species in different wetlands in southern Spain. We previously defined four groups of conductivity categories: fresh (< 0.8 mS cm−1), oligosaline (< 8 mS cm−1), mesosaline (8–30 mS cm−1) and eusaline (> 30 mS cm−1). A dbRDA analysis performed on a subset of 36 of the 53 wetlands, using a total of 25 environmental variables, showed that five environmental variables (conductivity, pH, wetland area, silicates, and total suspended solids) were the best explanatory variables for the diatom assemblage, with conductivity being the main explanatory variable. Nonmetric multidimensional scaling (nMDS) analysis performed on the set of 53 wetlands revealed significant differences in diatom composition among the four conductivity groups. The key species in the eusaline group were Tryblionella pararostrata, Halamphora sp.1 and Cocconeis euglypta, whereas in the mesosaline and oligosaline group, these were Navicula veneta, Tryblionella hungarica and Nitzschia inconspicua. Finally, in the fresh group dominated Achnanthidium minutissimum, Navicula veneta and Gomphonema exilissimum. This study on epipelic diatoms can therefore contribute to the knowledge of these organisms in a European region with a high diversity of wetland typologies.

The initial valves of two Cymbella species are observed under a scanning electron microscope, and the perizonium ultrastructure of Cymbella is revealed for the first time. The perizonium is composed of alternate nodes and internodes and lacks transverse perizonium bands. Four new species, Cymbella apiculatophora sp. nov., C. hunanensis sp. nov., C. juglandis sp. nov. and C. menyuanensis sp. nov., are described using light and scanning electron microscopy based on epilithon samples collected from rivers in Hunan and Qinghai Provinces, China. Cymbella menyuanensis is a typical Cymbella species that closely resembles species in the group around C. cymbiformis Agardh, the type species of the genus. Cymbella apiculatophora is similar to C. sinensis Metzeltin & Krammer, while Cymbella hunanensis is closer to the C. hustedtii Krasske group. The last species, C. juglandis, has a cymbelloid valve outline, an obscured intermissio, internal occlusions of the areolae, dorsally deflected distal raphe fissures and a divided apical pore field at each apex, and it does not appear to belong to any group. In addition, new observations on C. cf. excisiformis Krammer and C. hustedtii are reported. The current concept of the genus Cymbella does not represent a monophyletic group as shown by molecular phylogenetic analyses. However, these analyses are still at the preliminary stage and are not yet sufficient to support a complete revision of the genus. Thus, although extremely diverse ultrastructural features are observed in the six Cymbella species investigated in this paper, we prefer to keep them within Cymbella at this moment for the sake of nomenclatural stability.

Aim Understanding the roles of deterministic and stochastic processes in community assembly is essential for gaining insights into the biogeographical patterns of biodiversity. However, the way community assembly processes operate is still not fully understood, especially in oceanic islands. In this study, we examine the importance of assembly processes in shaping diatom communities in islands and continents, while also investigating the influence of climate and local water chemistry variables on species distributions. Location Global. Taxon Stream benthic diatoms. Methods We used diatom datasets from five continents and 19 islands and applied beta diversity analyses with a null model approach and hierarchical joint species distribution modelling. To facilitate comparisons with continents, we used continental area equivalents (CAEs), which represent continental subsets with comparable areas and the same number of study sites as their corresponding islands counterparts. Results We found that homogeneous selection (i.e., communities being more similar than the random expectation) was the dominant assembly process within islands whereas stochastic processes tended to be more important within continents. In addition, assembly processes were influenced by study scale and island isolation. Climatic variables showed a greater influence on species distribution than local factors. However, in islands, local environmental variables had a greater impact on the distributions of unique taxa as opposed to non-unique taxa. Main Conclusions We observed that the assembly processes of diatom communities were complex and influenced by a combination of deterministic and stochastic forces, which varied across spatial scales. In islands, there was no universal pattern of assembly processes, given that their influence depends on abiotic conditions such as area, isolation, and environmental heterogeneity. In addition, the sensitivity of species occurring uniquely in islands to local environmental variables suggests that they are perhaps less vulnerable to climatic changes but may be more influenced by changes in local physicochemistry.

