Contribution of the diatom Navicula sp. to the growth of Penaeus vannamei post-larvae in biofloc system: a quantitative stable isotope assessment.

The addition of Navicula sp. to shrimp nurseries can improve the growth of Penaeus vannamei reared in biofloc systems. However, the contribution of microalgae to the biofloc formation and the effective contribution to shrimp nutrition remain unknown. In this study, Navicula sp. was added to biofloc nursery systems of P. vannamei at distinct time frequencies for evaluating its nutritional contribution to shrimp growth. Nursery rearing was carried out in bioflocs for 35 days at a stocking density of 3000 post-larvae m-3. Shrimp were fed using a commercial feed plus fresh culture of Navicula sp. at different frequencies: no addition of Navicula sp. (WN - control), the addition of 10 × 104 cells mL-1 of the diatom every 5, 10 and 15 days (N5, N10 and N15, respectively). Food sources relative contribution to P. vannamei development was estimated using a Bayesian mixture model. The isotopic discrimination factor (Δ15N and Δ13C) for each food source was determined experimentally. After 35 days of culture, survival (∼93 %) was similar across all treatments but there was a significant difference in weight gain and feed conversion ratio. The N10 treatment (0.50 ± 0.05 g, 0.99 ± 0.01) exhibited better growth parameters when compared to the WN treatment (0.33 ± 0.07 g, 11.46 ± 0.30). Biofloc was the food source most assimilated by shrimp followed by Navicula sp. and commercial feed. Contribution of Navicula sp. was higher in the N5 treatment. In the treatments with diatom addition, an inverse correlation was observed between the relative contributions of biofloc and Navicula sp., indicating that Navicula sp. is not in the biofloc composition, but it is directly consumed by P. vannamei post-larvae. Biofloc and Navicula sp. exhibited larger contributions to the growth of shrimp, reinforcing the importance of natural food sources to the aquaculture of P. vannamei post-larvae.

Does the diversity of vegetation and diatoms correlate with soil and water factors in a tropical cloud forest's complex land use/land cover scenario?

Soil and water characteristics in micro basins with different land uses/land cover (LULC) can influence riparian vegetation diversity, stream water quality, and benthic diatom diversity. We analyzed 18 streams in the upper part of the La Antigua River basin, México, surrounded by cloud forests, livestock pastures, and coffee plantations. Concentrations of P, C, and N were elevated in the humus of forested streams compared to other land uses. In contrast, cations, ammonium, and total suspended solids (TSS) of water streams were higher in pastures and coffee plantations. These results indicate that LULC affects stream chemistry differently across land uses. Vegetation richness was highest (86-133 spp.) in forest streams and lowest in pastures (46-102), whereas pasture streams had the greatest richness of diatoms (9-24), likely due to higher light and temperatures. Some soil and water characteristics correlated with both true diversity and taxonomic diversity; soil carbon exchange capacity (CEC) correlated with vegetation diversity (r = 0.60), while water temperature correlated negatively (r = - 0.68). Diatom diversity was related to soil aluminum (r = - 0.59), magnesium (r = 0.57), water phosphorus (r = 0.88), and chlorophyll (r = 0.75). These findings suggest that land use affects riparian vegetation, while physical and chemical changes influence diatom diversity in stream water and soil. The lack of correlation between vegetation and diatom diversity indicates that one cannot predict the other. This research is an essential first step in understanding how land use changes impact vegetation and diatom diversity in mountain landscapes, providing valuable insights for environmental monitoring and conservation efforts in tropical cloud forests.

Assessment of river ecological status in the French West Indies based on diatom flora.

The Water Framework Directive (WFD) requires member states to routinely assess the river ecological status using community-based indices. However, there is still a lack of published WFD-compliant methods for the French West Indies, especially using diatom-based indices. Martinique and Guadeloupe exhibit diverse landscapes shaped by their complex geological history and tropical climatic conditions. These strong particularities make the existing indices developed for the European mainland unusable. Based on diatom sampling from to 2013 (607 samples) and through multivariate analyses, we developed the Indice Diatomique des Antilles (IDA). We first identified the key abiotic factors influencing diatom communities on both islands, and then characterized taxon sensitivity by considering their presence probability along a pressure gradient.. The index was based on the presence and relative abundance of these taxa in each sample. The last step consisted of using new data from the 2014-2022 sampling surveys (457 samples) as a validation dataset to verify IDA accuracy. Our results suggest that the IDA methodology is well designed to assess the ecological status of rivers in the West Indies.

