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This comprehensive study explores the intricate relationships between nutrient conditions and the growth patterns of Thalassiosira weissflogii and Chaetoceros calcitrans. Distinct flasks, subjected to varied nutrient compositions, were monitored for cell density and specific growth rates over a span of 168 hours. T. weissflogii exhibited distinct responses to F/2 Guillard media, with notable changes in cell density and growth rates, while C. calcitrans showcased nuanced dynamics under different nutrient conditions. The molecular confirmation, ITS gene sequence were done for the two microalgae strains that were bound to marine. High percentage similarity in the BLAST results of the microalgae sequences identified the species as Thalassiosira weissflogii (99.84%) and Chaetoceros calcitrans (99.79%). To accurately identify microalgae at the genus and species levels, a combination of the classical and genetic approaches is essential. The findings offer valuable insights into optimizing microalgae cultivation for biotechnological and environmental applications. [ABSTRACT FROM AUTHOR]

Most phytoplankton, including harmful algal bloom (HAB)-forming species, have an absolute requirement for vitamin B12 (cobalamin). However, the cycling of vitamin B12 in the ocean is still poorly understood. For example, in the Ariake Sea, where local fisheries have been affected by HABs, the impact of vitamin B12 on phytoplankton dynamics has never been evaluated. This study reports the surface distribution of cyanocobalamin (CN-B12, a type of vitamin B12) in the Ariake Sea and its adjacent areas. The field measurements were complemented with an additional onboard CN-B12 incubation experiment to elucidate the importance of the coenzyme on the growth of natural phytoplankton communities. Dissolved CN-B12 behaved dynamically and was often depleted in surface waters. Dominant phytoplankton in the Ariake Sea changed seasonally; all these taxa include vitamin B12 auxotrophs. The distribution of CN-B12 was controlled by dynamic production and consumption by natural phytoplankton and bacterial communities. We attempted to measure the concentration of particulate CN-B12; it was undetectable suggesting that CN-B12 form of vitamin B12 is not dominant inside the cell. No clear relationship existed between CN-B12 and any oceanographic parameters, suggesting that river discharge is unlikely a major source of CN-B12 in this area. Bottle incubation experiments showed that CN-B12 and nitrate additions promoted the growth of diatom Chaetoceros spp., implying that some phytoplankton groups are co-limited by them. These preliminary results suggest that vitamin B12 may affect the composition of the phytoplankton community in the Ariake Sea. [ABSTRACT FROM AUTHOR]

ABSTRACT This study evaluated the effect of co-feeding with commercial feed and live food (enriched or not with microalgae) on the growth and survival of Trachelyopterus galeatus larvae. Five treatments were carried out: commercial feed as a control (F); brine shrimp nauplii (BS); brine shrimp nauplii enriched with Chaetoceros sp. Microalgae (BSM); combined feed with brine shrimp nauplii (F+BS) and combined feed with brine shrimp nauplii enriched with microalgae (FBSM). The larvae (5.00±0.02 mg and 5.95±0.33mm) were reared for 30 days. There were no significant differences (P>0.05) in water quality between treatments, but there were significant differences in weight, weight gain and survival. The F+BS and F+BSM treatments, which involved co-feeding, showed the best results in final weight (0.168±0.004g and 0.169±0.007g) and weight gain (0.1278±0.004 g and 0.1294±0.007g), respectively. The treatments with live food, enriched or not, showed high survival rates of over 73%, with no significant differences between them. On the other hand, the exclusive use of feed resulted in low survival (36.7 ± 9.53%), indicating that this may result in low growth and make the production of T. galeatus larvae unfeasible.

Eleven species of brackish water Chaetoceros Ehrenberg newly recorded from Bangladesh have been illustrated and described in the present paper. The species are: Chaetoceros aequatorialis Cleve, C. constrictus Gran, C. decipiens Cleve, C. denicus Cleve, C. didymus Ehrenberg, C. diversus Cleve, C. pelagicus Cleve, C. pendulus Karsten, C. pseudobrevis Pavillard, C. seychellarus G.H.H. Karsten and C. tetrastichon Cleve. All of these species have been described here with citation of relevant references and collections examined. [ABSTRACT FROM AUTHOR]

