Photosymbiosis reduces the environmental stress response under a heat challenge in a facultatively symbiotic coral.

The symbiosis between corals and dinoflagellates of the family Symbiodiniaceae is sensitive to environmental stress. The oxidative bleaching hypothesis posits that extreme temperatures lead to accumulation of photobiont-derived reactive oxygen species ROS, which exacerbates the coral environmental stress response (ESR). To understand how photosymbiosis modulates coral ESRs, these responses must be explored in hosts in and out of symbiosis. We leveraged the facultatively symbiotic coral Astrangia poculata, which offers an opportunity to uncouple the ESR across its two symbiotic phenotypes (brown, white). Colonies of both symbiotic phenotypes were exposed to three temperature treatments for 15 days: (i) control (static 18 °C), (ii) heat challenge (increasing from 18 to 30 °C), and (iii) cold challenge (decreasing from 18 to 4 °C) after which host gene expression was profiled. Cold challenged corals elicited widespread differential expression, however, there were no differences between symbiotic phenotypes. In contrast, brown colonies exhibited greater gene expression plasticity under heat challenge, including enrichment of cell cycle pathways involved in controlling photobiont growth. While this plasticity was greater, the genes driving this plasticity were not associated with an amplified environmental stress response (ESR) and instead showed patterns of a dampened ESR under heat challenge. This provides nuance to the oxidative bleaching hypothesis and suggests that, at least during the early onset of bleaching, photobionts reduce the host's ESR under elevated temperatures in A. poculata.

Effects of the toxic dinoflagellate, Alexandrium pacificum, on the marine diatom, Chaetoceros muelleri, and mussel (Perna canaliculus) sperm and hemocytes.

Harmful algal blooms (HABs) of Alexandrium pacificum have affected the Marlborough Sounds in New Zealand since 2010, posing a threat to green-lipped mussel (GLM, Perna canaliculus) farming. Previous studies have shown A. pacificum has negative effects GLM embryos and larvae. To further investigate these toxic mechanisms, in vitro bioassays were conducted on GLM spermatozoa, hemocytes, and the diatom, Chaetoceros muelleri. The three cell types were exposed to several treatments of A. pacificum for 2 h and responses were measured using flow cytometry and pulse amplitude-modulated fluorometry. Significant spermatozoa mortality was recorded in treatments containing A. pacificum cells or fragments, while hemocyte and C. muelleri mortality was recorded in cell-free treatments of A. pacificum which contained paralytic shellfish toxins (PSTs). Variation in sensitivity between cell types as well as the sublethal effects observed, emphasise the diverse toxic mechanisms of A. pacificum on co-occurring species in the environment.

Highly Diverse Symbiodiniaceae Types Hosted by Corals in a Global Hotspot of Marine Biodiversity.

Symbiotic dinoflagellates in the genus Symbiodiniaceae play vital roles in promoting resilience and increasing stress tolerance in their coral hosts. While much of the world's coral succumb to the stresses associated with increasingly severe and frequent thermal bleaching events, live coral cover in Papua New Guinea (PNG) remains some of the highest reported globally despite the historically warm waters surrounding the country. Yet, in spite of the high coral cover in PNG and the acknowledged roles Symbiodiniaceae play within their hosts, these communities have not been characterized in this global biodiversity hotspot. Using high-throughput sequencing of the ITS2 rDNA gene, we profiled the endosymbionts of four coral species, Diploastrea heliopora, Pachyseris speciosa, Pocillopora acuta, and Porites lutea, across six sites in PNG. Our findings reveal patterns of Cladocopium and Durusdinium dominance similar to other reefs in the Coral Triangle, albeit with much greater intra- and intergenomic variation. Host- and site-specific variations in Symbiodiniaceae type profiles were observed across collection sites, appearing to be driven by environmental conditions. Notably, the extensive intra- and intergenomic variation, coupled with many previously unreported sequences, highlight PNG as a potential hotspot of symbiont diversity. This work represents the first characterization of the coral-symbiont community structure in the PNG marine biodiversity hotspot, serving as a baseline for future studies.

Prorocentrum canariense sp. nov., a case of pseudo-cryptic speciation in the cosmopolitan dinoflagellate P. compressum (Prorocentrales, Dinophyceae).