Novel method of removing metals from estuarine water using whole microbial mats.

This study addresses the limited understanding of chromium-microbial mat interactions in estuarine tidal flats. The aims were to evaluate (1) the efficiency of the microbial consortium in Cr(III) removal from seawater; (2) the elemental and mineralogical composition of the microbial mat as a natural system in the Cr removal, (3) the effects of metal on microphytobenthos, and (4) possible interactions of Cr with other metals present in the consortium. Microbial mats were exposed to Cr(III) solutions at different concentrations (2-30 mg Cr/L). Analysis such as metal concentration, organic matter content, chlorophyll a and phaeopigment concentrations, abundance of diatoms and cyanobacteria, SEM-EDS, and XRD were performed. Most of the Cr(III) was deposited, as chromium oxide/hydroxide, on the surface of all microbial mat components. The complete microbial mat, comprising sediments, detritus, EPS, and diverse microorganism communities, exhibited a remarkable capacity to accumulate Cr(III), retaining over 87% in the solution.

Seasonal variation in the biological succession of marine diatoms over 316L stainless steel in a coastal environment of Chile.

Characterizing seasonal changes in diatom community profiles in coastal environments is scarce worldwide. Despite diatoms being prevalent in microfouling, their role in microbially influenced corrosion of metallic materials remains poorly understood. This study reports the effect of seasonal variations on the settlement of marine diatoms and corrosion of 316 L stainless steel surfaces exposed to Chilean coastal seawater. Electron microscopy imaging revealed a diverse assembly of diatoms, exhibiting pronounced differences at genus level between summer and winter seasons, with a significant delay in diatom settlement during winter. Electrochemical measurements indicated an active role of diatoms in increasing corrosion current during biofilm development. While the final diatom composition was similar irrespective of the season, the analyses of diatom assemblages over time differed, showing faster colonization when silicate and nitrate were available. This study lays the foundation for future research on the dominant season-specific genera of diatoms to unveil the microbial interactions that could contribute to corrosion and to evaluate their potential as bioindicators for alternative surveillance strategies.

3D Printing characteristics and mechanical properties of a bio scaffold obtained from a Micro-CT Scan, using the fused deposition modeling technique

The objective is to determine which biopolymer has the best 3D printing characteristics and mechanical properties for the manufacture of a bioscaffold, using the fused deposition printing technique, with models generated from an STL file obtained from a Micro-CT scan taken from a bovine iliac crest bone structure. Through an experimental exploratory study, three study groups of the analyzed biopolymers were carried out with thirteen printed structures of each one. The first is made of 100% PLA. The second, 90B, we added 1g of diatom extract, and the third, 88C, differs from the previous one in that it also contains 1g of calcium phosphate. The 39 printed structures underwent a visual inspection test, which required the fabrication of a gold standard scaffold in resin, with greater detail and similarity to the scanned bone structure. Finally, the structures were subjected to a compressive force (N) to obtain the modulus of elasticity (MPa) and compressive strength (MPa) of each one of them. A statistically significant difference (p=0.001) was obtained in the printing properties of the biomaterial 88C, compared to 90B and pure PLA and the 88C presented the best 3D printing characteristics. In addition, it also presented the best mechanical properties compared to the other groups of materials. Although the difference between these was not statistically significant (p=0.388), in the structures of the 88C biomaterial, values of compressive strength (8,84692 MPa) and modulus of elasticity (43,23615 MPa) were similar to those of cancellous bone in the jaws could be observed. Because of this result, the 88C biomaterial has the potential to be used in the manufacture of bioscaffolds in tissue engineering.