Las comunidades biológicas están conformadas por grupos taxonómicos, donde el fitoplancton, como productor primario, tiene una relevancia ecológica: sirve para comprender la estructura y el funcionamiento de un ecosistema y la manera en la que los organismos interactúan con los parámetros fisicoquímicos. Con el fin de evaluar la riqueza y la abundancia del fitoplancton de la zona litoral del departamento del Atlántico y su asociación con las variables fisicoquímicas para conocer sus cambios espaciales y temporales, se realizaron monitoreos durante el año 2013. Se ubicaron cinco zonas a lo largo de la zona litoral como Astilleros, Santa Verónica, Puerto Velero, Puerto Colombia y Mallorquín. En cada una se establecieron tres estaciones, distribuidas en línea recta, con distancia entre ellas de 5 km. Para la recolecta de las muestras de fitoplancton y clorofila a (Cl-a), en cada una de las estaciones se filtraron 24 L de agua superficial, con un tambor cónico con malla de diámetro de poro de 24 µm y con botellas ámbar de 500 mL, respectivamente, las cuales se mantuvieron en oscuridad. Adicionalmente, se registraron in situ variables fisicoquímicas. Se identificaron un total de 560 cél.mL-1 de fitoplancton, agrupadas en 47 especies y cinco clases. Las Bacillariophyceae presentaron las mayores densidad y riqueza, seguidas de las Dinophyceae, Cyanophyceae, Euglenophyceae y Chlorophyceae. Chaetoceros sp. (83 cél.mL-1) y Chaetoceros lorenzianus (64 cél.mL-1) fueron las especies más abundantes y más representativas, precisamente por su abundancia. El análisis de Jaccard mostró una disimilitud de un 80 % entre las estaciones 5A, 5B y 5C, lo que indica una composición diferente. En general, las estaciones de monitoreo se comportaron como sitios contaminados con alta influencia de las aguas del río Magdalena.

The objective of this study was to identify morphological and molecular comparison of three marine Chaetoceros species using microscopic observations, sequence analysis of 18S rDNA, random amplified polymorphic DNA (RAPD-PCR) barcoding and nuclear magnetic resonance (NMR) spectroscopy. Chaetoceros were obtained from three different algae laboratories: Center of Excellence for Marine Biotechnology (CEMB), Chanthaburi Coastal Fisheries Research and Development (CHAN) and Institute of Marine Science, Burapha University (BIM). Genomic DNA for the RAPD-PCR analysis was extracted using the phenol–chloroform method, followed by 18S rDNA amplification. The blast results of 18S rDNA sequence confirmed the significantly matched to C. gracilis for Chaetoceros BIM and CHAN and C. muelleri for Chaetoceros CEMB(e-value = 0.0, identity = 99%). The RAPD-PCR results revealed differences in the three Chaetoceros isolates with polymorphisms between 30.43% and 60.00%, and Chaetoceros CEMB showed high polymorphic bands. Scanning electron microscopy revealed that Chaetoceros CEMB were larger and had larger setae compared to the other isolates (P < 0.05). The results of the NMR characterization of metabolites were consistent with the results of the sequence and morphological analyses. The concentrations of several metabolites, including chlorophyll c1, chlorophyll a, Myo-inositol, fucoxanthin, astaxanthin, lutein and zeaxanthin, were lower in Chaetoceros CEMB than in Chaetoceros BIM and CHAN. However, high concentrations of fatty acids, such as oleic acid, linoleic acid, α-linolenic acid and arachidic acid, were observed in all isolates. Generally, the results of this study will aid future studies examining the diversity of Chaetoceros in various cultural environments. [ABSTRACT FROM AUTHOR]

Se usó una zeolita natural cubana enriquecida para el cultivo de las microalgas marinas Tetraselmis suecica y Chaetoceros ceratosporum, especies utilizadas en la alimentación de larvas de camarón en cultivo. Se probaron diferentes concentraciones de zeolita (5, 10 y 25 mg/L) adicionándola al medio Guillard “f” (para C. ceratosporum) y “f/2” (para T. suecica) y se ensayaron diferentes porcentajes de utilización del medio (100, 75, 50 y 25% + zeolita en todos los casos). Se determinó velocidad de crecimiento (K), tiempo de duplicación (TD) yproducción (P) para la fase exponencial de los cultivos, que fueron desarrollados en condiciones controladas de iluminación, salinidad y temperatura. Los resultados demostraron que no hubo diferencias significativas, para α=0.05, entre los tratamientos con las diferentes proporciones de la zeolita, en ninguna de las dos especies. Todos los porcentajes de utilización del medio fueron diferentes al control, pero si comparamos los tratamientos de zeolitas, para el caso de T. suecica no se debe sustituir más del 25% del medio y para C. ceratosporum se puede sustituir hasta en un 50%. Los parámetros poblaciones no arrojaron diferencias significativas entre las diferentes proporciones de zeolita en ninguna de las especies. En T. suecica, cuando empleamos 75% del medio, se obtiene la mayor K y TD aunque la P para la fase exponencial fue menor significativamente que el control. Para C. ceratosporum la mayor K se obtuvo sustituyendo el 50% del medio, el TD fue similar para todos los tratamientos con zeolitas y la P fue mayor con el control porque no decayó el cultivo.

