Diatom Diversity Research Articles

Fatty acids diversity of diatoms

The study of the fatty acids content of total lipids in the biomass of centric and pennate diatoms made it possible to analyse the biotechnological potential of 62 microalgae strains isolated from diverse ecosystems. It has been established that the fatty acid profiles of diatoms are primarily rich in long-chain fatty acids (up to 97.9% of the total), to a lesser extent – in medium-chain and very-long-chain fatty acids. In the studied strains, the content of omega-3 fatty acids reached 38.7%. Considering the obtained results, it was concluded that among the studied diatoms, there are strains valuable for biotechnology.

Denticula, Hantzschia and Tryblionella (Bacillariaceae, Bacillariophyta) from northwestern Ceará freshwaters

Abstract Diatoms constitute a representative portion of the algal community of freshwater aquatic environments, but their studies are centered mostly in the south and southern regions of Brazil, making the microalgae biodiversity of water bodies in the semiarid practically unknown. In the state of Ceará, the few records of the Bacillariaceae are centered in the southern region of the state and are generally not identified at specific level. Denticula, Hantzschia, and Tryblionella are worldwide distributed diatom genera that belong to the family Bacillariaceae. The group is characterized by raphe located on a channel, internally supported by silica extensions, the fibulae. This is a taxonomic study on the genera Denticula, Hantzschia, and Tryblionella found in water bodies in northwestern Ceará state. Planktonic and periphytic samples were collected in four hydrographic basins, which are influenced by the semiarid climate, located in northwestern Ceará, northeastern Brazil. Fourteen infrageneric taxa were identified, described, and illustrated, all being pioneer citations for Ceará. The present study highlighted the underestimated diversity of diatoms in the semiarid region of Ceará and the need to cover undersampled or never explored regions to significantly contribute to the knowledge of the diatom flora and its distribution in Brazilian aquatic environments.

Diatoms of large flat reservoirs of the Volga River basin: ecological and cenotic aspects

Based on long-term studies of phytoplankton of the Volga River basin reservoirs, from the 1950s to the present, the main patterns of spatio-temporal changes in the ecological-floristic and coenotic parameters of diatoms are presented. A correlation was established between the species richness of diatoms and the morphometry of reservoirs. It is shown that under conditions of increasing trophy of reservoirs and climate change against the background of an increase in the diversity of diatoms due to alien invaders, their biomass began to decrease. The spring peak of diatoms became lower than the summer peak of cyanobacteria. The long-term variation of diatoms biomass was significantly associated with changes in hydrometeorological parameters. Between dominant species an increase of limnophilic species abundance tolerant to a high content of organic matter and salts was observed. The influence of zoning on the distribution of ecological and floristic groups of diatoms along the longitudinal profile of reservoirs has been established.

Diatoms diversity of Mahanandi, Kurnool district, Andhra Pradesh, India

The present study was undertaken to explore the diatom wealth of water bodies from the holy shrine Mahanandi and a water tank nearby Nandyal adjacent to Mahanandi, Kurnool district of Andhra Pradesh, India located between 15.4709° N, 78.6255° E. the algal samples were collected in different seasons. The preliminary taxonomic evaluation yielded 35 diatom taxa belonging to 17 genera viz. Bacillaria (1), Cocconeis (1), Craticula (2), Cymbella (5), Diploneis (1), Epithmia (1), Eunotia (1), Fragilaria (2), Gomphonema (6), Gyrosigma (2), Mastogloia (1), Nitzschia (1), Pinnularia (1), Rhopalodia (1), Surirella (2), Tryblionella (2) and Ulnaria (2).

