Philippe Rosa

Spatiotemporal changes in microphytobenthos assemblages in a macrotidal flat (Bourgneuf Bay,France)1

Spatiotemporal changes in microphytobenthos species composition were investigated in relation to structural variables—biomass; life‐forms; detritus ratio, pheopigment a (pheo a):chl a; and sediment characteristics—at mesoscale in a shellfish macrotidal ecosystem. To characterize algae assemblages, multivariate analyses were performed (multidimensional scaling [MDS] ordination and clustering), supported by correlations between structural variables. Microphytobenthos, dominated by 97% diatoms belonging to 89 taxa, was constituted by two main assemblages: The first one, composed of common species (occurrence >50%), mainly nanobenthic (size <30 μm) and epipsammic (sand‐fixed cells), was associated with mixed sediments. The major species contributing to this assemblage were Navicula perminuta, Achnanthes hauckiana, Fallacia tenera, A. lanceolata var. elleptica, Amphora spp., Plagiogrammopsis vanheurkii, and Plagiogramma tenuissimum (see Table 2 for taxonomic authors). Species diversity was high (N1∼ 11), often linked to high biomass values (>70 mg chl a · m−2) and low detritus ratio. Conversely, the second assemblage comprised occasional species (occurrence from 10% to 50%), mainly microbenthic (>30 μm) and epipelic (moving cells), occurring during summer at muddy sites. This assemblage, characterized by low diversity, high biomass variability, and high detritus ratio, was dominated by Scolioneis tumida or Plagiotropis vitrea and Navicula spartinetensis. Whereas hydrodynamics globally explained the gradual assemblage changes throughout the entire mudflat and the year, oyster beds and ridge and runnel features appeared to be local spatial structuring factors allowing the establishment of specific assemblages. This study suggests a significant role for epipsammon biomass, until now underestimated, in the functioning of this turbid coastal ecosystem.

Antioxidant and Free Radical Scavenging Properties of Marennine, a Blue-Green Polyphenolic Pigment from the Diatom Haslea ostrearia (Gaillon/Bory) Simonsen Responsible for the Natural Greening of Cultured Oysters

Among microalgae, the marine diatom Haslea ostrearia has the distinctive feature of synthesizing and releasing, into the surrounding environment, a blue-green polyphenolic pigment called marennine. The oyster-breeding industry commonly makes use of this natural phenomenon for the greening of oysters grown in the ponds of the French Atlantic coast. This article reports the in vitro antioxidant properties of pure marennine. Two kinds of evaluation systems were adopted to test the antioxidative activity of marennine: antioxidant capacity assays (beta-carotene and thymidine protection assays and iron reducing power assay) and free radical scavenging assays (DPPH*, O2*-, and HO*). In almost all cases, marennine exhibited significantly higher antioxidative and free radical scavenging activities than natural and synthetic antioxidants commonly used in food, as shown by comparing median effective concentration (EC 50) values, for each test independently. This medium molecular weight polyphenol (around 10 kDa) from microalgae is thus a potentially useful natural antioxidant. Because of its blue-coloring property and water solubility, it could also be used as a natural food-coloring additive.

Enhancement of marennine production by blue light in the diatom Haslea ostrearia

The marine diatom Haslea ostrearia Simonsen produces a blue pigment, marennine, which is used for greening oysters. This microalga is cultured industrially indoors with artificial light. The influence of light quality on marennine production by cultures of H. ostrearia was investigated in the laboratory and at a semi-pilot scale (300 L tanks). In the first series of experiments in the laboratory, a clone of H. ostrearia was cultured under light of different colors (white, blue, green, yellow, and red) and at two irradiances (‘low’ and ‘high’, 20 and 100 μmol photons m−2 s−1, respectively). Compared to the white light controls, growth was increased in blue light at the ‘low’, but not at the ‘high’ irradiance, and marennine production at the end of the exponential phase was the highest in cells grown under blue light, regardless of the light quality or intensity during growth. Increased marennine production during growth was also observed, whichever color of light (blue or white) was used during the acclimation phase. In a second series of experiments, intraclonal differences were studied by comparing marennine production in seven clones differing with regard to their mean cell size. The total marennine expressed either per cell or per culture volume, was higher in blue light for all the clones. Complementary experiments carried out under semi-industrial conditions confirmed this effect of blue light, which could be relevant for the industrial, indoor production of marennine.

Preliminary characterisation of the blue-green pigment “marennine” from the marine tychopelagic diatom Haslea ostrearia (Gaillon/Bory) Simonsen

Haslea ostrearia is a common marine tychopelagic diatom which has the particularity of synthesizing a blue-green hydrosoluble pigment called “marennine”. This pigment, when released into the external medium, is known to be responsible for the colour of oyster gills. Here we present results for main biophysical and biochemical characteristics of pure intra- and extracellular marennine. Tests for chemical determination show that the nature of the two forms of marennine cannot be distinguished and could be related to a polyphenolic compound. Nevertheless, based on spectral properties and the molecular weight, which is about 10751 ± 1 and 9893 ± 1 Da, for the intracellular and extracellular forms respectively, we assess that the pigment accumulated in the apex of the cell and the one released in the external medium have probably distinct molecular structures.

Purification of the blue-green pigment “marennine” from the marine tychopelagic diatom Haslea ostrearia (Gaillon/Bory) Simonsen

The diatom Haslea ostrearia that lives in oyster ponds has the distinctive feature of synthesizing “marennine”, a blue-green pigment of which the chemical nature still remains unknown. This pigment is responsible for the greening of oyster gills. Here, we report a new method for extraction and purification of intracellular (accumulated in the apex of the cell) and extracellular (released into the external medium) forms of the pigment. Intracellular marennine is obtained by extraction from blue algal pellets with a carbonate buffer. The extract is then centrifuged and filtered. Extracellular marennine is obtained by clarification of blue-coloured culture medium. Both extracts are then purified by a semi-preparative process, using ultrafiltration through membranes and anion-exchange chromatography. This procedure allows us to produce native pigment displaying the degree of purity required to enter upon the molecular characterisation of marennine. By this process, about 35% of the initial amount of pigment can be recovered. If necessary, this method could be easily scaled up to a larger production system to accommodate potential industrial applications.