Comparing taxonomic and morphological biodiversity of tintinnids (planktonic ciliates) of New Caledonia

International audienceTintinnid ciliates are planktonic grazers of nanoplankton. They have a lorica (or shell) into which the ciliate cell can withdraw. The lorica provides information on both the identity and the ecology of the organism because characteristics of the lorica distinguish species and the diameter of the oral opening is related to the size of prey ingested. We examined the relationship between biodiversity estimates based on classifying specimens as belonging to a species or a simple morphological group defined by lorica oral diameter (LOD) in a presumably species-rich area, a tropical lagoon. Two sites were sampled in the lagoon off Nouméa over an annual cycle. The tintinnid fauna was species-rich (76 species) and represented a relatively even distribution of LOD sizes compared to other sites both tropical and temperate. Median LOD varied with the fraction of the chlorophyll concentration > 10 µm. Total chlorophyll concentration was related to tintinnid concentration and in turn weakly correlated with numbers of species and LOD size-classes. Numbers of species were closely related to numbers of LOD size-classes as were H' of species and H' (Shannon index) of LOD size-classes. Thus, metrics of a morphological characteristic, related to the ecology of the organisms can be used to estimate species diversity

Eutrophisation en milieu lagonaire : compte-rendu subvention CORDET no 94 T 09

La finalité du programme ANTROPIC est de dresser un bilan des conditions du milieu (eutrophisation, hypersédimentation) dans la zone la plus urbanisée du lagon de Tahiti, de proposer des outils de diagnostic de l'état de l'environnement lagonaire utiles pour la gestion du milie

Mesures des activités bactériennes en eaux profondes

Rapport de l'atelier de bactériologie des Eaux Profondes organisé par le C.N.R.S. et l'I.N.S.U. Rapport final.info:eu-repo/semantics/publishe

Caractéristiques du milieu lagonaire autour de Papeete : influence des apports terrigènes et anthropiques : rapport final de convention

Le travail accompli dans le cadre de la présente convention consiste à décrire les caractéristiques du milieu avec une couverture spatiale satisfaisante et pour des conditions saisonnières contrastées, à prendre en compte le compartiment bactérien (abondance, production) dans les eaux lagonaires, à procéder à une évaluation préliminaire de l'importance de la sédimentation en différents points du lagon, à localiser et caractériser sur la base des résultats précédents les zones les plus menacées par les apports terrigènes et anthropique

Seasonal variability of cohesive sediment aggregation in the Bach Dang-Cam Estuary, Haiphong (Vietnam)

In the Bach Dang-Cam Estuary, northern Vietnam, mechanisms governing cohesive sediment aggregation were investigated in situ in 2008-2009. As part of the Red River delta, this estuary exhibits a marked contrast in hydrological conditions between the monsoon and dry seasons. The impact on flocculation processes was assessed by means of surveys of water discharge, suspended particulate matter concentration and floc size distributions (FSDs) conducted during a tidal cycle at three selected sites along the estuary. A method was developed for calculating the relative volume concentration for the modes of various size classes from FSDs provided by the LISST 100X (Sequoia Scientific Inc.). It was found that all FSDs comprised four modes identified as particles/flocculi, fine and coarse microflocs, and macroflocs. Under the influence of the instantaneous turbulent kinetic energy, their proportions varied but without significant modification of their median diameters. In particular, when the turbulence level corresponded to a Kolmogorov microscale of less than similar to 235 mu m, a major breakup of flocs resulted in the formation of particles/flocculi and fine microflocs. Fluctuations in turbulence level were governed by seasonal variations in freshwater discharge and by the tidal cycle. During the wet season, strong freshwater input induced a high turbulent energy level that tended to generate sediment transfer from the coarser size classes (macroflocs, coarse microflocs) to finer ones (particles/flocculi and fine microflocs), and to promote a transport of sediment seawards. During the dry season, the influence of tides predominated. The turbulent energy level was then only episodically sufficiently high to generate transfer of sediment between floc size classes. At low turbulent energy, modifications in the proportions of floc size classes were due to differential settling. Tidal pumping produced a net upstream transport of sediment. Associated with the settling of sediment trapped in a near-bed layer at low turbulent energy, this causes the silting up of the waterways leading to the harbour of Haiphong

Aggregation dynamics along a salinity gradient in the Bach Dang estuary, North Vietnam

International audienceVariations of the sticking properties of transparent exopolymeric particles (TEP) were investigated by studying the interactions between latex beads and TEP precursors collected along a salinity gradient in the Bach Dang estuary, North Vietnam. For each sampling station, a suspension of TEP and beads was prepared and the formation of mixed aggregates was monitored in the laboratory under controlled turbulence intensity. The number of beads attached to TEP per volume of TEP increased from 0.22 × 10−3 ± 0.15 × 10−3 μm−3 to 5.33 × 10−3 ± 1.61 × 10−3 μm−3, from low (28) salinities, respectively. The sudden increase in TEP sticking properties from salinity 10 to 15 suggests the occurrence of an "aggregation web" resulting from the stimulation of aggregation processes. For a given turbulence level, the formation of large aggregates should be enhanced seaward. The presence of a higher fraction of large aggregates seaward is supported by the increase of the slope of the particle size spectra measured in situ. The observed increase in TEP sticking properties toward high salinities may affect the vertical export pump in estuaries. This study suggests that the transition from a low to a high physico-chemical reactivity of TEP along estuaries may result in a succession from recycling for salinity 10