• Characterization of first Pseudo-Nitzschia Sp. infecting ssRNA viruses. • Genome assembly of ssRNA virus infecting toxigenic Pseudo-Nitzchia galaxiae. • qPCR assay development for novel virus monitoring. • Discovery of viral agents infecting Pseudo-Nitzschia calliantha. • Characterization of ChTenDNA virus type-II in a new oceanographic environment. Algal blooms impact trophic interactions, community structure and element fluxes. Despite playing an important role in the demise of phytoplankton blooms, only few viruses infecting diatoms have been cultured. Pseudo-nitzschia is a widespread diatom genus that commonly blooms in coastal waters and contains toxin-producing species. This study describes the characterization of a novel virus infecting the toxigenic species Pseudo-nitzschia galaxiae isolated from the northern Adriatic Sea. The ssRNA virus PnGalRNAV has 29.5 nm ± 1.2 nm icosahedral virions and a genome size of 8.8 kb. It belongs to the picorna-like Marnaviridae family and shows high specificity for P. galaxiae infecting two genetically and morphologically distinct strains. We found two genetically distinct types of this virus and screening of the global virome database revealed matching sequences from the Mediterranean region and China, suggesting its global distribution. Another virus of similar shape and size infecting Pseudo-nitzschia calliantha was found, but its genome could not be determined. In addition, we have obtained and characterized a new virus that infects Chaetoceros tenuissimus. The replicase protein of this virus is very similar to the previously described ChTenDNAV type-II virus, but it has a unique genome and infection pattern. Our study is an important contribution to the collective diatom virus culture collection and will allow further investigation into how these viruses control diatom bloom termination, carbon export and toxin release in the case of Pseudo-nitzschia. [Display omitted] [ABSTRACT FROM AUTHOR]

The marine algae Chaetoceros contains hexadecatrienoic acid, which suppresses methanogen development and improves the coulombic efficiency (CE) of microbial fuel cells (MFC). To inhibit the methanogens, optimum concentration of marine algae should be added to the anaerobic sludge to enhance the performance of MFC. A varying concentration of Chaetoceros ranging from 1 to 20 mg/mL was carried out for pretreatment of an anaerobic-mix consortium to suppress methanogens. MFC inoculated with pretreated anaerobic sludge with 10 mg/mL Chaetoceros showed a maximum power density of 21.62 W/m3 and a maximum CE of 37.25%, which was considerably higher than the treatment with other concentrations. At 10 mg/mL concentration, Tafel analysis of the anode in the MFC showed a higher exchange current density of 66.35 mA/m2 and a lower charge transfer resistance of 0.97 Ω.m2, revealing higher bio-electrochemical activity. The performance of MFC improved when the concentration of Chaetoceros was increased up to 10 mg/mL, but then began to decline as the concentration increased further. Thus, the optimum dose of Chaetoceros to be added in the mix-anaerobic consortium to optimize the power performance of MFC was determined, which can be carried out in scaled-up MFCs. HIGHLIGHTS Coulombic efficiency has improved to 37.25 at a dose of 10 mg/mL Chaetoceros sp. dosing.; A maximum power density of 21.62 W/m3 could be obtained at a concentration of 10 mg/mL of Chaetoceros sp.; A higher exchange current density of 66.35 mA/m2 was obtained at the optimum concentration.; The dosing was found to be sustainable at the optimum dosing.; Specific methanogenic activity was found to be less at the optimum dose.;

Although the extreme conditions of the deep sea are typically not suitable for the growth of photosynthetic algae, accumulating evidence indicates that there are diverse healthy phytoplankton living in this environment. However, living phytoplankton from the deep sea have rarely been isolated and cultivated, and so our understanding of where they come from and how they adapt to (or tolerate) the extreme deep‐sea environment is limited. Here, under long‐term dark stress and subsequent light treatment, we successfully isolated a diatom from a depth of 1,000 m in the Western Pacific Ocean. Morphological observations and molecular phylogenetic analysis revealed that it is affiliated to the genus Chaetoceros, and thus, we tentatively named it Chaetoceros sp. DS1. We observed that the chloroplast genome of this species, is most closely related to that of Chaetoceros simplex. It was shown to have a strong tolerance to darkness in that it maintained its morphological integrity and vitality for up to 3 months in complete darkness at room temperature. We also demonstrated that Chaetoceros sp. DS1 presented a facultative heterotrophic function. Its growth was promoted by many organic carbon sources (e.g., glycerine, ethanol, and sodium acetate) under low light conditions. However, under dark and high light conditions, the growth promotion effect of organic carbon was not obvious. Indeed, Chaetoceros sp. DS1 grew best under low light conditions, indicating that it likely came from the deeper layer of the euphotic zone. The facultative heterotrophic function of this diatom and tolerance to darkness may help it survive in these conditions or enter a dormant period in the deep sea. [ABSTRACT FROM AUTHOR]

