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Of the hitherto over 60 taxonomically identified species in the genus of Pseudo-nitzschia, 26 have been confirmed to be toxigenic. Nevertheless, the acquisition and evolution of the toxin biosynthesis (dab) genes by this extensive group of Pseudo-nitzschia species remains unclear. Through constructing chromosome-level genomes of three Pseudo-nitzschia species and draft genomes of ten additional Pseudo-nitzschia species, putative genomic integration sites for the dab genes in Pseudo-nitzschia species were explored. A putative breakpoint was observed in syntenic regions in the dab gene cluster-lacking Pseudo-nitzschia species, suggesting potential independent losses of dab genes. The breakpoints between this pair of conserved genes were also identified in some dab genes-possessing Pseudo-nitzschia species, suggesting that the dab gene clusters transposed to other loci after the initial integration. A "single acquisition, multiple independent losses (SAMIL)" model is proposed to explain the acquisition and evolution of the dab gene cluster in Pseudo-nitzschia species. A "single acquisition, multiple independent losses (SAMIL)" model is proposed to explain the acquisition and evolution of the domoic acid biosynthesis gene cluster in Pseudo-nitzschia species. [ABSTRACT FROM AUTHOR]

Harmful algal blooms are a major concern for the environment and industries like fisheries, healthcare, and tourism in coastal countries such as the Philippines. Blooms of diatoms (Bacillariophyceae) seldom cause harm, but half of the species in the cosmopolitan genus Pseudo-nitzschia produce the neurotoxin domoic acid. Only two published Pseudo-nitzschia surveys in the Philippines carried out morphology-based species identification. Molecular taxonomy has revealed a high level of cryptic diversity corresponding to minute morphological differences. This study sought to explore the diversity of and characterize the genus Pseudo-nitzschia in mariculture zones around Luzon Island using morphological and molecular information. Ten culture strains of Pseudo-nitzschia isolated from shellfish farms were used for morphological and molecular species identification. The secondary structure of the internal transcribed spacer 2 region revealed five strains from Pagbilao Bay to be most similar to P. brasiliana, the first record of this species in Luzon. Meanwhile, four Bacoor isolates and one from Pagbilao clustered within a monophyletic clade representing P. pungens, previously found in Manila Bay. Three single nucleotide polymorphisms and one hemi-compensatory base change were found among the P. pungens strains. Morphological characters, specifically cell shape, apex shape, and poroid density confirmed both species identities. Based on band striae, all P. pungens strains were of the nominal variety, P. pungens var. pungens. This study is among the first culture-based taxonomic studies of diatoms in the Philippines, in this case confirming the presence of harmful microalgae in the coastal ecosystems of the country. [ABSTRACT FROM AUTHOR]

Phytoplankton cells are now recognized as dynamic entities rather than as passive and isolated particles because they can actively modulate impacts of selection factors (nutrients, light, turbidity, and mixing) through a wide range of adaptations. Cell shape and/or chain length modulation is one of these processes but has predominantly been studied as an adaptation or an acclimatation to a specific growth limitation (light, nutrients, predation, etc.). In this study we have demonstrated that cell shape and size may have greater roles than previously known in phytoplankton ecology and species adaptation by permitting cell‐to‐cell signaling and more complex ecological processes that result from it. By exploring microscale biophysical interactions that lead to specific cell reorientation processes, we demonstrated that cell geometry not only modulates cell sinking rates but can also provide fast sensor responses to the cells' environment. Although gyrotaxis has been described in detail for motile phytoplankton cells, our findings illustrate that the reorientation process described here can occur even in non‐motile cells within their natural environment. An additional consistent behavior was also recently described for a diatom species (Pseudo‐nitzschia delicatessima), and with this study, we extend this observation to Pseudo‐nitzschia pungens and Pseudo‐nitzschia fraudulenta. Our observations emphasize the generality of this process, which adds a new level of complexity to our understanding of cellular interactions and their network of sensors. [ABSTRACT FROM AUTHOR]

Turbulence is one of the least investigated environmental factors impacting the ecophysiology of phytoplankton, both at the community and individual species level. Here, we investigated, for the first time, the effect of a turbulence gradient (Reynolds number, from Reλ = 0 to Reλ = 360) on two species of the marine diatom Pseudo-nitzschia and their associated bacterial communities under laboratory conditions. Cell abundance, domoic acid (DA) production, chain formation, and Chl a content of P. fraudulenta and P. multiseries were higher for intermediate turbulence (Reλ = 160 or 240). DA was detectable only in P. multiseries samples. These observations were supported by transcriptomic analyses results, which suggested the turbulence related induction of the expression of the DA production locus, with a linkage to an increased photosynthetic activity of the total metatranscriptome. This study also highlighted a higher richness of the bacterial community associated with the nontoxic strain of P. fraudulenta in comparison to the toxic strain of P. multiseries. Bacillus was an important genus in P. multiseries cultures (relative abundance 15.5%) and its highest abundances coincided with the highest DA levels. However, associated bacterial communities of both Pseudo-nitzschia species did not show clear patterns relative to turbulence intensity. [ABSTRACT FROM AUTHOR]

Pseudo‐nitzschia is a group of widely distributed planktonic diatoms. Some species produce the neurotoxin domoic acid. Herein, two new Pseudo‐nitzschia species were described from Chinese coastal waters and the South China Sea after combining morphological and molecular data, together with biogeographical traits. Pseudo‐nitzschia punctionis sp. nov. was similar to Pseudo‐nitzschia bipertita morphologically, but differed in poroid structure, which was undivided in P. punctionis but divided in two sectors in P. bipertita. This difference corresponded to the presence of two hemicompensatory base changes (HCBCs) in the secondary structure of internal transcribed spacer 2. Pseudo‐nitzschia polymorpha sp. nov. was sister to Pseudo‐nitzschia limii phylogenetically, but distinct by the various shapes of perforations on the valve and copula, which was supported by four HCBCs. In a metabarcoding analysis, multiple new ribotypes were identified within the two new species, and intraspecific genetic divergences were analyzed. Metabarcoding data revealed that P. punctionis had a broader temperature range (12.9–30.5°C) than P. polymorpha (22.3–30.5°C). Within the two new species, different traits were found among the amplicon sequence variants regarding temperature and biogeography, representing different microevolutionary directions under environmental selection. The two new species had different biogeographical traits when compared to their closely related species. Domoic acid was detected in strains of P. punctionis at a concentration of 13.5–17.7 fg/cell, but the toxin was not found in strains of P. polymorpha. A combination of characters based on laboratory strains and field metabarcoding data provided more data for delimiting Pseudo‐nitzschia species and gave new insights into their diversity and biogeography. [ABSTRACT FROM AUTHOR]

Harmful algal blooms caused by toxin‐producing species of the diatom genus Pseudo‐nitzschia have been linked to anomalously warm ocean conditions in the Northern California Current System. This study compares summertime concentrations of Pseudo‐nitzschia spp. and the toxin they produce, domoic acid, during a marine heatwave year (2019) and a climatologically neutral year (2021). An Imaging FlowCytobot was installed on a fishery survey vessel alongside environmental sensors to continuously sample phytoplankton and oceanographic parameters. This was paired with targeted manual sample collections for nutrients, chlorophyll, and domoic acid. Accumulations of Pseudo‐nitzschia spp. were associated with upwelling zones and established hotspot regions: the Juan de Fuca Eddy, Heceta Bank, and Trinidad Head. Overall, however, Pseudo‐nitzschia spp. and domoic acid concentrations were low during both summers and appear to have been limited by nitrate. Nutrient availability may therefore modulate the response of Pseudo‐nitzschia spp. to warm anomalies. Comparison of these results with 2015, another marine heatwave year but one that produced record concentrations of Pseudo‐nitzschia spp. and domoic acid, suggests that the timing of marine heatwave conditions in the nearshore relative to seasonal upwelling plays a key role in determining whether a Pseudo‐nitzschia spp. harmful algal bloom will occur. [ABSTRACT FROM AUTHOR]