El objetivo es determinar cuál biopolímero presenta las mejores características de impresión 3D y propiedades mecánicas para la fabricación de un bioandamiaje, utilizando la técnica de impresión por deposición fundida, con modelos generados a partir de un archivo en formato STL que se obtuvo de un Micro-CT Scan de una estructura osea de cresta iliaca bovina. Mediante un estudio exploratorio, se realizaron 3 grupos de estudio con trece estructuras impresas de cada uno. El primero, se compone 100% de PLA. El segundo, 90B, se le agrega 1g de extracto de diatomea, y el tercero, 88C, se diferencia del anterior ya que contiene además, 1g de fosfato de calcio. A las 39 estructuras impresas se les realizó una prueba de inspección visual, por lo que se requirió la confección de un patrón de oro en resina, con mayor detalle y similitud a la estructura ósea escaneada. Finalmente, las estructuras fueron sometidas a una fuerza compresiva (N) para la obtención del módulo de elasticidad (MPa) y de la resistencia compresiva (MPa) de cada una de ellas. Se obtuvo una diferencia estadísticamente significativa (p=0,001) en las propiedades de impresión del biomaterial 88C, con respecto al 90B y al PLA puro, presentando las mejores características de impresión 3D. Además, obtuvo las mejores propiedades mecánicas en comparación con los otros grupos de materiales. Aunque la diferencia entre estos no fue estadísticamente significativa (p=0,388), en las estructuras del biomaterial 88C, se pudieron observar valores de resistencia compresiva (8,84692 MPa) y módulo de elasticidad (43,23615 MPa) que son semejantes a los del hueso esponjoso de los maxilares. A razón de este resultado, el biomaterial 88C cuenta con el potencial para ser utilizado en la fabricación de bioandamiajes en la ingeniería tisular.

Domoic Acid Oxidative Effects on the Microalgae Phaeodactylum tricornutum.

Domoic acid (DA) is a natural occurring marine biotoxin. Oxidative stress generation due to DA exposure was reported in animals, but little is known on the phytoplankton community. The aim of this work was to verify whether exposure to DA in the marine diatom Phaeodactylum tricornutum favors reactive oxygen species (ROS) generation in the intracellular environment modifying its antioxidant capacity. Active species production, non-enzymatic antioxidant content, and antioxidant enzyme activities over the three growth phases of P. tricornutum exposed to 64 µM DA were evaluated. Results obtained in exponential growing cells showed a time-depending seven-fold increase in the 2',7' dichlorofluorescein diacetate dye oxidation rate. Superoxide dismutase and catalase activities showed a two-fold increase, and glutathione related enzymes activities were also significantly increased in treated diatoms as compared to controls. However, glutathione and ascorbate contents significantly decreased after incubation of the cells with DA. Similar effects were observed in latent and stationary phases of cell development. These results showed that DA could cause a severe oxidant-dependent impact on a non-toxic algae.

Niche Conservatism Drives the Elevational Diversity Gradient in Major Groups of Free-Living Soil Unicellular Eukaryotes.

Ancestral adaptations to tropical-like climates drive most multicellular biogeography and macroecology. Observational studies suggest that this niche conservatism could also be shaping unicellular biogeography and macroecology, although evidence is limited to Acidobacteria and testate amoebae. We tracked the phylogenetic signal of this niche conservatism in far related and functionally contrasted groups of common soil protists (Bacillariophyta, Cercomonadida, Ciliophora, Euglyphida and Kinetoplastida) along a humid but increasingly cold elevational gradient in Switzerland. Protist diversity decreased, and the size of the geographic ranges of taxa increased with elevation and associated decreasing temperature (climate), which is consistent with a macroecological pattern known as the Rapoport effect. Bacillariophyta exhibited phylogenetically overdispersed communities assembled by competitive exclusion of closely related taxa with shared (conserved) niches. By contrast, Cercomonadida, Ciliophora, Euglyphida and Kinetoplastida exhibited phylogenetically clustered communities assembled by habitat filtering, revealing the coexistence of closely related taxa with shared (conserved) adaptations to cope with the humid but temperate to cold climate of the study site. Phylobetadiversity revealed that soil protists exhibit a strong phylogenetic turnover among elevational sites, suggesting that most taxa have evolutionary constraints that prevent them from colonizing the colder and higher sites of the elevation gradient. Our results suggest that evolutionary constraints determine how soil protists colonize climates departing from warm and humid conditions. We posit that these evolutionary constraints are linked to an ancestral adaptation to tropical-like climates, which limits their survival in exceedingly cold sites. This niche conservatism possibly drives their biogeography and macroecology along latitudinal and altitudinal climatic gradients.

Biochemical and Molecular Aspects of Phosphorus Limitation in Diatoms and Their Relationship with Biomolecule Accumulation.