Taxonomy and ecology of Achnanthidium (Bacillariophyta, Achnanthidiaceae) from southeastern Brazil with the description of six new species

The present study aims to expand the knowledge on Achnanthidium species occurring in tropical areas of southern Brazil. For this purpose, 345 samples from 179 sampling sites distributed throughout the state of São Paulo were analyzed for ‘monoraphid’ diatom diversity. This paper focuses on samples with a high abundance of Achnanthidium species. The permanent slides and stubs were observed using light and scanning electron microscopy. Morphometric analysis was performed to discriminate between similar species through the Elliptical Fourier Descriptors analysis. For this, valve outlines from Brazilian species were compared to those from type material available from the literature. The ecological optimum and tolerance was calculated for taxa that presented more than 10 % of occurrence per habitat. In total, 12 Achnanthidium species were observed. Six are described as new: Achnanthidium acutum sp. nov., A. brasiliense sp. nov., A. parvicapitatum sp. nov., A. paulistanum sp. nov., A. ritae sp. nov. and A. vandevijveri sp. nov. The morphometric analysis supported the differentiation between some taxa. Nine species, with occurrences of at least 10 % per habitat, had their ecological optimum and tolerance calculated. In general, these species prefer slightly acidic to neutral pH, medium electrolyte cond. and mesotrophic water conditions.

Diversity and distribution of lacustrine diatoms along the Trans‐Mexican Volcanic Belt

Abstract The Trans‐Mexican Volcanic Belt is recognised as a highly biodiverse zone and we present a study of diatom diversity and species distributions in its lakes. We aimed to identify diatom taxa with the highest regional occupancy, explore diversity at a regional level, identify the main variables associated with species distributions, and present weighted average optima for variables that could provide a valuable reference for future palaeoenvironmental research. We used the relative abundances of diatoms in surficial lake sediments to estimate different diversity metrics and alpha, beta and gamma diversities. Groups of lakes with similar diatom assemblages were identified by means of cluster analysis whereas canonical correspondence analysis (CCA) was used to evaluate the association between diatom composition and climatic, morphometric, hydrochemical and trophic status related variables. Weighted average optima were estimated for salinity and temperature. From a total of 184 diatom taxa, three were endemic to one or two lakes and eight had the largest regional occupancy, two of which were associated with high salinity environments (Stephanocyclus meneghinianus, Nitzschia frustulum) and the rest with freshwater conditions (Aulacoseira ambigua, A. granulata, A. granulata var. angustissima, Discostella stelligera, Fragilaria crotonensis, Achnanthidium minutissimum). Surprisingly, endemic taxa as well as those with high regional occupancy were mostly planktic or epipelic motile forms, with high dispersal potential. Our results showed 13 clusters of lakes with similar diatom assemblages, in close agreement with beta diversity which predicted the presence of 12 communities. There was high species turnover (βSIM = 0.97) and CCA showed not only that the main environmental variable defining these groups was salinity, but also that temperature, precipitation, depth, and soluble reactive phosphorus were meaningful variables. There was no evidence of an altitude–diversity pattern. This study emphasises the strong influence that climatic variables have on species distribution when relatively broad geographical areas, with large climatic gradients are analysed.

Exploring diatom diversity through cultures - a case study from the Bow River, Canada

Diatom cultures can help answer taxonomic, biogeographic and ecological questions on a local and global scale. Unialgal cultures are derived from a single cell and provide abundant material for morphological and molecular analyses. The link between the historic morphological species concept and the molecular data is becoming increasingly important with the use of eDNA metabarcoding. Additionally, cultures provide insights into the life cycle of diatoms and thereby complement taxonomy and species ecology. In this study, we present an approach to extract benthic diatoms from an environmental sample to generate unialgal cultures. We explored diatom diversity in preserved assemblages and by culturing as many different taxa as possible from benthic freshwater samples taken on the same day from the Bow River in Calgary, Canada. With both methods we found a total of 221 different benthic diatom taxa, of which 182 were identified in the preserved diatom assemblages. Interestingly, an additional 39 taxa only appeared in the cultures. In total 129 strains were cultivated representing 71 different taxa. This study includes pictures of living cells demonstrating the additional merits of unialgal cultures, as they provide information on plastid details, auxospores and endosymbionts. Both, the identification of the diatom assemblages and the generation and identification of strains provide the foundation for additional water quality assessment tools, taxonomic insights and molecular references libraries.