Phytoplankton are photosynthetic microscopic organisms that inhabit the upper sunlit layer (euphotic zone) of marine and fresh water bodies. Phytoplankton, as the primary producer of the aquatic ecosystem’s food chain and are very sensitive to environmental changes as energy stored up in them determine the basic primary productivity of an ecosystem. There is dearth of information on the phytoplankton community of the Festac creek and thus the need for this study which aims at microscopically investigating the phytoplankton community of the Festac creek. The Phytoplankton diversity and distribution of the Festac creek, Lagos, Nigeria. was investigated for 12 months (November 2021 – October, 2022). Phytoplankton samples were collected monthly for 12 months, using a 55 μm mesh size standard plankton net towed horizontally from a motorized boat for 5 mins at < 4 Km/h and preserved by adding 4% unbuffered formalin. The drop count microscopic analysis method was used to study the phytoplankton species. A total of 34 phytoplankton species from 7 algal classes namely Bacillariophyceae (16 species), Cyanophyceae (9 species), Chlorophyceae (2 species), Conjugatophyceae (3 species), Dictyochophyceae (2 species), Tintinnid (1 species) and Dinophyceae (1 species) were recorded. Notable species were recorded such as: Lyngbya sp, Prorocentrum lima, Navicula sp. Nitzschia lineola, Phormidium bohneri, Oscillatoria limosa, Oscillatoria nigro viridis, Oscillatoria formosa and some other known marine species such as Coscinodiscus radiatus, Coscinodiscus marginatus Skeletonema costatum, Odontella sinensis, Thalassionema nizschoides, Fragillaria oceanica, Spirulina subsalsa and Tintinnopsis radix. The most abundant class was the Cyanophyceae (Blue-green algae) with Oscillatoria limosa being the most abundant species. This could be attributed to the constant addition of nutrient particularly nitrate and phosphate run offs from industries around the study area which enhances cyanobacterial growth and indicates that the Festac creek is eutrophic. [ABSTRACT FROM AUTHOR]

Pseudo-nitzschia species with the ability to produce the neurotoxin domoic acid (DA) are the main cause of harmful algal blooms (HABs) along the U.S. West Coast, with major impacts on ecosystems, fisheries, and human health. While most Pseudo-nitzschia (PN) HAB studies to date have focused on their characteristics at specific sites, few cross-regional comparisons exist, and mechanistic understanding of large-scale HAB drivers remains incomplete. To close these gaps, we compiled a nearly 20-year time series of in situ particulate DA and environmental observations to characterize similarities and differences in PN HAB drivers along the California coast. We focus on three DA hotspots with the greatest data density: Monterey Bay, the Santa Barbara Channel, and the San Pedro Channel. Coastwise, DA outbreaks are strongly correlated with upwelling, chlorophyll-a, and silicic acid limitation relative to other nutrients. Clear differences also exist across the three regions, with contrasting responses to climate regimes across a north to south gradient. In Monterey Bay, PN HAB frequency and intensity increase under relatively nutrient-poor conditions during anomalously low upwelling intensities. In contrast, in the Santa Barbara and San Pedro Channels, PN HABs are favored under cold, nitrogen-rich conditions during more intense upwelling. These emerging patterns provide insights on ecological drivers of PN HABs that are consistent across regions and support the development of predictive capabilities for DA outbreaks along the California coast and beyond.

Diatoms are microalgae that live in marine and freshwater environments and are responsible for about 20% of the world's carbon fixation. Population dynamics of these cells is finely regulated by intricate signal transduction systems, in which oxylipins are thought to play a relevant role. These are oxygenated fatty acids whose biosynthesis is initiated by a lipoxygenase enzyme (LOX) and are widely distributed in all phyla, including diatoms. Here, we present a de novo transcriptome obtained from the RNA-seq performed in the diatom species Pseudo-nitzschia arenysensis, using both a wild-type and a LOX-silenced strain, which will represent a reliable reference for comparative analyses within the Pseudo-nitzschia genus and at a broader taxonomic scale. Moreover, the RNA-seq data can be interrogated to go deeper into the oxylipins metabolic pathways. [ABSTRACT FROM AUTHOR]

Post-mining reservoirs are distinguished by characteristic environmental conditions where specific diatom communities can be observed. Reservoirs created as a part of the reclamation plan after human mining activities are marked by unique chemical and physical water parameters. In the course of research on the diatoms from Bogdałów reservoir, we examined the taxonomic and morphological diversity of Nitzschia taxa from the section Lanceolatae occurring in a post-mining lignite reservoir. Our study describes a new species of Nitzschia from a post-mining reservoir, Nitzschia nandorii Olszyński, Zakrzewski & Żelazna-Wieczorek, sp. nov. Morphometry and morphology analyses of new species were performed with light and scanning electron microscopy. Chloroplast morphology analysis was conducted with differential interference contrast microscopy and confocal laser scanning microscopy. Molecular data from SSU 18S, rbcL and psbC sequences were obtained from cultures of this taxon. Differential diagnosis of Nitzschia nandorii Olszyński, Zakrzewski & Żelazna-Wieczorek, sp. nov. with co-occurring taxa: N. lacuum and N. alpinobacillum was performed using morphological traits and nMDS analysis of the valves' morphometry. [ABSTRACT FROM AUTHOR]

Pseudo-nitzschia species are one of the leading causes of harmful algal blooms (HABs) along the western coast of the United States. Approximately half of known Pseudo-nitzschia strains can produce domoic acid (DA), a neurotoxin that can negatively impact wildlife and fisheries and put human life at risk through amnesic shellfish poisoning. Production and accumulation of DA, a secondary metabolite synthesized during periods of low primary metabolism, is triggered by environmental stressors such as nutrient limitation. To quantify and estimate the feedbacks between DA production and environmental conditions, we designed a simple mechanistic model of Pseudo-nitzschia and domoic acid dynamics, which we validate against batch and chemostat experiments. Our results suggest that, as nutrients other than nitrogen (i.e., silicon, phosphorus, and potentially iron) become limiting, DA production increases. Under Si limitation, we found an approximate doubling in DA production relative to N limitation. Additionally, our model indicates a positive relationship between light and DA production. These results support the idea that the relationship with nutrient limitation and light is based on direct impacts on Pseudo-nitzschia biosynthesis and biomass accumulation. Because it can easily be embedded within existing coupled physical-ecosystem models, our model represents a step forward toward modeling the occurrence of Pseudo-nitzschia HABs and DA across the U.S. West Coast.

Two new diatom species belonging to the genus Gomphonemopsis are described, Gomphonemopsis nana sp. nov. and Gomphonemopsis gaoi sp. nov. These two species were compared in detail with congeners. Gomphonemopsis nana is distinguished by its high stria density and small size. This species was found so far to be epiphytic only on the eelgrass collected from Qingdao Bay (Yellow Sea). Gomphonemopsis gaoi is characterized by its isopolar valves, simple proximal raphe endings and acutely rounded apices. This taxon was separated from the exoskeleton of marine copepods sampled from the Futian Mangrove Nature Reserve (South China Sea). In addition, two new combinations, Gomphonemopsis oahuensis (Hustedt) Lang Li, Yuhang Li & Changping Chen, comb. nov. and Gomphonemopsis platypus (Østrup) Lang Li, Yuhang Li & Junxiang Lai, comb. nov. are proposed. This study increases the records and knowledge of Gomphonemopsis along the coast of China. [ABSTRACT FROM AUTHOR]