Diatoms are the most abundant group of phytoplankton, and their success lies in their significant adaptation ability to stress conditions, such as nutrient limitation. Phosphorus (P) is a key nutrient involved in the transfer of energy and the synthesis of several cellular components. Molecular and biochemical mechanisms related to how diatoms cope with P deficiency are not clear, and research into this has been limited to a few species. Among the molecular responses that have been reported in diatoms cultured under P deficient conditions is the upregulation of genes encoding enzymes related to the transport, assimilation, remobilization and recycling of this nutrient. Regarding biochemical responses, due to the reduction of the requirements for carbon structures for the synthesis of proteins and phospholipids, more CO2 is fixed than is consumed by the Calvin cycle. To deal with this excess, diatoms redirect the carbon flow toward the synthesis of storage compounds such as triacylglycerides and carbohydrates, which are excreted as extracellular polymeric substances. This review aimed to gather all current knowledge regarding the biochemical and molecular mechanisms of diatoms related to managing P deficiency in order to provide a wider insight into and understanding of their responses, as well as the metabolic pathways affected by the limitation of this nutrient.

Influence of microphytobenthos on the sedimentary organic matter composition in two contrasting estuarine microhabitats.

The influence of microphytobenthic community on the composition of sedimentary organic matter was evaluated in two Bahía Blanca estuary microhabitats contrasting in vegetation and hydrodynamic conditions; namely, S1 located in a Sarcocornia perennis saltmarsh with macroscopic microbial mats and S2 in a mudflat without macroscopic microbial mats or vegetation. Moisture, organic matter, chlorophyll a, phaeopigments, carbohydrates (CH), proteins (PRT), and abundance and structure of microphytobenthic community were evaluated in surface sediments. Higher moisture was observed at S2 and was related to the proximity of this site to the subtidal zone and the effect of the environmental variables temperature and rain. No significant differences were found in organic matter content between sites; however, at S1, a higher concentration was registered during winter and early spring associated to the period of higher microphytobenthic biomass. Chlorophyll a and phaeopigments were higher at S1, attributed to the higher microphytobenthos abundance at this site. Differences in microphytobenthos were observed not only in quantity but also in community structure since at S1 filamentous cyanobacteria dominated the community, whereas at S2, higher abundance of centric diatoms and the absence of cyanobacteria were observed during most of the study. S1 showed higher concentration of proteins and carbohydrates which could be attributed to the higher production of fresh organic matter by microphytobenthos. The total protein and carbohydrate concentrations allowed us to classify both microhabitats into the meso-oligotrophic category, contrasting with the classification made by other authors using water column proxies.

Development of the Diatom Ecological Quality Index (DEQI) for peri-urban mountain streams in the Basin of Mexico.

In the Basin of Mexico, one of the most important economic regions in the country with over 22 million inhabitants, peri-urban streams have been transformed into sewers, drains, and pipes to avoid flooding or unsanitary conditions; the change affects not only the ecosystem's goods and services but also the aquatic communities that support the natural ecological processes. We aimed to develop a diatom-based diagnosis of the ecological quality of these aquatic ecosystems through the study of epilithic diatom response to regional environmental gradients. Samples of epilithic diatoms and water were collected in 45 sites representing 12 perennial streams, and multivariate analyses were performed on environmental and biological data. The ecological quality gradient to which diatoms responded was related to oxygen saturation, soluble reactive phosphorous, dissolved inorganic nitrogen, and hydromorphological quality. Three species groups were recognized according to their ecological preferences along CCA1 axis, indicators of high and low ecological quality, and tolerant species. By assigning an indicator value to each species group, we calculated the DEQI using the formula adapted from Pantle and Buck, indicating five different ecological quality classes. This index is proposed for complementing the ecological quality evaluation as a biological metric that responds to multiple regional stressors of the structure and function of these peri-urban streams in the Basin of Mexico.

Eunotia (Bacillariophyceae) from a subtropical stream adjacent to Iguaçu National Park, Brazil, with the proposition of a new species / Eunotia (Bacillariophyceae) de um riacho subtropical adjacente ao Parque Nacional do Iguaçu, Brasil, com a proposta de uma espécie nova

Abstract: Eunotia species from a stream located in the surrounding area of the Iguaçu National Park conservation unit were analyzed. Samples were monthly collected from September 2012 to August 2013. The periphytic material, manually obtained by squeezing aquatic macrophytes, was oxidized and analyzed under light and scanning electron microscopy. Twenty-one infrageneric taxa of Eunotia were identified, measured, and illustrated. Eunotia caniculoides sp. nov. is proposed as a new species, and eight taxa are new records for Paraná state.

