Over 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 journal
Hydrobiologia
, 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.
Sea turtles are distributed in tropical and subtropical seas worldwide. They play several ecological roles and are considered important indicators of the health of marine ecosystems. Studying ...epibiotic diatoms living on turtle shells suggestively has great potential in the study of turtle behavior because diatoms are always there. However, diatom identification at the species level is time consuming, requires well-trained specialists, and there is a high probability of finding new taxa growing on turtle shells, which makes identification tricky. An alternative approach based on DNA barcoding and high throughput sequencing (HTS), metabarcoding, has been developed in recent years to identify species at the community level by using a DNA reference library. The suitabilities of morphological and molecular approaches were compared. Diatom assemblages were sampled from seven juvenile green turtles (Chelonia mydas) from Mayotte Island, France. The structures of the epibiotic diatom assemblages differed between both approaches. This resulted in different clustering of the turtles based on their diatom communities. Metabarcoding allowed better discrimination between turtles based on their epibiotic diatom assemblages and put into evidence the presence of a cryptic diatom diversity. Microscopy, for its part, provided more ecological information of sea turtles based on historical bibliographical data and the abundances of ecological guilds of the diatom species present in the samples. This study shows the complementary nature of these two methods for studying turtle behavior.
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•Sampling sites present different combinations of geology, soil type and land use.•Soil pH and land use are main environmental controls on soil diatom communities.•Index applied on ...soil diatoms to infer anthropic disturbance in each site.•Sites with different land use show different disturbance levels.•Understanding soil diatom ecology is key for the development of a soil quality index.
A large amount of studies focuses on aquatic diatoms’ ecology and their use in the assessment of water quality. Little is known about terrestrial diatoms’ ecological behaviour and sensitivity to environmental factors. We hypothesise that terrestrial diatom communities can serve as a proxy of anthropic disturbance levels in terrestrial sites. To test our hypothesis, we apply an aquatic index to soil communities that is to deliver new information on the physiographic controls on soil diatoms. Diatom and soil samples were collected in the Attert River basin in Luxembourg during three seasons, in sites characterised by different combinations of geological, soil (schist, marl and sandstone) and land use (forest, grassland and agriculture) features. We found an effect of seasonality on soil diatom communities, reflected by different species dominance and abundances in samples during the three seasons. Soil pH and land use (which translates in a different amount of total carbon and nitrogen in soil) were identified as the variables having the largest impact in structuring the communities and as among the features with the highest importance in defining the ecological status of the sites (i.e. disturbed farmlands having higher pH and lower carbon and nitrogen content). However, the lack of information about the sensitivity of some of the most abundant terrestrial species in our study area caused some discrepancies between the expected (i.e. forested areas with low anthropic disturbance) and the obtained results, with several forested sites classified as having high anthropic disturbance. These results suggest that soil communities are likely to contain information about soil ecological status and highlight the importance of a better characterisation of terrestrial diatom species for developing a quality index based on soil communities.
Light microscopy (LM) and scanning electron microscopy (SEM) observations on a new species of the genus Pseudostaurosira from a spring of the Massif Central (France) are presented. The new species, ...with very small dimensions, presents similarities with other species previously observed in other parts of Europe. However, based on its morphology, the new species presents striae sometimes composed of only two areolae on the valvar surface: one big, round or elliptic near the mantle edge and the second smaller, slit-like or round (sometimes completely occluded externally) situated further toward the interior. Moreover, the size, the density of striae and the presence of volae allow the separation of Pseudostaurosira bardii from the other species. Morphologically similar species were also re-investigated in the current project, including the type material of Pseudostaurosira trainorii E.Morales, Pseudostaurosiropsis connecticutensis E.Morales and Pseudostaurosira cataractarum (Hustedt) C.E.Wetzel, E.Morales and Ector. They were also investigated and illustrated using SEM. The ecological preferences of Pseudostaurosira bardii are briefly discussed.
The regression of similarity against distance unites several ecological phenomena, and thus provides a highly useful approach for illustrating the spatial turnover across sites. Our aim was to test ...whether the rates of decay in community similarity differ between diatom growth forms suggested to show different dispersal ability. We hypothesized that the diatom group with lower dispersal ability (i.e. periphyton) would show higher distance decay rates than a group with higher dispersal ability (i.e. plankton).
Periphyton and phytoplankton samples were gathered at sites distributed over an area of approximately 800 km length in the Negro River, Amazon basin, Brazil, South America (3°08'00"S; 59°54'30"W). Distance decay relationships were then estimated using distance-based regressions, and the coefficients of these regressions were compared among the groups with different dispersal abilities to assess our predictions. We found evidence that different tributaries and reaches of the Negro River harbor different diatom communities. As expected, the rates of distance decay in community similarity were higher for periphyton than for phytoplankton indicating the lower dispersal ability of periphytic taxa.
Our study demonstrates that the comparison of distance decay relationships among taxa with similar ecological requirements, but with different growth form and thus dispersal ability provides a sound approach to evaluate the effects of dispersal ability on beta diversity patterns. Our results are also in line with the growing body of evidence indicating that microorganisms exhibit biogeographic patterns. Finally, we underscore that clumbing all microbial taxa into one group may be a flawed approach to test whether microbes exhibit biogeographic patterns.