Pseudo-nitzschia is a species-rich genus with many species able to induce harmful algae blooms (HABs) associated with the toxin, domoic acid (DA), production. Despite their high diversity revealed by taxonomical studies, the composition and spatial–temporal dynamics of Pseudo-nitzschia species in marine ecological systems are often inadequately resolved due to the insufficient resolution associated with morphology-based approaches applied in ecological studies. In this study, metabarcoding analysis was applied to identify Pseudo-nitzschia species and track their spatial–temporal dynamics in Jiaozhou Bay (JZB), a model marine ecosystem located in Qingdao, China. This metabarcoding analysis potentially uncovered 18 Pseudo-nitzschia species, including three Pseudo-nitzschia species identified in JZB in previous microscopy-based studies, four Pseudo-nitzschia species (P. micropora, P. multistriata, P. galaxiae, and P. fraudulenta) that have not been identified in JZB, and 11 potential Pseudo-nitzschia species whose molecular marker sequences are identical, demonstrating the strength of metabarcoding analysis in ecological research. Furthermore, this metabarcoding analysis also revealed differential spatial–temporal dynamics of many Pseudo-nitzschia species. While P. galaxiae was found to show a strong preference for summer months, P. pungens showed relatively high abundance in later summer and early autumn, P. delicatissima and P. multistriata showed higher abundance in autumn and winter, and P. micropora was more common in July. To ascertain driving forces for such differential seasonal preferences, we evaluated the impact of environmental factors on the spatial–temporal preferences of the Pseudo-nitzschia species, which revealed that temperature and other factors together contributed to the differential dynamic changes. This study demonstrated that metabarcoding analysis is an effective approach for tracking the composition and spatial–temporal dynamics of Pseudo-nitzschia species in marine ecological systems. [ABSTRACT FROM AUTHOR]

Pseudo-nitzschia spp. blooms are a recurrent problem in many coastal areas globally, imposing some significant threats to the health of humans, ecosystems and the economy. Monitoring programmes have been established, where feasible, to mitigate the impacts caused by Pseudo-nitzschia spp. and other harmful algae blooms. The detection of such blooms from satellite data could really provide timely information on emerging risks but the development of taxa-specific algorithms from available multispectral data is still challenged by coupled optical properties with other taxa and water constituents, availability of ground data and generalisation capabilities of algorithms. Here, we developed a new set of algorithms (PNOI) for the detection and monitoring of Pseudo-nitzschia spp. blooms over the Galician coast (NW Iberian Peninsula) from Sentinel-3 OLCI reflectances using a support vector machine (SVM). Our algorithm was trained and tested with reflectance data from 260 OLCI images and 4607 Pseudo-nitzschia spp. match up data points, of which 2171 were of high quality. The performance of the no bloom/bloom model in the independent test set was robust, showing values of 0.80, 0.72 and 0.79 for the area under the curve (AUC), sensitivity and specificity, respectively. Similar results were obtained by our below detection limit/presence model. We also present different model thresholds based on optimisation of true skill statistic (TSS) and F1-score. PNOI outperforms linear models, while its relationship with in situ chlorophyll-a concentrations is weak, demonstrating a poor correlation with the phytoplankton abundance. We showcase the importance of the PNOI algorithm and OLCI sensor for monitoring the bloom evolution between the weekly ground sampling and during periods of ground data absence, such as due to COVID-19. [ABSTRACT FROM AUTHOR]

The harmful algal bloom (HAB) species Pseudo-nitzschia multiseries is widely distributed worldwide and is known to produce the neurotoxin domoic acid, which harms marine wildlife and humans. Early detection and preventative measures are more critical than late management. However, the major challenge related to early detection is the accurate and sensitive detection of microalgae present in low abundance. Therefore, developing a sensitive and specific method that can rapidly detect P. multiseries is critical for expediting the monitoring and prediction of HABs. In this study, a novel assay method, recombinase polymerase amplification combined with lateral flow dipstick (RPA-LFD), is first developed for the detection of P. multiseries. To obtain the best test results, several important factors that affected the amplification effect were optimized. The internal transcribed spacer sequence of the nuclear ribosomal DNA from P. multiseries was selected as the target region. The results showed that the optimal amplification temperature and time for the recombinase polymerase amplification (RPA) of P. multiseries were 37 °C and 15 min. The RPA products could be visualized directly using the lateral flow dipstick after only 3 min. The RPA-LFD assay sensitivity for detection of recombinant plasmid DNA (1.9 × 100 pg/μL) was 100 times more sensitive than that of RPA, and the RPA-LFD assay sensitivity for detection of genomic DNA (2.0 × 102 pg/μL) was 10 times more sensitive than that of RPA. Its feasibility in the detection of environmental samples was also verified. In conclusion, these results indicated that the RPA-LFD detection of P. multiseries that was established in this study has high efficiency, sensitivity, specificity, and practicability. Management measures made based on information gained from early detection methods may be able to prevent certain blooms. The use of a highly sensitive approach for early warning detection of P. multiseries is essential to alleviate the harmful impacts of HABs on the environment, aquaculture, and human health. [ABSTRACT FROM AUTHOR]

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Domoic acid-producing blooms of the diatom genus Pseudo-nitzschia are pervasive in coastal environments globally. Domoic acid, a neurotoxin, accumulates via trophic transfer into marine food webs and is often associated with mass marine mammal mortality and stranding events. In Southern California, California sea lions (Zalophus californianus) are an indicator species for food web impacts of domoic acid because they are abundant secondary consumers, sensitive to domoic acid intoxication, and are actively monitored by stranding networks. However, domoic acid exposure may occur a distance from where a sea lion ultimately strands. This spatiotemporal variation complicates coupling domoic acid observations in water to strandings. Therefore, we sought to quantify whether monitoring data from four pier sites across the region, covering nearly 700 km of coastline from 2015-2019, could be used to predict adult and subadult sea lion strandings along the 68 km Orange County coastline surveyed by the Pacific Marine Mammal Center. We found that increased sea lion strandings were often observed just prior to an increase in particulate domoic acid at the piers, confirming that clusters of subadult and adult sea lion strandings with clinical signs of domoic acid intoxication serve as indicators of bloom events. In addition, domoic acid concentrations at Stearns Wharf, nearly 200 km from stranding locations, best predicted increased total sea lion strandings, and strandings of sea lions with domoic acid intoxication symptoms. Particulate domoic acid concentrations greater than 0.05 µg/L at Stearns Wharf were linked to stranding probabilities in Orange County ranging from 2.2% to 55% per week, and concentrations of 0.25 µg/L resulted in weekly stranding probabilities ranging from 16% to 81% depending on the stranding scenario modeled. [ABSTRACT FROM AUTHOR]

Domoic acid-producing blooms of the diatom genus Pseudo-nitzschia are pervasive in coastal environments globally. Domoic acid, a neurotoxin, accumulates via trophic transfer into marine food webs and is often associated with mass marine mammal mortality and stranding events. In Southern California, California sea lions (Zalophus californianus) are an indicator species for food web impacts of domoic acid because they are abundant secondary consumers, sensitive to domoic acid intoxication, and are actively monitored by stranding networks. However, domoic acid exposure may occur a distance from where a sea lion ultimately strands. This spatiotemporal variation complicates coupling domoic acid observations in water to strandings. Therefore, we sought to quantify whether monitoring data from four pier sites across the region, covering nearly 700 km of coastline from 2015-2019, could be used to predict adult and subadult sea lion strandings along the 68 km Orange County coastline surveyed by the Pacific Marine Mammal Center. We found that increased sea lion strandings were often observed just prior to an increase in particulate domoic acid at the piers, confirming that clusters of subadult and adult sea lion strandings with clinical signs of domoic acid intoxication serve as indicators of bloom events. In addition, domoic acid concentrations at Stearns Wharf, nearly 200 km from stranding locations, best predicted increased total sea lion strandings, and strandings of sea lions with domoic acid intoxication symptoms. Particulate domoic acid concentrations greater than 0.05 μg/L at Stearns Wharf were linked to stranding probabilities in Orange County ranging from 2.2% to 55% per week, and concentrations of 0.25 μg/L resulted in weekly stranding probabilities ranging from 16% to 81% depending on the stranding scenario modeled.