The planktonic dinoflagellate Prorocentrum compressum is widespread in warm and temperate seas. A strain identified as P. cf. compressum BEA 0681B isolated from the island of Gran Canaria, NE Atlantic Ocean, showed a divergence in rDNA/ITS phylogenies with respect to P. compressum. The Canarian strain was oval, with an average length-to-width ratio of 1.35, smooth thecal surface with less than 150 thecal pores, including oblique pores, sometimes with a bifurcated opening. In contrast, P. compressum was rounder, with a length-to-width ratio < 1.2, with reticulate-foveate ornamentation and 200-300 pores per valve. We propose Prorocentrum canariense sp. nov. These species clustered as the most early-branching lineage in the clade Prorocentrum sensu stricto. Although this clade mainly contains planktonic species, the closer relatives were the benthic species P. tsawwassenense and P. elegans. Interestingly, P. compressum and P. canariense sp. nov. are widely distributed in temperate and warm seas without an apparent morphological adaptation to planktonic life. The formation of two concentric hyaline mucilaginous walls could contribute to this success. We discuss the use of Prorocentrum bidens to solve the nomenclature issue of P. compressum that was described citing a diatom as basionym.

Diel transcriptional responses of coral-Symbiodiniaceae holobiont to elevated temperature.

Coral exhibits diel rhythms in behavior and gene transcription. However, the influence of elevated temperature, a key factor causing coral bleaching, on these rhythms remains poorly understood. To address this, we examined physiological, metabolic, and gene transcription oscillations in the Acropora tenuis-Cladocopium sp. holobiont under constant darkness (DD), light-dark cycle (LD), and LD with elevated temperature (HLD). Under LD, the values of photosystem II efficiency, reactive oxygen species leakage, and lipid peroxidation exhibited significant diel oscillations. These oscillations were further amplified during coral bleaching under HLD. Gene transcription analysis identified 24-hour rhythms for specific genes in both coral and Symbiodiniaceae under LD. Notably, these rhythms were disrupted in coral and shifted in Symbiodiniaceae under HLD. Importantly, we identified over 20 clock or clock-controlled genes in this holobiont. Specifically, we suggested CIPC (CLOCK-interacting pacemaker-like) gene as a core clock gene in coral. We observed that the transcription of two abundant rhythmic genes encoding glycoside hydrolases (CBM21) and heme-binding protein (SOUL) were dysregulated by elevated temperature. These findings indicate that elevated temperatures disrupt diel gene transcription rhythms in the coral-Symbiodiniaceae holobiont, affecting essential symbiosis processes, such as carbohydrate utilization and redox homeostasis. These disruptions may contribute to the thermal bleaching of coral.

ChRIPK1 caused necroptosis signaling pathway deficiency in Crassostrea hongkongensis.

RIPK1/TAK1 are important for programmed cell death, including liver death, necroptosis and apoptosis. However, there have been few published reports on the functions of RIPK1/TAK1 in invertebrates. In this study, full-length ChRIPK1 and ChTAK1 were cloned from C. hongkongensis through the rapid amplification of cDNA ends (RACE) technology. ChRIPK1 has almost no homology with human RIPK1 and lacks a kinase domain at the N-terminus but has a DD and RHIM domain. ChTAK1 is conserved throughout evolution. qRT‒PCR was used to analyze the mRNA expression patterns of ChRIPK1 in different tissues, developmental stages, and V. coralliilyticus-infected individuals, and both were highly expressed in the mantle and gills, while ChRIPK1 was upregulated in hemocytes and gills after V. coralliilyticus or S. aureus infection, which indicates that ChRIPK1 is involved in immune regulation. Fluorescence assays revealed that ChRIPK1 localized to the cytoplasm of HEK293T cells in a punctiform manner, but the colocalization of ChRIPK1 with ChTAK1 abolished the punctiform morphology. In the dual-luciferase reporter assay, both ChRIPK1 and ChRIPK1-RIHM activated the NF-κB signaling pathway in HEK293T cells, and ChTAK1 activated ChRIPK1 in the NF-κB signaling pathway. The apoptosis rate of the hemocytes was not affected by the necroptosis inhibitor Nec-1 but was significantly decreased, and ChRIPK1 expression was knocked down in the hemocytes of C. hongkongensis. These findings indicated that ChRIPK1 induces apoptosis but not necroptosis in oysters. This study provides a theoretical basis for further research on the molecular mechanism by which invertebrates regulate the programmed cell death of hemocytes in oysters.