This study investigated and compared the diatom flora from thermo-mineral springs in Auvergne (France) and Sardinia (Italy). Samples were collected from rock/cobbles and fine sediments in 16 springs ...between January 2015 and March 2017. A total of 207 taxa (59 genera) were found. Multivariate analyses revealed significant differences in species composition and abundance among diatom assemblages both within each geographic region and between Auvergne and Sardinia (global
= 0.516;
= 0.002), suggesting the importance of local and climatic factors in species distribution. Based on abundance and common occurrence in multiple sites, some taxa can be considered more representative of springs in each region:
for Auvergne and
,
,
and
for Sardinia. pH, conductivity and HCO
were the most significant environmental variables for diatom assemblages. Our results highlight the high heterogeneity of these spring systems. Future taxonomic insights can be useful to define the identity of some abundant and dominant taxa not identified at the species level in this study. Their identification is a crucial step for a more precise ecological characterization and comparison of these peculiar spring systems.
The spatial response of epiphytic diatom communities to environmental stress was studied in a moderately saline wetland area located in the plain of Danube-Tisza Interfluve, Hungary. The area is ...characterised by World War II bomb crater ponds and can be regarded as an excellent ecological model system where the dispersion of species is slightly limited by distance. To study the effect of environmental variables on the communities, canonical correspondence analysis was applied. Salinity, pH, total suspended solids, total phosphorous and depth proved to be significant environmental drivers in this analysis. The ecological status of the ponds was assessed with Ziemann's halobity index, as the trophity-depending metric cannot be applied to these habitats (due to the naturally high phosphorus content). Ponds in "good" ecological status significantly differed from those appertaining to water quality category of "not-good" ecological status considering characteristic of natural astatic soda pans (e.g. salinity, pH, ammonium, total phosphorous concentration, nitrogen:phosphorous ratio and turbidity). The differences between epiphytic diatom communities inhabiting the ponds were detected using non-parametric multidimensional scaling. The samples formed three groups according to the types of ponds ("transparent", "transitional" and "turbid") based on the width of the macrophyte belt around them. Indicator species related to the ecological status of the ponds and diatom communities contributing to the separation of groups of ponds were identified. One of the indicator species differed from species already described. Light and scanning electron microscopy features and phylogenetic analyses based on three genes (18S and 28S rRNA genes, rbcL) proved that it was a new species of Nitzschia genus, closely related to Nitzschia frustulum and Nitzschia inconspicua. Therefore, description of a new species, Nitzschia reskoi Ács, Duleba, C.E.Wetzel & Ector is proposed. We concluded that the increasing abundance of Nitzschia reskoi was a signal of the degradation of the intermittent saline wetlands.
Background and aims - During a survey of the soil diatom flora of the sub-Antarctic islands in the southern Indian Ocean, an unknown small-celled naviculoid taxon was discovered living in small ...cracks in cliffs bordering the ocean. The taxon showed a set of morphological
features only found in the genus Microcostatus. However, the unknown taxon could not be identified using the currently available literature.
Methods - Using both light microscopical and scanning electron microscopical techniques, the morphology of the unknown
Microcostatus taxon was documented. The new taxon is described, illustrated and compared with all other similar Microcostatus taxa worldwide.
Key results - Microcostatus elisabethianus possesses a unique combination of morphological features that
excludes conspecificity with all other members of the genus. It is characterized by a lanceolate valve outline with protracted, elongate apices, a very large, porous conopeum reaching the valve margins and uniseriate striae composed of only one macroareola and mantle areolae restricted to
the valve apices. The morphological features of the genus Microcostatus are evaluated and discussed. Notes on the occurrence and ecology of the new taxon are added.
Cocconeis rouxii was decribed by J.Héribaud & J.Brun from samples collected in mountainous freshwater sources in the Auvergne region, France. Despite being mentioned in earlier publications and ...classical European floristic books, this species has never been fully explained. Its morphology is poorly known, as it has confusing and sparse citations in the literature, despite being abundant in several samples from the Massif Central. Some inconclusive attempts to investigate the original gatherings during the 1980s, and the exclusion of the taxon in major floristic works, led to the almost complete abandonment of the name. We here detail with light and scanning electron microscopy one population found in the source Bernadette, located near its type locality. The species seems to be quite common in several regions of France with metamorphic geological properties (i.e. crystalline rocks).
Background and aims - Two unknown benthic diatom species belonging to the genus Achnanthidium Kütz., and found in French and Nepalese freshwater habitats, were investigated. Both species are here ...described as new and compared with the original material of Achnanthes
minutissima var. macrocephala Hust. ≡ Achnanthidium macrocephalum (Hust.) Round & Bukht. from Indonesia.
Methods - The morphology of three small and capitate Achnanthidium species was investigated using light microscopy (LM) and
scanning electron microscopy (SEM).
Key results - Achnanthidium coxianum sp. nov. (from the Himalaya) belongs to the group of species with hooked terminal raphe endings, while Achnanthidium peetersianum sp. nov. (from France) has variable terminal raphe
endings which are usually slightly bent. Achnanthidium macrocephalum is a much rarer species and illustrations concerning its identity in the literature do not conform to the type studied here.
Conclusions - The three species are similar in LM but clearly distinct
in SEM. The shape of the areolae and terminal raphe endings separate the species. Achnanthidium macrocephalum has often been misidentified in studies from many areas of the world. It is similar to the new species in valve outline and in its small dimensions.
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