Stable isotope evidence of benthic microalgae-based growth and secondary production in the suspension feeder Cerastoderma edule (Mollusca, Bivalvia) in the Marennes-Oleron Bay

The contribution of natural food sources to the growth and secondary production of the suspension feeding bivalve Cerastoderma edule (L.) was estimated under field conditions in the Marennes-Oleron Bay (Atlantic coast, France). Monthly estimates of abundance, biomass and cockle growth were combined with seasonal analyses of delta C-13 and delta N-15 ratios of juvenile and adult cockles, together with their potential food sources [i.e. suspended particular organic matter (POM), microphytobenthos, macroalgae and seagrass] sampled at mid-tide level in a muddy sandflat. Adult cockles grew mainly in spring. whereas juveniles grew in summer and autumn, following spat recruitment in early summer. Total annual production and elimination of cockles were estimated to be 32.5 and 34.7 g AFDW m(-2) yr(-1). Relative contributions of each year class to production were ca 40, 41, 11 and 6% for 0-group, 1-, 3- and 4-yr-old cockles in 1995, respectively. Quantitative assessment of proportions of food sources to the annual secondary production of cockles was obtained by using a simple carbon isotope-mixing model with microphytobenthos (delta C-13 = -16.0+/-0.6 parts per thousand) and POM (delta C-13 = -22.2+/-1.1 parts per thousand) as end-members. On average, more than 70% of the total annual cockle production originated from microphytobenthos, with a much higher contribution for the 0-group (88%) than for adult cockles (60%). The between-age difference was induced mainly by changes in the availability of food resources (benthic versus planktonic) during the non-synchronous growing seasons of juvenile and adult cockles.X1160sciescopu

Contrôle de surveillance DCE 2020 des macro-invertébrés benthiques de la masse d'eau de transition FRGT31 La Sèvre Niortaise : rapport final

L’objet de ce document est d’exposer la réalisation du suivi et de faire état des résultats du contrôle de surveillance DCE 2020 invertébrés benthiques de cette masse d’eau de transitio

Contrôle de surveillance DCE 2020 de la faune benthique de substrat meuble des masses d’eau de transition « Estuaire Charente - FRFT01 » et « Estuaire Seudre - FRFT02 » : rapport final

L’objet de ce document est d’exposer la réalisation des suivis RCS 2020 invertébrés benthiques de ces deux masses d’eau de transition

Food sources of the infaunal suspension-feeding bivalve Cerastoderma edule in a muddy sandflat of Marennes-Oleron Bay, as determined by analyses of carbon and nitrogen stable isotopes

Stable carbon and nitrogen isotope ratios were used to define the trophic base of the infaunal suspension-feeding bivalve Cerastoderma edule (L.) living on an intertidal muddy sandflat in Marennes-Oleron Bay, France. Suspended particulate organic matter (POM) collected from adjacent marine channels had a mean delta(13)C value of -22.2 +/- 1.1 parts per thousand (n = 19). Benthic primary producers on Ronceles-Bains tidal flats had delta(13)C values distinct from that of the POM: microphytobenthos (-16.0 +/- 0.6 parts per thousand), the macroalgae Enteromorpha compressa (-17.6 +/- 2.8 parts per thousand), Fucus serratus (-17.4 +/- 2.6 parts per thousand), Fucus vesiculosus (-18.5 +/- 1.6 parts per thousand), Phorphyra umbilicalis (-19.7 +/- 0.5 parts per thousand), Ulva rigida (-14.7 +/- 2.0 parts per thousand) and the seagrass Zostera noltii (-11.1 +/- 1.0 parts per thousand). Mean delta(15)N values of all macroalgae species ranged from 7.6 +/- 1.3 to 8.9 +/- 1.0 parts per thousand, while those for microphytobenthos, POM and seagrass were 5.3 +/- 0.8, 5.0 +/- 0.9 and 6.5 +/- 1.3 parts per thousand, respectively. The mean delta(13)C value of spat (-15.3 +/- 0.8 parts per thousand) and juvenile cockles (-15.7 +/- 0.7 parts per thousand) varied within a smaller range than those of 1 to 4 yr old adults (-18.2 +/- 1.2 parts per thousand). The delta(15)N values of 0-group cockles (spat and juveniles) and adult cockles are similar (8.0 +/- 0.9 parts per thousand for 0-group and 8.4 +/- 1.1 parts per thousand for adults). The results suggest. based on the average trophic enrichment found in the literature for C and N, and the relative abundance of each food source. that there are 2 major sources of organic matter assimilated by cockles of the studied flats: microphytobenthos and POM. Seasonal variations in delta(13)C values reflect a higher dependence of adult cockies on POM variability while spat and juveniles are more closely linked to microphytobenthos. The isotopic shifts indicate that the relative importance of the 2 major food sources depends on the age of the cockles and the season.X1195sciescopu

Impact of the oyster Crassostrea gigas on a microbial community in Atlantic coastal ponds near La Rochelle

To assess the in situ impact of oysters Crassostrea gigas on planktonic protist and bacteria communities and the potential contribution of protozoa to their food resource intake, the abundance and the diversity of protists and bacteria were followed in 2 Atlantic coastal ponds, with and without oysters. The protist biomass in such ponds was high, with a maximum in spring of 982 mug C l(-1) and a minimum in winter of 179 pg C l(-1). Whatever the season, the presence of oysters (20 m(-2) corresponding to an average of 23 mg dry weight m(-2)) induced a significant decrease in >5 pm protist abundance. On the contrary, planktonic organisms <5 pm, such as Chlorophyta flagellates and bacteria, developed similarly in both ponds. It can be assumed that such depletion in micro-sized protists was especially related to the grazing activity of C. gigas, which efficiently retains >5 pm particles. In spring, oyster grazing triggered dramatic changes in the protist community by lowering the taxonomic diversity. In autumn and winter, the presence of oysters deeply influenced the taxonomic structure of the protist communities: > Fun protists could only develop in the control pond, whereas they were removed by filtration in the oyster pond; on the contrary, >5 Fun protists that were not retained were favoured in the oyster pond. The results showed that hetero/mixotrophic protists represent an important potential resource in coastal ponds: flagellates >5 pm were the main protist resource for C. gigas; ciliates represented the second resource, with a substantial contribution in autumn; diatoms and dinoflagellates, though efficiently removed, represented a weak carbon resource. Our study supports the hypothesis that oysters may access the strong bacterioplanktonic production through hetero/mixotrophic protists, which would thus allow the transfer of carbon from the microbial loop towards C. gigas

Journal de recherche oceanographique 27 3-4 225

Original Abstract: Le protozoaire parasite Marteilia refringens est responsable d&#39;importantes mortalites au sein des elevages d&#39;huitres plates Ostrea edulis, et a participe a la disparition de 90% de la production depuis les annees 60. Une gestion optimale des risques de contamination des huitres plates au sein des zones endemiques necessite la connaissance du cycle parasitaire de M. refringens. L&#39;existence d&#39;un cycle heteroxene de M. refringens etait l&#39;hypothese la plus probable mais cette hypothese n&#39;avait jusqu&#39;alors pu etre testee. Apres 30 ans, grace a une approche multidisciplinaire associant un ecosysteme a faible biodiversite a des outils moleculaires de detection du parasite, nous avons demontre l&#39;implication d&#39;un copepode dans le cycle de vie de Marteilia refringens. L&#39;ecologie et la strategie parasitaire de Marteilia refringens, sont discutees en considerant ses deux hotes (l&#39;huitre et le copepode), et l&#39;ecosysteme ou plus precisement le biotope, en tant qu&#39;environnements du parasite