Uma pesquisa recente realizada pela Epagri e pelo IFSC analisou os dados gerados pelo programa estadual de monitoramento de florações de algas produtoras de toxinas gerados entre 2007 e 2019 e cruzou com dados gerados por modelos meteorológicos e por sensores de satélites, de forma a gerar informações que permitam entender melhor esses eventos. O estudo evidenciou que o gênero Dinophysis é o grupo de microalgas produtoras de toxinas que mais floresce em SC e que as toxinas diarreicas são as mais comumente detectadas nos moluscos. O estudo evidenciou também que as florações de Dinophysis podem ocorrer durante todos os meses do ano, mas tendem a se concentram nos meses de outono e inverno e se relacionam com as condições meteorológicas observadas durante esse período do ano. Outra informação importante é que as florações de Dinophysis não tendem a coincidir com florações de microalgas não tóxicas e que as estimativas de clorofila feitas com base em satélites não são um bom indicador da ocorrência desses eventos em Santa Catarina.

Diatoms are one of the most important phytoplankton groups in the world's oceans. There are responsible for up to 40% of the photosynthetic activity in the Ocean, and they play an important role in the silicon and carbon cycles by decoupling carbon from atmospheric interactions through sinking and export. These processes are strongly influenced by the taxonomic composition of diatom assemblages. Traditionally, these have been assessed using microscopy, which in some cases is not reliable or reproducible. Next-generation sequencing enabled us to study diversity in a high-throughput manner and uncover new distribution patterns and diversity. However, phylogenetic markers used for this purpose, such as various 18S rDNA regions, are often insufficient because they cannot distinguish between some taxa. In this work, we demonstrate the performance of the chloroplast-encoded rbcL marker for metabarcoding marine diatoms compared to microscopy and 18S-V9 metabarcoding using a series of monthly samples from the Gulf of Trieste (GoT), northern Adriatic Sea. We demonstrate that rbcL is able to detect more taxa compared to 18S-V9 metabarcoding or microscopy, while the overall structure of the diatom assemblage was comparable to the other two methods with some variations, that were taxon dependent. In total, 6 new genera and 22 new diatom species for the study region were identified. We were able to spot misidentification of genera obtained with microscopy such as Pseudo-nitzschia galaxiae, which was mistaken for Cylindrotheca closterium, as well as genera that were completely overlooked, such as Minidiscus and several genera from the Cymatosiraceae family. Furthermore, on the example of two well-studied genera in the region, namely Chaetoceros and particularly Pseudo-nitzschia, we show how the rbcL method can be used to infer even deeper phylogenetic and ecologically significant differences at the species population level. Despite a very thorough community analysis obtained by rbcL the incompleteness of reference databases was still evident, and we shed light on possible improvements. Our work has further implications for studies dealing with taxa distribution and population structure, as well as carbon and silica flux models and networks. [ABSTRACT FROM AUTHOR]

Çanakkale is located in Western Anatolia, a region known for extensive mining in the country. In this study, three new species: Nitzschia arslaniana sp. nov., Nitzschia efeiana sp. nov., and Nitzschia szaboiana sp. nov. are described from highly acidic environments in Çanakkale. In morphology, Nitzschia arslaniana is similar to Nitzschia inconspicua but Nitzschia inconspicua is broader, with a lower fibulae density. Nitzschia efeiana is similar to Nitzschia. bremensis, Nitzschia capitellata, Nitzschia homburgiensis, Nitzschia hybrida, Nitzschia palustris, and Nitzschia pellucida. However, Nitzschia efeiana has variable fibulae widths, thickened virgae on its external valve face, and an elevated ridge on the valve margin opposite the keel. Nitzschia szaboiana is similar to Nitzschia pusilla, but the later taxon has a higher striae density. This study highlights the unique species diversity of extreme environments, including anthropogenic extreme environments, by describing three new taxa in the same genus. [ABSTRACT FROM AUTHOR]

Mastogloia frickei Hustedt was found in Guam and studied with scanning electron microscopy. A species known by that name in Florida/Bahamas is shown to be a different species and is described as Mastogloia floridensis sp. nov. Both have alveolate striae, which is unusual in the genus. A third alveolate species was present in Florida samples and had been misidentified previously. It is described as Mastogloia lucayensis sp. nov. Ultrastructure observations of these species expand the diversity of alveolate stria morphology. [ABSTRACT FROM AUTHOR]

A floristic study of the diatoms (Bacillariophyceae) along the Marikina River in the eastern part of Metro Manila, Philippines, recorded at least 140 species belonging to 39 genera. Of these genera, one of the greatest number of species was observed in the genus Gomphonema (18 species). These species were identified and described under the bright field light microscope. Some species were further observed under the scanning electron microscope. A habitat description of the occurrence of the Gomphonema species is given. Twelve (12) out of the 18 species are new records for the country: G. brasiliense subsp. pacificum Moser, Lange-Bertalot & Metzeltin, G. chinense Liu & Kociolek, G. contraturris Lange-Bertalot & E.Reichardt, G. cuneolus E.Reichardt, G. exilissimum (Grunow) Lange-Bertalot & E.Reichardt, G. insigniforme E.Reichardt & Lange-Bertalot, G. javanicum Hustedt, G. kobayasii Kociolek & J.C.Kingston, G. pseudosphaerophorum H. Kobayasi, G. sundaense E.Reichardt, G. cf. qingyiensis L-X Zhang, P. Yu & Q-M You, and G. vibrio var. bohemicum (Reichelt & Fricke) R. Ross. Hence, this paper reports a total of 44 species of Gomphonema from the Philippines, including previous studies from 1937 to date. [ABSTRACT FROM AUTHOR]

Representatives of the Achnanthidium minutissimum complex have been studied from the Transbaikal region, Russia. The Transbaikal region is known for its unique algal flora and high levels of endemism. Despite the group of monoraphid diatoms being studied quite extensively in this region in recent years, only four species of Achnanthidium have been reported so far. Three new species are described based on LM and SEM microphotographs and molecular data: Achnanthidium baicalonanum sp. nov., A. obscurum sp. nov. and A. angustum sp. nov. Comparison with similar species is given. The new species differ from other species of the genus by valve shape, striae and areolae structure, shape of external distal raphe ends and central area. According to molecular data, the new species form separate branches within the A. minutissimum complex. Ecological preferences of the new species are examined. All of the new species are only known from the Transbaikal region. This study contributes to the understanding of Achnanthidium taxonomy and biogeography and will be an asset to future biomonitoring studies. [ABSTRACT FROM AUTHOR]

The farming of shellfish plays an important role in providing sustainable economic growth in coastal, rural communities in Scotland and acts as an anchor industry, supporting a range of ancillary jobs in the processing, distribution and exporting industries. The Scottish Government is encouraging shellfish farmers to double their economic contribution by 2030. These farmers face numerous challenges to reach this goal, among which is the problem caused by toxin-producing microplankton that can contaminate their shellfish, leading to harvesting site closure and the recall of product. Food Standards Scotland, a non-ministerial department of the Scottish Government, carries out a monitoring programme for both the toxin-producing microplankton and the toxins in shellfish flesh, with farms being closed when official thresholds for any toxin are breached. The farm remains closed until testing for the problematic toxin alone, often diarrhetic shellfish toxin (DST), shows the site to have dropped below the regulatory threshold. While this programme has proved to be robust, questions remain regarding the other toxins that may be present at a closed site. In this study, we tested archival material collected during site closures but only tested for DSTs as part of the official control monitoring. We found the presence of amnesic shellfish toxin (AST) in low concentrations in the majority of sites tested. In one case, the level of AST breached the official threshold. This finding has implications for AST monitoring programmes around Europe. [ABSTRACT FROM AUTHOR]