Membrane vectorial lipidomic features of coral host cells' plasma membrane and lipid profiles of their endosymbionts Cladocopium.

The symbiotic relationships between coral animal host and autotrophic dinoflagellates are based on the mutual exchange and tight control of nutritional inputs supporting successful growth. The corals Sinularia heterospiculata and Acropora aspera were cultivated using a flow-through circulation system supplying seawater during cold and warm seasons of the year, then sorted into host cells and symbionts and subjected to phylogenetic, morphological, and advanced lipid analyses. Here we show, that the lipidomes of the dinoflagellates Cladocopium C1/C3 and acroporide-specific Cladocopium hosted by the corals, are determined by lipidomic features of different thermosensitivity and unique betaine- and phospholipid molecular species. Phosphatidylserines and ceramiaminoethylphosphonates are not detected in the symbionts and predominantly localized on the inner leaflet of the S. heterospiculata host plasma membrane. The transmembrane distribution of phosphatidylethanolamines of S. heterospiculata host changes during different seasons of the year, possibly contributing to mutualistic nutritional exchange across this membrane complex to provide the host with a secure adaptive mechanism and ecological benefits.

The Effecting Mechanisms of 100 nm Sized Polystyrene Nanoplastics on the Typical Coastal Alexandrium tamarense.

Due to the increase in nanoplastics (NPs) abundance in aquatic environments, their effects on phytoplankton have aroused large research attention. In this study, 100 nm sized polystyrene NPs were chosen to investigate their effecting performance and mechanisms on a typical dinoflagellates Alexandrium tamarense. The results indicated the population growth and photosynthetic efficiencies of A. tamarense were significantly inhibited by NPs exposure, as well as the increase in cellular total carotenoids and paralytic shellfish toxins (PSTs). Meanwhile, the cellar ROS levels increased, corresponding to the increased activities or contents of multiple antioxidant components, including SOD, CAT, GPX, GR, GSH and GSSG. The transcriptional results support the physiological-biochemical results and further revealed the down-regulation of genes encoding the light reaction centers (PSI and PSII) and up-regulation of genes encoding the antioxidant components. Up-regulation of genes encoding key enzymes of the Calvin cycle and glycolytic pathway together with the TCA cycle could accelerate organic carbon and ATP production for A. tamarense cells resistant to NPs stress. Finally, more Glu and acetyl-CoA produced by the enhanced GSH cycle and the glycolytic pathway, respectively, accompanied by the up-regulation of Glu and Arg biosynthesis genes supported the increase in the PST contents under NPs exposure. This study established a data set involving physiological-biochemical changes and gene information about marine dinoflagellates responding to NPs, providing a data basis for further evaluating the ecological risk of NPs in marine environments.

Five Karenia species along the Chinese coast: With the description of a new species, Karenia hui sp. nov. (Kareniaceae, Dinophyta).

Dinoflagellates within the genus Karenia are well known for their potential to cause harmful algal blooms and induce detrimental ecological consequences. In this study, five Karenia species, Karenia longicanalis, Karenia papilionacea, Karenia mikimotoi, Karenia selliformis, and a new species, Karenia hui sp. nov., were isolated from Chinese coastal waters. The new species exhibits the typical characteristics of the genus Karenia, including a linear apical groove and butanoyl-oxyfucoxanthin as the major accessory pigment. It is distinguished from the other Karenia species by a wide-open sulcal intrusion onto the epicone, a conical epicone with an apical crest formed by the rim of the apical groove, and a hunchbacked hypocone. It is most closely related to Karenia cristata, with a genetic divergence of 3.16 % (22 bp out of 883 bp of LSU rDNA). Acute toxicity tests indicated that the five Karenia species from China are all toxic to marine medaka Oryzias melastigma. Karenia selliformis and K. hui were very toxic to O. melastigma, resulting in 100 % mortality within 4 h and 24 h, respectively. Further analysis by high-performance liquid chromatography revealed that four species, K. selliformis, K. longicanalis, K. papilionacea and K. mikimotoi were capable of producing Gymnodimine-A (GYM-A). The highest GYM-A content was in K. selliformis (strain HK-43), in which the value was 889 fg/cell. No GYM-A was detected in the new species K. hui, however and its toxin remains unknown. Below we provide a comprehensive report of the morphology, phylogeny, pigment composition, and toxicity profiles of Karenia species along the Chinese coast. These findings contribute new insights for monitoring of Karenia species, with important toxicological and ecological implications.