The effects of environmental, climatic and spatial factors on diatom diversity in Sphagnum peatlands in central and northeastern China

The effects of environmental, climatic and spatial factors on diatom diversity in Sphagnum peatlands in central and northeastern China

Diatom Diversity and Ecology of the Sebou Watershed (Morocco)

Diatom Diversity and Ecology of the Sebou Watershed (Morocco)

The Epilithic Diatom Community as a Bioindicator of water quality Brangkal Subwatershed in the Mojokerto Area

Diatoms are widely used as bioindicators of water quality because of their short life cycle and sensitivity to changes of environmental conditions in waters. One type of diatom that is used as a bioindicator is an epilithic diatom. Epilithic diatoms are one of the diatom microalgae communities attached to rock, so they are difficult to be carried away by currents. This study aimed to determine the type, composition, abundance, diversity, and dominance of epilithic diatoms found in the waters of the Brangkal subwatershed, and to determine the quality of water in the Brangkal subwatershed based on the epilithic diatom tropic index. Epilithic diatom samples were taken from 4 stations in the Brangkal subwatershed, Mojokerto Regency at the beginning of the dry season (July-August). The analysis carried out includes abundance, diversity index, dominance index, and Diatom Trophic Index (TDI). Based on the results of the study, 17 genera of epilithic diatoms were found, with the highest abundance of epilithic diatoms, including Navicula, Cocconeis, Nitszchia, and Gomphonema. The diversity index of all stations was in the medium category, with a value between 1.206 to 1.882. The lowest dominance index at station 1 was 0.167 and the highest was at station 4 with 0.373. In addition, the observed water quality is based on the Diatom Trophic Index (TDI), stations 1 to 3 are in a good category, and stations 4 are in a bad category.

Diversity and ecology of freshwater diatoms as pollution indicators from the freshwater Ponds of Kanyakumari district, Tamilnadu

The present study explores the diversity and ecology of freshwater diatom in the Kanyakumari district, Tamilnadu. Six freshwater ponds namely, Thuckalay pond, Eraniel pond, Pampanvilai pond, Villukuri pond, Erachakulam and Thottiyodu pond were selected from Kalkulam Taluk in Kanyakumari district. A total of 27 taxa of 17 genera were recorded from these freshwater ponds. Among the freshwater diatom species, Gomphonema montanum was found to be the predominant species in all stations except St- 2. The correlation analysis between diatom density and physico-chemical parameters revealed a significant positive correlation of diatoms (Nitzschia sp., Navicula sp., Cyclotella meneghiniana and Stauroneis sp) with nitrate, phosphate and lead at sampling statins St- 2 and 6. CCA analysis revealed that the concentration of calcium, chloride, pH, alkalinity, silica, and ammonia were found to favor the occurrence of dominant species such as Cymbella turgiduta, Gomphonema sp., Rhopalodia sp., in St-3 and St-4. Among all ponds, certain parameters like total alkalinity, nitrite, phosphate, sodium, cobalt, potassium perhaps reflect the influence of agricultural waste, sewage waste, or anthropogenic activities. The statistical indices in coherence with the dominance of pollution indicator species such as Nitzschia palea, Melosira granulata and Cyclotella meneghiniana revealed that the stations St-2, 4 and 6 were heavily polluted, whereas St- 1, 3 and 5 were less polluted.

Interlinking diatom frustule diversity from the abyss of the central Arabian Sea to surface processes: physical forcing and oxygen minimum zone.

