Looking back, looking forward: a review of the new literature on diatom teratological forms (2010–2020)

AbstractOver the last years, issues concerning diatom teratological forms and environmental stress have received growing interest within the scientific community. Publications on this topic dated back to 1890 and were summarized in a review published in 2009 by the journalHydrobiologia, accounting for high citation rates (i.e. 117 citations Scopus and 232 citations Google Scholar, October 2020). This wide interest stimulates the authors to further unravel teratological forms significance in the light of the most recent publications (2010–2020). Diatom teratological forms are one of the best individual-level biomarkers since they provide a rapid response to several environmental stressors, including new emerging pollutants. The mechanisms involved in teratological valve likely involve both cytoskeleton and silicon metabolic pathway impairments. However, teratologies do not seem to weaken the reproduction capacity and viability of the affected individuals. We recognized eight types of teratologies as involving different parts of the valve, depending on genus. In order to summarize the information obtained by several years of research, we suggest a four-step procedure aimed at providing a theoretical pathway that researchers should follow to better explain results obtained in next-future studies and representing a starting point for the development of an environmental index based on teratological forms

Response of epilithic diatom communities to environmental gradients in subtropical temperate Brazilian rivers

This work aims to analyse the response of epilithic diatom communities to enviranmental gradients in subtropical temperate southern Brazilian rivers to contribute to the development of a widely applicable methodology for water-quality monitoring. Samples for physical, chemical and biological determination were collected monthly, fram December 2001 to November 2002 and fram March 2003 to February 2004, at 9 stations along the rivers Pardo and Pardinho in the hydrographical basin of Rio Pardo, State of Rio Grande do Sul (RS), Brazil. Physical and chemical variables (water temperature, pH, dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, nitrates, nitrites, phosphates and total dissolved solids) and biological variables (epilithic diatom communities) were used as parameters for water-quality assessment. The data matrix was examined by means of a multivariate ordination using Detrended Correspondence Analysis (DCA). In total, 270 taxa were identified to specific or infra-specific levels. The results showed that of all the physical and chemical variables used, the main gradient along the DCA first axis was eutraphication, which was indicated by its significant correlation with phosphates (p < 0.00l). Hence, the species' scores on the DCA axis were used as an operational criterion for indicating their tolerance to eutrophication. From this analysis, the 10 taxa that were the most tolerant to eutrophication were: Cyclotella meneghiniana, Fallacia monoculata, Nitzschia acicularis, N. clausii, N. nana, N. palea, Nitzschia sp., Pinnularia sp., Sellaphora pupula sensu lato and Ulnaria acuso The present study showed that epilithic diatom assemblages reflect anthropogenic changes in hydrographic basins in subtropical temperate streams, especially pollution by organic enrichment and eutraphication. Key words: Diatoms, eutrophication, biomonitoring, southern Brazilian rivers.Este trabajo pretende analizar la respuesta de la comunidad de diatomeas epilíticas a gradientes ambientales en ríos brasileños templados subtropicales, con el objetivo de contribuir al desarrollo de una metodología ampliamente aplicable para la monitorización de la calidad del agua. Diversas muestras para determinaciones físicas, químicas y biológicas fueron recogidas mensualmente, de diciembre de 2001 a noviembre de 2002, y de marzo de 2003 afebrero de 2004, en nueve esta­ciones de muestre o distribuidas a lo largo de los ríos Pardo y Pardinho, localizados en la Cuenca Hidrográfica del Río Pardo, Estado del Río Grande del Sur; Brasil. Variables físicas y químicas (temperatura del agua, pH, oxígeno disuelto, demanda bioquímica de oxígeno, demanda química de oxígeno, nitratos, nitritos, fosfato y sólidos totales disueltos) y biológicas (co­munidad de diatomeas epilíticas) fueron usadas como parámetros para evaluar la calidad del agua. El conjunto de datos fue analizado por medio de una ordenación multivariante usando el Análisis de Correspondencias sin Tendencias (DCA). En total, 270 taxones fueron identificados a nivel especifico o infra-especifico. Los resultados indicaron que, entre todas las variables físicas y químicas usadas, el principal gradiente establecido a lo largo del primer eje DCA fue la eutrojización, señalada por su correlación significativa con la concentración de fosfatos (p < 0.001). De esta forma, los valores alcanzados por las especies en el primer eje DCA fueron usados como un criterio operativo para indicar su tolerancia a la eutrojización. Los 10 taxones más tolerantes a la eutrojizaciónfueron: Cyc10tella meneghiniana, Fallacia monoculata, Nitzschia acicularis, N. c1ausii, N. nana, N. palea, Nitzschia sp., Pinnularia sp., Sellaphora pupula sensu lato y Ulnaria acuso El presente estudio muestra que la comunidad de diatomeas epilíticas refleja cambios antropogénicos en ríos templados subtropicales de cuencas hidrográjicas, especialmente la contaminación por enriquecimiento orgánico y eutrofización

