A mesoscale study on diatoms from the Santos Basin (23 degrees S to 28 degrees S), southern Brazil, was carried out during early spring 2019, based on 60 oceanographic stations stretching from coastal to open-ocean waters. Multivariate analysis based on counting diatom valves on permanent slides was performed in relation to the main environmental parameters (temperature, salinity, nutrients, and depth). Four diatom associations were discriminated, affected by the water masses and environmental drivers operating in the Santos Basin. The inner- to mid-shelf association was influenced by nutrient discharge from rivers and estuaries, as well as the Subtropical Shelf Front; Actinocyclus octonarius, Chaetoceros didymus, Fragilariopsis doliolus, and Pseudo-nitzschia pungens were the highest relative valve contributors. Another association composed of uncommon diatoms occurred as isolated peaks along the continental slope and was affected by meanders and eddies of the Brazil Current, as well as deep waters brought up by local coastal upwelling. Delphineis surirella, Navicula pennata, Pleurosigma diversestriatum, Pseudo-nitzschia cf. delicatissima, Pseudo-nitzschia calliantha, and Skeletonema tropicum were its main components. A typical subtropical/tropical association from oligotrophic warm waters was delimited in outer-shelf and oceanic waters such as Azpeitia spp., Asteromphalus spp., and Roperia tesselata. The fourth association comprised diatoms widely distributed across the Santos Basin, overlapping with the tropical association in certain areas. In this association, Nitzschia bicapitata, Thalassionema nitzschioides, Chaetoceros spp. and Bacteriastrum hyalinum were the most important taxa. Multivariate analysis identified for the first time diatom associations related to water masses and their properties in the Santos Basin on a regional scale. These patterns of mesoscale distribution provide a more detailed understanding of diatom biogeography than previously documented in broader-scale investigations.
A new araphid diatom genus in the class Fragilariophyceae is described from laminated, Eocene, lake sediments at the Horsefly fossil locality, British Columbia, Canada. Forticellula wolfei gen. et sp. nov. was observed in 16 samples from diatomaceous shale and mudstone rock specimens archived at the University of Alberta, Edmonton, Alberta, Canada. Forticellula frustules possess small, oval to subcircular valves each with a narrow sternum, large apical pore fields, a rimoportula, and striae that are continuous onto a deep mantle. The taxon did not produce spines. The cingulum is deep and consists of numerous open copulae (girdle bands), each with multiple rows of pores on both sides of a thickened hyaline strip, and a wide ligula with short striae. Up to 22 girdle bands were recorded, and practically all cells were still fully intact, indicating a strong and stable cingulum. The suite of characters was unique and different from all known genera in the class Fragilariophyceae, and specifically in the families Staurosiraceae, Fragilariaceae and Tabellariaceae, justifying the description of a new genus. The new genus is best placed as a stem taxon within the Tabellariaceae lineage. The Horsefly fossil locality is also the type locality of the extinct diatom genus, Eoseira, which was reported from 13 of the samples harbouring Forticellula. Samples with abundant numbers of Forticellula typically had numerous remains of heliozoans and paraphysomonad chrysophytes, Mallomonas spp., other araphid diatoms, and low numbers of Eoseira. Conversely, samples with abundant concentrations of Eoseira also harboured Aulacoseira spp., but minimal Forticellula frustules. It is concluded that Forticellula lived as single cells, probably attached to substrates, and favoured shallow, littoral environments.
This study presents an integrative taxonomic investigation of five epilithic diatom species from the Han River Basin, South Korea: Fistulifera minima sp. nov., Fragilaria triangulispina sp. nov., Mayamaea striatissima sp. nov., Nitzschia pontifera sp. nov., and Tryblionella cancellata sp. nov. Their taxonomic status is evaluated through detailed morphological analyses using light and scanning electron microscopy, combined with molecular evidence from the plastid rbcL and nuclear SSU rRNA genes. Phylogenetic reconstructions based on plastid rbcL sequences recovered each lineage as a well-supported monophyletic group, and SSU rRNA data provided complementary support where comparable reference sequences were available. Morphological observations are explicitly evaluated in the context of historically established and morphologically similar taxa, enabling refined delimitation of species boundaries. This study refines diagnostic criteria for several small-celled naviculoid, nitzschioid, and araphid diatom lineages. The results contribute to improving taxonomic resolution of morphologically conservative taxa and expand current knowledge of freshwater diatom diversity in East Asia.
