Diatom Species Diversity Research Articles

Diversity and Abundance of Epiphytic Diatoms on Seagrass Leaves (Enhalus acoroides) in Poncan Gadang Island Sibolga City, North Sumatra

The seagrass ecosystem is one of the marine ecosystems that has an important role, namely as a source of life for organisms in the sea. Diatoms are microalgae widely distributed throughout the aquatic environment and are even found in plants, including seagrass leaves. Diatoms greatly influence life in the waters because they play an essential role as a food source for various marine organisms and play a role in the transfer of carbon, nitrogen, and phosphate. This research was conducted in February 2023 on Poncan Gadang Island, Sibolga City, North Sumatra. The study aims to determine the density, relative abundance, abundance, and diversity of epiphytic diatom species on seagrass (Enhalus acoroides) leaves in Poncan Gadang Island. The method used is the survey method, using three stations to take samples. The determination of 3 stations is based on the density of the seagrass beds ecosystem. Sampling of diatoms was carried out by brushing the surface of seagrass leaves about 5x2 cm on the front and back of the leaves. The samples obtained were then analyzed in the laboratory. There were 12 types of diatoms found, consisting of Cocconeis sp., Rhizosolenia sp., Biddulphia sp., Amphipluera sp., Thalassiotrix sp., Nitzchia sp., Synedra sp., Melosira sp., Pleurogosigma sp., Skeletonema sp., Licmiphora sp., and Thalassionema sp. the average value of epiphytic diatom abundance in seagrass leaves ranged from 2160.85 – 4649.94 ind/cm². The epiphytic diatom diversity (H') values ranged from 2.53 to 2.72

Moss-associated diatoms from Malaysian montane cloud forest with a description of two new species

Although tropical montane cloud forests (TMCFs) occupy less than half of a percent of the Earth’s land surface, they are the most species-rich and species-dense ecosystems worldwide. Despite numerous studies on various organisms in this environment, diatoms remain a group that is practically unknown. Our work focused on samples of terrestrial bryophytes collected from various substrata at a single site in the Malaysian cloud forest. Despite originating from only one site, the samples contained a high diversity of diatom species and represented a wide range in pH (3.6–6.3). In our study, 62 diatom taxa were observed (8–24 per sample), of which 19 could not be identified with certainty, and were referred to established taxa of similar morphology (as cf. or aff.). Among these however, two species are described as new on the basis of their unique valve morphology: Geissleria bryophila sp. nov. and Eunotia brinchangiana sp. nov.

Identification of diatoms from different rivers in Chhattisgarh

Diatoms are unique microalgae found in almost all water bodies. They are the only single-celled organisms with a siliceous cell wall or frustules and are ubiquitous in water bodies. Their presence and diversity make them valuable in forensic investigations, particularly in cases of drowning. Diatoms can serve as trace evidence by linking suspects to crime scene. The diversity of diatom species varies across different areas influenced by environmental factors and seasonal variations. Extensive research has been conducted on diatoms in various states of India, but the diversity of diatoms was not studied in the major rivers of the Chhattisgarh region. In this study, we aimed to address this gap by conducting a taxonomic analysis of diatoms and adding them to a new database. Samples were collected from different rivers in Chhattisgarh resulting in the identification of 34 diatom species. This study contributes to understanding diatom diversity in the region and enhances the forensic potential of diatoms in future investigations.

Diatoms. A viable tool for quantifying surface water pollution

The current work focused on the water quality of the Bega and Timis rivers measured by two methods. One of them is the method by which the water was analyzed from a physical-chemical point of view, and the other aimed at quantifying the degree of water pollution by biological methods. In this sense, diatoms were used. In the study, samples of water and diatoms were taken using specific techniques from the Bega and Timis rivers, starting from near the area of their formation until near the border with Serbia. Four sampling points were chosen on the Timis River plus one sampling point on the Surgani River, which is a tributary of the Timis, and six sampling points on the Bega River. The points were chosen specifically, being located downstream of the major sources of pollution. In order to locate the points, information was collected from the studies carried out as part of an extensive monitoring that spanned several years. The abundance and diversity of diatom species were used to calculate the Biological Diatom Index (BDI) and the Saprobity Index (SI). These two indices provide valuable information about organic or heavy metal pollution of water bodies.