Resumo: Espécies de Eunotia Ehrenberg de um ambiente lótico localizado em área adjacente à unidade de conservação Parque Nacional do Iguaçu foram analisadas. As coletas foram realizadas mensalmente de setembro de 2012 a agosto de 2013. O material perifítico obtido do espremido manual de macrófitas aquáticas foi oxidado e analisado sob microscopia óptica e eletrônica de varredura. Vinte e um táxons de Eunotia foram identificados, medidos e ilustrados. Eunotia caniculoides sp. nov. é proposta como uma nova espécie e oito táxons constituem novos registros para o estado do Paraná.

Genetic barcoding of Ecuadorian epilithic diatom species suitable as water quality bioindicators.

Diatom identification is a key step in using these microorganisms as water quality bioindicators. Morphological diagnosis is a difficult task due to the enormous number of species and their microscopic size. This can be overcome using molecular tools to complement the diagnosis. The main goal of this work was to obtain the DNA barcode of Ecuadorian epilithic diatoms with a wide geographical distribution, a well-defined ecological range and characteristics that allow them to be reliable indicator species. Unialgal diatom cultures were obtained from environmental samples of Ecuadorian Andean streams. Morphological characterization of cultures was carried out under SEM microscopy. For molecular characterization, 18SV4 and rbcL barcodes were sequenced from each strain and blasted against a GenBank database. A phylogenetic tree for each barcode was constructed using the ML method including sequences of strains of the studied species from different geographical locations. The results showed the following five species to be suitable as bioindicators and these were isolated. Sellaphora seminulum (strain JA01b, c), Nitzschia fonticola (strain SP02a) and N. palea (strain CA01a) are tolerant to eutrophication; Eolimna minima (strain CH02a) is a mesotrophic water bioindicator, and Achnanthidium minutissimum (strain JA01a) is an oligotrophic water bioindicator. The comparison with the GenBank database of the barcoding regions supported the morphological identification. The barcoding sequences of the strains showed a high percentage of identity with the sequences reported in INSDC databases for the same species. The topology of the phylogenetic trees demonstrates that epilithic diatoms from Ecuador are closely related to those of same species isolated from other geographical regions. This study is a first attempt to establish a morphological and molecular taxonomic reference library for neotropical diatoms. This study demonstrates that it would be feasible to use the existing barcoding data for diatoms to develop molecular tools for the bioassessment of aquatic ecosystems in the Ecuadorian Andean region.

L'identification des diatomées est une étape clé dans l'utilisation de ces microorganismes comme bioindicateurs de la qualité de l'eau. Le diagnostic morphologique est une tâche difficile en raison du nombre considérable d'espèces et de leur dimension microscopique. Il est possible de surmonter cette difficulté en utilisant des techniques moléculaires pour compléter le diagnostic. L'objectif principal de ce travail était d'obtenir le code-barre de l'ADN des diatomées épilithiques équatoriennes ayant une large distribution géographique, une niche écologique bien définie et des caractéristiques leur permettant d'être des espèces indicatrices fiables. Des cultures de diatomées unialgales ont été obtenues à partir d'échantillons environnementaux de cours d'eau des Andes équatoriennes. La caractérisation morphologique des cultures a été réalisée sous microscopie MEB. Pour la caractérisation moléculaire, les codes-barres 18SV4 et rbcL ont été séquencés à partir de chaque souche et comparés à la base de données GenBank. Pour chaque code-barres, un arbre phylogénétique a été construit à partir de la méthode ML comprenant des séquences de souches des espèces étudiées, provenant de différents lieux géographiques. Les résultats ayant montré que les cinq espèces suivantes étaient appropriées comme bioindicateurs, elles ont été isolées. Sellaphora seminulum (souche JA01b, c), Nitzschia fonticola (souche SP02a) et N. palea (souche CA01a) sont tolérantes à l'eutrophisation ; Eolimna minima (souche CH02a) est un bioindicateur d'eau mésotrophe, et Achnanthidium minutissimum (souche JA01a) est un bioindicateur d'eau oligotrophe. La comparaison avec la base de données GenBank des régions de code-barres a supporté leurs identifications morphologiques. Les séquences de code-barres des souches ont montré un pourcentage élevé d'identité génétique avec les séquences signalées dans les bases de données de l'INSDC pour la même espèce. La topologie des arbres phylogénétiques démontre que les diatomées épilithiques de l'Équateur sont étroitement liées à celles des mêmes espèces isolées d'autres régions géographiques. Cette étude est une première tentative d'établir une bibliothèque de référence morphologique et taxonomique moléculaire pour les diatomées néotropicales. Cette étude démontre qu'il serait possible d'utiliser les données de code-barres existantes pour les diatomées afin de développer des instruments moléculaires pour la bioévaluation des écosystèmes aquatiques dans la région andine équatorienne.