Periphyton communities in streams are naturally variable in space and time and this, along with repeatability and reproducibility, needs to be recognized when using diatoms to inform decisions about the management of freshwater resources. This paper examines five types of uncertainty on four stream waterbodies in northern England, and assesses the implications for decision-making associated with the Water Framework Directive. Effects can be ranked (lowest to highest) as follows: within-analyst variation (repeatability) < site-level variability at the time of sample collection < between-operator variation (reproducibility) < within water body variation similar to between-season variation. The extent of within water body and between season variation varied between sites, suggesting that generalizations are difficult, although these sources of environmental variation both exceeded most measures of analytical variation. Analytical and within-site variation can be controlled, to some extent by adherence to protocols, but both also include a stochastic component. Within water body and between season variation can be controlled by more intensive sampling, but this comes at a cost. Therefore, it is important that the scale of this be recognized and acknowledged explicitly.
We describe here the first SEM observations on the auxospores of two species of Epithemia, E. reicheltii and E. lacus-douglasi, from Douglas Lake, Michigan, USA. Both species were found in abundance with auxospores in October of 2024. The auxospores of both species were semicircular in shape, initially covered with an organic matrix, which split as incunabular caps. Internal to this matrix were transverse incunabular rows of quadrangular, imbricating scales overlapping towards the valve ends, with the longer abaxial edges fimbriate and the other edges straight. And, internal to the scales, was a single, siliceous covering - the primary longitudinal perizonial band - which had transversely-oriented fissures. Internal to the primary band were three (or four) dorsally positioned secondary longitudinal perizonial bands. The complex coverings of the auxospores of these Epithemia species are unique amongst the diatoms.
Although diatom research in northern Africa has expanded in recent years, many desert and oasis ecosystems still lack detailed taxonomic investigation. The geographical setting, which forms unique environmental conditions, suggests that many unexplored ecosystems may serve as habitats for species new to science. The research involved material from the oases of Sudan, including one newly forming, isolated from human activity. The current difficult political situation in this region prevents fieldwork and the collection of new samples. A total of 102 diatom taxa were identified. Qualitative analysis of the assemblages allowed for the distinction of four groups of sites. Different species composition in oases could be associated with the type of water supply, environmental gradients, and water management. Based on morphological taxonomy, two species new to science were described: Mastogloia deserti sp. nov. and Rhopalodia oasis sp. nov. This study presents the taxonomic diversity of diatoms in Sudanese oases and highlights the importance of these habitats as potential biodiversity 'hotspots'. Additionally, the conducted analysis of ecological preferences expands knowledge about the ecology of diatom species in extreme habitats.
This study investigated the inter-specific competition between the diatom Chaetoceros tenuissimus and the harmful algae Karenia mikimotoi and Chattonella marina under varying initial cell densities. Experiments were conducted using both monoculture and co-culture methods in a controlled laboratory environment. The results indicated that the growth of C. tenuissimus, K. mikimotoi, and C. marina in monoculture was not influenced by the initial cell densities (1000 or 10 000 cells ml(-1)). However, an increase in initial inoculation density accelerated the time to reach maximum cell density and the onset of the stationary growth phase. The initial cell density significantly impacted the inter-specific competition between C. tenuissimus and K. mikimotoi, with the species at higher concentrations prevailing in the competition. In the competition experiments with four different initial concentration combinations of C. tenuissimus and C. marina, neither species were eliminated by the other. Simulation of the co-culture experiments using the Lotka-Volterra inter-specific competition model revealed that C. marina could only outcompete C. tenuissimus when its initial cell concentration was significantly higher. In the experiment in which each filtrate was exposed to the other species, no clear inhibitory effect was observed in any of the combinations. This study contributed to a better understanding of the inter-specific relationships between harmful algae and diatoms.
Light and scanning electron microscopical observations on the type population of E. rupestris W. Smith are presented. Light microscopy shows valves that are asymmetrical to the apical axis, a canal raphe positioned along the dorsal margin, and costate fibulae that extend across most of the valve. In girdle view, 'capitate costae' are evident. Scanning electron microscopy shows the valve to have a raphe with a distinct keel bordered by wide openings. Striae are very fine (ca 50 in 10 & micro;m) and are shown to lack volae externally and internally. These observations indicate that this species is morphologically more similar to species in the genus Rhopalodia O. M & uuml;ller than to the genus Epithemia Br & eacute;bisson ex K & uuml;tzing. The lack of volae in R. rupestris (W. Smith) Krammer is unique among rhopalodioid diatoms. Variations in the areolar occlusions across the Rhopalodiaceae are discussed.