Salinity-Dependent Species Richness of Bacillariophyta in Hypersaline Environments

Hypersaline habitats are among the most polyextreme habitats on Earth, but they contain a rather large diatom species diversity. A review of the diatom species’ richness was made on three scales: 1. a separate lake in Crimea; 2. all hypersaline waters in Crimea; and 3. the world totality as a whole. In total, 51 species were found in Lake Chersonesskoye during sampling from 2004 to 2018. In ten Crimean hypersaline lakes, 91 species were noted in total. All diatom species found in the studied hypersaline water bodies of the world belong to 458 species, which is 2.7% of the total number of known species of Bacillariophyta. In all three scales, the similarity of the species’ composition between water bodies as well as studied periods was not found. Most of all the identified species were found only in one of the studied water bodies, and only 59 species (13% of the total list) were found in more than three water bodies. An analysis showed that no more than 40% of the species that exist in hypersaline waters have been identified on a global scale. The diatom shell nanostructure from hypersaline waters has specific peculiarities that may be valuable for some technological applications. The knowledge of diatoms in hypersaline waters not only has pure scientific importance but also covers some needs of bio- and nanotechnologies.

Diatom evidence for late Holocene environmental change in a permafrost peatland in the northern Greater Khingan Mountains, Northeast China

High-latitude permafrost peatlands are sensitive to global warming, and understanding their paleohydrological evolution is critical for assessing future hydrological and environmental changes. This paper presents a diatom record from a peat deposit covering the past 3300 years to reconstruct the moisture and acidity conditions in the Tuqiang permafrost peatland in the northern Greater Khingan Mountains of northeast China. Our findings are integrated with previously published records of plant macrofossils, palynology, and geochemistry from the same profile. From 3300 to 2800 cal yr BP, planktonic and benthic diatoms were equally abundant, indicating relatively high moisture conditions, while the low abundance of acidophilous diatoms reflects relatively high pH during this interval. Pollen data show dominance by sedges with input from the surrounding Pinus forest, while LOI data and lithology suggest that the site was a non-peat accumulating wetland. During the period 2800–1100 cal yr BP, the dominance of planktonic diatoms indicates a wetter local environment, concurrent with the dominance of peat-forming sedges (Eriophorum), indicating the development of a peatland. Between 1100 and 500 cal yr BP, a short-lived increase in acidophilous diatoms (Eunotia) marks a decrease in pH. Since 500 cal yr BP, the dominance of benthic diatoms reflects a drier environment, while a vegetation shift from an Eriophorum-dominated rich fen to a Sphagnum- and Ericaceae-dominated poor fen. An increase in Eunotia diatoms prior to the Sphagnum peak may indicate that diatoms are more sensitive to local acidified habitats than moss. Peatland development in the northern Greater Khingan Mountains was likely induced by the onset of a cooler and wetter climate starting at approximately 2800 cal yr BP, a scenario supported by regional paleoclimate records. Since 700 cal yr BP, the peatland has been affected by both anthropogenic activities and climatic changes, as a drying climate and intensified human activities around the study area reduced diatom species diversity and peat accumulation. Under the background of future global warming and enhanced human activities, the decreasing species diversity and carbon accumulation rate of peatlands in high-latitude permafrost regions need more attention.

Diatom Assemblages and Their Interrelationships between Different Water Quality Parameters in Gorveshwari River of Bangladesh

The main objectives of this study were to assess the diversity of diatom species and explain how physico-chemical factors and trophic levels interact with diatom assemblages. An assemblage of diatom communities in a riverine environment was assessed through forthright sampling for a period of 7 months from September 2019 to March 2020. Three sampling sites from the upstream, midstream and downstream parts of a river located in the northwest part of Bangladesh were selected for water quality analysis. A variety of multivariate data analyses were done to evaluate the environmental and biological data as well as to observe their interrelationships. A total of 7 genera of Diatom namely Nitzschia, Diatoma, Melosira, Synedra, Tabillaria, Navicula, and Fragillaria were recorded. Nitzschia was the most dominant genus compared to the other genus at downstream with an abundance of 1.92×103 cells/L while Tabillaria sp. was noted as a rare one with the lowest abundance of 0.37×103 cells/L at the midstream site. The interrelationship analysis clarified that water temperature positively altered the distribution of Melosira, Navicula, and Tabillaria while its abundance was less dependent on dissolved oxygen and pH. The results from a 2-dimensional Nonmetric Multidimensional Scaling (NMS) revealed the abundance of diatom at downstream was statistically higher than upstream and midstream. Hence, the study concluded that the diatom composition was very sensitive to the physico-chemical parameters according to water direction and could be used as a bio-indicator to assess the surface water quality. HIGHLIGHTS Diatom species composition was very sensitive to water quality indicators Diatom assemblages can be used as a bio-indicator to assess the water quality Diatom concentration was statistically higher at downstream compared to upstream and midstream GRAPHICAL ABSTRACT