Anthropogenic influence on the sediment chemistry and diatom assemblages of Balamtetik Lake, Chiapas, Mexico.

Balamtetik is the receiving body of the Rio Grande de Comitán and is located just at the outskirts of the Montebello National Park, Chiapas, México. Multi-elemental, infrared spectra, 137Cs, 210Pb, and diatom analyses in a 75-cm sediment core were used to reconstruct the recent disturbance history of the lake. The sequence chronology, based mostly on 137Cs profiles, allowed to infer high sedimentation rates in Balamtetik (~ 7 mm/year) and a nearly cyclic series of disturbance events that can be related to anthropogenic causes such as deforestation and increased development of agriculture and urban areas at local and regional scale. These disturbance events show high local and regional erosion (high Ca, TIC, and Ti), soil organic matter (IR spectra), eutrophication (high P and diatoms), and anoxic bottom water conditions (low Mn) and can be dated to the early 1950s, the late 1950s, and from the 1980s until the 2000s. The entrance of wastewaters is related with an increase in salinity inferred by the diatom record and the organic matter type. The first two disturbance events are related to changes in land use during the agrarian reform that started during the 1940s; the last event is related with the increase in local population and the introduction of intensive agriculture. This last phase of disturbance corresponds with the reports of fish mortality events around 2003; however, high lake turbidity and anoxic bottom waters seem to have been established since the 1980s. The record from Lake Balamtetik also shows that during the intermediate periods, there was a recovery of the lake and its catchment; however, the future trends might be different, as the increase in the speed of organic matter and nutrients arrival to the lake reduces its resilience.

The genus Tryblionella W. Smith (Bacillariaceae, Bacillariophyta) in southern Brazil salt marshes / O gênero Tryblionella W. Smith (Bacillariaceae, Bacillariophyta) em marismas do Sul do Brasil

Abstract: Tryblionella is a large epipelic genus, widespread from fresh to marine waters. Most of the studies including the genus are based only in light microscopy. Few recent studies are exclusively dedicated to Tryblionella and the ultrastructure of some species is still little known. In this paper we present eleven species of Tryblionella found in epiphyton and microphytobenthos in Patos Lagoon salt marshes. All the species are described, illustrated in light and scanning electron microscopy and comments about their taxonomy, distribution and ecology are provided. Two taxa are reported for the first time in the State of Rio Grande do Sul and one in Southern Brazil. The number of species registered in this study comprises nearly a half of the number of species registered in the country. The high richness observed may be related to the dynamics of the salt marshes, which provides both the mixing of fresh and marine waters communities and the diversity of microhabitats. The great variability among the species analyzed allowed to extend the general concept of Tryblionella, adding features which were not considered in the previous characterizations of the genus.

Resumo: Tryblionella é um gênero de diatomáceas epipélicas, distribuído de águas doces a marinhas. A maioria dos estudos que incluem o gênero baseia-se apenas em microscopia óptica. Poucos estudos recentes são exclusivamente dedicados à Tryblionella e a ultraestrutura de algumas espécies ainda é pouco conhecida. No presente artigo, apresentamos onze espécies de Tryblionella encontradas no epifíton e no microfitobentos nas marismas da Lagoa dos Patos. Todas as espécies foram descritas, ilustradas em microscopia óptica e eletrônica de varredura e comentários sobre a taxonomia, distribuição e ecologia foram fornecidos. Dois táxons foram registrados pela primeira vez para o estado do Rio Grande do Sul e um para a região Sul do Brasil. O número de espécies registradas neste estudo compreende cerca de metade das espécies registradas para o país. A grande riqueza observada pode estar relacionada à dinâmica das marismas, que proporciona tanto a mistura de comunidades de águas doces e marinhas quanto diversidade de microhabitats. A grande variabilidade entre as espécies analisadas permitiu que o conceito geral de Tryblionella fosse ampliado, incluindo características que não haviam sido consideradas nas caracterizações anteriores do gênero.