Interspecific abundance-occupancy relationships (AOR) have been addressed as one of the most important questions regarding the spatial ecology of diatoms. Whereas positive interspecific AOR is a common feature of ecological communi- ties, little is known about its causes and consequences. Studies to date confirm that AOR depends mostly on the ecological features exhibited by the species pool ana- lyzed, particularly niche characteristics and habitat guilds. The present study aims to test the persistence of such patterns using pond diatoms at a mesoscale level. Epiphytic and planktonic diatoms were collected in 29 shallow ponds throughout the Northern Iberian Plateau. Analysis of covariance (ANCOVA) tests revealed contrasting patterns when both assemblages are compared; for a given abundance level, epiphytic species were present in twice as many locations as planktonic ones, with noticeable effects also attributable to cell biovolume and motile guild. Contrary to our expectations, niche characteristics, measured in terms of species sensitivity and indicator value with respect to abiotic variables, had a negligible effect on AOR models. The consequences of such results are briefly discussed at a theoretical level.

This research presents a significant contribution to the methodologies and protocols for studying diatom communities in cryoconite holes on glaciers. Cryoconite holes are unique microenvironments found on glacial surfaces that support intricate microbial ecosystems, with diatoms playing a pivotal role in these communities. The refined methodologies developed in this study include optimizing sampling techniques to ensure that collections are both representative and diverse, which is crucial for accurate ecological assessments. Additionally, advanced digestion processes have been implemented to effectively isolate and purify diatom samples while minimizing contaminants, thereby improving sample integrity. Improved microscopic mounting techniques enhance visual clarity, facilitating more precise identifications of diatoms under the microscope. Furthermore, integrating DNA-based taxonomy broadens the taxonomic scope, providing valuable molecular insights into the diversity and evolutionary relationships of diatoms. Collectively, these protocols aim to enhance the reliability, depth, and multidimensional understanding of diatom ecology in cryoconite holes and broader glacial ecosystems, ultimately contributing to the field of glaciology and microbial ecology.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Flore diatomique des bassins versants de l'Agnéby et de la Mé (Côte d'Ivoire)

Relative % (±SE) frequency of diatoms and collection dates for selected streams in the Lahontan Basin …………………………………………i APPENDIX TABLE 1b. Relative % (±SE) frequency of diatoms and collection dates for selected streams in the Lahontan Basin …………………………………………x APPENDIX TABLE 1c: Relative % (±SE) frequency of diatoms and collection dates for selected streams in the Lahontan Basin ………………………………………xix APPENDIX TABLE 1d: Relative % (±SE) frequency of diatoms and collection dates for selected streams in the Lahontan Basin ……………………………………xxviii APPENDIX TABLE 1e: Relative % (±SE) frequency of diatoms and collection dates for selected streams in the Lahontan Basin ……………………………………..xxvii APPENDIX TABLE 1f: Relative % (±SE) frequency of diatoms and collection dates for selected streams in the Lahontan Basin ………………………………………xlvi APPENDIX TABLE 1g: Relative % (±SE) frequency of diatoms and collection dates for selected streams in the Lahontan Basin ………………………………………..lv APPENDIX TABLE 1h: Relative % (±SE) frequency of diatoms and collection dates for selected streams in the Lahontan Basin ………………………………………lxiv APPENDIX TABLE 1i: Relative % (±SE) frequency of diatoms and collection dates for selected streams in the Lahontan Basin ……………………………………. lxxiii APPENDIX TABLE 1j: Relative % (±SE) frequency of diatoms and collection dates for selected streams in the Lahontan Basin …………………………………….lxxxii APPENDIX TABLE 1k: Relative % (±SE) frequency of diatoms and collection dates for selected streams in the Lahontan Basin ……………………………………….xci APPENDIX TABLE 1l: Relative % (±SE) frequency of diatoms and collection dates for selected streams in the Lahontan Basin …………………………………………c APPENDIX TABLE 1m: Relative % (±SE) frequency of diatoms and collection dates for selected streams in the Lahontan Basin ……………………………………….cix