This paper describes Encyonema macieliarum sp. nov., collected from epilithic substrates in lotic environments of the Ibicu & iacute; river catchment (southern Brazil, Pampa Biome). The material was examined with the LM and SEM. Morphological analysis and PCA helped to separate the new species from the most similar taxon: Encyonema sprechmannii. The new species E. macieliarum can be differentiated from the others within the genus by a set of characteristics, which includes its valve outline, stria pattern, and absence of intermission. The species is found in oligotrophic to mesotrophic environments, in streams with more stable flow. This finding contributes to the morphological understanding of Encyonema and emphasizes the taxonomic relevance of the underexplored Pampa Biome.
The lack of reliable proxies capturing multi-seasonal interactions limits our understanding of long-term seasonal succession patterns. Lake diatoms, being sensitive to seasonal climate changes, serve as a valuable proxy for reconstructing seasonal variability. However, extracting seasonal phenological signals from multi-year sediment records remains challenging. Conducting continuous multi-year, monthly-to-seasonal modern diatom investigations using sediment traps is a crucial approach to validate their applicability for long-term seasonal reconstruction. This study revisited the subtropical alpine Yunlong Lake in the monsoon region of southwestern China, conducting two additional years (May 2021 to April 2023) of monthly trap monitoring following prior research (September 2013 to August 2015). Integrated with concurrent meteorological, hydrological, and hydrochemical data, we systematically analyzed seasonal diatom dynamics and their climatic implications. Key results include: (1) Marked interannual differences in diatom assemblage composition. Benthic diatoms dominated in the second year, while planktonic taxa decreased significantly. This shift was driven by largely-reduced warm-season rainfall, which led to lower water levels, expanded benthic habitats, and increased light availability. Thus, the planktonic-to-benthic diatom ratio serves as a sensitive indicator of long-term monsoon precipitation variability. (2) Principal component analysis revealed pronounced seasonal succession patterns among planktonic diatoms, particularly during high-water-level periods in the first year. During warm seasons (May to November), Achnanthidium catenatum and Aulacoseira granulata var. angustissima showed cyclic recurrent blooms. In the cold season (December to April) of the first year, a sequential proliferation of planktonic taxa - from larger forms (Aulacoseira ambigua, Discostella asterocostata) to smaller ones (Discostella stelligera, Lindavia balatonis, and Discostella pseudostelligera) - was observed, consistent with earlier findings. These dynamics were regulated by temperature-mediated shifts in mixing-stratification regimes and nutrient availability, indicating that water temperature directly and/or indirectly controls seasonal diatom succession. Overall, these results demonstrate that diatom assemblages in Yunlong Lake effectively reflect cyclic seasonal climate variations in monsoon regions.
The examination of the phytoplankton communities of the Tonle Sap Lake, particularly the diatom flora, has highlighted the unique microflora of the lake. One new genus (Praecyclostephanos Tudesque, Le Cohu & Van de Vijver) and several new species have recently been described (Aulacoseira micropunctata Tudesque, Le Cohu & Van de Vijver, A. spiralorimoportula Tudesque, Le Cohu & Van de Vijver, Cyclotubicoalitus tonlesapensis (Tudesque, Le Cohu & Van de Vijver) K.Schultz, Tudesque & Van de Vijver, and Urosolenia anlongreangensis Tudesque, Le Cohu & Van de Vijver), highlighting a high level of endemism. A recent survey conducted in 2022 investigated the taxonomy and distribution of the planktonic diatom flora and recorded the presence of a novel Aulacoseira species. Detailed light and scanning electron microscope observations show that this species possesses a unique combination of taxonomic characteristics not found in any other known taxon. In particular, this short-chained species, which lacks linking spines and has small and barely visible rimoportulae, exhibits a characteristic pronounced thickening on the mantle - also known as the M & uuml;ller step on one of its valves. This article provides high-resolution micrographs and a diagnosis of the new species, examines its distinctiveness, and further underscores the taxonomic singularity of the diatom flora of the Tonle Sap Lake.
Over the course of more than 150 years, Dickieia, Staurophora and Krsticiella were established as genera for some naviculoid (sensu Cleve) diatoms, defined using different criteria: colony form and frustule shape, chloroplast and valve morphology, and variation in symmetry. However, they share many structural features, and this paper argues that Dickieia and Staurophora should be combined in a single genus, Dickieia. The diagnostic characters for the genus are outlined and the included taxa summarized, with comments on the value of size and shape in species delimitation. The status of Krsticiella is discussed in relation to the choice of these diagnostic characters. Although the authorities for the genus name, Dickieia, have usually been cited as Berkeley in K & uuml;tzing, an earlier publication by Berkeley & Ralfs has priority, and the relevant corrections (including to the generitype, Dickieia ulvoides) are made.
