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The study represents new bioanalytical characterization of mainly organic components of the poorly investigated extracellular polymeric substances (EPS) of the enigmatic diatom Didymosphenia geminata, an invasive, worldwide expanding species endangering diverse ecosystems. This microalga attaches its siliceous cells to rocky substrates using fibrous stalks, which are made of an EPS-based matrix stabilized by crystalline calcite. The EPS were analyzed using selected methods, including microscopic, spectroscopic, and spectrometric techniques. We identified diverse types of biomolecules. The presence of lipids, condensed aromatics, and heteroaromatic compounds in the EPS has been confirmed using high-resolution mass spectrometry (HR-MS). Additionally, both sulfur-containing functionalities and carboxylic acids were determined too using infrared (IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. For the first time, lignin compounds have been detected as one of the components of the EPS of the D. geminata diatom, using HR-MS and fluorescence microscopy (FM) in combination with specific staining techniques. By increasing the understanding of the chemistry and structural features of the stalks, we aim to develop potential applications and methods for removing these stalks from affected regions in the future, or, alternatively, to use them as a large-scale source of sustainable biocomposite material. [ABSTRACT FROM AUTHOR]

As climate change accelerates, low summer stream flows are becoming increasingly common in the Colorado Rocky Mountains, USA. The diatom Didymosphenia geminata (Lyngb.) M. Schmidt, typically observed under low-flow and low-P conditions, produces nuisance growth—persistent and extensive proliferation, covering the bottoms of streams in thick algal mats. Nuisance blooms of this diatom physically alter the benthic environment and thereby affect freshwater invertebrates directly and indirectly by altering stream food webs. We compared 9 y of survey data (2013–2021) of D. geminata proliferation with the composition of the macroinvertebrate communities at 8 stream sites near the Rocky Mountain Biological Laboratory in western Colorado. We counted and identified samples of benthic macroinvertebrates and used a glass-bottomed viewing box to estimate D. geminata biovolume at 2 scales: macrohabitat conditions (site level: 2013–2021) and microhabitat conditions (sample level: 2020–2021). At both scales, increases in D. geminata proliferation were associated with shifts in macroinvertebrate community composition that could be explained by altered abundances of focal taxa, specifically declines in Heptageniidae (Ephemeroptera) and increases in Chironomidae (Diptera). Abundances of Baetidae (Ephemeroptera) were unaffected by increased D. geminata biovolume. These changes indicate degradation of stream habitat for some sensitive groups of macroinvertebrates, which may affect higher trophic levels, such as trout, in these mountain stream ecosystems. As climate change trends toward lower summer streamflow, understanding the effects of proliferation of this ecosystem engineer is key to predicting the impact of climate change on stream food webs. [ABSTRACT FROM AUTHOR]

Background and aims: In 2013, blooms similar to those produced by Didymosphenia geminata (Lyngbye) M. Schmidt around the world, were detected in the Grande River basin, Tierra del Fuego province, and in 2014 in de las Vueltas River in Santa Cruz province. The aim of this paper is to analyze the valve morphology and morphometry of these materials to establish if they correspond to D. geminata or to other species of the genus that is producing the massive growth in southern Patagonia. M&M: Samples were collected at Grande River in 2013 and 2015 and, in de las Vueltas River in 2015 and 2016. Samples were analyzed with light and electron microscopy. For morphometric analyses 100 specimens from each sample were measured and statistical analyses were carried out using the R statistical package. Results: The studied populations have the same fine morphology described for other populations collected in Patagonia. Nevertheless, in some sampling sites from Santa Cruz province, we found a morphotype with a markedly smaller size, subcapitated poles, little marked constrictions of the poles, a broad central area (relative to cell size) and 1 to 3 stigmata, that was never reported in South America. Conclusions: The studied populations correspond to D. geminata ssp. geminata Metzeltin & Lange-Bertalot. From a morphological point of view the smaller morphotype present in Santa Cruz belongs to the same subspecies but can be easily misidentified during the routine monitoring programs carried out with light microscope due its size and valve outline.

Background and aims: In 2013, blooms similar to those produced by Didymosphenia geminata (Lyngbye) M. Schmidt around the world, were detected in the Grande River basin, Tierra del Fuego province, and in 2014 in de las Vueltas River in Santa Cruz province. The aim of this paper is to analyze the valve morphology and morphometry of these materials to establish if they correspond to D. geminata or to other species of the genus that is producing the massive growth in southern Patagonia. M&M: Samples were collected at Grande River in 2013 and 2015 and, in de las Vueltas River in 2015 and 2016. Samples were analyzed with light and electron microscopy. For morphometric analyses 100 specimens from each sample were measured and statistical analyses were carried out using the R statistical package. Results: The studied populations have the same fine morphology described for other populations collected in Patagonia. Nevertheless, in some sampling sites from Santa Cruz province, we found a morphotype with a markedly smaller size, subcapitated poles, little marked constrictions of the poles, a broad central area (relative to cell size) and 1 to 3 stigmata, that was never reported in South America. Conclusions: The studied populations correspond to D. geminata ssp. geminata Metzeltin & Lange-Bertalot. From a morphological point of view the smaller morphotype present in Santa Cruz belongs to the same subspecies but can be easily misidentified during the routine monitoring programs carried out with light microscope due its size and valve outline. [ABSTRACT FROM AUTHOR]