Most studies that consider the relationship of diatoms and water quality have focused their attention on the questions and practicalities of water pollution or perturbations in some form or another. Many models and studies have demonstrated the environmental tolerances or changes in structure of diatom communities related to environmental challenges. This focus on the impacted end of the water quality spectrum has led, of necessity, to issues ultimately related to habitat restoration. We contend that a concentrated effort to develop more fully the theory and there is a need for practice related to oligotrophy, the other, ignored end of the water quality spectrum. We explore the historical usages of the term oligotrophy, as well as the challenges and promise of autecological and community approaches to understanding oligotrophy, and the possibility of focusing more on conservation rather than restoration in water quality issues.

This study was carried out in 17 high mountain lakes and a pond in the Artabel Lakes Nature Park (Gümüşhane) on August 15, 2013 and August 13, 2016. In the present study, epipelic, epilitic and epiphytic algal flora of lakes were determined and a total of 95 taxa were recorded belonging to Bacillariophyta division. 9 of the taxa belonging to Bacillariophyta were determined to be new records for the freshwater diatom flora of Turkey. These taxa were identified as Aulacoseira lacustris (Grunow) Krammer f. tenuior Houk, Klee and Passauer, Orthoseira roeseana (Rabenhorst) Pfitzer, Cyclotella ambigua Grunow, Planothidium distinctum (Messikommer) Lange-Bertalot, Psammothidium helveticum (Hustedt) Bukhtiyarova and Round, Diploneis petersenii Hustedt, Frustulia crassinervia (Brébisson ex

The main goal of this study is to determine the composition, diversity and ecology of benthic diatoms in Karagöl Lake in Karagöl-Sahara National Park. Monthly sampling (from sediments, stones and aquatic plants in littoral zone of the lake) taken in three consecutive years revealed 57 diatom taxa with Gomphonema and Pinnularia being the most abundant species while other genera are represented with three or fewer species. Lindavia ocellata was the most dominant taxon in the samplings examined throughout the whole study. The values of diversity and evenness indices are high during the spring and early summer. Based on cluster analysis for monthly samples of epipelic diatom, there are two different groups at the lowest similarity level. The associations between August 2010 and September 2010 months are the most significant with 86.02%. The organism number of epipelic diatoms showed positive correlation (P&lt;0.01) with dissolved oxygen, while negative correlation (P&lt;0.05) with tempe...

Background and aims – Confusion over the taxonomic identity of Neidium iridis (Ehrenb.) Cleve (= Navicula iridis Ehrenb.) has persisted for more than 130 years with identifications of valve shapes varying from elliptical to linear and sizes from 100 to 300 µm. This confusion can be linked to the rarity of the species and poor attention to the original line drawings of Ehrenberg. This study examines the type material of Navicula iridis and further uses additional material from North America to define the species Neidium iridis. Methods – Mica and material from Christian Gottfried Ehrenberg’s Collection were studied to examine Navicula iridis. Light and electron microscope techniques were used to document the variability of valve morphology of original material in comparison with other fossil and recent materials. Key results – Ehrenberg designated no nomenclatural type for Navicula iridis at the place of its first description, and until recently the original material was not studied....

The first record of the genus Pliocaenicus from middle Miocene deposits is presented in this paper. This record from Changbai (Jilin Province, China) places the origin of the genus further back into the middle Miocene. The genus has been so far reported from the late Miocene/early Pliocene till Recent. The population from Changbai belongs to the group of Pliocaenicus species possessing complex alveolae, such as P. cathayanus Wang, P. jilinensis Wang and P. omarensis (Kuptsova) Stachura-S. et Khursevich. Both P. cathayanus and P. jilinensis have been described from China (Pliocene deposits), and are only known from the type locality. The third species, P. omarensis is reported from Eurasia and Africa (age range: late Miocene-Pleistocene). In this report we describe P. changbaiense, a new species from China, and focus on those characters having the potential for developing further an evolutionary and taxonomical concept in Pliocaenicus. We anticipate that these will contribute to our understanding of the driving forces of diatom dispersal.