Academic literature on the topic 'Ostreopsis spp'

Ostreopsis spp. has been reported for the first time from the Egyptian Mediterranean waters. Macroalgal samples were collected monthly between June 2005 and December 2007, from the rocks at Abu Qir, from less than 1.5 m depth, and their associated microalgae examined. Populations of two Ostreopsis morphotypes were found to occur in this location, east of Alexandria, viz., O. cf ovata Fukuyo and Ostreopsis morph1. The Ostreopsis spp. was abundant and dominant during the summer. They were more abundant as epiphytes of the brown algae Padina sp. and Sargassum sp., less abundant on the red algae Corallina sp., Jania sp., Laurencia sp. and even less so on the green algae Ulva spp. Ostreopsis cf. ovata was also identified during the summer months on the same macroalgal species, although in a much lower abundance. Ostreopsis spp. alternated in dominance with the benthic cyanobacteria Oscillatoria spp. and the diatom Licmophora sp. Other benthic dinoflagellates recorded at low abundance included Amphidinium carterae, Gymnodinium sp. and Prorocentrum lima.

A study on the presence and relative abundance of benthic harmful algal bloom (BHAB) forming dinoflagellate species was carried out in the coral reefs of Sampadi Island, Sarawak, Malaysia. The study involved deployment of fiberglass screens as an artificial substrate for the benthic epiphytic microalgae. The screens were placed for 24 h above the seafloor along a 100 m transect at 10 m intervals. BHAB species attached to the screens were identified and cell abundances were enumerated under a light microscope. The BHAB community at the study site was dominated by Prorocentrum spp. and Coolia spp. Other BHAB species collected included Amphidinium spp., Gambierdiscus spp. and Ostreopsis spp. Total cell densities collected on the screens ranged from 5 to 100 cells per 100 cm2. The two BHAB groups of primary concern, Gambierdiscus spp. and Ostreopsis spp. were detected at relatively low abundances of 0.6–4.2% and 1.8–16% respectively. This study has shown that potentially toxic BHAB species were present in the coral reef and the artificial substrate approach could provide a convenient quantitative method for the collection of clean samples for identification and enumeration purposes.

Palytoxin is one of the most complex and biggest molecules known to show extreme acute toxicity. The dinoflagellate Ostreopsis spp., the producer organism of palytoxin, has been shown to be distributed worldwide, thus making palytoxin an emerging toxin. Rat-derived hepatocytes (Clone 9) and BE (2)-M17 human neuroblastoma cells were used to test palytoxin or palytoxin-like compounds by measuring the cell metabolic rate with Alamar Blue. The dose-dependent decrease in viability was specifically inhibited by ouabain in the case of BE (2)-M17 neuroblastoma cells. This is a functional, dynamic and simple test for palytoxins with high sensitivity (as low as 0.2 ng/ml). This method was useful for toxin detection in Ostreopsis extracts and naturally contaminated mussel samples. A comparative study testing toxic mussel extracts by LC (liquid chromatography)-MS/MS (tandem MS), MBA (mouse bioassay), haemolysis neutralization assay and a cytotoxicity test indicated that our method is suitable for the routine determination and monitoring of palytoxins and palytoxin-like compounds.

Abstract Mixotrophy has been shown to be a common trait among dinoflagellates and its importance in the nutritional ecology of harmful algae has been hypothesized. Benthic harmful species have not been extensively investigated as their planktonic counterparts and there are major gaps in the knowledge of their nutritional strategies. In this study the occurrence of phagotrophy was investigated in natural assemblages of benthic dinoflagellates using epi-fluorescence microscopy with DAPI and LysoSensor staining. The study was conducted at five sites along the coast of Rio de Janeiro that were visited in January, August and December 2010. In total, 1659 dinoflagellate cells were observed. From these, only 0.4% of 1195 Ostreopsis cf. ovata and 2.2% of 134 Coolia spp. cells presented evidence of phagotrophy with vacuoles stained by LysoSensor or a DAPI (4',6-diamidino-2-phenylindole) stained inclusion. Stained vacuoles were not registered in the 330 Prorocentrum spp. cells observed. Few O. cf. ovata cells contained round red inclusions ("red spots") that were not stained either by DAPI or LysoSensor, suggesting that these structures are not ingested prey. The results showed that phagotrophy was not a frequent nutritional strategy in benthic dinoflagellates during the study period.

