Basin scale variability of Ostreopsis spp. blooms provides evidence of effectiveness of an integrated sampling approach.

Ostreopsis spp. blooms have been occurring in the last two decades in the Mediterranean Sea in association with a variety of biotic and abiotic substrata (macroalgae, seagrasses, benthic invertebrates, sand, pebbles and rocks). Cells proliferate attached to the surfaces through mucilaginous trichocysts, which lump together microalgal cells, and can also be found in the plankton and on floating aggregates: such tychoplanktonic behavior makes the quantitative assessment of blooms more difficult than planktonic or benthic ones.

High-resolution phylogenetic analysis reveals long-term microbial dynamics and microdiversity in phytoplankton microbiome.

Phytoplankton-bacteria interactions represent the evolution of complex cross-kingdom networks requiring niche specialization of diverse microbes. Unraveling this co-evolutionary process has proven challenging because microbial partnerships are complex, and their assembly can be dynamic as well as scale- and taxon-dependent. Here, we monitored long-term experimental evolution of phytoplankton-bacteria interactions by reintroducing the intact microbiome into an axenized dinoflagellate Alexandrium tamarense to better understand microbiome assembly dynamics and how microbiome composition could shift and stabilize over 15 months.

Do photosynthetic cells communicate with each other during cell death? From cyanobacteria to vascular plants.

As in metazoans, life in oxygenic photosynthetic organisms relies on the accurate regulation of cell death. During development and in response to the environment, photosynthetic cells activate and execute cell death pathways that culminate in the death of a specific group of cells, a process known as regulated cell death (RCD). RCD control is instrumental, as its misregulation can lead to growth penalties and even the death of the entire organism.

Dinophyceae can use exudates as weapons against the parasite Amoebophrya sp. (Syndiniales).

Parasites in the genus Amoebophrya sp. infest dinoflagellate hosts in marine ecosystems and can be determining factors in the demise of blooms, including toxic red tides. These parasitic protists, however, rarely cause the total collapse of Dinophyceae blooms.

Variable inter and intraspecies alkaline phosphatase activity within single cells of revived dinoflagellates.

Adaptation of cell populations to environmental changes is mediated by phenotypic variability at the single-cell level. Enzyme activity is a key factor in cell phenotype and the expression of the alkaline phosphatase activity (APA) is a fundamental phytoplankton strategy for maintaining growth under phosphate-limited conditions. Our aim was to compare the APA among cells and species revived from sediments of the Bay of Brest (Brittany, France), corresponding to a pre-eutrophication period (1940's) and a beginning of a post-eutrophication period (1990's) during which phosphate concentrations have undergone substantial variations.

Current distribution and potential expansion of the harmful benthic dinoflagellate Ostreopsis cf. siamensis towards the warming waters of the Bay of Biscay, North-East Atlantic.

In a future scenario of increasing temperatures in North-Atlantic waters, the risk associated with the expansion of the harmful, benthic dinoflagellate Ostreopsis cf. siamensis has to be evaluated and monitored. Microscopy observations and spatio-temporal surveys of environmental DNA (eDNA) were associated with Lagrangian particle dispersal simulations to: (i) establish the current colonization of the species in the Bay of Biscay, (ii) assess the spatial connectivity among sampling zones that explain this distribution, and (iii) identify the sentinel zones to monitor future expansion.

Uptake of dissolved inorganic and organic nitrogen by the benthic toxic dinoflagellate Ostreopsis cf. ovata.

Environmental factors that shape dynamics of benthic toxic blooms are largely unknown. In particular, for the toxic dinoflagellate Ostreopsis cf. ovata, the importance of the availability of nutrients and the contribution of the inorganic and organic pools to growth need to be quantified in marine coastal environments.

Benthic Dinoflagellate Integrator (BEDI): A new method for the quantification of Benthic Harmful Algal Blooms.