Protists and other organisms on a minute snail periostracum / Protistas e outros organismos em um pequeno periostracum de caracol

Abstract Since the foundation of the Malacological Center in 1980, Universidad Centro Americana (UCA), Managua-Nicaragua, has been monitoring and collecting the marine, terrestrial, fluvial and lake mollusk population of the country. Many specimens have been photographed by Scanning Electronic Microscope (SEM), and in one of these, observation of the hairy periostracum reveals a seemingly thriving population of minute protists in possible symbiosis with their host. Adequate magnification and comparison with previous studies allowed the determination of these hosts as diatoms, testaceous amoebae, yeast, phacus, spores and other undetermined organisms which occur in tropical forests on rocks, trees and leaves. Here illustrated are diatoms and other organisms detected for the first time on the periostracum of a tropical rainforest mollusk.

Resumo Desde a fundação do Centro Malacológico em 1980, a Universidad Central Americana (UCA), Manágua-Nicarágua, vem acompanhando e coletando a população de moluscos marinhos, terrestres, fluviais e lagoas do país. Muitos espécimes foram fotografados pelo microscópio eletrônico de varredura (SEM) e, em um deles, a observação do periostracum peludo revela uma população aparentemente próspera de protistas de minuto em possível simbiose com o hospedeiro. A ampliação adequada e a comparação com estudos anteriores permitem a determinação dessas diatomáceas, amebas testaceas, leveduras, phacus, esporos e outros organismos indeterminados que ocorrem em florestas tropicais em rochas, árvores e folhas. Aqui estão as diatomeas e outros organismos pela primeira vez detectados no periostracum de um molusco tropical.

Ácidos grasos en cepas de microalgas del Banco de Germoplasma de Organismos Acuáticos del Instituto del Mar del Perú (IMARPE)

Se determinó la composición de ácidos grasos de 54 cepas microalgales colectadas del Perú y mantenidas en el Banco de Germoplasma de Organismos Acuáticos (IMARPE) con la finalidad de determinar su uso nutricional en la acuicultura. Para ello se realizaron cultivos en un volumen de 50 mL y se determinaron los porcentajes relativos de ácidos grasos mediante transesterificación directa y cromatografía de gases. En el grupo Chlorophyta las microalgas que presentaron los mayores valores de porcentaje relativo de ácidos grasos fueron Chlamydomonas reinhardtii (16:0; 41.2%), Scenedesmus obtusus (18:1n-7; 33.6%), Acutodesmus dimorphus (18:1n-9; 37.1%), Desmodesmus armatus (18:3n-3; 32.2%) y Tetraselmis contracta (16:4n-3; 16.5%). En cambio en el grupo Bacillariophyta, los ácidos grasos más abundantes fueron 16:1n-7 en Chaetoceros didymus (20.2%), 18:4n-3 en Navicula sp. (28.3%) y EPA en Asterionellopsis sp. (31.5%). Por otro lado, en el grupo Dinophyta, todas las cepas superaron el 20% de DHA, en particular, la cepa de Akashiwo sanguinea presentó el mayor porcentaje relativo de este ácido graso (29.9%) y de los ácidos grasos 16:0 (24.8%) y EPA (16%). Se discute el uso de estas cepas según su contenido de ácidos grasos.

In This work, we determinate the fatty acids composition and their nutritional value in 54 microalgal strains, collected from Peru and stored in Banco de Germoplasma de Organismos Acuáticos (IMARPE). The cultures were grown to 50 mL and analyzed by direct transesterification and gas chromatography. In the Chlorophyta group, the microalgaes that present the highest relative percentage of fatty acids were Chlamydomonas reinhardtii (16:0; 41.2%), Scenedesmus obtusus (18:1n-7; 33.6%), Acutodesmus dimorphus (18:1n-9; 37.1%), Desmodesmus armatus (18:3n-3; 32.2%) and Tetraselmis contracta (16:4n-3; 16.5%). Moreover in the Bacillariophyta group, the most abundant fatty acids were 16:1n-7 in Chaetoceros didymus (20.2%), 18:4n-3 in Navicula sp. (28.3%) and EPA in Asterionellopsis sp. (31.5%). By the other hand, in the Dinophyta group, all strains exceed the 20% of DHA, in particular Akashiwo sanguinea, it was strain to have the highest percentage of this fatty acid (29.9%) in addition to 16: 0 (24.8%) and EPA (16%). We discussed uses of these strains is according to their fatty acids content.