Plankton merupakan organisme kecil yang melayang di dalam badan air pada perairan dan memiliki kemampuan bergerak yang pasif. Perubahan kondisi lingkungan menentukan kehadiran komunitas plankton yang hadir. Plankton terbagi menjadi fitoplankton dan zooplankton. Fitoplankton merupakan plankton yang dapat melakukan fotosintesis. Salah daerah pesisir yang berada di Kota Langsa adalah Pulau Pusong. Penelitin ini bertujuan untuk mengetahui jenis fitoplankton apa saja yang terdapat di perairan sekitar Pulau Pusong dan kondisi lingkungan di perairan sekitar Pulau Pusong. Pencuplikan sampel plankton di perairan Pulau Pusong dilakukan sebanyak empat titik sampling. Pengukuran sampel air dilakukan dengan tiga ulangan. Ada 30 jenis fitoplankton yang diperoleh yang terdiri dari genus yaitu Bacillaria, Bacteriastrum, Biddulphia, Ceratium, Chaetoceros, Coscinusdiscus, Dactyliosolen, Dithylum, Eucampia, Leucosolonia, Merismopedia, Navicula, Nitzschia, Odentella, Planktonella, Pseudo-nitzschia, Pyrocystis, Rhizosolenia, dan Thalassionema.

Unusual occurrence of planktonic diatom species, Chaetoceros bacteriastroides and Chaetoceros pseudosymmetricus, was noticed in three different marine ecosystems of Adriatic Sea: the Krka Estuary and Telaščica Bay in the Central Adriatic, and in southern Adriatic offshore. From 2010 to 2015, these two Chaetoceros species were recorded in heterogeneous environmental conditions and in a very low abundances. Both species are regarded as very rare in world oceans, and consequently knowledge of their distribution and ecology is rather poor. Primarily described from tropical waters and showing Indo-Pacific distribution, C. bacteriastroides and C. pseudosymmetricus findings in Adriatic represent the northernmost records in world's oceans and seas. For C. pseudosymmetricus this is also the first occurrence in European seas. Areal expansion and introduction of new phytoplankton species in the Adriatic Sea might be related to different circulation regimes in the Ionian Sea and the concurrent rise in sea temperature in the Mediterranean in the last decade. Recent investigations have shown that entering currents, of either Atlantic/Western Mediterranean or Eastern Mediterranean origin, modify the composition of the plankton community in the Adriatic by bringing different newcomers.

Nutrient inputs to coastal waters are among the main contributors to phytoplankton blooms that can damage coastal ecosystems. To understand the main causal factors and timing of phytoplankton blooms in Patong Bay, where phytoplankton blooms have frequent occurred for the last decade, variations in phytoplankton abundance and the dissolved inorganic nutrients (nitrogen (DIN), phosphorus (DIP), and dissolved silica (DSi)) were monitored weekly from December 2021 to December 2022. The results revealed that ratios of DIP and DSi to DIN in seawater had increased rapidly in approximately 1–7 days prior to the blooms of Chaetoceros and Eunotogramma. This suggests that the diatom blooms in this area are significantly controlled by an excess of DIP and DSi, in otherwise appropriate environmental conditions. Our findings provide a thorough understanding of the role of excess nutrients on phytoplankton blooms in urban coastal waters, supporting informed coastal management actions. [Display omitted] • Runoff discharge is the major source of dissolved inorganic nutrients in Patong Bay. • Variations of DSi and DIP in seawater involve biological processes; DIN involves biogeochemistry. • Excessive DSi and DIP relative to DIN can induce diatom blooms. [ABSTRACT FROM AUTHOR]