This study analyzed the diversity and abundance of diatom frustules including the ancillary parameters using the core top sediments from five locations (21, 19, 15, 13, and 11°N) along the central Arabian Sea (64°E), an area profoundly influenced by atmospheric forcing (monsoons) and oxygen minimum zone (OMZ) with high spatial variability. Significantly higher organic carbon (0.97 ± 0.05%) and diatom frustules (5.92 ± 0.57 × 104 valves g-1) were noticed in the north (21, 19, 15°N) where natural nutrient enrichment via open-ocean upwelling, winter convection, and lateral advection support large diatom-dominated phytoplankton blooms and intense OMZ. Conversely, the south (13, 11°N) depicted significantly lower organic carbon (0.74 ± 0.08%) as well as frustules (4.02 ± 0.87 × 104 valves g-1) as this area mostly remains nutrient-poor dominated by small-medium-sized phytoplankton. The north was dominated by large-sized diatoms like Coscinodiscus that could escape grazing and sink consequently due to higher ballasting. Furthermore, the presence of the intense OMZ in the north might reduce grazing pressure (low zooplankton stock) and mineralization speed facilitating higher phytodetritus transport. Relatively smaller chain-forming centric (Thalassiosira) and pennate diatoms (Pseudo-nitzschia, Fragilaria, Nitzschia, etc.) were found throughout the transect with higher abundance in the south. The euphotic diatom diversity from the existing literature was compared with the frustule diversity from the sediments suggesting not all diatoms make their way to the abyss. Such distinct spatial north-south variability in diatom frustule size as well as abundance could be attributed to cell size, grazing, and water column mineralization rates related to OMZ.

Whole-genome scanning reveals environmental selection mechanisms that shape diversity in populations of the epipelagic diatom Chaetoceros.

Diatoms form a diverse and abundant group of photosynthetic protists that are essential players in marine ecosystems. However, the microevolutionary structure of their populations remains poorly understood, particularly in polar regions. Exploring how closely related diatoms adapt to different environments is essential given their short generation times, which may allow rapid adaptations, and their prevalence in marine regions dramatically impacted by climate change, such as the Arctic and Southern Oceans. Here, we address genetic diversity patterns in Chaetoceros, the most abundant diatom genus and one of the most diverse, using 11 metagenome-assembled genomes (MAGs) reconstructed from Tara Oceans metagenomes. Genome-resolved metagenomics on these MAGs confirmed a prevalent distribution of Chaetoceros in the Arctic Ocean with lower dispersal in the Pacific and Southern Oceans as well as in the Mediterranean Sea. Single-nucleotide variants identified within the different MAG populations allowed us to draw a landscape of Chaetoceros genetic diversity and revealed an elevated genetic structure in some Arctic Ocean populations. Gene flow patterns of closely related Chaetoceros populations seemed to correlate with distinct abiotic factors rather than with geographic distance. We found clear positive selection of genes involved in nutrient availability responses, in particular for iron (e.g., ISIP2a, flavodoxin), silicate, and phosphate (e.g., polyamine synthase), that were further supported by analysis of Chaetoceros transcriptomes. Altogether, these results highlight the importance of environmental selection in shaping diatom diversity patterns and provide new insights into their metapopulation genomics through the integration of metagenomic and environmental data.

Recommendations for the preservation of environmental samples in diatom metabarcoding studies

Implementation of DNA metabarcoding for diatoms for environmental monitoring is now moving from a research to an operational phase, requiring rigorous guidelines and standards. In particular, the first steps of the diatom metabarcoding process, which consist of sampling and storage, have been addressed in various ways in scientific and pilot studies and now need to be rationalised. The objective of this study was to compare three currently applied preservation protocols through different storage durations (ranging from one day to one year) for phytobenthos and phytoplankton samples intended for diatom DNA metabarcoding analysis. The experimental design used samples from four freshwater and two marine sites of diverse ecological characteristics. The impact of the sample preservation and storage duration was assessed through diatom metabarcoding endpoints: DNA quality and quantity, diversity and richness, diatom assemblage composition and ecological index values (for freshwater samples). The yield and quality of extracted DNA only decreased for freshwater phytobenthos samples preserved with ethanol. Diatom diversity was not affected and their taxonomic composition predominantly reflected the site origin. Only rare taxa (< 100 reads) differed among preservation methods and storage durations. For biomonitoring purposes, freshwater ecological index values were not affected by the preservation method and storage duration tested (including ethanol preservation), all treatments returning the same ecological status for a site. This study contributes to consolidating diatom metabarcoding. Thus, accompanied by operational standards, the method will be ready to be confidently deployed and prescribed in future regulatory monitoring.

