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The objective of this study is to verify whether low amounts of fine sand added to a muddy sediment matrix can be detected and quantified with accuracy using a Mastersizer 3000 (Malvern Panalytical) laser diffraction particle-size analyzer equipped with a Hydro LV large volume liquid dispersion module. To achieve this goal, a postglacial sediment sample was sieved to recover naturally co-occurring sand and clay-silt fractions. Sand in the range of 1%-7% by weight was added to the clay-silt at three concentrations (88, 132, and 276 mg dry weight) and each sample was duplicated. A very strong linear relationship was found between the measured % volume of sand added and the actual weight of sand added to the mud. Sand representing as low as 1% by weight could be detected. On average, there was only a 0.7% absolute difference between the measured and actual % sand values (range 0.02%-1.65%). Sample concentration had a negligible impact on the measured % sand. A range of plausible values for the refractive and absorption indexes, essential parameters for the Mie theory calculation of the size distribution from the measured light scattering, also had very small impact on the measured % sand. The demonstrated possibility of detecting a small input of fine sand to muddy sediment provides a basis for studies using grain-size data to reconstruct past and modern detrital inputs and sediment transport variations. Key words: laser diffraction, particle-size analysis, grain size, sediments L'objectif de l'etude est de verifier si de faibles quantites de sable fin ajoutees a une matrice de sediments boueux peuvent etre detectees et quantifies avec exactitude a l'aide du granulometre a diffraction laser Mastersizer 3000 (Malvern Panalytical) equipe d'un module de dispersion en voie liquide a large volume Hydro LV. A cette fin, un echantillon de sediment postglaciaire a ete tamise pour en recuperer les fractions de sable et d'argile-silt s'y trouvant a l'etat naturel. Du sable dans une fourchette de 1-7 % en poids a ete ajoute a trois concentrations d'argile-silt (88, 132 et 276 mg en poids sec), et chaque echantillon a ete repete. Une relation lineaire tres forte est relevee entre le pourcentage volumique mesure de sable ajoute et le poids reel de sable ajoute a la boue. Du sable representant aussi peu que 1 % du poids a pu etre detecte. En moyenne, la difference absolue entre les pourcentages mesures et reels de sable (fourchette de 0,02-1,65 %) n'est que de 0,7 %. L'incidence de la concentration de l'echantillon sur le pourcentage de sable mesure est negligeable. Une fourchette de valeurs plausibles des indices de refraction et d'absorption, des parametres essentiels pour le calcul selon la theorie de Mie de la granulometrie a partir de la diffusion de la lumiere mesuree, a aussi tres peu d'incidence sur le pourcentage de sable mesure. La possibilite demontree de detecter un petit apport de sable fin dans des sediments boueux fournit la base pour des etudes utilisant des donnees granulometriques pour reconstituer les apports detritiques et les variations du transport de sediments passes et actuels. [Traduit par la Redaction] Mots-cles : diffraction laser, analyse granulometrique, granulometrie, sediments, Introduction An accurate characterization of sediment particle-size distribution is essential to understand the genesis of sediments, untangle transport mechanisms, infer past hydrologic and climatic conditions, track sea-level variations, map and [...]

Bay-scale empirical evaluations of how bivalve aquaculture alters plankton composition, and subsequently ecological functioning and higher trophic levels, are lacking. Temporal, inter- and within-bay variation in hydrodynamic, environmental, and aquaculture pressure complicate plankton monitoring design to detect bay-scale changes and inform aquaculture ecosystem interactions. Here, we used flow cytometry to investigate spatio-temporal variations in bacteria and phytoplankton (< 20 μm) composition in four bivalve aquaculture embayments. We observed higher abundances of bacteria and phytoplankton in shallow embayments that experienced greater freshwater and nutrient inputs. Depleted nutrient conditions may have led to the dominance of picophytoplankton cells, which showed strong within-bay variation as a function of riverine vs marine influence and nutrient availability. Although environmental forcings appeared to be a strong driver of spatio-temporal trends, results showed that bivalve aquaculture may reduce near-lease phytoplankton abundance and favor bacterial growth. We discuss confounding environmental factors that must be accounted for when interpreting aquaculture effects such as grazing, benthic-pelagic coupling processes, and microbial biogeochemical cycling. Conclusions provide guidance on sampling considerations using flow cytometry in aquaculture sites based on embayment geomorphology and hydrodynamics. [ABSTRACT FROM AUTHOR]

