Priscilla Decottignies

BIOFILM GRAZING IN A HIGHER VERTEBRATE: THE WESTERN SANDPIPER, CALIDRIS MAURI

We show that a higher vertebrate can graze surficial intertidal biofilm, previously only considered a food source for rasping invertebrates and a few specialized fish. Using evidence from video recordings, stomach contents, and stable isotopes, we describe for the first time the grazing behavior of Western Sandpipers (Calidris mauri) and estimate that biofilm accounts for 45-59% of their total diet or 50% of their daily energy budget. Our finding of shorebirds as herbivores extends the trophic range of shorebirds to primary consumers and potential competitors with grazing invertebrates. Also, given individual grazing rates estimated at seven times body mass per day and flock sizes into the tens of thousands, biofilm-feeding shorebirds could have major impacts on sediment dynamics. We stress the importance of the physical and biological processes maintaining biofilm to shorebird and intertidal conservation.

Does allelopathy affect co-culturing Haslea ostrearia with other microalgae relevant to aquaculture?

Haslea ostrearia is a marine diatom known to produce marennine, a water-soluble blue-green pigment responsible for the greening of oysters in ponds along the French Atlantic coast. This phenomenon occurs seasonally when H. ostrearia blooms in oyster ponds, and it increases the economic value of cultured oysters. From an ecological perspective, H. ostrearia blooms are accompanied by a decrease in the abundance of other microalgae, suggesting that this diatom produces allelochemicals. Recent studies showed that purified marennine has other biological activities, for instance antioxidant, antibacterial, and antiviral activities, which could be used in aquaculture to promote this pigment as a natural antipathogen agent. One important issue regarding the possible use of H. ostrearia in aquaculture as a mixed algal diet, however, is the importance of marennine allelopathy. In this study, we investigated the allelopathic effect of H. ostrearia on the growth of five microalgal species relevant to aquaculture: Chaetoceros calcitrans, Skeletonema costatum, Phaeodactylum tricornutum, Tetraselmis suecica, and Tisochrysis lutea. Allelopathic tests were realized by co-culturing these microalgae with H. ostrearia in batch and in semi-continuous mode, based on initial biovolume ratios. Our findings showed that inhibition of the growth of microalgae due to the presence of H. ostrearia and marennine was species dependent. Skeletonema costatum, C. calcitrans, and T. lutea were significantly more sensitive, whereas T. suecica and P. tricornutum appeared to be more resistant. Growth irradiance significantly influenced the allelopathic effect against the sensitive species S. costatum, and the H. ostrearia production of marennine increases with irradiance. Data presented in this study partly support the hypothesis that marennine released into the culture medium possibly acts as an allelochemical compound, thus explaining the dominance of H. ostrearia and the loss of sensitive algae in oyster ponds, but also that some species are insensitive, which allows co-culturing and use in a mixed algal diet in aquaculture.

Multiple Beneficial Lipids Including Lecithin Detected in the Edible Invasive Mollusk Crepidula fornicata from the French Northeastern Atlantic Coast

The invasive mollusk Crepidula fornicata, occurring in large amounts in bays along the French Northeastern Atlantic coasts, may have huge environmental effects in highly productive ecosystems where shellfish are exploited. The present study aims at determining the potential economic value of this marine species in terms of exploitable substances with high added value. Lipid content and phospholipid (PL) composition of this mollusk collected on the Bourgneuf Bay were studied through four seasons. Winter specimens contained the highest lipid levels (5.3% dry weight), including 69% of PLs. Phosphatidylcholine (PC) was the major PL class all year, accounting for 63.9% to 88.9% of total PLs. Consequently, the winter specimens were then investigated for PL fatty acids (FAs), and free sterols. Dimethylacetals (DMAs) were present (10.7% of PL FA + DMA mixture) revealing the occurrence of plasmalogens. More than forty FAs were identified, including 20:5n-3 (9.4%) and 22:6n-3 (7.3%) acids. Fourteen free sterols were present, including cholesterol at 31.3% of the sterol mixture and about 40% of phytosterols. These data on lipids of C. fornicata demonstrate their positive attributes for human nutrition and health. The PL mixture, rich in PC and polyunsaturated FAs, offers an interesting alternative source of high value-added marine lecithin.