Halamphora minima (Catenulaceae, Bacillariophyta), new brackish diatom species from the mudflat in Hampyeong Bay, Korea

The diversity of benthic diatoms living in the tidal flats is thought to be very high but has been somewhat marginalized from our main concern. We propose a new species, Halamphora minima sp. nov. isolated as monoclonal cultures from a tidal mudflat based on light and scanning electron microscopy and molecular analysis. This species is the smallest known species of the genus Halamphora to date. Other main characteristics that distinguish this species are the biseriate separated by strongly developed costa for the majority of the valve face, and density of dorsal striae. Phylogenetic analysis of the chloroplast ribulose bisphosphate carboxylase large chain gene showed that H. minima seems to be related to H. foramina, H. sydowii and H. tumida, but the phylogenetic location of H. minima was not clear due to the low bootstrap.

Benthic Diatom Diversity and Eutrophication in Temporarily Closed Estuaries

Benthic Diatom Diversity and Eutrophication in Temporarily Closed Estuaries

Effect of Seawater and Surface-Sediment Variables on Epipelic Diatom Diversity and Abundance in the Coastal Area of Negeri Sembilan, Malaysia

Benthic diatoms are important components of marine shallow-water habitats that may affect primary production, stabilize sediment, and produce extracellular polymeric substances. Benthic diatoms are useful for estimating the trophic status of marine ecosystems. In this study, we investigated the diversity and abundance of benthic diatoms to integrate these data with the physicochemical characteristics of shallow coastal areas in Negeri Sembilan. A total of 39 species of epipelic diatoms were extracted by removing organic matter from sediments that were dominated by pennate diatoms. Results showed that Diploneis crabro, Eunotogramma laevis, Actinoptychus sp., and Cocconeisplacentula were the important species in the area. The abundance varied between 1.85 × 103 and 3.43 × 103 cells/g, and the diversity index fluctuated between 2.13 and 2.58. The abundance had significant positive correlations with seawater surface temperature (SST) but had negative correlations with pH and NH3. The diversity on the other end was positively correlated with SST but negatively correlated with total suspended solids and SiO2. Principal component analysis (PCA) demonstrated that the abundance of D. crabro, E. laevis, and Actinoptychus sp. can be attributed to high levels of NO2−, NH3, and total dissolved solids. PCA also showed positive correlations of C. placentula with NO3−and SiO2 but negative ones with PO43− and pH. The epipelic diatom community showed high diversity with high variations throughout the study area.

Role of Altitude in Formation of Diatom Diversity of High Mountain Protected Glacier Lakes in the Kaçkar Mountains National Park, Rize, Turkey