[Phytoplankton population dynamics along the Casablanca - El Jadida Atlantic coast]. / Dynamique du peuplement phytoplanctonique le long de l'axe côtier Casablanca ­ El Jadida.

Our taxonomic study from March 2014 to November 2015 along the atlantic coast between Casablanca and El Jadida revealed that phytoplanktonic structure is mainly represented by Diatoms (Bacillariophyceae), Dinoflagellates (Dinophyceae), Silicoflagellates (Dictyophyceae) and Euglenophyceae with a clear dominance of Diatoms and Dinoflagellates. A total of 101 taxa of planktonic algae have been identified revealing a relatively diversified taxocenosis. In terms of respective diversity, the Diatoms are represented by 62 taxa (61.4%), the Dinoflagellates by 36 taxa (35.6%) whereas the other two groups of Silicoflagellates and Euglenophyceae are only represented by 3 species (3.0%). Regarding potentially toxic species, more than fifteen taxa have been identified, most of which were Dinoflagellates and Diatoms (Pseudo-nitzschia australis and Pseudo-nitzschia cuspidata). The total phytoplankton densities exhibited great spatial and temporal variations as shown by analyses of diversity (H') and equitability (E) indices at the different coast sites investigated throughout the 2014-2015 years. Massive proliferation of some toxic species (e.g. Pseudo-nitzschia australis and Pseudo-nitzschia cuspidata, Lingulodinium polyedrum, Karenia mikimotoi) was also noticed. In addition, our study revealed the presence of opportunistic species (e.g. Eutreptiella, Thalassiosira, Prorocentrum scutellum) and of the new ectoparasite Dinoflagellate Amyloodinium ocellatum for the first time in Morocco. The detection of such diversity of toxic species, sometimes with alarming concentrations, should prompt the competent authorities to broaden the spectrum and frequency of biomonitoring to uncontrolled seafood harvesting sites.

Title: Dynamique du peuplement phytoplanctonique le long de l'axe côtier Casablanca ­ El Jadida. Abstract: Notre étude taxonomique entre mars 2014 et novembre 2015 le long de la côte atlantique entre Casablanca et El Jadida a permis de déceler une flore phytoplanctonique représentée par les Diatomées, Dinoflagellés, Silicoflagellés et Euglenophycées avec une nette dominance des Diatomées et des Dinoflagellés. Au total, 101 taxons d'algues planctoniques ont été identifiés, témoignant d'une taxocénose relativement diversifiée. Dans cet ensemble, les Diatomées sont représentées par 62 taxons (61,4 %), les Dinoflagellés par 36 taxa (35,6 %) et les deux autres groupes (Silicoflagellés et Euglénophycées) ne sont représentés que par 3 espèces seulement (3,0 %). En ce qui concerne les espèces potentiellement toxiques, plus d'une quinzaine de taxons ont été identifiés dont la plupart sont des Dinoflagellés et des Diatomées (Pseudo-nitzschia australis et Pseudo-nitzschia cuspidata). L'analyse de l'évolution spatiotemporelle des indices de diversité (H') et d'équitabilité (E) révèle des fluctuations saisonnières prononcées sans montrer, pour autant, une grande analogie entre les différents sites prospectés. Par ailleurs, les densités phytoplanctoniques totales présentent de grandes variations à la fois spatiales et temporelles (sur les deux cycles annuels). La présence de proliférations massives de certaines espèces potentiellement toxiques (Pseudo-nitzschia australis et Pseudo-nitzschia cuspidata, Lingulodinium polyedrum, Karenia mikimotoi), d'une nouvelle espèce de Dinoflagellé ectoparasite pour le Maroc (Amyloodinium ocellatum) et d'autres espèces opportunistes (Eutreptiella, Thalassiosira, Prorocentrum scutellum) a été notée au cours de cette étude. La détection des espèces potentiellement toxiques, parfois à des concentrations alarmantes, devrait inciter les autorités compétentes à élargir le spectre et la fréquence de biosurveillance aux sites non contrôlés.

