Yves Rincé’s research while affiliated with Laboratoire des Sciences du Numérique de Nantes and other places

The structure of intertidal benthic diatoms assemblages in the Tagus estuary was investigated during a 2-year survey, carried out in six stations with different sediment texture. Nonparametric multivariate analyses were used to characterize spatial and temporal patterns of the assemblages and to link them to the measured environmental variables. In addition, diversity and other features related to community physiognomy, such as size-class or life-form distributions, were used to describe the diatom assemblages. A total of 183 diatom taxa were identified during cell counts and their biovolume was determined. Differences between stations (analysis of similarity (ANOSIM), R = 0.932) were more evident than temporal patterns (R = 0.308) and mud content alone was the environmental variable most correlated to the biotic data (BEST, ρ = 0.863). Mudflat stations were typically colonized by low diversity diatom assemblages (H′ ~ 1.9), mainly composed of medium-sized motile epipelic species (250–1,000 μm3), that showed species-specific seasonal blooms (e.g., Navicula gregaria Donkin). Sandy stations had more complex and diverse diatom assemblages (H′ ~ 3.2). They were mostly composed by a large set of minute epipsammic species (<250 μm3) that, generally, did not show temporal patterns. The structure of intertidal diatom assemblages was largely defined by the interplay between epipelon and epipsammon, and its diversity was explained within the framework of the Intermediate Disturbance Hypothesis. However, the spatial distribution of epipelic and epipsammic life-forms showed that the definition of both functional groups should not be over-simplified.

2012): Haslea karadagensis (Bacillariophyta): a second blue diatom, recorded from the Black Sea and producing a novel blue pigment, European Journal of Phycology, 47:4, 469-479 This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

The effects of copper on growth, photosynthesis and carbonic anhydrase activity in four marine diatoms were investigated under controlled conditions. Two species (Amphora acuthuscula and Nitzschia palea) were collected from the Southeast Vietnamese coast, and the other two (Amphora coffeaeformis and Entomoneis paludosa) were native from the French Atlantic coast. Adding 1.5 and 3.0 mu M of Cu to artificial seawater did not affect the growth rate, but did reduce the maximum cell density in all four diatom species. Photosynthetic parameters were determined from gross photosynthesis versus irradiance (P vs. E), and relative electron transport rate versus irradiance (rETR vs. E) Curves. In A. acutiuscula, a similar pattern was observed for the P vs. E and rETR vs. E curves, indicating that 3.0 mu M Cu significantly affected all photosynthetic parameters. In the other three species, the P vs. E and rETR vs. E curves did not show this pattern. The effect of Cu on photosynthesis depended on species, either increasing or reducing the electron transport rate in the thylakoid and oxygen production. External carbonic anhydrase activity followed a similar pattern to gross photosynthesis at growth irradiance, indicating it plays a major role in the supply of inorganic carbon to carboxylase(s).

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.

Haslea ostrearia, a tychopelagic marine diatom distributed world-wide, characteristically settles in oyster-ponds. This diatom synthesizes and releases into the external medium a blue-green polyphenolic pigment called "marennine" (Mn), which is responsible for oyster greening. During the bloom of H. ostrearia in ponds, mainly occurring in autumn along the French Atlantic coast (Marennes-Oléron), a decrease in the abundance of other microalgae, including several diatom species, is observed. In this article, we investigate in vitro the influence of the intra- and extracellular forms of the pigment (IMn and EMn) on the development of diatoms usually coexisting with H. ostrearia in oyster-ponds: Skeletonema costatum, Nitzschia closterium, Haslea crucigera and Entomoneis pseudoduplex. We show that there is no significant difference between IMn and EMn in their ability to reduce, in a dose-dependent manner, the growth of these benthic diatoms. S. costatum, N. closterium and H. crucigera are significantly more sensitive to the inhibitory effect of marennine than E. pseudoduplex. In comparison, H. ostrearia tolerates much higher concentrations of its pigment and can even be stimulated at low marennine concentration. Using an experimental set-up to study independently the inhibitory effect of marennine due to light attenuation, we demonstrate that all the species tested are also inhibited in a dose-dependent manner by a shading effect, without a significant difference between IMn and EMn. Taken together, these results suggest that S. costatum, N. closterium and H. crucigera are inhibited by a cumulative effect of chemical mediation and light attenuation induced by marennine. E. pseudoduplex is inhibited solely by the shading effect. Finally, H. ostrearia is inhibited by the shading effect and stimulated by chemical mediation. The in vitro experimental data presented herein are discussed in relation to an ecophysiological function of marennine, leading us to assume that the form of the pigment released into the external medium could act as an allelochemical at the level of the pond as a whole. Allelopathy may therefore play an important role in interspecific competition and contribute to H. ostrearia bloom maintenance.

Benthic diatom biomass on an intertidal mudflat was estimated by field spectrometry, a non-intrusive optical method operating in the visible–infrared wavelength range. Spectral reflectance (400–900 nm) of natural assemblages was related to the amount of principal photosynthetic and accessory pigments measured by high-performance liquid chromatography (HPLC) in the top 2 mm of sediment. Relationships established in situ were compared with those obtained in the laboratory with monospecific cultures. However, to compare both types of reflectance spectra differing in their overall shape (continuum) and to isolate the pigment absorption features from other effects, we applied hyperspectral data processing, the Modified Gaussian Model (MGM), to remove the continuum and model the main absorption bands by a succession of Gaussian curves. The Gaussian band depths associated with the absorption by chlorophyll a and the pigments specific to diatoms (chlorophyll c, fucoxanthine, diadinoxanthin) displayed linear relationships with the logarithm of chlorophyll a.

The effects of season and qualitative selection capacity on trophic relationships between two sympatric invasive suspension-feeders, Crepidula fornicata and Crassostrea gigas, were investigated in Bourgneuf Bay (France) from January 2003 to June 2004. Carbon and nitrogen stable isotopic deviations, δ13C and δ15N, of common Atlantic slippersnails and Pacific oysters were analysed relative to isotopic composition and availability of end-members.Slippersnail deviations were less variable over the sampling period compared with those of oysters. Significant differences between δ13C and δ15N of C. fornicata and C. gigas were found from winter to early summer, and linked to major isotopic changes in oysters. We identified three distinct seasonal periods: January to March when oysters were 15N-enriched compared to slippersnails and to themselves at other times of the year, April to June–July when oysters showed a 15N-depletion and a more marked 13C-depletion compared to slippersnails and to themselves at other times of the year, and July–August to December when both species presented similar carbon and nitrogen deviations. Species-specific differences in qualitative selection capability may explain these seasonal differences in isotopic deviations. Whereas the isotopic composition of the indiscriminate suspension-feeding slippersnails reflects the composition of the seston throughout the year, the oyster is capable of qualitative selection. The oyster isotopic compositions are consistent with a facultative activation of selection mechanisms under conditions of qualitative and quantitative food limitation, notably the preferential ingestion and assimilation of the dominant organic source in the suspended pool.We conclude that C. fornicata and C. gigas are trophic competitors only in winter and spring at this site, where detrital end-members are major POM components. These results underscore (1) the importance of long-term (annual) studies in the evaluation of potential trophic competition, and (2) the necessity to include the qualitative selection capacities of suspension-feeders in future interpretations of trophic relationships in marine coastal ecosystems.