Several automated molecular methods have emerged for distinguishing eukaryote species based on DNA sequence data. However, there are knowledge gaps around which of these single‐locus methods is more accurate for the identification of microalgal species, such as the highly diverse and ecologically relevant diatoms. We applied genetic divergence, Automatic Barcode Gap Discovery for primary species delimitation (ABGD), Assemble Species by Automatic Partitioning (ASAP), Statistical Parsimony Network Analysis (SPNA), Generalized Mixed Yule Coalescent (GMYC) and Poisson Tree Processes (PTP) using partial cox1, rbcL, 5.8S + ITS2, ITS1 + 5.8S + ITS2 markers to delineate species and compare to published polyphasic identification data (morphological features, phylogeny and sexual reproductive isolation) to test the resolution of these methods. ASAP, ABGD, SPNA and PTP models resolved species of Eunotia, Seminavis, Nitzschia, Sellaphora and Pseudo‐nitzschia corresponding to previous polyphasic identification, including reproductive isolation studies. In most cases, these models identified diatom species in similar ways, regardless of sequence fragment length. GMYC model presented smallest number of results that agreed with previous published identification. Following the recommendations for proper use of each model presented in the present study, these models can be useful tools to identify cryptic or closely related species of diatoms, even when the datasets have relatively few sequences. [ABSTRACT FROM AUTHOR]

Species of Chaetoceros sect. Stenocincta are frequently observed in marine phytoplankton. To study species diversity within the section Stenocincta, monoclonal strains were established from Chinese coastal waters and Norwegian Sea. Following detailed morphological observations and molecular evidence inferred from nucleus-encoded large subunit ribosomal DNA, the descriptions of C. affinis and C. willei are emended based on isolates from their respective type localities. Additionally, three new species are described. Chaetoceros donghaiensis sp. nov. is characterized by short straight chains, with thin setae only, and terminal setae that tend to cross distally. Chaetoceros forceps sp. nov. is unique by its thick terminal setae, each with an inflation near the end, with each pair forming a V-shape, resembling forceps. Chaetoceros lepidus sp. nov. is characterized by short, straight chains, narrowly elliptical valve faces, setae all located in the apical plane, and arched intercalary setae in opposite directions to the chain axis in broad girdle views. Three other distinct clades, which may also represent new species, were discerned in the LSU rDNA phylogeny, but more morphological characters are needed before formal proposals can be made. These species/clades formed a well-supported monophyletic lineage, supporting the current circumscription of section Stenocincta. This section is characterized by colonies in straight chains, cells with one chloroplast only, narrow lanceolate apertures, and terminal setae generally thicker than intercalary ones or both similar and thin. However, in C. diversus the terminal setae are thin and distinctly thicker pairs of intercalary setae are usual. [ABSTRACT FROM AUTHOR]

Pennate diatoms belonging to the genus Pseudo-nitzschia are important components of phytoplankton assemblages in aquatic environments. Among them, the bloom-forming species Pseudo-nitzschia calliantha and Pseudo-nitzschia multistriata are known as domoic acid producers, and are thus considered harmful for aquatic organisms and for human health. For these reasons, monitoring the abundance of such species, as well as identifying the growth conditions enhancing or inhibiting their growth, could help to predict eventual risks for aquatic communities and for humans by direct or indirect exposure to these toxic algae. In this work, we assessed the effects of different parameters (irradiance, temperature, salinity, and nutrients) on six Pseudo-nitzschia species by evaluating their specific growth rates and total RNA content. Our results—corroborated by statistical analyses of regression and correlation plots of control samples and samples exposed to stressful conditions, showed, as expected, a general decrease in growth rates under suboptimal levels of temperature, irradiance, salinity, and nutrient supply (especially under silicon depletion), that was usually accomplished by a general increase in RNA content inside cells. We hypothesized that increments in RNA levels in cells exposed to unfavorable conditions could be due to a relatively fast activation of the mechanisms of stress response. [ABSTRACT FROM AUTHOR]

Phytoplankton dynamics are regulated by external cues, such as light and nutrients, as well as by biotic interactions and endogenous controls linked to life cycle characteristics. The planktonic pennate diatom Pseudo‐nitzschia multistriata, with a heterothallic mating system with two opposite mating types (MTs), represents a model for the study of diatom life cycles. P. multistriata is a toxic species, able to produce the neurotoxin domoic acid. First described in Japan in 1993, it was detected at the long‐term monitoring station MareChiara (Gulf of Naples, Italy) in 1995. Since then, P. multistriata has been reported from several worldwide coastal sites. A large body of knowledge has been produced on its ecology, genetic diversity, and life cycle characteristics. The availability of these data, the ecological relevance of the Pseudo‐nitzschia genus, and its controllable life cycle with a short generation time made it an ideal species to develop a genetic model system for diatoms. To enable functional studies, a 59 Mb genome sequence and several transcriptomic data were produced, and genetic transformation was optimized. These tools allowed the discovery of the first mating‐type determining gene for diatoms. Gene expression studies and metabolomics analyses defined genes and molecules underpinning different phases of the process of sexual reproduction. This model system, developed to explore the genetics of diatom life cycles, offers the opportunity to parallel experimental observations in the laboratory using in situ meta‐omics analyses along space and time, empowering knowledge on the biology and ecology of the genus. [ABSTRACT FROM AUTHOR]

A characteristic, panduriform, large (ca 80 μm in length) diatom was sporadically detected in the Hungarian rivers in 2021 and 2022. Surirella tientsinensis Skvortzov emend. Liu was regarded as an Asian endemic species practically from its description until the second decade of the 21st century. Here we present the first Hungarian occurrence of the taxon from 2021, which is the second record for Europe, after the previously published Ukrainian data. In 2022 Surirella tientsinen sis was detected from two other Hungarian river sampling localities. Due to the unmistakable outlook of the species, probably it is a new member of the Hungarian diatom flora, and its parallel occurrences in some localities within a short time, is noteworthy. [ABSTRACT FROM AUTHOR]

The temporal distributions of microphytoplankton were studied monthly over 2 years in the shelf and the offshore waters of the "low nutrients low chlorophyll" (LNLC) southeastern (SE) Mediterranean Sea. The microphytoplankton were comprised mostly of diatoms (0–542 cells L−1, ~4 × 106–44 × 106 cells m−2) of the genera Rhizosolenia , Thalassionema, Chaetoceros , Leptocylindrus and Pseudo-nitzschia, and dinoflagellates (1–89 cells L−1, ~1 × 106–10 × 106 cells m−2) of the genera Tripos (formally known as Ceratium), Ornithocercus, Protoperidinium, Ceratocorys and Dinophysis. During the winter mixing, microphytoplankton abundance was ~2-fold higher than during the stratified summer months, in accordance with the higher inorganic nutrient levels. Diatoms were mostly found in the upper illuminated layers (0–100 m), while dinoflagellate distribution was patchy and spread from surface down to 200 m. We also calculated that diatoms and dinoflagellates contribute negligibly (~4%) to the total vertical carbon flux in the offshore water, suggesting fast recycling of organic matter at the photic layer. Our results provide a baseline to better understand carbon and biogenic silica fluxes at the LNLC SE Mediterranean Sea. [ABSTRACT FROM AUTHOR]

The composition of the phytoplankton community in Tokyo Bay was analyzed using samples collected monthly at 0 and 5 m depths from 2003 to 2017, along with environmental factors. Three diatom genera—Skeletonema, Thalassiosira, and Pseudo-nitzschia—dominated over the study period. The sum of the three genera accounted for 75% of the total phytoplankton cell density. Skeletonema was the most abundant taxon, of which the cell density reached > 104 cells mL−1. A pattern of seasonal change in the community composition was detected, and the varying compositions were grouped into three seasons: a mixing season (November–February), an early stratified season (March–June), and a late stratified season (July–October). The mixing season was characterized by high nutrient content (dissolved inorganic nitrogen > 30 µM) and low temperature (< 17 °C), and the late stratified season was characterized by high temperature (> 22 °C) and low salinity (< 28 at the surface). In a modified seasonal Mann–Kendall test, we did not find any increasing or decreasing trend of three diatom genera in the analysis for whole months. However, the test applied to each seasonal group revealed a significant increasing trend of Pseudo-nitzschia abundance in the late stratified season at 0 m depth. In contrast, Skeletonema abundance showed a decreasing trend at a 5 m depth in the same season. The succession of the phytoplankton community was more obvious when the yearly trend was analyzed for each season. [ABSTRACT FROM AUTHOR]