Dinoflagellate chloroplasts as a model for extreme genome reduction and fragmentation in organelles - The COCOA principle for gene retention.

The genomes of peridinin-containing dinoflagellate chloroplasts have a very unusual organisation. These genomes are highly fragmented and greatly reduced, with most of the usual complement of chloroplast genes relocated to the nucleus. Dinoflagellate chloroplasts highlight evolutionary changes that are found to varying extents in a number of other organelle genomes. These include the chloroplast genome of the green alga Boodlea and other Cladophorales, and the mitochondrial genomes of blood-sucking and chewing lice, the parasitic plant Rhopalocnemis phalloides, the red alga Rhodosorus marinus and other members of the Stylonematophyceae, diplonemid flagellates, and some Cnidaria. Consideration of the coding content of the remnant chloroplast genomes indicates that organelles may preferentially retain genes for proteins important in initiating assembly of complexes, and the same is largely true for mitochondria. We propose a new principle, of CO-location for COntrol of Assembly (COCOA), indicating the importance of retaining these genes in the organelle. This adds to, but does not invalidate, the existing hypotheses of the multisubunit completion principle, CO-location for Redox Regulation (CORR) and Control by Epistasy of Synthesis (CES).

Functional diversity of bacterial microbiota associated with the toxigenic benthic dinoflagellate Prorocentrum.

Interactions between bacterial microbiota and epibenthic species of the dinoflagellate Prorocentrum may define the onset and persistence of benthic harmful algal blooms (bHABs). Chemical ecological interactions within the dinoflagellate phycosphere potentially involve a complex variety of organic molecules, metabolites, and toxins, including undefined bioactive compounds. In this study, the bacterial diversity and core members of the dinoflagellate-associated microbiota were defined from 11 strains of three epibenthic Prorocentrum species, representing three geographically disjunct locations within Mexican coastal waters. Microbiota profiles in stable monoclonal Prorocentrum cultures were obtained by sequencing amplicons of the V3-V4 region of the 16S rRNA gene. Thirteen classes of bacteria were identified among dinoflagellate clones, where Alphaproteobacteria, Gammaproteobacteria, and Bacteroidia were consistently dominant. The bacterial community structure exhibited significantly different grouping by the location of origin of dinoflagellate clones. No significant diversity difference was found among free-living or unattached bacteria in the dinoflagellate culture medium (M) compared with those in closer association with the dinoflagellate host cells (H). Twelve taxa were defined as core members of the bacterial assemblage, representing the genera Algiphilus, Cohaesibacter, Labrenzia, Mameliella, Marinobacter, Marivita, Massilia, Muricauda, Roseitalea, and an unclassified member of the Rhodobacteraceae. The core members are inferred to significantly contribute to primary and secondary metabolic functions, but no direct correlation with dinoflagellate toxigenicity was apparent. Overall the bacterial profile and implied gene functionality indicated a suite of positive interactions, suggesting either mutualism or commensalism with the dinoflagellate. The further characterization and interpretation of specific gene functions and interactions between bacteria and dinoflagellates, such as epibenthic members of genus Prorocentrum, are key to understanding their role in toxigenesis and bHAB development.

A review on the diversity and distribution of athecate dinoflagellates in South Atlantic and in the Atlantic sector of the Southern Ocean: Research insights and gaps.

This review summarizes the state of knowledge on athecate dinoflagellates occurring within the South Atlantic Ocean and Atlantic sector of the Southern Ocean. We compiled data from 105 articles and selected 33 addressing any aspect of athecate dinoflagellate studies. Our aim is to discuss the patterns in athecate dinoflagellate distribution by building a thorough species list and an occurrence map based on species recorded in coastal and oceanic waters. We found 69 species totaling 141 occurrences in the entire South Atlantic Ocean basin. Contradicting global trends, most species distributed throughout this region are subtropical. We linked this trend to a higher local effort in dinoflagellate research instead of higher biodiversity, especially when compared to usual hotspots in biodiversity attributed to tropical oceans. The Subantarctic and Antarctic regions had a low number of occurrences, with 12 and 5, respectively. Except for the occurrence of Gyrodinium lachryma in the Antarctic Zone, all records are unique, poorly described and never recorded again for species such as Gymnodinium baccatum and Gymnodinium antarcticum. This demonstrates that the state of knowledge regarding athecate dinoflagellates in the South Atlantic and especially in the Antarctic region is still limited due to a lack of directed investigation.