The microbial growth curve is widely studied within microbiology classes and bacteria are usually the microbial model used. Here, we describe a novel laboratory protocol involving flow cytometry to assess the growth dynamics of the unicellular microalgae "Isochrysis galbana." The algal model represents an appropriate alternative to bacteria because its slower growth rate allows a better visualization of the growth phases, which makes the logistic of the laboratory sessions easier. Flow cytometry is a technique commonly used for cell enumeration in ecology, microbiology, and medical sciences because of its accuracy and speed. In this experiment, microbial growth was observed under two light conditions and cell abundance was monitored using a flow cytometer and a haemocytometer. The chlorophyll a fluorescence of each cell was also measured by the flow cytometer and was used as an index of cellular content of photosynthetic pigments. Students were asked to compare the results obtained with the two techniques and to explain the effect of light conditions on the growth curve shape and dynamics. (Contains 3 figures and 1 table.)

Recently, there is a greater interest for the development of mussel Mytilus edulis hatcheries, particularly for the production and commercialization of triploid bivalves. The aims of this study were to examine the efficiency of inducing triploid mussels by various treatments and to determine the effect of triploidy on larval development. To produce triploids, extrusion of the second polar body of fertilized eggs was inhibited by 6-(dimethylamino)purine (6-DMAP), cold-shock, or heat-shock treatments. Triploidy was detected by flow cytometry for all the treatments. Treatment with 6-DMAP was the most efficient with a rate of triploidy of 90%, followed by heat-shock (56%) and cold-shock (30%) treatments. No survival differences were observed between diploids and 6-DMAP-induced triploid larvae from the D-shape stage up to their settlement. Moreover, increased growth was observed in triploid larvae compared to diploid larvae. Overall, this study showed that 6-DMAP is a highly efficient method to induce triploidy in mussels, with triploid larvae having faster growth compared to diploid. [ABSTRACT FROM AUTHOR]

The Hyalella azteca (Saussure) complex includes numerous amphipod cryptic species in freshwater habitats in America as revealed by DNA barcoding surveys. Two ecomorphs (small and large) have evolved numerous times in this complex. Few phenotypic criteria have been found to differentiate between the numerous species of this complex. The present study aims to explore genome size differences between some species of the H. azteca complex co-occurring in a Canadian boreal lake using flow cytometry. Nuclear DNA content was estimated for 50 individuals belonging to six COI haplotypes corresponding to four provisional species of the H. azteca complex. Species from the large ecomorph had C-values significantly larger than species from the small ecomorph, whereas slight differences were found among species of the small ecomorph. These differences in genome sizes might be linked to ecological and physiological differences among species of the H. azteca complex. Key words: Hyalella azteca, genome size, cryptic species. Le complexe Hyalella azteca (Saussure) est constitue d'un ensemble d'especes cryptiques d'amphipodes se retrouvant dans des habitats lentiques du continent americain tel qu'il a ete revele par des etudes de code-barres genetiques. Deux ecomorphes (petit et grand) ont evolue plusieurs fois dans ce complexe. Peu de criteres phenotypiques sont connus pour differencier les nombreuses especes de ce complexe. Cet article vise a explorer les differences possibles de tailles de genome de certaines especes du complexe H. azteca se retrouvant dans un lac boreal canadien en utilisant la cytometrie en flux. Le contenu en ADN nucleaire a ete estime pour 50 individus appartenant a six haplotypes COI correspondant a quatre especes potentielles du complexe H. azteca. Les especes presentant un ecomorphe grand ont une taille de genome significativement plus grande que les especes presentant un ecomorphe petit, tandis que de legeres differences ont ete trouvees entre certaines especes du petit ecomorphe. Ces differences de tailles de genome pourraient etre un indice de differences ecologiques et physiologiques entre certaines especes du complexe H. azteca. Mots-cles : Hyalella azteca, tailles du genome, especes cryptiques. [Traduit par la Redaction], Introduction Cryptic species are defined as two or more species that are morphologically similar (Bickford et al. 2007) but may be recognized as distinct species owing to high genetic divergences [...]

Abstract: Recent genome size estimates for Arctic amphipods have revealed the largest genomes known in the Crustacea. Here we provide additional data for 7 species of caridean shrimp collected from [...]

Abstract: The genome sizes of 8 species of amphipods collected from the Canadian Arctic were estimated by flow cytometry. Haploid genome sizes ranged from 2.94 [+ or -] 0.04 pg [...]

Abstract: We profiled five ice-covered lakes and two ice-covered fiords of Ellesmere Island at the northern limit of High Arctic Canada to examine their environmental characteristics, and to evaluate the [...]