Diversity of diatoms in biological soil crusts of the northern region of the Urals on the basis of morphological and metagenomic approaches

We studied the diversity of diatoms in biological soil crusts which formed on cryogenic soils in the mountain tundras of the Polar, Subpolar and Northern Urals. We used the permanent Elyashev's medium and DNA metabarcoding for diatom species diversity. In total, 58 diatoms taxa (rank below the genus) identified based on morphological and metagenomic data analysis. The most diverse genera are Pinnularia, Eunotia, and Nitzschia.

Ecological distribution of modern diatom in peatlands in the northern Greater Khingan Mountains and its environmental implications.

Relationships between diatom assemblages and environmental variables in peatlands of the northern Greater Khingan Mountains are helpful for understanding the indicative significance of diatoms to environment changes, and potentially provide a reference for environmental monitoring and paleoenvironment reconstruction in the edge of monsoon region. In this study, we analyzed modern diatom assemblages and their relationships with environment factors in 30 surface samples from shrubby-herbaceous and herbaceous peatlands based on ordination analysis. Benthic and epiphytic Pennatae diatoms are mainly ecological types, whereas planktonic Centricae diatoms are relatively fewer. The most diverse genera are Pinnularia and Eunotia. Eunotia paludosa and Achnanthidium minutissimum dominated in shrubby-herbaceous peatlands, while Navicula minima and Fragilaria capucina dominated in herbaceous peatlands. The diatom community structures are different in different vegetation types and the diatom species diversity in herbaceous peatlands is higher than that in shrubby-herbaceous peatlands. CODMn and pH are the most important environmental factors affecting diatom species composition and diversity. Eunotia bilunaris, Eunotia mucophila, and Eunotia paludosa can be used as indicators of acidic water environments. Caloneis silicula, Fragilaria capucina, Hantzschia amphioxys, and Navicula radiosa can be applied to indicate the weak alkaline conditions. Eunotia bilunaris and Eunotia paludosa can indicate low conductivity, while Sellaphora pupula indicates the medium-high conductivity. Fragilaria capucina and Navicula radiosa can indicate oligotrophic habitats.

Аутекологічні особливості та характеристика еконіш діатомових водоростей (Bacillariophyta Karsten) пониззя р. Ворскла

The species diversity of diatoms in the lower reaches of the Vorskla River, which belong to the territory of the Regional Landscape Park "Nizhnovorsklyansky", is analyzed. The material for the work comes from algological samples collected in the lower reaches of the Vorskla River in the spring and autumn periods. A section of about 7 km of the lower reaches of the Voskla River, a section of the Vorskla Bay and the Kamyanke Reservoir, floodland water bodies, swamps and wetlands were surveyed. Collection of algae samples was carried out from different ecology groups. Samples were processed in live and fixed state using the method of direct microscopy. A total of 288 taxa were identified. An analysis of the autecology of 133 representatives of diatoms in relation to the main environmental factors (temperature, acidity, salinity) has been carried out. The obtained digital data were processed by generally accepted methods of statistical research. Based on Ellenberg scales, phytoindication methods are used to characterize the ecological niche and to clarify the nature of the interaction between the main ecofactors of the noted representatives of <i>Bacillariophyta</i>. Based on the analysis of the values of the range of variation of ecofactors, the range of the optimum zone for the studied species was established, and according to the tolerance amplitude (BP) they were divided into 4 classes (stenotopic, hemistenotopic, hemieurytopic and eurytopic). It is established that the ecological niche of the studied taxa is characterized by a shift towards a neutral environment in terms of acidity (6.5 ≤ рН ≥ 7.5) and salinity 0–2‰. Groups of stenotopic species to the temperature, salinity and acidity of the environment, which can be sensitive indicators of changes in these environmental factors, have been identified. According to the results of hierarchical clustering, the affinity of the studied indicator species was established. Clusters that unite a complex of species characterized by similar values of ecological amplitude to the leading environmental factors were formed.