Evidence for the production of asexual resting cysts in a free-living species of Symbiodiniaceae (Dinophyceae).

Coral reef ecosystems are the most productive and biodiverse marine ecosystems, with their productivity levels highly dependent on the symbiotic dinoflagellates belonging to the family Symbiodiniaceae. As a unique life history strategy, resting cyst production is of great significance in the ecology of many dinoflagellate species, those HABs-causing species in particular, however, there has been no confirmative evidence for the resting cyst production in any species of the family Symbiodiniaceae. Based on morphological and life history observations of cultures in the laboratory and morpho-molecular detections of cysts from the marine sediments via fluorescence in situ hybridization (FISH), cyst photography, and subsequent singe-cyst PCR sequencing, here we provide evidences for the asexual production of resting cysts by Effrenium voratum, the free-living, red tide-forming, and the type species of the genus Effrenium in Symbiodiniaceae. The evidences from the marine sediments were obtained through a sequential detections: Firstly, E. voratum amplicon sequence variants (ASVs) were detected in the cyst assemblages that were concentrated with the sodium polytungstate (SPT) method from the sediments collected from different regions of China Seas by high-throughput next generation sequencing (NGS); Secondly, the presence of E. voratum in the sediments was detected by PCR using the species-specific primers for the DNA directly extracted from sediment; Thirdly, E. voratum cysts were confirmed by a combined approach of FISH using the species-specific probes, light microscopic (LM) photography of the FISH-positive cysts, and a subsequent single-cyst PCR sequencing for the FISH-positive and photographed cysts. The evidences from the laboratory-reared clonal cultures of E. voratum include that: 1) numerous cysts formed in the two clonal cultures and exhibited a spherical shape, a smooth surface, absence of ornaments, and a large red accumulation body; 2) cysts could maintain morphologically intact for a storage of two weeks to six months at 4 °C in darkness and of which 76-92 % successfully germinated through an internal development processes within a time period of 3-21 days after being transferred back to the normal culturing conditions; 3) two or four germlings were released from each cyst through the cryptopylic archeopyle in all cysts with continuous observations of germination processes; and 4) while neither sexual mating of gametes nor planozygote (cells with two longitudinal flagella) were observed, the haploidy of cysts was proven with flow cytometric measurements and direct LM measurements of fluorescence from cells stained with either propidium iodide (PI) or DAPI, which together suggest that the cysts were formed asexually. All evidences led to a conclusion that E. voratum is capable of producing asexual resting cysts, although its sexuality cannot be completely excluded, which guarantees a more intensive investigation. This work fills a gap in the knowledge about the life cycle, particularly the potential of resting cyst formation, of the species in Symbiodiniaceae, a group of dinoflagellates having unique life forms and vital significance in the ecology of coral reefs, and may provide novel insights into understanding the recovery mechanisms of coral reefs destructed by the global climate change and suggest various forms of resting cysts in the cyst assemblages of dinoflagellates observed in the field sediments, including HABs-causing species.

Role of turbulence in Dinophysis spp. growth, feeding, and toxin leakage in culture.