Combining morphological and molecular approaches, a new diatom species is described in the genus Mayamaea from a Special Nature Reserve, Okanj bara in Serbia, an alkaline and subsaline soda pan with pronounced seasonal drying. Mayamaea pannonica sp. nov. possesses typical characteristics of the genus Mayamaea, such as uniseriate striae and hymenes that cover the areolae from the outside. It can easily be distinguished from similar species by the valve outline and shape of the central area. Although presently no culture of the species is available, we identified in an amplicon data set from the same sample a partial 18S rRNA gene sequence that is thought to represent the new species, with high probability. A comparison of our sequence to those present in the Diat.barcode and NCBI databases showed that the sequence is closely related to, but significantly different from, that of Mayamaea terrestris. Natural saline habitats in Serbia and neighbouring countries are under anthropogenic threat and climate change, so knowing which species live here is the first step in preserving these unique habitats. [ABSTRACT FROM AUTHOR]

Diatoms of the genus Pseudo-nitzschia are producers of the neurotoxin domoic acid that causes serious damage to marine fauna and aquaculture farms. These microalgae are known as the most abundant group of toxic phytoplankton in Peter the Great Bay, Northwestern Sea of Japan, during the bloom season, which, as was previously reported for members of this group in the study region, lasts in the autumn months. Autumnal blooms of toxic diatoms Pseudo-nitzschia spp. were studied in the period from 2017 to 2022 in Ussuri Bay, the largest body of water in Peter the Great Bay, which harbors numerous recreational area and aquaculture farms. As a result, the following changes in the composition of bloom-forming species were recorded: blooms were caused by the Pseudo-nitzschia delicatissima group in the period from 2017 to 2020 and by P. multistriata in 2021–2022. An assumption has been made that one of the factors responsible for blooms of P. multistriata, known as one of the most widespread species in Asian warm-water areas, is an abnormally high water temperature in the autumn of 2021 in the study area. [ABSTRACT FROM AUTHOR]

Increased occurrences of harmful algal blooms (HAB) in the Gulf of Mexico, and even worldwide, yield concern for increases in brevetoxin exposure leading to respiratory illness or even death, highlighting the need for extensive scientific research and human health monitoring. It is known that major events such as tropical storms and hurricanes are followed by periods of increased red tides caused by HABs; however, the nature by which phytoplankton blooms proliferate following major events remains a topic of great interest and research. The impact of Hurricane Michael on October 10, 2018 on HABs in the Florida panhandle was examined by analyzing data from the Florida Fish and Wildlife Conservation Commission in coordination with Normalized Fluorescence Line Height (nFLH) data from the University of South Florida College of Marine Science. Results presented here demonstrate four phases of HABs during storm events: 1. Pre-storm concentrations, 2. Decreased concentration during the storm, 3. Elevated concentrations following the storm and 4. Recovery period. This time frame can serve to be important in understanding the health dynamics of coastal systems following major storm events. [ABSTRACT FROM AUTHOR]

Despite its small area, Araçá Bay (AB) holds cultural, historical, and economic value and displays great benthic biodiversity. Thus, it is crucial to monitor its environmental health, including knowing the main groups of phytoplankton and their temporal variability. The shallow waters of Araçá Bay are continuously modified by the complex hydrography of the adjacent São Sebastião channel (SSC), challenging standard experimental designs for phytoplankton collection. Here we report changes in phytoplankton composition at intervals of five to six weeks from September 2013 to August 2014 in both Araçá Bay and SSC. Samples were collected twice daily for three consecutive days to increase taxonomic resolution. Our goal was to provide an inventory of species occurrences to aid future public policies and environmental management of the area. Analyses revealed high species richness and 166 different phytoplankton taxa. Diatoms and dinoflagellates were always numerically dominant, but taxa occurrence changed markedly. Diatoms of the genera Pseudo-nitzschia were abundant during spring and summer concurrently to signatures of South Atlantic Central Water in the SSC, while Thalassiosira occurred when waters displayed relatively lower salinity. The inventory demonstrated several potentially harmful species of microalgae and cyanobacteria, strongly suggesting investments in monitoring programs in this area that currently experience an increase in population. [ABSTRACT FROM AUTHOR]

The toxic diatom genus Pseudo-nitzschia is distributed from equatorial to polar regions and is comprised of >57 species, some capable of producing the neurotoxin domoic acid (DA). In the Pacific Arctic Region spanning the Bering, Chukchi, and Beaufort seas, DA is recognized as an emerging human and ecosystem health threat, yet little is known about the composition and distribution of Pseudo-nitzschia species in these waters. This investigation characterized Pseudo-nitzschia assemblages in samples collected in 2018 during summer (August) and fall (October-November) surveys as part of the Distributed Biological Observatory and Arctic Observing Network, encompassing a broad geographic range (57.8° to 73.0°N, -138.9° to -169.9°W) and spanning temperature (-1.79 to 11.7°C) and salinity (22.9 to 32.9) gradients associated with distinct water masses. Species were identified using a genus-specific Automated Ribosomal Intergenic Spacer Analysis (ARISA). Seventeen amplicons were observed; seven corresponded to temperate, sub-polar, or polar Pseudo-nitzschia species based on parallel sequencing efforts (P. arctica, P. delicatissima, P. granii, P. obtusa, P. pungens, and two genotypes of P. seriata), and one represented Fragilariopsis oceanica. During summer, particulate DA (pDA; 4.0 to 130.0 ng L-1) was observed in the Bering Strait and Chukchi Sea where P. obtusa was prevalent. In fall, pDA (3.3 to 111.8 ng L-1) occurred along the Beaufort Sea shelf coincident with one P. seriata genotype, and south of the Bering Strait in association with the other P. seriata genotype. Taxa were correlated with latitude, longitude, temperature, salinity, pDA, and/or chlorophyll a, and each had a distinct distribution pattern. The observation of DA in association with different species, seasons, geographic regions, and water masses underscores the significant risk of Amnesic Shellfish Poisoning (ASP) and DA-poisoning in Alaska waters. [ABSTRACT FROM AUTHOR]

The more frequent occurrence of marine harmful algal blooms (HABs) and recent problems with newly-described toxins in Puget Sound have increased the risk for illness and have negatively impacted sustainable access to shellfish in Washington State. Marine toxins that affect safe shellfish harvest because of their impact on human health are the saxitoxins that cause paralytic shellfish poisoning (PSP), domoic acid that causes amnesic shellfish poisoning (ASP), diarrhetic shellfish toxins that cause diarrhetic shellfish poisoning (DSP) and the recent measurement of azaspiracids, known to cause azaspiracid poisoning (AZP), at low concentrations in Puget Sound shellfish. The flagellate, Heterosigma akashiwo, impacts the health and harvestability of aquacultured and wild salmon in Puget Sound. The more recently described flagellates that cause the illness or death of cultivated and wild shellfish, include Protoceratium reticulatum, known to produce yessotoxins, Akashiwo sanguinea and Phaeocystis globosa. This increased incidence of HABs, especially dinoflagellate HABs that are expected in increase with enhanced stratification linked to climate change, has necessitated the partnership of state regulatory programs with SoundToxins, the research, monitoring and early warning program for HABs in Puget Sound, that allows shellfish growers, Native tribes, environmental learning centers and citizens, to be the "eyes on the coast". This partnership enables safe harvest of wholesome seafood for consumption in the region and helps to describe unusual events that impact the health of oceans, wildlife and humans. [ABSTRACT FROM AUTHOR]