Les efflorescences algales nuisibles (HABs) associées aux dinoflagellés benthiques toxiques du genre Ostreopsis sont des phénomènes observés de plus en plus fréquemment à travers le monde et sont responsables de problèmes sanitaires, économiques et écologiques. L’augmentation du nombre d’observations de ce dinoflagellé depuis les dernières décennies laisse penser que les changements climatiques, et plus particulièrement le réchauffement des océans, seraient en partie responsable de son expansion, notamment dans les zones tempérées. Cependant, ce lien entre réchauffement des eaux et développement d’efflorescences d’Ostreopsis est difficile à prouver et certaines données concernant les aires de répartition ou la réponse des cellules aux variations thermiques sont encore manquantes. Ces travaux de thèse ont fourni des nouveaux éléments pour répondre à cette problématique en abordant trois thématiques principales : 1) la phénologie des efflorescences, 2) la distribution d’espèce le long d’un gradient latitudinal et 3) les adaptations physiologiques à un gradient de température. Ces questions ont été abordées en gardant l’effet de la température sur l’écologie des espèces étudiées comme fil conducteur principal et lien entre les trois questions posées. Les travaux ont été menés avec une approche multidisciplinaire incluant des analyses statistiques de jeux de données, des approches génétiques basées sur l’ADN environnemental, ainsi que des approches d’écophysiologie et d’écotoxicologie. Les données utilisées ont été acquises à la fois à partir de prélèvements de terrain et d’expériences en milieu contrôlé au laboratoire. Pour répondre au premier objectif, nous avons analysé la série temporelle issue du suivi d’efflorescences d’O. cf. ovata à Monaco, mis en place depuis 2007 et toujours poursuivi à ce jour, afin de mettre en relation la phénologie des efflorescences avec les paramètres environnementaux. Bien que, d’après nos analyses, aucun facteur physico-chimique mesuré ne soit en mesure d’expliquer la phénologie des efflorescences, une forte corrélation positive entre l’accumulation d’anomalies positives des températures de surface au printemps et la date de début des efflorescences a été mise en évidence, suggérant que plus les températures printanières seraient élevées, plus les efflorescences d’O. cf. ovata à Monaco seraient précoces. La deuxième question de la thèse a été abordée en analysant de nouveaux échantillons collectés dans le cadre d’une campagne d’échantillonnage conduite le long des côtes du Golfe de Gascogne en août-septembre 2018. Cette campagne avait pour objectif d’établir l’aire de répartition actuelle d’Ostreopsis spp. dans cette zone à fort gradient thermique sud-nord, afin de poser les bases pour l’analyse d’une possible future expansion en cas de réchauffement des eaux. Les résultats traités ont combiné une approche classique d’échantillonnage benthique, l’utilisation de substrats artificiels pour la collection d’ADN environnemental analysés via des outils moléculaires (rt-qPCR) ainsi qu’une approche de modélisation Lagrangienne visant à établir la connectivité physique entre différents sites de prélèvement. Nous avons pu montrer que seule l’espèce O. cf. siamensis était présente dans le Golfe, et que celle-ci pouvait être retrouvée jusqu’à l’entrée de La Manche, bien que les populations formant des efflorescences n’aient été observées que dans la partie sud-est du Golfe. Cette étude nous a permis d’identifier des zones sentinelles le long du Golfe de Gascogne où il serait intéressant de mettre en place de nouveaux suivis à long terme afin d’observer la potentielle expansion vers le nord d’O. cf. siamensis. La réponse d’Ostreopsis spp. face à des changements de température a été étudiée en termes de capacité de croissance, d’adaptations physiologiques et de toxicité, au cours d’une expérience d’acclimatation thermique. Différentes souches monoclonales ont été comparées [...]
Harmful algal blooms (HABs) associated with the toxic benthic dinoflagellate Ostreopsis spp. are increasing around the world and responsible for sanitary, economic and ecological issues. The increasing number of reports of this dinoflagellate in recent decades suggests that climate change, and more particularly ocean warming, may be partly responsible for its expansion, especially in temperate zones. However, this link between warming waters and the development of Ostreopsis spp. blooms is difficult to prove and data concerning distribution areas or cellular responses to thermal variations are still lacking. This PhD thesis work provides new elements to answer this issue by addressing three main themes: 1) the phenology of blooms, 2) the distribution of species along a latitudinal gradient and 3) physiological adaptations to a temperature gradient. These questions were addressed by keeping the effect of temperature on the ecology of Ostreopsis spp. as the main thread and link between the three questions asked. This work was carried out using a multidisciplinary approach including statistical analyzes of datasets, genetic approaches based on environmental DNA, as well as ecophysiology and ecotoxicology approaches. The data used were acquired both from samples collected in the field and from experiments in a controlled environment in the laboratory. To meet the first objective, we analyzed the time series resulting from the ongoing monitoring of O. cf. ovata summer blooms in Monaco (NW Mediterranean Sea) set up since 2007 in order to determine the relationship between blooms phenology and environmental parameters. Although no environmental factor measured was able to fully explain the phenology of blooms, a strong positive correlation was found between positive sea surface temperature anomalies during spring and the timing of blooms, suggesting that the warmer the spring, the earlier the blooms of O. cf. ovata in Monaco. The second question of the thesis was addressed by analyzing new samples collected as part of a sampling campaign conducted along the coast of the Bay of Biscay in August-September 2018. This campaign aimed to establish the current distribution of Ostreopsis spp. in this area exhibiting a strong South-North thermal gradient, in order to initiate the analysis of a possible future expansion due to ocean warming. The processed results combined a classic benthic sampling approach, the use of artificial substrates for the collection of environmental DNA analyzed through molecular tools (rt-qPCR) as well as a Lagrangian modeling approach aiming at establishing the connectivity between sampling areas. We showed that only O. cf. siamensis was present in the Bay and that it could be found in certain areas up until the entrance to the English Channel, although blooms of O. cf. siamensis were only observed in the southeastern part of the Bay. This study allowed us to identify sentinel zones along the Bay of Biscay where new long-term monitoring could be set up in order to observe the potential expansion of O. cf. siamensis towards the North of the bay. Finally, the response of Ostreopsis spp. in relation with varying temperatures was studied in terms of growth capacity, physiological adaptations and toxicity in a thermal acclimation experiment. Different monoclonal strains were compared, including strains of O. cf. siamensis isolated in the Bay of Biscay during our 2018 campaign, as well as strains of O. cf. ovata from the northwestern Mediterranean Sea, correspongind to the two areas studied this thesis. The first results of this experiment indicate that the strains of O. cf. siamensis are able to acclimate and grow at temperatures between 16 ° C and 25 ° C, with an optimum growth temperature estimated around 22 ° C. In addition, the strains of O. cf. siamensis exhibited a higher level of toxicity at 22°C and 25°C than at 16°C and 19°C, indicating an effect of temperature on the toxicity of Ostreopsis spp. [...]