Epilithic diatom assemblages and environmental quality of the Su Gologone karst spring (centraleastern Sardinia, Italy)

Karst springs are considered among the most vulnerable groundwater-dependent ecosystems. Despite their ecological value and importance as strategic water sources, Mediterranean karst springs are still poorly investigated. The aim of this study was to analyse the epilithic diatom assemblages and to test their usefulness as indicators of environmental quality on the Su Gologone spring (central-eastern Sardinia, Italy), a biotope of great natural value and a precious source of drinking water. A total of 89 diatom taxa were found with 25 new records for Sardinian running waters. Species richness, Shannon-Wiener and Pielou indices showed good biotic integrity. The dominant taxa were alkaliphilous, halophobous-oligohalobous exigent, xeno-oligosaprobic and characteristic of oligotrophic waters. The eutrophication/pollution index − diatom based (EPI-D) and the Navicula Nitzschia Surirella indices indicated respectively an excellent/good biological water quality and a low physical disturbance. However, the biological and chemical oxygen demand, and the microbiological variables (E. coli, fecal and total coliforms) revealed an organic contamination of the water, although moderate. The judgment provided by the EPI-D should be verified after updating of the index. In fact, 10 taxa found in this study are not currently considered by the EPI-D method

Chamaepinnularia thermophila (Bacillariophyceae) : synonymy with Navicula tongatensis Hustedt and update of its geographic distribution and ecology

Abstract Chamaepinnularia thermophila is a small and poorly known diatom species. After the first description from a hot spring in Guadalupe in 1952, its presence appeared to be limited to a few other springs of the French Antilles. The objective of this study is to report new information on aspects of taxonomy, distribution and ecology of this species. Accurate analysis under light and scanning electron microscope of the material collected on different substrates (cobbles, macrophytes and fine sediments) from a thermo-mineral spring of Sardinia (Italy) allowed us to document the first record of the species in the Mediterranean area. Furthermore, the comparison with Navicula tongatensis from Hustedt's original material, carried out because of their similarity, revealed identical morphological characteristics suggesting their consequent synonymy. Based on the information available in the literature and our data, C. thermophila is a rare species present mainly in tropical areas, in thermal springs with alkaline pH, medium to high conductivity and low to moderate nutrient content. The occurrence of the species at sites with very different environmental characteristics seems unusual, but it could indicate a broader ecological range. This study contributes to the standardization of the nomenclature used for this species so far and provides the first framework on its global geographic distribution and ecology

A polyphasic approach to the study of the genus Nitzschia (Bacillariophyta): three new planktonic species from the Adriatic Sea

The paraphyletic diatom genus Nitzschia comprises over 1000 morphologically distinct pennate taxa, known from the benthos and plankton of freshwater, brackish and marine environments. The principal diagnostic characters for delimitation of Nitzschia species include valve shape, the position and structure of the raphe, presence/absence and shape of the proximal raphe endings and terminal raphe fissures, areola structure, and specific morphometric features such as cell size, and stria and fibula density. In this study, we isolated 12 diatom strains into culture from samples collected at the surface or greater depths of the southeastern Adriatic Sea. Morphological analyses included LM, SEM and TEM observations, which, along with specific morphometric features, allowed us to distinguish three new Nitzschia species. These findings were congruent with the results of phylogenetic analyses performed on nuclear‐encoded SSU (18S) rDNA and chloroplast‐encoded rbcL and psbC genes. One of the new species (Nitzschia dalmatica sp. nov.) formed a lineage within a clade of Bacillariaceae containing members of the Nitzschia sect. Dubiae, which was sister to Psammodictyon. A second lineage was part of a novel clade that is significantly distinct from other Nitzschia species sequenced so far and includes Nitzschia adhaerens sp. nov. and N. cf. adhaerens. A further new species was found, Nitzschia inordinata sp. nov., which appeared as the sister group to the N. adhaerens clade and the conopeoid Nitzschia species in our phylogenetic trees. Our findings contribute to the overall diversity of genus Nitzschia, especially in identifying some deep branches within the Bacillariaceae, and highlight under‐scoring of this genus in marine plankton.info:eu-repo/semantics/acceptedVersio