Copyright of Iranian Journal of Forest & Range Protection Research is the property of Research Institute of Forests & Rangelands and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Didymosphenia geminata is a stalk-forming freshwater diatom which was historically found primarily in oligotrophic lakes and streams, but has recently become a nuisance species in many lotic systems worldwide. In the last 5–8 years, D. geminata has become established in Boulder Creek and South Boulder Creek, two regulated montane streams in the Front Range of the Colorado Rocky Mountains. Factors that may influence the growth of D. geminata were monitored during the summer of 2006. D. geminata abundance decreased in Boulder Creek after an unusual flood event caused by 3 days of sustained rainfall in the headwaters of the watershed. However, within a week, coverage had been restored to pre-flood levels. Variations in D. geminata abundance among sites were found to be negatively correlated with total dissolved phosphorus concentrations and bed movement, as measured by Shields stress. In contrast, D. geminata abundance was not significantly correlated with temperature, conductivity, pH, total suspended solids, or dissolved inorganic nitrogen. Our results suggest that bed movement may be a dominant scouring mechanism that acts to control the growth and distribution of D. geminata. The potential role of total dissolved phosphorus and bed movement in decreasing D. geminata coverage adds to the limited base of knowledge regarding controls on the growth and distribution of this species, and could be investigated by researchers studying D. geminata blooms in other stream ecosystems.

Introducción y objetivos: Didymosphenia geminata, diatomea declarada “Especie Exótica Invasora” en Argentina por la Secr. Ambiente y Desarrollo Sustentable de la Nación. Esta especie coloniza rocas y puede formar grandes matas mucilaginosas que cubren el lecho de los ríos, ocasionando un considerable impacto estético y provocando serias alteraciones en los ecosistemas. En los últimos 9 años la especie ha colonizado ríos andino-patagónicos y ha aumentado considerablemente su distribución en la región. El objetivo de este trabajo es analizar la dinámica de esta especie en la Patagonia argentina mediante el uso de SIG. M&M: los datos provienen de resultados obtenidos por el grupo de trabajo en las provincias del Neuquén y del Chubut e información abierta y libre disponible en la web. Se generó una base de datos a escala regional abarcando desde Neuquén a Tierra del Fuego. Resultados: fueron incorporados a un SIG, lo que permitió generar mapas de distribución a nivel provincial y nacional. Conclusiones: los datos disponibles hasta marzo de 2018 muestran que D. geminata, ha expandido su distribución entre 2010 y 2018 desde la provincia del Chubut hacia el norte alcanzando la provincia de Neuquén y hacia el sur llegando a Tierra del Fuego.

This study addresses for the first time the chemistry and biological activity of polysaccharides isolated from Didymosphenia geminata. Fourier-transform infrared spectroscopy (FTIR) and high-performance thin-layer chromatography (HPTLC) techniques were used to characterize the crude and acidic polysaccharides of D. geminata; galactose and xylose were found to be the main monomer components. The antioxidant activity as well as the effect on the expression of IL-6 and TNF-α in RAW 264.7 murine cell lines were determined for both types of polysaccharides. The antioxidant activity of crude polysaccharides proved to be stronger than acidic polysaccharides by means of quenching experiments of ABTS·+ and Trolox equivalent antioxidant capacity (TEAC) (p < 0.05). Crude polysaccharides induced an increase in both IL-6 and TNF-α contents. Acidic polysaccharides produced a similar effect on these cytokines, but to a lesser extent. These results suggest that polysaccharides from D. geminata could be explored as natural antioxidant and immunomodulatory agents in medicine and the nutraceutical industry. This investigation suggests an opportunity to turn the invasive mats of D. geminata, which currently cause environmental problems, into a source of polysaccharides with nutraceutical application. [ABSTRACT FROM AUTHOR]

The nuisance species Didymosphenia geminata is thought to have been spread by humans across North and South America and New Zealand. This diatom is of interest for its ability to form thick benthic mats in streams, altering ecosystem properties. Little is known, however, about its historic distribution and the parameters that are associated with its growth in absence of human influence. Although it is considered to be native to Arctic regions, its status at lower latitudes is uncertain. We measured the concentration of D. geminata cells in a sediment core from Beauty Lake, WY, a record that dates back to the Late Pleistocene. From approximately 11,233–8750 years before present (ybp), a Didymosphenia maximum persisted, with peak concentrations of 3774±20 valves/mg dry sediment (9985 ybp). The period corresponded to low flux of Al, Fe, and P within the sediments, supporting the importance of low P in controlling distribution. Furthermore, we demonstrate that D. geminata arrived in Beauty Lake shortly after deglaciation of the watershed. This species arrived without the aid of human introduction, implying an inherent ability for dispersal. We also examined the sediment record of nearby Yellowstone Lake, WY for the presence of D. geminata during the same time interval, but cells were not detected. The Yellowstone caldera is composed of rhyolite, a rock rich in silica (Si) and modest amounts of P. We conclude that both watersheds were exposed to the potential colonization by D. geminata, but just as the North Island of New Zealand has not been able to support this diatom because of P concentrations exceeding a threshold, the Yellowstone watershed is not able to support it either. [ABSTRACT FROM AUTHOR]