Environmental changes clarified by pollen and diatom proxy records in the sedimentary archive of the northwestern Japan Sea during last 21.0 kyr

High-temporal resolution pollen and diatom records from the northwestern Japan Sea document environmental changes over the last 21.0 kyr. Vegetation and climate changes were evaluated using the forest-steppe (SFI) and the pollen temperature (Tp) indices. The highest SFI occurred between ca. 21.0 ka and 16.6 ka and indicates the presence of a relatively dry climate and large areas of forest-steppe in the region. Boreal forests covered the mountain slopes. The broad-leaved trees survived in refugia located in lower mountain belts. Beginning ca. 16.6 ka, SFI decreases, while Tp increases, especially between ca. 11.0 ka and 5.7 ka. However, variations in these indices indicate fluctuating climates during the deglaciation. Significant vegetation changes occurred in the Holocene. Mixed deciduous forests with a predominance of Quercus became widely present beginning ca. 9.8 ka. The area of forest-steppe was reduced occurring only in local habitats. Pinus became one of the most common taxa in the forest ca. 5.3 ka. The geographic features of the coring area have determined in the past the persistence throughout the record of cold-water diatom flora. Cold-water diatoms have dominated in both cool and warm intervals; however, a small increase in the percentage and species diversity of warm-water diatoms was noted for warming. Low sea level during the Last Glacial Maximum (LGM) and early Holocene changed the general patterns in the sea circulation and in the vectors of the longshore currents, which transported the waters formed in the shallow areas of the northeastern and northern parts of the Japan Sea. A slight increase in sublittoral benthic diatoms indicates a lowered sea level during the LGM. The increase in sublittoral planktonic diatoms reflects a gradual rise in sea level during the Bølling–Allerød (BA) and Younger Dryas (YD). A greater component of oceanic diatom species at Holocene indicates the inflow of Pacific waters across both the Tsushima and Tsugaru straits. This study of pollen and diatom records demonstrates a clear response to climatic fluctuations and sea level changes in the Japan Sea during the Late Pleistocene and Holocene.

Distribution of Diatoms in the Navigable Sections of Beijing-Hangzhou Grand Canal.

To establish a diatom database by analyzing the quatity, species distribution and differences of diatom in water samples of the whole navigable sections of the Beijing-Hangzhou Grand Canal, to provide a reference for the inference of the drowning site. Water samples were collected at 22 sites in the navigable sections of the Beijing-Hangzhou Grand Canal (Jining section to Yangzhou Section), and the diatoms at each site were qualitatively and quantitatively analyzed by using graphite digestion-scanning electron microscopy. Sampling site T (Laohuaijiang River Line, Gaoyou City, Yangzhou City, Jiangsu Province) had the highest number of diatoms, while sampling site O (Siyang County, Suqian City, Jiangsu Province) had the lowest number of diatoms, with a large gap of 68 times. At sampling site Q (Jiangpu District, Huaian city, Jiangsu Province), there were 19 species of diatoms. The sampling site O had the least diatoms, with 7 species. There were no significant differences in species evenness and species diversity at each sampling site (P>0.05). Some sampling sites have characterized diatoms, such as Caloneis at station A (Taibai Lake, Weishan County, Shandong Province), Rhoicosphenia at station B (Nanyang Town, Weishan County, Shandong Province), Amphora at station I (Taierzhuang District, Zaozhuang City, Shandong Province) and Epithemia at station J (Pizhou 310 national highway, Xuzhou City, Jiangsu Province). The species richness of diatoms gradually increased from north to south. Diatom species richness and species diversity might be higher in areas with complex environments and large population flow. Climate type has a certain influence on the distribution of diatoms.