Oil spills have immediate adverse effects on marine ecological functions. Accurate assessment of the damage caused by the oil spill is of great significance for the protection of marine ecosystems. In this study the observation data of Chaetoceros and shellfish before and after the Penglai 19-3 oil spill in the Bohai Sea were analyzed by the least-squares fitting method and radial basis function (RBF) interpolation. Besides, an oil transport model is provided which considers both the hydrodynamic mechanism and monitoring data to accurately simulate the spatial and temporal distribution of total petroleum hydrocarbons (TPH) in the Bohai Sea. It was found that the abundance of Chaetoceros and shellfish exposed to the oil spill decreased rapidly. The biomass loss of Chaetoceros and shellfish are 7.25×1014~7.28×1014 ind and 2.30×1012~2.51×1012 ind in the area with TPH over 50 mg/m3 during the observation period, respectively. This study highlights the evaluation of ecological resource loss caused by the oil spill, which is useful for the protection and restoration of the biological resources following the oil spill.

Information on taxa distribution is a prerequisite for many research fields, and biological records are a major source of data contributing to biogeographic studies. The Global Biodiversity Information Facility (GBIF) and the Ocean Biogeographic Information System (OBIS) are important infrastructures facilitating free and open access to classical biological data from several sources in both temporal and spatial scales. Over the last ten years, high throughput sequencing (HTS) metabarcoding data have become available, which constitute a great source of detailed occurrence data. Among the global sampling projects that have contributed to such data are Tara Oceans and the Ocean Sampling Day (OSD). Integration of classical and metabarcoding data may aid a more comprehensive assessment of the geographic range of species, especially of microscopic ones such as protists. Rare, small and cryptic species are often ignored in surveys or mis-assigned with the classical approaches. Here we show how integration of data from various sources can contribute to insight in the biogeography and diversity at the genus- and species-level using Chaetoceros as study system, one of the most diverse and abundant genera among marine planktonic diatoms. Chaetoceros records were extracted from GBIF and OBIS and literature data were collected by means of a Google Scholar search. Chaetoceros references barcodes where mapped against the metabarcode datasets of Tara Oceans (210 sites) and OSD (144 sites). We compared the resolution of different data sources in determining the global distribution of the genus and provided examples, at the species level, of detection of cryptic species, endemism and cosmopolitan or restricted distributions. Our results highlighted at genus level a comparable picture from the different sources but a more complete assessment when data were integrated. Both the importance of the integration but also the challenges related to it were illustrated. Chaetoceros data collected in this study are organised and available in the form of tables and maps, providing a powerful tool and a baseline for further research in e.g., ecology, conservation and evolutionary biology.

We recently demonstrated the rapid adaptation of Red Sea phytoplankton to ocean warming, with associated constraints on physiological performance. However, the possible tradeoff between thermal adaptation and the organism's tolerance to other environmental drivers in a warmer future remains understudied. Here, we designed an evolutionary selection environment where the Red Sea diatom Chaetoceros tenuissimus was adapted to ambient (26°C) and warming (30°C) temperature scenarios for over 2,000 generations. These strains were subsequently exposed to a range of copper (Cu) dose over three assay temperatures (26, 30, and 35°C), to assess whether adaptation to experimental warming is accompanied by a reformed tolerance to toxic pollutants. Most previous studies on Cu toxicity in marine phytoplankton were conducted within a smaller range of temperature (20–25°C), indicating the need for further assessments to reveal the potential complex interactive effects between pollutants and more significant warming in the future. The acute Cu toxicity was estimated in terms of reduction in cell abundance (cells mL−1), growth rate (μ) and PSII photosynthetic efficiency (Fv/Fm), with 48 h median effective concentration values (EC50) ranging from 2.22 to 20.19 μg L−1. We found a statistically significant interaction between assay temperature, selection temperature, and Cu doses in all the criteria tested. However, under the extreme warming scenario (35°C), the Cu sensitivity was significantly reduced, indicating cumulative antagonistic effects between these factors. Adaptation of phytoplankton to higher temperatures may help maintain their heavy metal tolerance, although a shift in temperature during the tests clearly altered their sensitivities. We conclude that selection for warming had made cells more resistant to Cu at the selection temperature in comparison to ambient-adapted population tested at 26°C. However, in warming-adapted cells, this response was traded off against cupper resistance at 26°C.