The Puelo and Petrohué rivers were surveyed between April 2016 and February 2017 to assess the presence and seasonal abundance of Didymosphenia geminata in the wild aquatic systems of these two important rivers in southern Chile. Didymo was reported in the Puelo River in 2012, while it was declared absent from the Petrohué River before this study commenced in the fall of 2016. Results showed that cells of D. geminata were recorded in both rivers, in the Phytobenthos as well as in the water column. However, the classical mucilage which characterizes this plague was only recorded in one of the sampled rivers (Puelo). The mucilage was not recorded in any of the sections sampled in the Petrohué River, which was attributed to the high concentration of phosphorous present in the system. The concentration of phosphorous recorded throughout the study in the Puelo River was low. However, differences in the recorded presence or absence of D. geminata between sampling sites on the Petrohué River was mainly attributable to the availability of incident sunlight. This study records for the first time the presence of D. geminata in the Petrohué River. [ABSTRACT FROM AUTHOR]

Copyright of Boletín de la Sociedad Argentina de Botánica is the property of Sociedad Argentina de Botanica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: Since 2006, the Restigouche River watershed, eastern Canada, has been affected by nuisance growths of the mat‐forming diatom, Didymosphenia geminata. In 2010, in view of the potential impacts of this alga on the local Atlantic salmon fishery, we created a volunteer monitoring network to assess D. geminata mat severity within the watershed. Over the course of 6 monitoring summers, more than 1,200 observations of D. geminata mat severity were reported in 20 subwatersheds of the Restigouche River basin. Observations were mapped to illustrate the yearly severity of D. geminata mats throughout the watershed. Metrics were then extracted from this dataset to assess the spatial and temporal variability of mat severity. At the reach scale, D. geminata occurrence was predominantly found in riffles compared to any other river habitat type. At the watershed scale, a two‐sample Kolmogorov–Smirnov test highlighted a significant effect of maximum spring discharge on mean annual D. geminata mat severity, indicating that when maximum spring discharge is high, severity of D. geminata mats in the following months is significantly lower. Additionally, maximum spring discharge explained 71% of the variability in annual mat severity. This study contributes to the understanding of mat severity dynamics and illustrates the value of volunteer monitoring networks for studying complex ecosystem dynamics. [ABSTRACT FROM AUTHOR]

The complete mitogenome of the stalk-forming diatom Didymosphenia geminata collected from Mineral County, WV, USA was sequenced on the Ion Torrent PGM and Proton sequencers. The D. geminata mitogenome is 37,765 bp and encodes 35 protein coding genes, 25 tRNAs, and both large and small subunit ribosomal RNA genes. The nad11 gene is split into two domains as observed in Phaeodactylum tricornutum, and D. geminata also lacks the large repeat region found in the P. tricornutum mitogenome. Gene order and content within the D. geminata mitogenome is similar to the diatom Berkeleya fennica.

Defining the geographic origins of free-living aquatic microorganisms can be problematic because many such organisms have ubiquitous distributions, and proving absence from a region is practically impossible. Geographic origins become important if microorganisms have invasive characteristics. The freshwater diatom Didymosphenia geminata is a potentially ubiquitous microorganism for which the recent global expansion of nuisance proliferations has been attributed to environmental change. The changes may include declines in dissolved reactive phosphorus (DRP) to low levels (e.g., <2 mg/m3) and increases in dissolved inorganic nitrogen (DIN) to >10 mg/m3 because both these nutrient conditions are associated with nuisance proliferations of D. geminata. Proliferations of D. geminata have been observed in South Island, New Zealand, since 2004. We aimed to address the ubiquity hypothesis for D. geminata in New Zealand using historical river water nutrient data and new molecular analyses. We used 15 years of data at 77 river sites to assess whether trends in DRP or DIN prior to the spread of D. geminata were consistent with a transition from a rare, undetected, species to a nuisance species. We used new sequences of chloroplast regions to examine the genetic similarity of D. geminata populations from New Zealand and six overseas locations. We found no evidence for declines in DRP concentrations since 1989 that could explain the spread of proliferations since 2004. At some affected sites, lowest DRP occurred before 2004. Trends in DIN also did not indicate enhanced suitability for D. geminata. Lack of diversity in the chloroplast intergenic regions of New Zealand populations and populations from western North America is consistent with recent dispersal to New Zealand. Our analyses did not support the proposal that D. geminata was historically present in New Zealand rivers. These results provide further evidence countering proposals of general ubiquity in freshwater diatoms and indicate that, as assumed in 2004, D. geminata is a recent arrival in New Zealand. [ABSTRACT FROM AUTHOR]

The presence of three Gomphoneis species from Chubut Province in Argentina is documented with light and scanning electron microscopy. Two of the taxa, G. patagoniana and G. eriense var. variabilis, are part of the Herculeana subgroup of Gomphoneis. Gomphoneis patagoniana is a newly discovered species and G. eriense var. variabilis is reported from Argentina for the first time. These two species have evident axial plates, differentiated apical pore fields (APFs), a stigmal opening that is round externally and slit-like internally, and areolae that are mostly tri-radiate in shape. The third species, G. frenguellii, is also newly discovered and described. Presence of four isolated stigmoids, undifferentiated APFs and lack of an axial plate indicates G. frenguellii is a member of the Elegans subgroup of the genus. Presence of these newly described species, and the previously unreported taxon, may also be associated with the invasive species Didymosphenia geminata. Given there is no long history of reports of Gomphoneis in the country and, in the case of G. eriense var. variabilis, its previously known distribution, it is possible that the origin of this Gomphoneis taxon is from western North America. [ABSTRACT FROM AUTHOR]