Environmental Heterogeneity Determines Diatom Colonisation on Artificial Substrata: Implications for Biomonitoring in Coastal Marine Waters

Benthic diatoms form an important component of the microphytobenthos and have long been utilised as suitable bioindicators in aquatic systems. However, knowledge on benthic diatom community succession on hard substrata (biofilm) remains understudied in austral marine coastal systems. In this study, we investigated benthic diatom colonisation on artificial substrates (Plexiglass) over a period of 5 weeks at two locations with different physical environments along the warm temperate coast of South Africa. Results revealed relatively similar physico-chemical conditions but highly contrasting diatom community development were observed between the two sites. While there were some shared taxa, site-specific dynamics resulted in significantly different diatom species diversity and richness, facilitated by common (e.g., Nitzschia ventricosa and Cocconeis scutellum) and a large percentage of rarely observed species such as Cocconeis testudo and Lyrella lyra. A total of 134 species belonging to 44 genera were observed during the study. The overall diatom composition differed spatio-temporally during the experimental period, with the fluctuating species occurrences and abundances highlighting the rapid microalgal species turnover within days, under natural conditions. Environmental variables were shown to have varying influences as drivers of the diatom community descriptors. Multivariate modelling confirmed that study site and the interaction between site and sampling occasion were important predictors of diatom abundances, and the overall observed community composition. The current results suggest that benthic diatoms on artificial substrata could be incorporated as suitable indicators of change along the coastline subject to further investigations, taking into account site-specific differences driven by habitat complexity and environmental variability. The experimental method proved to be efficient and can be implemented to study the response of benthic diatoms to localised nutrient enrichment around the coastline.

Assessing the efficiency of low-cost cleaning methods for diatoms from intertidal sediment samples

This study aims to compare the effectiveness of several low-cost reagents in obtaining high-quality diatom slides for microphytobenthos research. We evaluated the performance of eight reagents in sediment samples of beach intertidal zones. For each of the tested reagents, different pre-treatment conditions (pre-washed; non-washed) and three different temperatures (room temperature at 26 °C, 60 °C, and 100 °C) were also evaluated. For each treatment (combinations between reagents, temperatures, and pre-treatment conditions), we counted diatoms cells that met the criteria necessary for taxonomic identification (Whole/Half frustules or valves without cell material) in 30 randomly chosen fields of view in definitive preparations made from the treated samples. We also compared the treatments regarding species richness and diversity observed in the definitive preparations. The reagents influenced more the conditions of diatoms cells than the temperature and pre-treatment. H2O2, HNO3, NaClO were the methods that had the best performance in relation to the number of identifiable items. The six treatments with H2O2 presented similar amounts of identifiable items, regardless of pre-treatment and temperature. HNO3 presented a higher number of identifiable items in non-washed and pre-washed treatments at 60 °C and non-washed at 100 °C. NaClO had its best performance the following treatments: non-washed at room temperature and non-washed and pre-washed at 60 °C. H2O2 and HNO3 also showed better results for diatom species richness and diversity, followed by NaClO. The use of H2O2 was more robust since it obtained good results regardless of temperature and pre-treatments and should be preferred. HNO3 and NaClO should be used only with the appropriate temperatures, and pre-washing should be avoided.

Environmental Concentrations of Sulfonamides Can Alter Bacterial Structure and Induce Diatom Deformities in Freshwater Biofilm Communities.

Since the early 1920s, the intensive use of antibiotics has led to the contamination of the aquatic environment through diffuse sources and wastewater effluents. The antibiotics commonly found in surface waters include sulfamethoxazole (SMX) and sulfamethazine (SMZ), which belong to the class of sulfonamides, the oldest antibiotic class still in use. These antibiotics have been detected in all European surface waters with median concentrations of around 50 ng L–1 and peak concentrations of up to 4–6 μg L–1. Sulfonamides are known to inhibit bacterial growth by altering microbial production of folic acid, but sub-lethal doses may trigger antimicrobial resistance, with unknown consequences for exposed microbial communities. We investigated the effects of two environmentally relevant concentrations (500 and 5,000 ng L–1) of SMZ and SMX on microbial activity and structure of periphytic biofilms in stream mesocosms for 28 days. Measurement of sulfonamides in the mesocosms revealed contamination levels of about half the nominal concentrations. Exposure to sulfonamides led to slight, transitory effects on heterotrophic functions, but persistent effects were observed on the bacterial structure. After 4 weeks of exposure, sulfonamides also altered the autotrophs in periphyton and particularly the diversity, viability and cell integrity of the diatom community. The higher concentration of SMX tested decreased both diversity (Shannon index) and evenness of the diatom community. Exposure to SMZ reduced diatom species richness and diversity. The mortality of diatoms in biofilms exposed to sulfonamides was twice that in non-exposed biofilms. SMZ also induced an increase in diatom teratologies from 1.1% in non-exposed biofilms up to 3% in biofilms exposed to SMZ. To our knowledge, this is the first report on the teratological effects of sulfonamides on diatoms within periphyton. The increase of both diatom growth rate and mortality suggests a high renewal of diatoms under sulfonamide exposure. In conclusion, our study shows that sulfonamides can alter microbial community structures and diversity at concentrations currently present in the environment, with unknown consequences for the ecosystem. The experimental set-up presented here emphasizes the interest of using natural communities to increase the ecological realism of ecotoxicological studies and to detect potential toxic effects on non-target species.