Microbialite-like structures in Cladophora sp. (Ulvophyceae) mats from a subtropical Andean basin: ecological implications / Estructuras de tipo microbialito en Cladophora sp. (Ulvophyceae) de una cuenca andina subtropical: implicaciones ecológicas

Abstract The solubility equilibrium of calcite is influenced by physicochemical, climatic and biological factors. Annual cycles of exceptionally prolonged drought, in conjunction with naturally occurring diffuse organic pollution, generate the unique conditions for the precipitation of lithified carbonate structures (microbialites). The aim of this article is to analyze the possible implications of calcite precipitation produced in mats of Cladophora sp. in an Andean subtropical basin, considering it is the first time this phenomenon is described for the region. We collected samples from selected sites at the Lules River Basin, in four sampling dates between the years 2003 and 2004, within a monitoring work of 15 years. Samples were analyzed using an electron microscope and X-ray diffraction analysis. We found that Gomphonema sp. attached to Cladophora sp. contributes to precipitation of calcite and formation of microbialite like structures, in the studied area. This work presents an initial discussion of the discovery of microbialites-like structures attached to Cladophora sp. mats in a subtropical Andean stream and the environmental conditions that lead to their production, as well as the possible ecological implications of these microbialites.(AU)

Resumen La fase sólida de las sales de los cuerpos de agua juega un papel importante en la concentración de los elementos mayoritarios. El equilibrio de solubilidad de la calcita está influenciado por factores fisicoquímicos, climáticos y biológicos. Los ciclos anuales de sequía excepcionalmente prolongada, junto con la contaminación orgánica difusa de origen natural, generan condiciones únicas para la precipitación de estructuras de carbonato litificado (microbialitos). El objetivo de este artículo es analizar las posibles implicaciones de la precipitación de calcita producida en Cladophora sp. en una cuenca subtropical andina, considerando que es la primera vez que se describe este fenómeno para la región. Recolectamos muestras en sitios seleccionados en la Cuenca del Río Lules, en cuatro fechas de muestreo entre 2003 y 2004, en el marco de un trabajo de monitoreo de quince años. Usamos red Surber para realizar los muestreos. Las muestras de algas, una vez libres de macroinvertebrados, se secaron y pesaron. Analizamos utilizando microscopía electrónica y difracción de rayos X. Encontramos que Gomphonema sp. unido a Cladophora contribuye a la precipitación de calcita y la formación de estructuras similares a microbialitos, en el área estudiada. Este trabajo presenta una discusión inicial sobre el descubrimiento de estructuras similares a microbialitos unidas a filamentos de Cladophora sp. en una cuenca andina subtropical y las condiciones ambientales que conducen a su producción, así como las posibles implicaciones ecológicas de lo mencionado anteriormente.(AU)

Mat thickness associated with Didymosphenia geminata and Cymbella spp. in the southern rivers of Chile.

Didymosphenia geminata is a diatom that can alter aquatic systems. Several investigations have shown as chemical, and hydraulic factors have a great influence on the proliferation of D. geminata, but the study of other microalgae that could be associated with it has been poorly addressed. The objective of this study is to evaluate the relationship between mat thickness, D. geminata and another taxon that produces mucilage, Cymbella, while also considering physical and chemical factors. For this, two samples were taken, one in the spring of 2013 and the other in the autumn of 2014, from eight rivers in central-southern Chile-South America, where the benthic community was characterized, and the thickness of the mat was measured. The results show that the mat thickness on sites with the presence of both taxa is doubled, and while sites with D. geminata presence showed mat peak on autumn, sites with Cymbella spp. presence showed on spring. Also, higher values of mat thickness associated with low cell densities of D. geminata and intermediate cell densities of Cymbella spp. Finally, physicochemical variables that better explain mat thickness are phosphorus and water temperature. An alternation process of mucilage production may explain these results by these taxa strongly related to physicochemical variables. The present study contributes evidence about the relationship between mat thickness D. geminata and other microalgae contribution, and aquatic condition for this development.