The application of biomass derived from the nuisance fresh-water diatom species Didymosphenia geminata toward the adsorption and removal of heavy-metal ions from water is reported. The cell-free polysaccharide-based stalks of these diatoms are used as adsorbents to remove harmful metal ions: Pb(II), Ni(II), and Cd(II). Detailed analyses of the adsorption kinetics using both pseudo-first-order model and pseudo-second-order models are performed. The results show a strong correspondence to a pseudo-second-order kinetic model. The Langmuir and Freundlich models are used to describe the adsorption isotherms. The correlation coefficients ( r2) of the Langmuir model are equal to 0.994 (Pb2+), 0.995 (Cd2+), and 0.995 (Ni2+), and the r2 for the Freundlich model are equal to 0.991 (Pb2+), 0.991 (Cd2+), and 0.987 (Ni2+). The experimental data for all metal ions strongly support the Langmuir isotherm model. It is shown that stalks of D. geminata exhibit exceptional sorption capacity ( qm) for Pb(II) ions of 175.48 mg g−1. Additionally, a high sorption capacity for Cd(II) (145.86 mg g−1), and Ni(II) (130.27 mg g−1) is observed. The thermodynamic aspects of the adsorption process of selected metal ions are also discussed. Preliminary tests investigating applications of D. geminata stalks for sewage purification from galvanic industry and battery and accumulator production were performed. These comprehensive studies show that D. geminata can be robustly applied for the removal of harmful metal ions from wastewater. [ABSTRACT FROM AUTHOR]

Nuisance proliferations of the invasive benthic alga Didymosphenia geminata (Bacillariophyceae) are of major concern in many temperate regions due to their severe effects on river habitats and communities. Proliferations result from the production of basal stalk material, stimulated by phosphorus limited, high light conditions. An unresolved disconnect occurs where nitrogen and phosphorus are observed to stimulate D. geminata cell division, but, within a realised niche, disappearance or establishment failure occurs where dissolved reactive phosphorus ( DRP) concentrations occur above c. 2-5 μg/L., Our aims were to examine the mechanisms behind D. geminata bloom stimulation and absence/disappearance. We examined: (1a) whether prolonged nitrogen (Na NO3 - N) and phosphorus (NaH2 PO4 - P) addition would stimulate cell division, and (1b) whether subsequent nutrient limitation stimulated stalk production; (2) whether the mechanism behind D. geminata absence at >5 μg/L DRP, occurred either as (2a) a deleterious consequence of prolonged N + P exposure or (2b) was associated with increasing densities of co-occurring algae; and (3) whether water velocity stimulated D. geminata cell division thereby influencing outcomes., Didymosphenia geminata cell densities, frequencies of dividing cells, stalk production and densities of competing algae were examined in flow-through channel mesocosms over 8 weeks. Treatments included: Waitaki River water (control); N + P amended water; and two treatments in which nutrient amendments were changed over time, these being N + P to N, and N + P to Waitaki water., Continued N + P amendment was positively correlated with D. geminata cell densities. N-replete P-limited channels, however, accrued greatest densities of D. geminata cells, stalk fragments and dividing cells. Results suggest that within a realised niche short term N + P amendment followed by chronic P limitation could either hasten and/or worsen bloom development., Water velocity influenced community successional trajectories and D. geminata fitness outcomes. Across all nutrient and velocity treatments, a decline in D. geminata cell densities and cell division was correlated with increasing densities of competing algae., Phosphorus limitation stimulating stalk production appears to be an example of physiological stress resulting in increased fitness (known as eustress) and D. geminata dominance. This contrasts with a general pattern of competitive exclusion as nutrient concentrations increase. [ABSTRACT FROM AUTHOR]

Didymosphenia geminata has received a great deal of attention in the last 25 years, and considerable effort has gone into determining the origin, ecological impact, and economic consequences of its invasive behavior. While environmental conditions are a controlling influence in distribution, the extreme success of the species may be tied to its basic biology and life history. Little is known, however, about population dynamics, size restoration and reproduction of D. geminata. The objective of this study was to determine the temporal patterns in cell size frequency, size restoration strategy, and synchronization of life cycles between populations in close proximity. We implemented FlowCam technology to measure the length of more than 100,000 D. geminata cells from two sites in South Boulder Creek, Colorado over 1 year. We applied finite mixture modeling to uncover temporal patterns in size distribution. Our results show that collections of D. geminata exhibited a complex, multimodal size distribution, almost always containing four overlapping age cohorts. We failed to observe direct visual evidence of the sexual phase. Multiple abrupt and directional shifts in size distribution, however, were documented providing conclusive evidence of cell size restoration. Lastly, nodules in close proximity were asynchronous with respect to size frequency profiles and size diminution, highlighting the relevance of spatial heterogeneity in in situ diatom size dynamics. This study is the first to document the complexity of diatom cell size distribution in a lotic system, size restoration in D. geminata, and the variability in rates of size reduction at microhabitat spatial scales. [ABSTRACT FROM AUTHOR]