Insight into nearshore diatom assemblages from an island ecosystem: Composition, spatial variation, and benthic contribution to the pelagic community (Bird Island, South Africa)

Marine epilithic diatom abundance and species richness are highly variable along the South African coastline. To determine the variability in spatial diversity and benthic–pelagic​ exchanges, we conducted a baseline study of the Bird Island ecosystem in Algoa Bay. Diatom samples were collected from the rocky substrate and the adjacent water column in conjunction with physico-chemical variables at five localities around the island. Species belonging to Achnanthes, Cocconeis, Licmophora and Navicula genera were found to be widely distributed around the island. Diatom species abundance and diversity varied around the island and a dominance of typically benthic species in the surf zone, coupled with a low abundance of truly planktonic species, was evident. The low number of planktonic diatoms in the water column and their absence in benthic samples in this study suggests an intertidal system driven largely by benthic diatoms. Elevated dissolved inorganic nitrogen (DIN), indicative of the guano influence from resident seabirds, along with temperature and turbidity, influenced the observed diatom composition and distribution. This study reveals an interplay between benthic and planktonic diatoms in the nearshore environment providing some insight into their contribution to the intertidal and subtidal food web. It further provides important information for future comparisons of benthic diatoms on Bird Island in light of their ecological indicator properties under global environmental change scenarios for this region.

Effects of an hypersaline effluent from an abandoned potash mine on freshwater biofilm and diatom communities

Potash abandoned mines cause severe environmental damage to their bordering environment, with significant impacts on freshwater ecosystems mostly through uncontrolled discharge of hypersaline effluents. This study aimed to evaluate the ecological impact caused by a hypersaline effluent from an abandoned potash mine (Menteroda, Germany) on freshwater biofilms and, specifically, on diatom communities. Biofilm from a pristine stream was exposed under controlled conditions in microcosms to a mining effluent (ME), and its structural (algal biomass, community composition, diatom metrics) and functional (photosynthetic activity, nutrient uptake) responses were evaluated over time and compared with unexposed biofilms used as control. Biofilm exposed to ME showed drastic functional responses after one day of exposure, with a significant decrease in photosynthetic efficiency and nutrient uptake, that were recovered over time. Biofilm exposed to ME showed a progressive increase in diatom metrics (abundance, density and growth rate) over time, compared to the control. However, a significant decrease in diatom species diversity, richness and cell size was also observed in biofilm exposed to ME. This study revealed that the ME affected the biofilm causing short-term functional responses, which were recovered simultaneously with a drastic diatom community structure shift.

Morphology and occurrence of two epibiotic marine gomphonemoid diatoms in China

Gomphonemoid diatoms exist in both freshwater and marine environment, but marine gomphonemoid taxa are morphologically different from Gomphonema. Although the marine gomphonemoid group has been expanded with many new taxa in recent years, only the genus Gomphonemopsis was described from Chinese seas. The present study reports on species diversity and classification of marine epiphytic diatoms on seaweeds and epizoic diatoms on animals collected from several stations in the South Yellow Sea and East China Sea. Two marine gomphonemoid diatoms, Pseudogomphonema kamtschaticum and Gomphoseptatum aestuarii, were observed and identified by light and electron microscopy, representing the first record in China of these two species and genera. Our observations matched the basic features of original species descriptions. Except that we observed in P. kamtschaticum showed various areolae shapes (e. g., slit-like, "I"-like, "C"-like and circular), and ornamented macroareolae with small warts were observed in G. aestuarii. Both P. kamtschaticum and G. aestuarii were epiphytic on the seaweed Sargassum hor neri, and P. kamtschaticum was found as epizoic on an ophiuroid species of the Ophiura genus. Therefore, we have increased the records of and knowledge about marine gomphonemoid diatoms to three genera with four species in China, including Gomphonemopsis.