Interactions between phytoplankton and bacteria play a central role in mediating biogeochemical cycling and food web structure in the ocean. The cosmopolitan diatoms Thalassiosira and Chaetoceros often dominate phytoplankton communities in marine systems. Past studies of diatom-bacterial associations have employed community-level methods and culture-based or natural diatom populations. Although bacterial assemblages attached to individual diatoms represents tight associations little is known on their makeup or interactions. Here, we examined the epibiotic bacteria of 436 Thalassiosira and 329 Chaetoceros single cells isolated from natural samples and collection cultures, regarded here as short- and long-term associations, respectively. Epibiotic microbiota of single diatom hosts was analyzed by cultivation and by cloning-sequencing of 16S rRNA genes obtained from whole-genome amplification products. The prevalence of epibiotic bacteria was higher in cultures and dependent of the host species. Culture approaches demonstrated that both diatoms carry distinct bacterial communities in short- and long-term associations. Bacterial epibonts, commonly associated with phytoplankton, were repeatedly isolated from cells of diatom collection cultures but were not recovered from environmental cells. Our results suggest that in controlled laboratory culture conditions bacterial–diatom and bacterial–bacterial interactions select for a simplified, but specific, epibiotic microbiota shaped and adapted for long-term associations.

Potential production of fucoxanthin from a marine diatom (Chaetoceros sp.) isolated from the Pranburi River mouth, Gulf of Thailand was investigated. Results showed that Chaetoceros sp. had a high growth rate. Specific growth rate (µ) was approximately 0.59 day-1, while doubling time was approximately 1.18 days under irradiance of 70 µmol photons·m-2·s-1. Specific growth rate increased with increasing irradiance (µ=1.04 at 140 µmol photons·m-2·s-1). The doubling time of this Chaetoceros sp. was only 0.67 days under irradiance of 140 µmol photons·m-2·s-1. Results from HPLC analysis demonstrated that Chaetoceros sp. gave maximum fucoxanthin production at 7.68 mg·g-1 dry weight or 5.87 pgcell-1 under irradiance of 140 µmol photons·m-2·s-1. Findings implied that the selected Chaetoceros sp. showed higher potential for commercial-scale fucoxanthin production than other seaweeds and diatoms. [ABSTRACT FROM AUTHOR]

The chemical composition of five marine microalgae (Dunaliella sp., Dunaliella salina , Chaetoceros calcitrans , Chaetoceros gracilis and Tisochrysis lutea) was investigated through nuclear magnetic resonance (NMR) spectroscopic study of the soluble material obtained by sequential extraction with hexane, ethyl acetate (AcOEt) and methanol of biomass from stationary phase cultures. Hexane extracted the major lipids present in the microalgae during the stationary phase of growth, which correspond to storage lipids. Triacylglycerols (TGs) were the only storage lipids produced by Dunaliella and Chaetoceros. In contrast, T. lutea predominantly stored polyunsaturated long-chain alkenones, with sterols also detected as minor components of the hexane extract. The molecular structure of brassicasterol was determined in T. lutea and the presence of squalene in this sample was also unequivocally detected. Monogalactosyldiacylglycerols (MGDGs) and pigments were concentrated in the AcOEt extracts. C. calcitrans and D. salina constituted an exception due to the high amount of TGs and glycerol produced, respectively, by these two strains. Chlorophylls a and b and β-carotene were the major pigments synthesized by Dunaliella and chlorophyll a and fucoxanthin were the only pigments detected in Chaetoceros and T. lutea. Information concerning the acyl chains present in TGs and MGDGs as well as the positional distribution of acyl chains on the glycerol moiety was obtained by NMR analysis of hexane and AcOEt extracts, with results consistent with those expected for the genera studied. Fatty acid composition of TGs in the two Dunaliella strains was different, with polyunsaturated acyl chains almost absent in the storage lipids produced by D. salina. Except in C. calcitrans , the polar nature of soluble compounds was inferred through the relative extraction yield using methanol as the extraction solvent. Glycerol was the major component of this fraction for the Dunaliella strains. In T. lutea 1,4/2,5-cyclohexanetetrol (CHT) and dimethylsulfoniopropionate (DMSP) preponderated. CHT was also the major polyol present in the Chaetoceros strains in which DMSP was not detected, but prominent signals of 2,3-dihydroxypropane-1-sulfonate (DHSP) were observed in the 1H NMR spectra of methanolic extracts. The presence of DHSP confirms the production of this metabolite by diatoms. In addition, several other minor compounds (digalactosyldiacyglycerols (DGDGs), sulphoquinovosyldiacylglycerols (SQDGs), amino acids, carbohydrates, scyllo -inositol, mannitol, lactic acid and homarine) were also identified in the methanolic extracts. The antibacterial and antibiofilm activities of the extracts were tested. The AcOEt extract from C. gracilis showed a moderate antibiofilm activity. Image 1 • 34 metabolites of diverse nature are identified through NMR analysis. • T. lutea is characterized by PULCA, brassicasterol, squalene and DMSP production. • FFA composition depend on the microalgae and FFA distribution in TG and MGDG differs. • Dunaliella strains biosynthesize β-carotene and Chaetoceros and T. lutea fucoxanthin. • DHSP production is shown as a distinctive feature of diatoms. [ABSTRACT FROM AUTHOR]