Despite the potential negative human health, ecological and economic impact, the ecology of harmful benthic dinoflagellate blooms remains largely unknown. This is probably due to the complex interactions among biotic and abiotic drivers that influence blooms, but also to the difficulty in quantifying cell abundance in a comparable way over large spatial and temporal scales. One of the recognized priorities for bHABs (benthic Harmful Algal Blooms) assessment is developing and standardizing methods that can provide comparable data.

Passive Sampling and High Resolution Mass Spectrometry for Chemical Profiling of French Coastal Areas with a Focus on Marine Biotoxins.

Passive samplers (solid phase adsorption toxin tracking: SPATT) are able to accumulate biotoxins produced by microalgae directly from seawater, thus providing useful information for monitoring of the marine environment. SPATTs containing 0.3, 3, and 10 g of resin were deployed at four different coastal areas in France and analyzed using liquid chromatography coupled to high resolution mass spectrometry.

Sampling of Ostreopsis cf. ovata using artificial substrates: Optimization of methods for the monitoring of benthic harmful algal blooms.

In the framework of monitoring of benthic harmful algal blooms (BHABs), the most commonly reported sampling strategy is based on the collection of macrophytes. However, this methodology has some inherent problems. A potential alternative method uses artificial substrates that collect resuspended benthic cells.

Particulate carbon and nitrogen determinations in tracer studies: The neglected variables.

We address two issues in the determination of particulate carbon and nitrogen in suspended matter of aquatic environments. One is the adsorption of dissolved organic matter on filters, leading to overestimate particulate matter. The second is the material loss during filtration due to fragile algal cells breaking up.

Stress-related responses in Alexandrium tamarense cells exposed to environmental changes.

Organisms tend to be sensitive to drastic changes in environmental conditions. For unicellular microorganisms, variations in physico-chemical conditions are particularly challenging and may result in acclimation, entrance into quiescence, or death through necrotic or autocatalytic pathways. This study focuses on the thecate dinoflagellate Alexandrium tamarense.

Flow cytometric characterization of hemocytes of the sunray venus clam Macrocallista nimbosa and influence of salinity variation.

Sunray venus clam Macrocallista nimbosa is a native bivalve mollusc of Florida, USA, currently evaluated as a potential new aquaculture species. Very little is known about the physiology and hemocyte characteristics of this species. Bivalve hemocytes are generally involved in various physiological functions including nutrition, tissue repair, detoxification and immune defense.

Discrepancies between net particulate carbon production and (13) C-labelled bicarbonate uptake by Alexandrium catenella (Dinophyceae): grazing controls the balance between autotrophic and non autotrophic carbon acquisition(1).

Inorganic carbon uptake by Alexandrium catenella estimated from incorporation of (13) C labelled bicarbonate (an estimate of carbon gain by autotrophy) was compared to increases in particulate carbon (PC) that integrate all processes leading to carbon gain by cells (autotrophy, heterotrophy, mixotrophy). During blooms of A. catenella in the field, the (13) C tracer technique could account for only 47% (range 29%-59%) of the increase in PC in conventional 24 h incubations.

SHORT-TERM TEMPORAL VARIABILITY OF AMMONIUM AND UREA UPTAKE BY ALEXANDRIUM CATENELLA (DINOPHYTA) IN CULTURES(1).

In batch cultures of four Mediterranean strains (from France, Italy, and Spain) of Alexandrium catenella (Whedon et Kof.) Balech growing on a daily light cycle, ammonium and urea uptake were estimated by the (15) N tracer technique. Ammonium uptake could be described by Michaelis-Menten kinetics along a substrate gradient of 0.

Ocean urea fertilization for carbon credits poses high ecological risks.

The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversity, with thousands of tonnes of urea in order to stimulate algal blooms and sequester carbon is flawed for multiple reasons. Urea is preferentially used as a nitrogen source by some cyanobacteria and dinoflagellates, many of which are neutrally or positively buoyant. Biological pumps to the deep sea are classically leaky, and the inefficient burial of new biomass makes the estimation of a net loss of carbon from the atmosphere questionable at best.