Assessing the impact of land use and liming on stream quality, diatom assemblages and juvenile salmon in Wales, United Kingdom

Many freshwaters in base-poor upland areas of Britain continue to be affected by acidification as a result of deposition of air pollutants, and agricultural and forestry practices. The effects of land use and annual liming on stream chemistry, diatoms and salmon populations were investigated over eight years in the upper catchment of the River Wye, Wales, United Kingdom. Variations in water chemistry, diatom species composition and diversity, and in the index Diatom Acidification Metric (DAM) were compared between different types of land cover and flow conditions, and before and after applications of lime. Two methods of liming, hydrological source (catchment) liming and sand liming (in-stream liming), were used to reduce stream acidity. Electrofishing was carried out for several years before and after liming to monitor the recovery of salmon populations.Prior to liming, water chemistry differed between stream sub-catchments with differing land use. ANC, Ca concentrations and pH were lower, and Al concentrations were higher, in areas with conifers and acid grassland than in areas with improved grassland and broadleaf woodland. After liming pH increased, but the effects differed between sites and were dependent upon pH levels before any liming began, flow conditions, and the method of liming. An increase in pH during high flows was evident at many sites where acid episodes had occurred prior to liming.Diatom species richness and diversity were low, many sites supporting only 10–15 species. Correlations of richness and diversity with water chemistry were not significant but there was a tendency for low pH sites to support very few species. Species richness was highest in areas adjoining broadleaf woodland and improved grassland, and lowest in areas adjoining conifer plantations.Diatom species composition changed after liming and depended on the type of dominant land cover in the catchment areas and the method of liming. Species tolerant of low pH, in particular Eunotia exigua, became less abundant and were replaced by acid-sensitive species, predominantly Achnanthidium minutissimum. DAM index values and ecological quality ratios (EQR), which were both lower in conifer and acid grassland areas before liming than elsewhere, improved after liming and in many areas the ecological status class of limed streams became good or high. The change to diatom assemblages with predominantly acid-sensitive species after liming correlated with increasing numbers of juvenile salmon and their expansion upstream to sites that had lacked fish prior to liming.

Effects of aquatic vegetation cover (Schoenoplectus decipiens) on microalgal biomass and assemblage structure in temporary wetlands of a semi-arid region (Eastern Cape Karoo, South Africa)

Temporary depression wetlands are often overlooked from a conservation and research perspective, despite recent evidence suggesting that their cumulative contribution to biodiversity at the landscape level is substantial. Here, we present observations aimed at understanding the significance of macrophyte cover in relation to the lower trophic levels, more particularly microalgae, within these highly dynamic wetlands. Thirteen such wetlands were sampled during October 2015, December 2015 and March 2016 in the Eastern Cape Karoo region of South Africa, to test the hypotheses that densely vegetated wetlands will have lower microalgal biomass and smaller algal size classes than sparsely vegetated wetlands. PERMANOVA results indicated that neither planktonic nor benthic microalgal biomass differed significantly between macrophyte cover categories (sparse, moderate and extensive cover), although there was a strong difference between the planktonic and benthic biotopes themselves. Planktonic and benthic microalgal assemblages were dominated by cryptophytes and chrysophytes (flagellates) throughout the study, with smaller nanoplankton being more abundant in wetlands with moderate or extensive macrophyte cover and larger microplankton dominating sparsely vegetated sites. Median benthic diatom species richness and diversity were higher under sparse macrophyte cover, but these differences were not significant, and no convincing evidence was found for an effect of macrophyte cover on microalgal biomass and assemblage composition in these temporary wetlands. Using distance-based Redundancy Analysis, dissolved inorganic nitrogen appeared to be the only environmental predictor for which a significant relationship with microalgal assemblage composition was reported. This study adds to the evidence from other assemblages (e.g. invertebrates) suggesting that the generalist nature of species occupying these systems allows them to adapt to the ever-changing conditions typical of ephemeral environments.