Information on taxa distribution is a prerequisite for many research fields, and biological records are a major source of data contributing to biogeographic studies. The Global Biodiversity Information Facility (GBIF) and the Ocean Biogeographic Information System (OBIS) are important infrastructures facilitating free and open access to classical biological data from several sources in both temporal and spatial scales. Over the last ten years, high throughput sequencing (HTS) metabarcoding data have become available, which constitute a great source of detailed occurrence data. Among the global sampling projects that have contributed to such data are Tara Oceans and the Ocean Sampling Day (OSD). Integration of classical and metabarcoding data may aid a more comprehensive assessment of the geographic range of species, especially of microscopic ones such as protists. Rare, small and cryptic species are often ignored in surveys or mis-assigned with the classical approaches. Here we show how integration of data from various sources can contribute to insight in the biogeography and diversity at the genus- and species-level using Chaetoceros as study system, one of the most diverse and abundant genera among marine planktonic diatoms. Chaetoceros records were extracted from GBIF and OBIS and literature data were collected by means of a Google Scholar search. Chaetoceros references barcodes where mapped against the metabarcode datasets of Tara Oceans (210 sites) and OSD (144 sites). We compared the resolution of different data sources in determining the global distribution of the genus and provided examples, at the species level, of detection of cryptic species, endemism and cosmopolitan or restricted distributions. Our results highlighted at genus level a comparable picture from the different sources but a more complete assessment when data were integrated. Both the importance of the integration but also the challenges related to it were illustrated. Chaetoceros data collected in this study are organised and available in the form of tables and maps, providing a powerful tool and a baseline for further research in e.g., ecology, conservation and evolutionary biology. [ABSTRACT FROM AUTHOR]

Small-scale turbulence in the surface ocean is ubiquitous, influencing phytoplankton dynamics with consequences for energy flow. The underlying mechanisms that drive changes in phytoplankton dynamics under turbulence are not well constrained. We investigated growth of four phytoplankton species at different turbulence levels in oscillating grid tanks. We also measured transparent exopolymer particles (TEP) from phytoplankton exudates, which play a major role in biogeochemical fluxes in the ocean. Turbulence levels in the tanks reflected in situ conditions in surface waters from the open ocean to higher turbulent environments such as estuaries. Growth rates were unaffected by turbulence while TEP concentrations as xanthan gum (XG) equivalents normalized to algal cells showed generally higher levels in the high turbulence compared to the low turbulence treatments particularly during initial algal growth. Results from a mixing experiment without algal cells and XG also revealed enhanced formation of TEP-like particles under high mixing conditions, indicating that TEP formation in the phytoplankton turbulence treatments was mainly driven by physical processes, such as enhanced encounter rates of TEP-precursors under high mixing. Our results underline the importance of small-scale turbulence on TEP formation with possible consequences for particle aggregation and vertical carbon fluxes in the ocean. [ABSTRACT FROM AUTHOR]

Microalgae are microscopic organisms that are usually identified based on the morphological features. However traditional classification are complicated by high levels of morphological plasticity and convergence that will lead to uncertain identification especially at the species level. Therefore, molecular marker is advantageous to distinguish and correctly identify microalgae at the lowest taxonomic level based on the genetic information and phylogenetic analyses. In the present study, we have characterized five strains of microalgae that were deposited in Borneo Marine Research Institute based on 18S rDNA gene sequences. The BLAST results of microalgae sequences showed high percentage similarities that revealed the species as Chaetoceros gracilis (99.77%), Thalassiosira weissflogii (99.70%), Nannochloropsis oceanica (100%) and Isochrysis sp. (99.97%). Combination of both classical and genetic approach is vital to clearly identify microalgae at generic and species levels. [ABSTRACT FROM AUTHOR]