Microscopic versus qPCR (quantitative polymerase chain reaction) analyses were compared for the detection of Didymosphenia geminata in biofilms and water filtrates from seven Gaspésie rivers (Canada). For the qPCR approach, two DNA extraction kits (QIAamp DNA Micro Kit, Qiagen and PowerSoil DNA Isolation Kit, Mo Bio Laboratories) and two pairs of primers were considered. The pair of primers D602F/D753Rext did not amplify D. geminata DNA whereas the pair of primers D602F/ D753R was specific for D. geminata. Presence-absence diagnosis based on qPCR and microscopic analyses were consistent: D. geminata was detected in six of the seven rivers, both in the biofilm and filtrate samples. However, technical replications were needed at certain sites to observe the presence of D. geminata cells by microscopy. This underscores the necessity of replicate analyses, which is cost-effective to achieve when using qPCR due to the capacity to process tens of samples in a single PCR run in the context of a large scale assessment. [ABSTRACT FROM AUTHOR]

Didymosphenia geminata is a benthic bloom-forming diatom that is invasive in many temperate, oligotrophic freshwater ecosystems. D. geminata blooms are unusual, resulting from prolific basal stalk production stimulated by phosphorus limitation. The adaptive value of stalk production and bloom development is disputed. We examined blooms in relation to stalk biomass, biovolume and phosphatase activity. An austral summer survey of 15 sites within the Waitaki River of New Zealand compared reference communities (no detectable D. geminata), with those impacted by high and low D. geminata biomass. Sites were compared for differences in phosphatase location and activity using chromogenic substrates, community composition using morphological identifications, and overlying water and pore-water chemistry. Experimental microcosms subjected live proliferations to varied phosphate concentrations, and phosphatase rates and location were examined. Survey results identified phosphatase activity increased with D. geminata biomass, with lowest rates in reference communities. Pools of labile nutrients were detected in D. geminata mats, and in vitro hydrolysis rates were rapid in replete phosphoester conditions (~0.2 mmol l h cm at 16°C), with activity concentrated on stalks. Our results suggest D. geminata bloom development is an adaptation to maximise supply of phosphate under chronic phosphorus limitation. [ABSTRACT FROM AUTHOR]

The stalked diatom Didymosphenia geminata forms proliferations of stalk-dominated mats in rivers. Over its range in New Zealand, mats rarely occur where average dissolved reactive phosphorus (DRP) concentrations exceed ~2 mg m−3, but do occur in rivers with dissolved inorganic nitrogen ( DIN) concentrations up to ~250 mg m−3. Previous studies indicated that low DRP concentrations limit D. geminata cell division and stimulate stalk production and mat development, even at very low ambient DIN concentrations (~10 mg m−3)., We ran two nutrient-enrichment experiments in instream channels in an oligotrophic river with a persistent D. geminata proliferation to (i) test the hypothesis that elevated DRP concentrations reduce or prevent mat development by reducing stalk production; and (ii) investigate the effect of DIN enrichment on D. geminata growth and mat development., In Experiment 1, treatments comprised low-level enrichment with DRP (to 1.6 mg m−3, from superphosphate fertiliser), DIN (to 13.5 mg m−3, from ammonium sulphate), and both DRP and DIN. Compared to unenriched controls, DIN and DRP enrichment enhanced D. geminata cell densities, biomass, cell division (frequency of dividing cells), stalk biovolume and percentage cover of mats, indicating both N- and P limitation for all growth metrics. In the DRP-enriched treatments, biomass accrual may have been stimulated rather than reduced as predicted because DRP concentrations did not exceed the putative 2 mg m−3 threshold., In Experiment 2, we expanded the range of DRP enrichment using additions of orthophosphate as well as superphosphate, and added DIN to all treatments. Higher DRP concentrations (up to 4 mg m−3) initially enhanced D. geminata growth. By the end of the experiment, D. geminata-dominated biomass in the orthophosphate treatments was lower than in the superphosphate or DIN-only treatments., Outflows from the experimental channels caused slight nutrient enrichment in the river downstream. During Experiment 1, this DRP and DIN enrichment had no detectable effect on D. geminata standing crop on the riverbed. During Experiment 2, D. geminata standing crop downstream of the experiment declined relative to the unenriched area upstream., The specific mechanism linking P enrichment to D. geminata biomass decline is unclear. In the experimental channels there was evidence for a predominance of cell division over stalk production in orthophosphate treatments, as hypothesised. In the river, we observed higher rates of sloughing in the river downstream of the experiment than upstream. There was no evidence that competition from other algal taxa reduced D. geminata standing crop., The results supported the hypothesis that DRP enrichment at concentrations over ~2 mg m−3 leads to reduced D. geminata biomass and % cover in this river. However, biomass reduction occurred only when DRP was added as orthophosphate, not as superphosphate., N limitation of D. geminata growth in river water with ambient mean DIN concentrations below ~6 mg m−3 suggests that D. geminata proliferations may be stimulated by increases in DIN concentration in rivers where both DIN and DRP are naturally low. The threshold for N limitation was ~10 mg m−3. [ABSTRACT FROM AUTHOR]