IntroductionIn recent years, environmental DNA (eDNA) amplicon sequencing has been used to unveil plankton diversity in the field. Nevertheless, molecular methods, such as this, are rarely used in harmful algal bloom (HAB) monitoring programs, which mainly rely on morphological identification by conventional light microscopy.MethodsThe present study focused on a shallow marine environment (Ría de Vigo, Northwest Spain), where sediment and plankton samples were collected from 2016 to 2018.ResultsThe application of eDNA amplicon sequencing allowed us to simultaneously detect 25 potential harmful species (mainly diatoms and dinoflagellates) included in the IOC-UNESCO Taxonomic Reference List of Harmful Microalgae. Among these, causative agents of amnesic shellfish poisoning (Pseudo-nitzschia spp.) paralytic shellfish poisoning (Gymnodinium catenatum and Alexandrium minutum), azaspiracid producers (Azadinium poporum) and ichthyotoxic haptophytes (Chrysochromulina leadbeateri), were identified. Some toxic microalgae were better represented in sediment (e.g., Pseudo-nitzschia pungens, Gymnodinium catenatum) or planktonic fractions (e.g., Pseudo-nitzschia, Gymnodinium smaydae), confirming the importance of including both sediment and plankton fractions in eDNA monitoring studies. Despite the limitations of sequencing short amplicons, it was possible to discern in this study six Pseudo-nitzschia species and associate each of them with each seasonal peak produced in summer periods. Furthermore, several species previously unreported in Ría de Vigo (Pseudo-nitzschia turgidula, Chrysochromulina leadbeateri, Azadinium poporum) could be detected.DiscusionThese results point out the application of eDNA amplicon sequencing to expand our knowledge about harmful species in HAB monitoring programs and early warning systems for low abundant and rare taxa.

Abstract Diatoms’ bloom dynamics, with seasonal cycling of waxes and wanes of cell abundance, imply frequent bottleneck and expansion events that can leave signatures in the genetic structure and diversity of populations. We explored changes in genetic diversity and structure within multiple species of the planktonic marine diatom genus Pseudo‐nitzschia living in sympatry in the Gulf of Naples (Tyrrhenian Sea, Italy) over 48 sampling dates (from 2011 to 2013) by means of metabarcode data. The genus Pseudo‐nitzschia includes complexes of cryptic species along with morphologically distinguishable ones. We assessed the resolution power of the hypervariable V4 region of the 18S rDNA in delimiting species using different algorithms and a set of reference sequences. We measured intra‐specific genetic diversity and differentiation among species over three annual cycles. Between‐species divergence was higher in the P. pseudodelicatissima complex, while signs of incomplete lineage sorting and/or introgression were detected in the P. delicatissima complex. Most of the species showed significant population differentiation over time, due to changes in haplotypic composition over the three years. Some haplotypes were lost and new ones appeared, with high polymorphism in species of the P. delicatissima complex. We hypothesize that the observed temporal changes in genetic structure result from frequent founder events linked to a population dynamic characterized by cyclical alternation of clonal expansions and bottlenecks and discuss possible factors affecting the microevolutionary pathways in these planktonic diatoms.

Diatoms are one of the most important phytoplankton groups in the world’s oceans. There are responsible for up to 40% of the photosynthetic activity in the Ocean, and they play an important role in the silicon and carbon cycles by decoupling carbon from atmospheric interactions through sinking and export. These processes are strongly influenced by the taxonomic composition of diatom assemblages. Traditionally, these have been assessed using microscopy, which in some cases is not reliable or reproducible. Next-generation sequencing enabled us to study diversity in a high-throughput manner and uncover new distribution patterns and diversity. However, phylogenetic markers used for this purpose, such as various 18S rDNA regions, are often insufficient because they cannot distinguish between some taxa. In this work, we demonstrate the performance of the chloroplast-encoded rbcL marker for metabarcoding marine diatoms compared to microscopy and 18S-V9 metabarcoding using a series of monthly samples from the Gulf of Trieste (GoT), northern Adriatic Sea. We demonstrate that rbcL is able to detect more taxa compared to 18S-V9 metabarcoding or microscopy, while the overall structure of the diatom assemblage was comparable to the other two methods with some variations, that were taxon dependent. In total, 6 new genera and 22 new diatom species for the study region were identified. We were able to spot misidentification of genera obtained with microscopy such as Pseudo-nitzschia galaxiae, which was mistaken for Cylindrotheca closterium, as well as genera that were completely overlooked, such as Minidiscus and several genera from the Cymatosiraceae family. Furthermore, on the example of two well-studied genera in the region, namely Chaetoceros and particularly Pseudo-nitzschia, we show how the rbcL method can be used to infer even deeper phylogenetic and ecologically significant differences at the species population level. Despite a very thorough community analysis obtained by rbcL the incompleteness of reference databases was still evident, and we shed light on possible improvements. Our work has further implications for studies dealing with taxa distribution and population structure, as well as carbon and silica flux models and networks.

Fragilaria and Ulnaria are two closely related diatom genera for which the delimitation and circumscription of several species is unclear. We studied strains isolated from Lake Baikal and compared them with the species from freshwater reservoirs in Europe and Asia using phylogenetic and species delimitation methods, microscopy and interclonal crossing experiments. The results of the phylogenetic analyses of the fragments of rbcL and 18S rRNA genes revealed that baikalian F. radians clade was independent from the representatives of the genus from other localities. Among Ulnaria we found the following 18S rRNA phylogenetic tree groups at species level: U. acus, U. ulna and U. danica. Genetic distance between genera varied between 3.9–10.2% substitutions in rbcL gene and 3.2–11.5% in 18S rRNA. The boundary between intraspecies and interspecies polymorphism for studied species of Ulnaria and Fragilaria in these marker genes was around 0.8% substitutions. Morphometric characters of individual strains showed their variability and division into F. radians, U. acus and U. ulna together with U. danica. Strains of U. acus and U. danica from different localities of Europe and Asia were sexually compatible inside the species. Sexual reproduction has never been observed in monoclonal cultures, either between this species or with strains of the Fragilaria. [ABSTRACT FROM AUTHOR]

Domoic acid (DA) is a neurotoxin mainly produced by Pseudo-nitzschia diatom, which belongs to the genera Rhomboida. It can combine with the receptors of glutamate of neurotransmitters, then affecting the normal nerve signal transmission of the organism and causing nervous system disorders. However, as a natural marine drug, DA can also be used for pest prevention and control. Although the distribution of DA in the world has already been reported in the previous reviews, the time and location of its first discovery and the specific information are not complete. Therefore, the review systematically summarizes the first reported situation of DA in various countries (including species, discovery time, and collection location). Furthermore, we update and analyze the factors affecting DA production, including phytoplankton species, growth stages, bacteria, nutrient availability, trace metals, and so on. These factors may indirectly affect the growth environment or directly affect the physiological activities of the cells, then affect the production of DA. Given that DA is widely distributed in the environment, we summarize the main technical methods for the determination of DA, such as bioassay, high-performance liquid chromatography (HPLC), enzyme-linked immunosorbent assay (ELISA), biosensor, and so on, as well as the advantages and disadvantages of each method used so far, which adds more new knowledge in the literature about DA until now. Finally, the DA research forecast and its industrial applications were prospected to prevent its harm and fully explore its potential value. [ABSTRACT FROM AUTHOR]

Domoic acid (DA) is a potent neurotoxin produced by worldwide distributed diatoms of the genus Pseudo-nitzchia (PSN) and is responsible for Amnesic Shellfish Poisoning (ASP) in humans. King scallop Pecten maximus, a bivalve species of high commercial interest, is regularly subjected to blooms of Pseudo-nitzschia sp., thus accumulating and retaining high levels of DA for extended periods, leading to prolonged fisheries and aquaculture closures and important economic losses following increasingly recurrent toxic PSN blooms. The underlying mechanisms behind this accumulation and long toxin retention remain poorly understood so far. Fishermen and the aquaculture industry ask for methods to accelerate DA depuration in contaminated scallops, which has led to investigate the effect of some substances such as the antioxidant N-Acetylcysteine (NAC), which was previously found to improve up to four-fold DA depuration in P. maximus adductor muscle. Our study investigated the potential of NAC to accelerate DA depuration in all scallop tissues, including the digestive gland (DG), where most of the toxin is accumulated. Twenty-four contaminated adult scallops were collected following a toxic P. australis bloom in the Bay of Brest (France) and half were treated with the antioxidant NAC (250 mg L−1) for 6 days. HPLC toxin quantification analyses did not revealed any significant differences in the DA burdens in the DG between treated scallops and the control group. DA amounts in the adductor muscle and gonads were below the HPLC detection limit in both groups. Our results revealed that NAC does not thus appear as a commercially suitable solution for fisheries and aquaculture industries as DA depuration enhancer in the tested conditions. [ABSTRACT FROM AUTHOR]