Abstract Chaetoceros is a dominant genus of marine planktonic diatoms with worldwide distribution. Due to the difficulty of extracting setae from Chaetoceros images, automatic segmentation of Chaetoceros is still a challenging task. In this paper, we address this difficult task by regarding the whole segmentation process as unsupervised pixel-wise classification without human participation. First, we automatically produce positive (object) and negative (background) samples for follow-up training, by combining the advantages of two image processing algorithms: Grayscale Surface Direction Angle Model (GSDAM) for extracting setae information and Canny for detecting cell edges from low-contrast and strong-noisy microscopic images. Second, we develop pixel-wise training by using the produced samples in the training process of Deep Convolutional Neural Network (DCNN). At last, the trained DCNN is used to label other pixels into object and background for final segmentation. We compare our method with eight mainstream segmentation approaches: Otsu's thresholding, Canny, Watershed, Mean Shift, gPb-owt-ucm, Normalized Cut, Efficient Graph-based method and GSDAM. To objectively evaluate segmentation results, we apply six well-known evaluation indexes. Experimental results on a new Chaetoceros image dataset with human labelled ground truth show that our method outperforms the eight mainstream segmentation methods in terms of both quantitative and qualitative evaluation. [ABSTRACT FROM AUTHOR]

To understand the diversity of the diatom genus Chaetoceros Ehrenberg, the C. lorenzianus complex was previously chosen as a model and three new species were described. In the present study, yet another new species, Chaetoceros pauciramosus sp. nov., was discovered from Chinese tropical waters and the temperate south-eastern Baltic Sea. In the latter locality it has been known since 2003 and identified as C. cf lorenzianus , and now found to comprise a dominating component of the autumn phytoplankton community. Vegetative cells and resting spores were examined by light and electron microscopy. The LSU and SSU of the nuclear rDNA were sequenced. The characters suggesting that C. pauciramosus belongs to C. lorenzianus complex are: 1) the vegetative cells contain four or more chloroplasts, 2) the cells have stiff setae and form regular straight chains, 3) the terminal setae differ in the direction from the intercalary setae. The relationship was well-supported by molecular phylogenetic analyses inferred from both LSU and SSU markers. The primary valve of the resting spore has two conical elevations, each with dichotomously branching processes, similar to other species in the C. lorenzianus complex. Each process forms a tree-like structure with the pointed distal tips which possess one or two thin spikes, that distinguishes C. pauciramosus from allied taxa. In the phylogenetic trees, Chaetoceros pauciramosus clustered with C. elegans , in agreement with their morphologically similar resting spores. [ABSTRACT FROM AUTHOR]

Adaptability and growth of two marine diatoms, little known today, Chaetoceros gracilis and Skeletonema costatum microalgae, have been studied. Indoor cultures in 5 L photobioreactors under controlled conditions and outdoor cultivation in 80 L photobioreactors under uncontrolled environmental conditions have been evaluated. Maximum biomass productivities of 28.0 ± 0.16 and 32.0 ± 0.60 mgL −1 d −1 were obtained when S. costatum was cultivated on large-scale with air or air + CO 2 bubbling, respectively, and specific growth rates about 0.13–0.25 d −1 were exhibited. Biomass productivities slightly lower were achieved by C. gracilis and doubling times nearly half, 2.79–2.87 to 4.95–6.30 days, were obtained in pilot scale cultures against laboratory scale. Finally, lipid extraction and its analysis were conducted. Palmitic and stearic acids were the major components. Therefore, scale up cultivation of these two species is a feasible process and it allows to obtain a biomass with high potential for biodiesel production. [ABSTRACT FROM AUTHOR]

This study investigates how primary production responded to changes in nutrient availability, sea-level, and sea-ice coverage at the Umnak Plateau during Marine Isotope Stage (MIS) 5 and parts of MIS 4 and MIS 6. The Umnak Plateau during MIS 4 and MIS 6 had low primary production resulting from extensive sea-ice coverage that enhanced stratification and limited nutrient replenishment. This nutrient limitation was relieved during the deglaciation going into MIS 5 when previously exposed continental shelves were flooded and the eastern Aleutian Island passes were opened by an increase in sea-level, resulting in an increase in productivity. Opening and closing of the eastern Aleutian Island passes during the rest of MIS 5 reflected fluctuations in sea-level and likely affected nutrient sources and productivity at the Umnak Plateau. Nutrients during sea-level lowstands were likely sourced by the Aleutian North Slope Current, whereas most of the sea-level high stands throughout MIS 5 had nitrogen sourced by an increase in nitrogen fixation and the assimilation of remineralized nitrogen, which led to highly depleted nitrogen isotope values never before seen for the northern Pacific. Higher sea-level and productivity near the beginning of MIS 5 likely reflected MIS 5e; however, a discrepancy between two diatom productivity proxies suggests that changing environmental conditions stimulated a change in the dominant diatom species. This highlights the complexities associated with productivity in the Bering Sea and emphasizes the need to continue studying how productivity and ecosystems changed during previous warm periods. [ABSTRACT FROM AUTHOR]