Dinophysis, a mixotrophic dinoflagellate that is known to prey on the ciliate Mesodinium rubrum, and retain its chloroplasts, is responsible for diarrhetic shellfish poisoning (DSP) in humans and has been identified on all U.S. coasts. Monocultures of Dinophysis have been used to investigate the growth of Dinophysis species in response to variations in environmental conditions, however, little is known about the roles of system stability (turbulence) and mixotrophy in the growth and toxicity of Dinophysis species in the U.S.. To begin to address this gap in knowledge, culturing experiments were conducted with three species (four strains) of Dinophysis, that included predator-prey co-incubation (Dinophysis spp.+ M. rubrum) and prey-only (M. rubrum) flasks. Cultures were investigated for effects of low or high turbulence on Dinophysis spp. growth, feeding, and amounts of intra- and extracellular toxins: okadaic acid and derivatives (diarrhetic shellfish toxins, DSTs) and pectenotoxins (PTXs). Turbulence did not have a measurable effect on the rates of ingestion of M. rubrum prey by Dinophysis spp. for any of the four strains, however, effects on growth and particulate and dissolved toxins were observed. High turbulence (ε = 10-2 m2s-3) significantly slowed growth of both D. acuminata and D. ovum relative to still controls, but significantly stimulated growth of the D. caudata strain. Increasing turbulence also resulted in significantly higher intracellular toxin content in D. acuminata cultures (DSTs and PTXs), but significantly reduced intracellular toxin content (PTXs) in those of D. caudata. An increase in turbulence appeared to promote toxin leakage, as D. ovum had significantly more extracellular DSTs found in the medium under high turbulence when compared to the still control. Overall, significant responses to turbulence were observed, whereby the three strains from the "Dinophysis acuminata complex" displayed a stress response to turbulence, i.e., decreasing growth, increasing intracellular toxin content and/or increasing toxin leakage, while the D. caudata strain had an opposite response, appearing stimulated by, or more tolerant of, high turbulence.

The effects of the toxic dinoflagellate Alexandrium on feeding, reproduction and mortality of the copepod Acartia: A systematic review employing weighted linear models.

The study of interactions between copepods of the genus Acartia and toxic dinoflagellates of the genus Alexandrium has been an important topic during the last four decades. Feeding behavior and physiological responses of copepods have been studied in laboratory and field experiments, sometimes with contradictory results. More recently, an evolutionary adaptive mechanism leading to enhanced tolerance of Alexandrium toxins in a population of Acartia experiencing chronic exposure to these dinoflagellates has been reported. In the present work, we collected data from the existing studies on the effects of Alexandrium on feeding, reproduction and mortality of Acartia. With these data, we performed a systematic review consisting of a secondary analysis employing general or generalized linear models, weighting data from different studies by the reciprocal of their standard deviation. Our first aim was to overcome shortcomings of individual studies: limited ranges of the variables and overlooked variables (experiment length, population adaptation). These shortcomings could have led to inconsistent conclusions by missing heterogeneous patterns in copepod responses and in the interactions between variables. Our second aim was to test the enhanced physiological performance of chronically exposed relative to naïve copepod populations over a wide geographic range. We found that the feeding rate is enhanced by increased food biomass, irrespective of the food type. Toxins do not have a clear effect on egg production and have a bi-phasic effect on egg hatching success, which was negative above a specific threshold. Toxins also increased mortality. Experiment length had a positive effect on egg production and negative on egg hatching. Naïve copepod populations showed consistently lower ingestion of Alexandrium and egg hatching rates, thereby supporting the spread of the aforementioned mechanism across populations over a wide geographic range.

Distribution and Level of Bioactive Monoacylglycerols in 12 Marine Microalgal Species.

Microalgae are currently considered an attractive source of highly valuable metabolites potentially exploitable as anticancer agents, nutraceuticals and cosmeceuticals and for bioenergy purposes. Their ease of culturing and their high growth rates further promote their use as raw material for the production of specialty products. In the present paper, we focused our attention on specific glycerol-based lipid compounds, monoacylglycerols (MAGs), which displayed in our previous studies a selective cytotoxic activity against the haematological U-937 and the colon HCT-116 cancer cell lines. Here, we performed a quali/quantitative analysis of MAGs and total fatty acids (FAs) along with a profiling of the main lipid classes in a panel of 12 microalgal species, including diatoms and dinoflagellates. Our results highlight an inter- and intraspecific variability of MAG profile in the selected strains. Among them, Skeletonema marinoi (strain FE7) has emerged as the most promising source for possible biotechnological production of MAGs.

Purification and Screening of the Antialgal Activity of Seaweed Extracts and a New Glycolipid Derivative against Two Ichthyotoxic Red Tide Microalgae Amphidinium carterae and Karenia mikimotoi.