The benthic diatom assemblages of the glacier Avusor Great Lake and Koçdüzü Great Lake were investigated in August 2019. A total of 71 diatom species belonging to 34 genera were determined in the samples, 49 species from Avusor Great Lake and 37 from Koçdüzü Great Lake. Only 15 diatom species were common to both lakes. Total floristic similarity between the neighbouring lakes was only 21.12%. Genera with the highest number of species were Eunotia (8), Gomphonema (6), Pinnularia (6), Navicula (5) and Aulacoseira (4). The diatom flora of both lakes was formed by cosmopolitan species with a large influence from species in alpine and subalpine area. A comparison of the diatom assemblages of the investigated lakes showed differences in both relative abundance and species present in the individual lakes. Bioindicative analysis showed that the water of Koçdüzü Great Lake is more alkaline and less saturated with organic substances than Avusor Great Lake. In both lakes, the communities are composed of species adapted to living in the benthos of fresh waters of moderate temperature well enriched with oxygen. In both lakes, the water quality was Class 2 with a saprobity index of S = 1.08 in Avusor Great Lake and 0.97 in Koçdüzü Great Lake, but their communities were composed of species with both oligotrophic and mesotrophic status. Statistical comparison of the species composition of studied lakes with other high mountain lakes and the lakes in northern Turkey revealed the role of altitude as the main factor in the formation of diatom floras.

A 17-year time-series of diatom populations‘ flux and composition in the Mauritanian coastal upwelling

Understanding seasonal and multiyear variability of primary producers’ populations in the Mauritanian coastal upwelling system along the northwestern African margin may help to predict future impact of climate change (e.g., nutrient availability, productivity, and phyto- and zooplankton dynamics). For this, continuous, long time-series are required. A major challenge in obtaining these time-series is the logistics associated with the uninterrupted, in-situ sampling over several years. Sediment traps represent a reliable alternative. In this study, we assess the variations of the diatom community in samples almost continuously collected between June 2003 and March 2020 with 17 sediment traps deployed at site CBeu (=Cape Blanc eutrophic), located at c. 20°N-18°45’W, offshore Mauritania in the Canary Current Eastern Boundary Upwelling Ecosystems (CC-EBUE). In addition to describing the multiyear dynamics of the total diatom flux and major shifts in the species-specific composition of the populations, our study addresses questions such as (i) how constant is the intrannual pattern of populations’ occurrence, (ii) what the amplitude of annual changes is, and (iii) how populations’ shifts relate to physical setting dynamics. Matching the occurrence of most intense seasonal upwelling, highest diatom flux maxima mainly occur in spring and summer between 2003 and 2020. The diverse diatom community (e.g., benthic, coastal upwelling, coastal planktonic, and open-ocean diatoms) closely follows the annual cycle of atmospheric and hydrologic conditions. Benthic diatoms dominate during spring and summer (e.g., upwelling season), while open-ocean diatoms contribute the most in fall and winter when the upper water column stratifies. As no persistent –either decreasing or increasing trend of diatom productivity over the 17 sampled years, our results are at odds with Bakun’s hypothesis of upwelling intensification. Anchoring temporal changes of diatoms in a wider environmental frame allows for insights into the complex dynamics of the Mauritanian upwelling ecosystem and the populations’ response to climate forcing. This helps in establishing the scientific basis for modeling future states of the CC-EBUE and/or comparable environments.

Distribution of marine benthic diatoms on the coasts of the sea of Marmara and their responses to environmental variables

The Sea of Marmara, located in northwest Turkey, comprises challenging environmental conditions and is an important bridge between the Black Sea and the Aegean Sea. In this study, we assessed the trophic situation of the coasts of the Sea of Marmara using the benthic diatom composition and their relation to the environmental variables in the spring and autumn of 2019 and 2020. A total of 120 samples were collected and 452 species were observed; Navicula Bory and Nitzschia Hassal were represented with the highest numbers of taxa. Analysis of Similarity (ANOSIM) revealed that diatom communities differed significantly between the spring-autumn periods and years. Canonical Correspondence Analysis (CCA) showed that diatoms grouped under water, temperature, salinity, dissolved oxygen, and TIN influence. TRIX observations revealed a highly mesotrophic-eutrophic status along the coasts. Our study contributes to the knowledge of diatom diversity, distribution and community changes in spring and autumn on the coasts Sea of Marmara. Our findings suggest that marine benthic diatoms could be used as eutrophication indicators in the coastal waters for long-term monitoring with the support of environmental parameters.