The nuisance diatom Didymosphenia geminata has recently increased in abundance worldwide and has spread through oligotrophic rivers in the South Island of New Zealand. However, it remains absent from the North Island. Its proliferation in oligotrophic environments has prompted work on phosphorus acquisition, but potential nitrogen acquisition pathways have received little attention. We partially sequenced the nifD gene, encoding a component of nitrogenase, from South Island samples containing D. geminata and compared its diversity with that of North Island sites independently ranked as high, medium and low risk for infestation. Godleyacean cyanobacteria were present in all four South Island provinces investigated, and also in three North Island sites rated medium or high risk. Most high-risk sites were dominated by Nostoc sequences, as were some infested South Island sites. Monte Carlo simulations and the weighted UniFrac metric showed that nifD diversity in low-risk North Island sites differed significantly from sites rated medium and high risk, and from infested South Island sites; however, random resampling showed that the data were insufficient to separate didymo-infested and high-risk sites from medium-risk sites. The relationships we discovered suggest that success of D. geminata in New Zealand could be mediated by indigenous nitrogen-fixing cyanobacteria. [ABSTRACT FROM AUTHOR]

Two non-native stalk-forming diatoms that were recently observed in the West Branch of the Farmington River, a tributary of the Connecticut River in Connecticut (USA), are characterized morphologically and barcode marker sequences were obtained for each of them.Cymbella janischii, the dominant stalk-forming species during the summer of 2012, previously had not been found in the northeastern USA. Samples ofC. janischiiwere examined microscopically and used to obtain four sequences of the barcode marker, the V4 region of the 18S rDNA gene. Phylogenetic analysis indicated that the four independent sequences ofC. janischiiwere distinct from, but most closely related to, published sequences ofC. janischiifrom Idaho andC. mexicanafrom Texas, USA. A second non-native stalk-producing diatom, resemblingDidymosphenia geminata, was found in November 2012 – June 2013 and first reported asDidymospheniasp. Over this period, the observed cells had a compressed morphology and were consistently small compared withD. geminata. Sequences of the V4 region, obtained from three independent direct polymerase chain reactions (PCR) of single cells isolated from the Connecticut samples, indicated a close relationship to three published sequences ofD. geminatafrom Italy, New Zealand and the USA, and toD. sibericaandD. dentatafrom Russia. Frustules of the cells used in the PCR reactions were recovered and examined using scanning electron microscopy, providing a direct link between the observed morphology and sequence data. The morphology of the novel ConnecticutDidymospheniataxon was compared with that of otherDidymospheniataxa, being most similar toD. pumila,D. laticollis,D. grunowiiand smaller cells ofD. geminata. Didymospheniasp. had a triundulate morphology with a consistent length of 40–60 µm. Given the unique morphological features of this diatom, it is proposed as a new species,Didymosphenia hulliiKhan-Bureau, sp. nov. [ABSTRACT FROM PUBLISHER]

Didymosphenia geminata is an alga of major concern in temperate regions due to ongoing spread and unprecedented bloom formation. The aim of this study was to identify physical and chemical habitat conditions which affect D. geminata at catchment to patch scales. To examine this, we conducted a field-based survey of 55 distinct waterways across the South Island of New Zealand. D. geminata was detected at 82 % of waterways, grew within the periphyton at 54 % and at 25 % occurred as blooms. We tested 137 variables at scales ranging from catchment to small patches. The primary predictors of D. geminata waterway presence were still waterbodies (positive effect P < 0.05) and nitrate + nitrite (negative effect P = 0.08). D. geminata biomass was best explained by increasing river stability ( P < 0.01) and decreasing nitrate + nitrite concentrations ( P < 0.01). A patch-scale subsidy-stress relationship was also apparent with water velocity ( P < 0.05). Our large-scale survey showed D. geminata was influenced by varied conditions at multiple spatial scales, preferentially occurring and blooming within stable, lake or dam-fed oligotrophic habitats. This work supports the finding that D. geminata blooms in response to nutrient limitation; however, results here reinforce that accrual is constrained by physical processes at multiple scales. [ABSTRACT FROM AUTHOR]

The climatic-change related increase of temperatures, are expected to alter the distribution and survival of freshwater species, ecosystem functions, and also the effects of toxicants to aquatic biota. This study has thus assessed, as a first time, the modulating effect of climate-change drivers on the mercury (Hg) toxicity of freshwater algal photosynthesis. Natural benthic algal communities (periphyton) have been exposed to Hg under present and future temperature scenarios (rise of 5 °C). The modulating effect of other factors (also altered by global change), as the quality and amount of suspended and dissolved materials in the rivers, has been also assessed, exposing algae to Hg in natural river water or a synthetic medium. The EC 50 values ranged from the 0.15–0.74 ppm for the most sensitive communities, to the 24–40 ppm for the most tolerant. The higher tolerance shown by communities exposed to higher Hg concentrations, as Jabarrella was in agreement with the Pollution Induced Community Tolerance concept. In other cases, the dominance of the invasive diatom Didymosphenia geminata explained the tolerance or sensitivity of the community to the Hg toxicity. Results shown that while increases in the suspended solids reduced Hg bioavailability, changes in the dissolved materials – such as organic carbon – may increase it and thus its toxic effects on biota. The impacts of the increase of temperatures on the toxicological behaviour of periphyton (combining both changes at species composition and physiological acclimation) would be certainly modulated by other effects at the land level (i.e., alterations in the amount and quality of dissolved and particulate substances arriving to the rivers). [ABSTRACT FROM AUTHOR]