Marine heat waves (MHWs) have been associated with extensive harmful algal blooms (HABs) in the northeast Pacific Ocean, but the degree to which these large-scale oceanographic events are mirrored in nearshore environments has not been well established. We compared phytoplankton assemblages in the Lower Columbia River Estuary (LCRE) during two Pacific MHWs that took place in 2015 and 2019, with observations from 2017, a year with no MHW. These data were paired with environmental data from the summers of 2015–2019 to characterize differences in estuarine conditions during MHWs that promote phytoplankton assemblage transitions and identify HAB-conducive conditions. Bloom densities of HAB taxa, Pseudo-nitzschia spp. (4.16 × 106 cells L−1) and Gymnodinium catenatum (5.66 × 106 cells L−1), were noted in the estuary during 2015 and 2019, respectively, 2 years where Pacific MHWs occurred during the summer months. These blooms coincided with estuary temperatures that were 1–2 ℃ above and river discharge volumes 46–48% lower than decadal daily averages. We identified patterns in the densities of several algal taxa associated with MHW-mediated low discharge in the LCRE, such as declines in tychopelagic diatoms and increasing abundance of pelagic marine taxa. We conclude that low river discharge, through extension of saline habitat area and longer residence times, likely contributed to the development of the observed marine HABs in the estuary. MHWs and associated declines in discharge are projected to become more common in the Pacific Northwest with climate change, which may alter late summer phytoplankton assemblages in the LCRE. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) present an emerging threat to human and ecosystem health in the Alaskan Arctic. Two HAB toxins are of concern in the region: saxitoxins (STXs), a family of compounds produced by the dinoflagellate Alexandrium catenella, and domoic acid (DA), produced by multiple species in the diatom genus Pseudo-nitzschia. These potent neurotoxins cause paralytic and amnesic shellfish poisoning, respectively, in humans, and can accumulate in marine organisms through food web transfer, causing illness and mortality among a suite of wildlife species. With pronounced warming in the Arctic, along with enhanced transport of cells from southern waters, there is significant potential for more frequent and larger HABs of both types. STXs and DA have been detected in the tissues of a range of marine organisms in the region, many of which are important food resources for local residents. The unique nature of the Alaskan Arctic, including difficult logistical access, lack of response infrastructure, and reliance of coastal populations on the noncommercial acquisition of marine resources for nutritional, cultural, and economic well-being, poses urgent and significant challenges as this region warms and the potential for impacts from HABs expands. [ABSTRACT FROM AUTHOR]

Diatoms are photosynthetic microorganisms playing a key role in the functioning of aquatic ecosystems; they are at the base of the food web and are the main drivers of biogeochemical processes. These microalgae have a unique diplontic life cycle in which the vegetative phase entails a cell size reduction that would lead to the extinction of the cell population if the size was not restored, usually by sexual reproduction. The switch from asexual to sexual reproduction needs to be finely synchronized and regulated to ensure its success; to this aim, cells evolved complex chemical crosstalk that mediates mating. We focused our attention on the marine diatom Pseudo-nitzschia multistriata, investigating the reciprocal perception of the opposite mating type (MT) and the genes and signaling molecules putatively involved in the process. From previously available transcriptomic data, we selected a panel of genes deregulated during the early phase of sexual reproduction, confirming for some of them a role during mate perception and establishing a hierarchy governing their behavior. Moreover, we explored the nature of the molecules controlling sexual reproduction in this species, unveiling that the signaling is mediated by the secretion of protein and non-protein cues from the MT− and MT+, respectively. Our results point to a model in which the two MTs stimulate each other, but the stimulation by the MT− is amplified after MT+ perception in a positive feedback manner. [ABSTRACT FROM AUTHOR]

• The queen scallop Aequipecten opercularis cannot be considered a fast DA depurator. • The subcellular localization of DA in A. opercularis is similar to that of the slowest DA depurator Pecten maximus. • Long retention of a part of DA initially accumulated in queen scallops is due to late autophagy. • The exploitation of A. opercularis stocks following ASP-outbreaks must be cautious. Domoic acid (DA) is a dangerous phycotoxin produced by several strains of diatoms of the genus Pseudo-nitzschia, and responsible for Amnesic Shellfish Poisoning (ASP) in humans. The increasingly intense ASP-outbreaks along the English Channel over the last three decades have forced persistent harvest closures of economically important and highly contaminated bivalve stocks exhibiting slow DA-depuration rates, like the king scallop Pecten maximus. Under this scenario, other pectinid species, such as the queen scallop Aequipecten opercularis have been empirically proposed as alternative resources to redress the high economic losses due to the banning of the exploitation of P. maximus. Nevertheless, the kinetics of DA depuration in A. opercularis have not been assessed so far, and its direct extraction after ASP-episodes could represent a serious threat to public health. Hence, the main objective of this work was to estimate the DA-depuration rate in the digestive gland (DG) of naturally contaminated scallops A. opercularis after a toxic Pseudo-nitzschia australis bloom subjected to experimental depuration in the laboratory for 30 days. This study also intended to go further in the knowledge about the anatomical distribution of DA in scallop tissues, and corroborate the implications of autophagy in DA-sequestration in the DG of this species as recently hypothesized. In the DG, the DA-depuration rate (0.018 day−1) suggested that even with toxin burdens as low as 40 mg⋅kg−1 in the DG, queen scallops may remain contaminated for about 70 days, thus longer under intensely contamination scenarios. The subcellular analyses corroborated DA-sequestration mainly through late-autophagy within residual bodies in the DG, without differences in the frequencies of anti-DA labeled residual bodies across the entire depuration process. These results revealed that A. opercularis cannot be considered a fast DA-depurator, and represent a baseline knowledge for decision-making about harvesting natural beds of queen scallops after toxic Pseudo-nitzschia blooms. The findings of this work also represent a cornerstone for further research to accelerate DA-depuration in this species. [ABSTRACT FROM AUTHOR]

• High-resolution imaging can reveal relationships between phytoplankton genera. • Pseudo-nitzschia tends to bloom concurrently with or right after other phytoplankton. • Such bloom periods coincide with higher water temperatures and lower salinity. • The width of Pseudo-nitzschia chains or their estimated biovolume may be used to approximate harmful algal bloom risk in the absence of toxin data. Phytoplankton populations in the natural environment interact with each other. Despite rising global concern with Pseudo-nitzschia blooms, which can produce the potent neurotoxin domoic acid, we still do not fully understand how other phytoplankton genera respond to the presence of Pseudo-nitzschia. Here, we used a 4-year high-resolution imaging dataset for 9 commonly found phytoplankton genera in Narragansett Bay, alongside environmental data, to identify potential interactions between phytoplankton genera and their response to elevated Pseudo-nitzschia abundance. Our results indicate that Pseudo-nitzschia tends to bloom either concurrently with or right after other phytoplankton genera. Such bloom periods coincide with higher water temperatures and lower salinity. Pseudo-nitzschia image abundance tends to increase the most from March-May and peaks during May-Jun, whereas the image-derived biovolume and width of Pseudo-nitzschia chains increase the most during Jan-Feb. For most phytoplankton genera, their relationship with Pseudo-nitzschia abundance is noticeably different from their relationship with Pseudo-nitzschia image features. Despite the complexity in the phytoplankton community, our analysis suggests several ecological indicators that may be used to determine the risk of harmful algal blooms. [ABSTRACT FROM AUTHOR]