Utilisation of intertidal mudflats by the Dunlin Calidris alpina in relation to microphytobenthic biofilms

AbstractThe small-scale spatial distribution of Dunlin Calidris alpina staging and wintering in Bourgneuf Bay (France) was investigated on two different mudflats colonized by either epipsammic- or epipelic-dominated microphytobenthos assemblages. Shorebird counts were conducted monthly at ebb tide from October 2011 to May 2012 and from November 2012 to May 2013. Multiple linear regressions followed by hierarchical partitioning of variance showed that microphytobenthos biomass was not a significant factor to explain Dunlin densities. However, on epipelic-dominated mudflats, Dunlins did not show their typical “tide follower” behaviour and instead significantly selected the highest microphytobenthos biomass zones. The biomass of a gastropod predator of an important local Dunlin prey, Retusa obtusa, was negatively correlated with Dunlin densities. This paper provides new suggestions in the ways that biofilms on mudflats affect small shorebird foraging.ZusammenfassungDie Nutzung von Wattflächen durch AlpenstrandläuferCalidris alpina im Hinblick auf mikrophytobenthische Biofilme Die kleinräumige Verteilung von Alpenstrandläufern Calidris alpina, die in der Bucht von Bourgneuf (Frankreich) rasten und überwintern, wurde auf zwei verschiedenen Wattflächen untersucht, die von Mikrophytobenthosgemeinschaften besiedelt wurden, welche entweder von epipsammischen oder epipelischen Arten dominiert wurden. Watvogelzählungen wurden monatlich bei Ebbe von Oktober 2011 bis Mai 2012 durchgeführt. Multiple lineare Regressionen, gefolgt von der hierarchischen Partitionierung der Varianz, zeigten, dass die Biomasse des Mikrophytobenthos keinen signifikanten Einfluss auf die Dichte der Alpenstrandläufer hatte. Auf von epipelischen Arten dominierten Wattflächen zeigten Alpenstrandläufer jedoch nicht ihr typisches “Gezeitenfolgeverhalten”, sondern wählten stattdessen die Zonen mit der höchsten Mikrophytobenthosbiomasse. Die Biomasse einer Schnecke, die eine wichtige lokale Beute des Alpenstrandläufers frisst (Retusa obtusa), zeigte eine negative Korrelation mit der Alpenstrandläuferdichte. Diese Studie liefert neue Hinweise, dass Biofilme auf Wattflächen das Nahrungsverhalten kleiner Watvögel beeinflussen.

Optimizing metamorphosis in Paracentrotus lividus aquaculture using alternative macroalgae species to Corallina sp.

Metamorphosis induction cues (by chemical mediation or direct contact) were tested in Paracentrotus lividus using three different macroalgae treatments: Corallina sp., Palmaria palmata, and Laminaria digitata. Higher percentages of metamorphosis were reached in Paracentrotus lividus larvae by direct contact with a Palmaria palmata substrate.

Cell size-based, passive selection of the blue diatom Haslea ostrearia by the oyster Crassostrea gigas

Pre-ingestive selection has been identified as a feeding mechanism of oysters that may influence their uptake of particles and microalgal cells. Oysters can feed specifically on the pennate diatom Haslea ostrearia, which produces the blue pigment marennine that is responsible for the greening of oysters. Because the size of particles or cells plays a significant role in the selection process, and given that diatoms experience a decrease in size as a consequence of vegetative reproduction, H. ostrearia consumption and marennine uptake might be influenced by pre-ingestive selection. We examined the role of H. ostrearia cell size in the selective feeding of Crassostrea gigas. Individual flow-through chambers were used to deliver mixtures of H. ostrearia of varying cell length to oysters. Inflow, outflow and pseudofaecal samples were collected from chambers during oyster feeding. Video-endoscopy was used to sample material in the dorsal and ventral particle tracts. Diatom cells counts showed that pseudofaeces contained on average larger cells than the ambient medium. However, proportions of the different populations of H. ostrearia in pseudofaeces were identical to those in the ventral tracts, indicating that no selection was performed by the labial palps. Video-endoscopy, plus imaging by scanning electron microscopy, of gills and labial palps revealed that only those larger H. ostrearia that were orientated dorsoventrally could enter the principal filaments (pfs) and then access the dorsal acceptance tract. These results show that for particles like Haslea cells with only one axis exceeding the width of the pfs, the selection on the oyster gills is passive and based on cell size.