The objective of this paper is to determine the alteration of the taxonomic composition and functional structure of macroinvertebrate community associated with a massive growth of the invasive algae Didymosphenia geminata downstream of a mountain reservoir (Pajares Reservoir, La Rioja, Northern Spain). As the massive growth of the alga disappears a few kilometres downstream of the reservoir associated with the input of nutrients from a nearby village sewage, we may compare the community composition between nine stations in three different conditions: three stations heavily affected by the presence of D. geminata, three further downstream stations without the algal massive growth but affected by river regulation and three control stations (unregulated and without the algae). Results show a significant disturbance of the composition and structure of macroinvertebrate community in sites affected by the stream flow regulation downstream of the dam compared with unregulated streams, but the alterations are more dramatic in the area where the growth of D. geminata is massive because of the total substrate occupation by the algal filaments. Scrapers and others invertebrates living on the coarse substrate are especially affected at such sites. Moreover, an important increase in the relative abundance of chironomids is associated with the algal massive growth, especially in case of Eukiefferiella devonica and Cricotopus spp., reducing the assemblage diversity and leading to the taxonomic and functional homogenization of the community. Changes in the reservoir management (such as releasing the water from surface rather than from the hypolimnion) may be useful to control the massive growth of D. geminata and thus reducing the effects of river regulation on macroinvertebrate assemblage composition. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Didymosphenia geminata has recently and rapidly greatly expanded its range and abundance, sometimes as an exotic invasive and other times as a nuisance ('native invader') within its hypothesized native range, including the northeastern United States. D. geminata mats are visually conspicuous and can grow >10 cm thick. Mats first appeared in the eastern Catskill mountains (New York) in 2009. Our objectives were to (1) document D. geminata growth in three impounded or regulated rivers in the eastern Catskill mountains from 2010 to 2012 and (2) measure the effects of D. geminata mats on macroinvertebrates. The highest D. geminata cell densities were downstream of reservoir outflows in two of three streams. D. geminata mat development peaked in the summer each year, but maximum coverage and cell density was variable among years. D. geminata cover was negatively correlated with 10 days maximum antecedent shear stress, and the year with lowest mean D. geminata cover had multiple tropical storms and floods, suggesting that low variation in flow allows for D. geminata mat proliferation. Across sites, D. geminata density was negatively correlated with nitrate concentrations. D. geminata density was negatively related to macroinvertebrate richness suggesting that D. geminata mats may negatively affect aquatic food webs. D. geminata appears to be a nuisance species with similar habitat characteristics and growth where it is both a native invader and an invasive species. [ABSTRACT FROM AUTHOR]

Periphyton blooms dominated byDidymosphenia geminatahave been reported from hundreds of rivers.D. geminatablooms consist of thick mats that cover kilometers of riverbed. Benthic habitat conditions are altered when large areas of sediment and native periphyton are replaced byD. geminatamats and these habitat changes may lead to changes in the composition and abundance of benthic invertebrates. Mensurative studies have provided circumstantial evidence of changes in invertebrate communities in response toD. geminatablooms. However, those studies may have confounded the effects ofD. geminataand other environmental variables. To identify direct effects ofD. geminataon invertebrate communities, we conducted a paired before–after, control-impact (BACIP) experiment in threeD. geminata-infested rivers. The experimental impact was the removal ofD. geminatamats from 35–50 m2areas of riverbed. We tested for effects ofD. geminataremoval on macroinvertebrate community metrics, including total density, taxon richness, and the prevalence of Ephemeroptera, Plecoptera, and Trichoptera (EPT) and trophic groups. The BACIP analysis indicated thatD. geminataremoval caused a decrease in total density at two rivers, a decrease in the density of dipterans and an increase in % EPT invertebrates at one river, and an increase in % algivorous invertebrates at another river. A multivariate analysis indicated that there was more variation in invertebrate community structure among rivers than between treatments within rivers. The limited effects ofD. geminataremoval on invertebrate communities were probably related to the composition of colonist pools and the relatively small cleared areas; cleared areas were surrounded by large areas ofD. geminata-covered habitat and the colonist pools were dominated by taxa that inhabitD. geminatamats. [ABSTRACT FROM AUTHOR]

Highlights: [•] We have developed qPCR-based methods for the detection of Didymosphenia geminata. [•] The method has high specificity, single cell sensitivity with a broad dynamic range. [•] The method has been validated on samples collected from 5 different countries. [•] The method is now being implemented for surveillance nationally and internationally. [Copyright &y& Elsevier]