Nitzschia austriaca Hustedt: a characteristic diatom of Hungarian inland saline waters including a morphological comparison with the type material

A detailed scanning electron microscopic investigation was carried out to clarify the taxonomic status of a small sigmoid Nitzschia species, a potential indicator of Central European soda waters. We found this taxon to be one of the dominant epiphytic diatoms collected from sodic bomb crater ponds at Apaj (Hungary). The large population allowed for a morphometric comparison based on frustule ultrastructure with the type material of the most similar species, Nitzschia austriaca Hustedt that was originally described from a soda pan in the region. The results clearly demonstrated an overlap between the Apaj population and the type material of N. austriaca (based on NMDS analysis), therefore we argue that they represent the same taxon. An emended diagnosis of N. austriaca is given. Total suspended solids and total phosphorous proved to be the most important factors predicting the occurrence of the species, with possible interactive effects of conductivity and pH. We then expanded the distribution of the species by revisiting data originating from previous large-scale surveys targeting sodic habitats in Hungary. On the basis of our results, N. austriaca is a characteristic species for Central European soda waters, including the protected astatic soda pans, indicating their typical chemical and physical characteristics.</jats:p

Interesting diatoms from a special habitat

The epiphytic diatoms of the soda ponds of bomb craters were sampled in 2014. The small ponds (area: 7.1-86.5 m2, depth: 4 to 60 cm) are located in the northern part of the Kiskunság National Park (47°7.403 'N, 19°8.187'E), near the village of Apaj in Hungary. Their salinity ranges from fresh water to moderately saline levels (conductivity of 1.3 to 7.1 mS cm-1). This area has patchy surface salinization, because the flow pattern of groundwater results extensive surface salinization in those discharge areas where the infiltrating freshwater does not superimpose the upwelling saline water. The salts origin from the overpressured NaCl-type water of the Pre-Neogene basement and the NaHCO3-type water of the Neogene sediments. The ponds can be characterized by different areal extent, depth and salinity, various conductivity, hydroperiod (1–9 months, the deepest ones do not dry out in years with high amount of precipitation due to probably more or less continuous supply by groundwater), plant coverage and width of macrophyte belt. All of the ponds were sampled except for the ones with very short (shorter than one month) hydroperiod. A total of 80 diatom taxa, representing 33 genera, were identified in these ponds. The genus Nitzschia was represented by the largest number of species (16), followed by the genus Gomphonema with 9 taxa. IndVal analysis identified 15 species with significant indicator values for ponds. Some interesting, rare or new diatoms for Hungarian flora have also been recorded, including Gomphonema jadwigiae, Halamphora dominici, Navicula wiesneri, Nitzschia austriaca, N. vitrea, Surirella peisonis

Morphology and distribution of Brevilinea kevei sp. nov. (Bacillariophyceae), a new diatom from Europe

An unknown small naviculoid diatom was found in the epiphyton samples from Hungary (in Kanyari Holt-Tisza oxbow) and in the epilithon samples from France (Canal de Berry at Épineuil-le-Fleuriel). Detailed observations using light and scanning electron microscopy were used to describe Brevilinea kevei Ács &amp; Ector sp. nov. It can be separated from Brevilinea pocosinensis Siver et al. (which was the only described species in the genus) by its size (smaller than B. pocosinensis), shape (elliptic valve, never capitate) and ecological requirements. Brevilinea pocosinensis lives in acidic conditions while B. kevei in neutral ones. Differential diagnostic criteria with respect to similar taxa, especially Fallacia indifferens (Hustedt) D.G. Mann, together with ecological implications of this finding are briefly discussed.</jats:p