Ichthyotoxic red tide is a problem that the world is facing and needs to solve. The use of antialgal compounds from marine macroalgae to suppress ichthyotoxic red tide is considered a promising biological control method. Antialgal substances were screened and isolated from Bangia fusco-purpurea, Gelidium amansii, Gloiopeltis furcate, Hizikia fusifarme, Laminaria japonica, Palmaria palmata, and Sargassum sp. to obtain new materials for the development of algaecides against ichthyotoxic red tide microalgae using bioactivity-guided isolation methods. The fractions of seven macroalgae exhibited selective inhibitory activities against Amphidinium carterae and Karenia mikimotoi, of which the ethyl acetate fractions had the strongest and broadest antialgal activities for the two tested red tide microalgae. Their inhibitory effects on A. carterae and K. mikimotoi were even stronger than that of potassium dichromate, such as ethyl acetate fractions of B. purpurea, H. fusifarme, and Sargassum sp. Thin-layer chromatography and ultraviolet spectroscopy were further carried out to screen the ethyl acetate fraction of Sargassum sp. Finally, a new glycolipid derivative, 2-O-eicosanoyl-3-O-(6-amino-6-deoxy)-ß-D-glucopyranosyl-glycerol, was isolated and identified from Sargassum sp., and it was isolated for the first time from marine macroalgae. The significant antialgal effects of 2-O-eicosanoyl-3-O-(6-amino-6-deoxy)-ß-D-glucopyranosyl-glycerol on A. carterae and K. mikimotoi were determined.

Heat stress in symbiotic dinoflagellates: Implications on oxidative stress and cellular changes.

Global warming has been shown to harmfully affect symbiosis between Symbiodiniaceae and other marine invertebrates. When symbiotic dinoflagellates (the genus Breviolum) were in vitro exposed to acute heat stress of +7 °C for a period of 5 days, the results revealed the negative impact on all physiological and other cellular parameters measured. Elevated temperatures resulted in a severe reduction in algal density of up to 9.5-fold, as well as pigment concentrations, indicating the status of the physiological stress and early signs of photo-bleaching. Reactive oxygen species (ROS) were increased in all heated dinoflagellate cells, while the antioxidant-reduced glutathione levels initially dropped on day one but increased under prolonged temperature stress. The cell viability parameters were reduced by 97 % over the heating period, with an increased proportion of apoptotic and necrotic cells. Autofluorescence (AF) for Cy5-PE 660-20 was reduced from 1.7-fold at day 1 to up to 50-fold drop at the end of heating time, indicating that the AF changes were highly sensitive to heat stress and that it could be an extremely sensitive tool for assessing the functionality of algal photosynthetic machinery. The addition of the drug 5-AZA-2'-deoxycytidine (5-AZA), which inhibits DNA methylation processes, was assessed in parallel and contributed to some alterations in algal cellular stress response. The presence of drug 5-AZA combined with the temperature stress had an additional impact on Symbiodiniaceae density and cell complexity, including the AF levels. These variations in cellular stress response under heat stress and compromised DNA methylation conditions may indicate the importance of this epigenetic mechanism for symbiotic dinoflagellate thermal tolerance adaptability over a longer period, which needs further exploration. Consequently, the increased ROS levels and changes in AF signals reported during ongoing heat stress in dinoflagellate cells could be used as early stress biomarkers in these microalgae and potentially other photosynthetic species.

Identification of bacteria in potential mutualism with toxic Alexandrium catenella in Chilean Patagonian fjords by in vitro and field monitoring.

The dinoflagellate Alexandrium catenella is a well-known paralytic shellfish toxin producer that forms harmful algal blooms, repeatedly causing damage to Chilean coastal waters. The causes and behavior of algal blooms are complex and vary across different regions. As bacterial interactions with algal species are increasingly recognized as a key factor driving algal blooms, the present study identifies several bacterial candidates potentially associated with Chilean Alexandrium catenella. This research narrowed down the selection of bacteria from the Chilean A. catenella culture using antibiotic treatment and 16S rRNA metabarcoding analysis. Subsequently, seawater from two Chilean coastal stations, Isla Julia and Isla San Pedro, was monitored for two years to detect Alexandrium species and the selected bacteria, utilizing 16S and 18S rRNA gene metabarcoding analyses. The results suggested a potential association between Alexandrium species and Spongiibacteraceae at both stations. The proposed candidate bacteria within the Spongiibacteraceae family, potentially engaging in mutualistic relationships with Alexandrium species, included the genus of BD1-7 clade, Spongiibbacter, and Zhongshania.