Nowadays Didymosphenia geminata is one of the most frequently studied diatoms in the world, due to its massive development in most continents. In Poland, up to the 1990's only a small number of specimens were recorded, from streams in the Tatra Mountains and the Dunajec River. D. geminata was found in 2007-2008 in the middle and upper sections of the Wisłok River, while in 2009 and 2011 it was also found in the Wisłoka, Ropa, Bielcza and San. The cells belonged to one morphotype "geminata" and were characterized by high variability of size. It develops in mesotrophic, well-oxygenated, upper parts of flowing waters with rapid currents. It was most abundant below reservoirs on the San, Wisłok and Wisloka. [ABSTRACT FROM AUTHOR]

The aquatic nuisance species Didymosphenia geminata was first documented in Rapid Creek of South Dakota’s Black Hills during 2002. Since then, blooms have occurred primarily in a 39-km section of Rapid Creek while blooms were rarely observed in other Black Hills streams. In this study, we evaluated factors related to the presence and development of visible colonies of D. geminata in four streams of the Black Hills. At the watershed scale, stream gradient was negatively associated with the occurrence of D. geminata whereas stream width was positively related to D. geminata presence. At the stream scale, D. geminata coverage was inversely related to canopy coverage and iron concentration. At the local scale, shading by bridges virtually eliminated growth of D. geminata colonies under bridges. At all three scales, proxy measures of light such as stream width, canopy coverage, and bridge shading revealed that light availability was an important factor influencing the presence and coverage of D. geminata colonies. In general, streams that had relatively wide stream reaches (mean = 9.9 m), shallow gradients (mean = 0.22%), and little canopy cover (mean = 13%) were associated with D. geminata blooms. In addition, iron concentrations in streams with D. geminata colonies were lower than in streams without blooms. [ABSTRACT FROM AUTHOR]

One of the most striking features of the diatom Didymosphenia geminata, which has increased markedly in abundance in a number of countries in recent years, is the very large branched stalks. In order to help understanding their role, an ultrastructural study was carried out on two populations, one from a stream in northern England and the other from a river on Vancouver Island, Canada. In both cases, the main part of the stalk had a central reticulate core surrounded by an outer region with dense fibres. A longitudinal structure in the uppermost part of the stalk just under the collar surrounding the base of the cell may perhaps correspond to a tube. The structure of the septa formed where branches divide is also described. Phosphomonoesterase activity known to be present in the stalks was shown to occur in the inner peripheral layers of the stalks and especially in the collar area. The results show that stalks have a complex structure suggesting their importance for their phosphatase activity to overcome low inorganic phosphate concentrations. Their large surface may function in herbivory avoidance, a better exposure of cells to turbulent conditions to increase nutrient uptake, adsorption of limiting elements and gas exchange. [ABSTRACT FROM AUTHOR]

We set out to explore whether the inclusion of perceptions into risk assessment might be a key to unlocking the human factor in the vectoring of aquatic non-indigenous species. To this end, we developed a risk assessment model that used people's perception of concern and stated behavioural intentions to measure consequence. We trialled this risk model using a test scenario of the non-indigenous species Didymosphenia geminata (a freshwater diatom) being introduced to Tasmania, Australia: a location where it is currently not present. Likelihood was determined by calculating the probability of Didymosphenia entering the test region based on exposure to D. geminata (travel history of arriving air passengers and the passenger's participation in freshwater recreational activities) and mitigation activities (whether their recreational equipment had been washed). The likelihood of a Didymosphenia incursion into Tasmania was determined to be rare. Consequence was determined by targeting three recreational user groups that participate in activities related to the movement of this species in other countries: trout anglers, hikers, and kayakers. Consequence was measured as respondent's level of concern and stated behavioural intentions if the respondent was confronted with an incursion of Didymosphenia. The consequence of a Didymosphenia incursion ranged from moderate to catastrophic. Thus, the total derived risk was determined to be low-medium. The use of perception to inform the consequence component of the risk assessment proved useful as individuals behaviours are often attributable to the introduction of species, and thus are an important consideration for risk management and education. At a local level these outcomes provide direction to biosecurity of unregulated pathways. At a global level, this risk assessment is a useful tool to assess the potential vectoring of a nonindigenous aquatic species, and potential human actions that might impede the management of a non-indigenous species once it crosses a border. [ABSTRACT FROM AUTHOR]

The freshwater stalked diatom, Didymosphenia geminata, has increased its proliferation in new and native ranges with the potential for significant ecological impacts to streams around the world. Uncertainty remains regarding the water chemistry in which D. geminata thrives despite recent advances in the understanding of its suitable physical habitat. Stream surveys were conducted in the central and the northern Sierra Nevada, CA, USA, to determine whether D. geminata distribution patterns were related to water chemistry and bedrock geology. Surveys included measurements of physical, chemical, and biological parameters from 50 stream reaches in 35 different streams. The water chemistry variable, percent Ca ( P < 0.001) provided the best fit models (binary logistic regression AUC 0.84) for predicting the presence of D. geminata in Sierra Nevada streams. Other significant water chemistry predictors included the percent SO and Mg concentrations. The bedrock geology variable, percent meta-sedimentary rock in a watershed ( P < 0.001), provided the best fit model (binary logistic regression AUC 0.77) for predicting the presence of D. geminata. This study further defines the environmental conditions in which D. geminata thrives, provides insight into D. geminata ecophsyiology, and will help refine current distribution and risk assessment models. [ABSTRACT FROM AUTHOR]