Until recently, benthic microalgae (BMA), like other microbes, were thought to be cosmopolitan in time and space, limited only by environmental conditions. Spatial and temporal dispersal limitations, however, do appear to apply to BMA. While drivers of biogeographic patterns have been explored to some extent, studies examining temporal variation in BMA communities are lacking. Herein, DNA metabarcoding was used to characterize diatom communities of saltmarsh sediments at three temporal scales: seasonally over 10 months, at two tidal phases (spring and neap) across four different seasons, and at three stages within a tidal cycle (from ebb to flood during one day from two tidal phases across four seasons). Rare (< 0.1%) diatoms were analyzed separately from abundant taxa and the whole community. Thirty-one environmental parameters were measured to identify potential drivers of any observed variation. Community structure, biomass, and alpha-diversity varied significantly across season, between lunar phases in specific seasons, and across certain tidal cycles. Overall, community stability was relatively high even though diatom taxa tended to positively covary. Most taxa (similar to 72%) were rare, and higher alpha-diversity was observed in this group. The rare subcommunity also exhibited higher temporal turnover and lower stability than abundant taxa. Community variation was primarily directed by purely temporal factors, which reflects a greater degree of dispersal limitation relative to other microbes. Temporally-structured environmental factors likewise substantially influenced community change. Stochastic (or unmeasured) processes were also notable, whereas the role of purely environmental factors (Spartina density, height of living and dead Spartina, and water temperature) was small. Our results show that time and environmental conditions worked together to produce increasing dissimilarity in community structure over the 10-month sampling period. While further studies are necessary, understanding BMA community variation through time may allow researchers to predict communities' response, and thus the ecosystem's response, to environmental change.
The salt stream originating from the Lyudmilinskaya brine well in Solikamsk, Russia, exhibits high mineralization (similar to 11,000 mg/L) and low diatom species diversity, with 29 species identified. The core diatom community consists primarily of Synedra famelica, Staurosira subsalina, Navicula gregaria, Navicula peregrina, and Navicula salinarum. Additionally, six diatom species (Nitzschia inconspicua, Nitzschia microcephala, Prestauroneis protracta, Staurosirella martyi, Surirella striatula, and Synedra famelica) were recorded that had not been previously documented in water bodies of the Perm Region. Teratological forms have been noted for three species of diatoms: Synedra famelica, Halamphora coffeiformis, and Achnanthes brevipes var. intermedia.
Diatoms resembling Pinnularia gibba Ehrenberg constitute a complex of species that are difficult to identify because they intergrade morphologically. We assessed the morphological diversity of this group in the eastern United States using 458 sediment core samples from a national-scale lake survey and applying the 'voucher flora' method. In contrast to the traditional approach to diatom identification - which previously yielded just six taxa from the P. gibba group in these samples - we found 38 distinct morphological entities. Some of these entities could be further grouped because they fit within the boundaries of previously described taxa, while others represented novel taxa. Based on this revision, we establish six new species and two new varieties: P. geilerae sp. nov., P. undulatoides sp. nov., P. vanderburghiae sp. nov., P. manoyloviae sp. nov., P. aquilonariformis sp. nov., P. hurleiae sp. nov., P. hurleiae var. minuta var. nov., and P. clericii var. minor var. nov. Eight additional morphological entities may represent previously undescribed taxa, but due to their limited representation in our dataset, they could not be formally described. Autecological analysis revealed a substantial variation in ecological profiles of the studied Pinnularia taxa, highlighting the benefits of using fine-grained taxonomy in bioassessments.
Several strains of Achnanthidium isolated from various water bodies of Mongolia were investigated by light and scanning electron microscopy and molecular genetic methods. On the basis of this investigation, two new species from the A. minutissimum complex are described, A. mongolicum sp. nov. and A. khovsgolense sp. nov. Strains belonging to previously described species A. baicalonanum and A. angustum were also found, expanding our knowledge of the distribution and biogeography of these species. A strain of A. parallelum was studied and designated as an epitype for this species, adding to the reference database of genetic sequences of Achnanthidium taxa, as Achnanthidium is a highly heterogeneous genus with known cryptic diversity in some species complexes, and molecular data are vital in our understanding of its taxonomy. Based on the results of molecular investigation, the relationship between the genera Achnanthidium, Psammothidium and Rossithidium is discussed.
