Plankton community structure in response to hydrothermal iron inputs along the Tonga-Kermadec arc

The Western Tropical South Pacific (WTSP) basin has been identified as a hotspot of atmospheric dinitrogen fixation due to the high dissolved iron ([DFe]) concentrations (up to 66 nM) in the photic layer linked with the release of shallow hydrothermal fluids along the Tonga-Kermadec arc. Yet, the effect of such hydrothermal fluids in structuring the plankton community remains poorly studied. During the TONGA cruise (November-December 2019), we collected micro- (20-200 μm) and meso-plankton (>200 μm) samples in the photic layer (0-200 m) along a west to east zonal transect crossing the Tonga volcanic arc, in particular two volcanoes associated with shallow hydrothermal vents (< 500 m) in the Lau Basin, and both sides of the arc represented by Melanesian waters and the South Pacific Gyre. Samples were analyzed by quantitative imaging (FlowCam and ZooScan) and then coupled with acoustic observations, allowing us to study the potential transfer of phytoplankton blooms to higher planktonic trophic levels. We show that micro- and meso-plankton exhibit high abundances and biomasses in the Lau Basin and, to some extent, in Melanesian waters, suggesting that shallow hydrothermal inputs sustain the planktonic food web, creating productive waters in this otherwise oligotrophic region. In terms of planktonic community structure, we identified major changes with high [DFe] inputs, promoting the development of a low diversity planktonic community dominated by diazotrophic cyanobacteria. Furthermore, in order to quantify the effect of the shallow hydrothermal vents on chlorophyll a concentrations, we used Lagrangian dispersal models. We show that chlorophyll a concentrations were significantly higher inside the Lagrangian plume, which came into contact with the two hydrothermal sites, confirming the profound impact of shallow hydrothermal vents on plankton production

Inter-comparaison des mesures de courant dans l'Atlantique Tropical

The present reports contains the results of a study designed to compare the current measurements from various sensors (ARGO floats, Drifters, Buoys sensors, ADCP) in Tropical Atlantic in order to estimate their complementarity and to analyse the seasonal cycle of surface and deep currents in the area.Ce rapport présente les résultats d'une étude visant à comparer les mesures de courant réalisées par différents capteurs (flotteurs ARGO, Drifters, Bouées fixes, ADCP) dans l'Altantique Tropical afin d'estimer leur complémentarité et d'analyser le cycle saisonnier des courants de surface et de fond dans la région

Multifrequency acoustics measurements during the PIRATA FR25 cruise in the Eastern Tropical Atlantic Ocean

International Conference AWA (ICAWA), Dakar, SEN, 17-/11/2015 - 19/11/201

Multifrequency acoustics measurements during the PIRATA FR25 cruise in the Eastern Tropical Atlantic Ocean

International Conference AWA (ICAWA), Dakar, SEN, 17-/11/2015 - 19/11/201

Manuel de l'utilisateur de Matecho : version 05

Un article relatif à une version précédente de ce manuel a été publié dans :Perrot, Y., Brehmer, P., Habasque, J., Roudaut, G., Béhagle, N., Sarre, A., and Lebourges-Dhaussy, A. 2018. Matecho: An Open-Source Tool for Processing Fisheries Acoustics Data. Acoust. Aust. 46(2): 241–248. doi:10.1007/s40857-018-0135-x.Matecho is an integrated and supervised Matlab processing chain, which allows realizing scientific echo-sounder data treatments. It allows applying, under user control, recent echo-sounder data processing methods needed to prepare and present acoustic data to their analysis and interpretation in the field of fisheries acoustics researches.Matecho est une chaîne de traitement Matlab intégrée et supervisée, qui permet de réaliser des traitements de données d'échosondeurs scientifiques. Elle permet d'appliquer, sous le contrôle de l'utilisateur, les méthodes récentes de traitement des données d'échosondeurs nécessaires à la préparation et à la présentation des données acoustiques pour leur analyse et leur interprétation dans le domaine de la recherche en acoustique des pêches

The Concept of “Pelagic metapopulation” as exemplified by the case of jack mackerel Trachurus murphyi in the South Pacific Ocean

International audienceno abstrac

Observations of plankton communities in the Senegalese upwelling system

International Conference AWA (ICAWA), Dakar, SEN, 17-/11/2015 - 19/11/201

Observations of plankton communities in the Senegalese upwelling system

International Conference AWA (ICAWA), Dakar, SEN, 17-/11/2015 - 19/11/201

Matecho: An Open-Source Tool for Processing Fisheries Acoustics Data

WOS:000442525800006International audienceMatecho is an automated processing method to extract information and perform echo-integration and fish shoal extraction from various scientific echo-sounder sources providing digital acoustic data on fisheries and aquatic ecosystem. The open-source initiative helps foster collaboration and technological transfer. Matecho supports various formats, such as the international standard format for the exchange of fisheries acoustics raw and edited data. The procedure allows the semiautomatic cleaning of echogram data and the application of automatic data filters, i.e., transient noise, attenuated signal and impulsive noise removal and background noise reduction. Echo-integration processing is executed for each depth layer and integrates their characteristics per elementary sampling unit. Sound scattered layers are automatically detected by segmentation from the echo-integrated echogram, and shoals are extracted according to an iterative process of aggregation of filtered echogram echoes that allows, in both cases, the calculation of the ad hoc parameters describing morphological, spatial location and acoustic characteristics of sound scattered layers and shoals. Matecho is open-source software for researchers and provides end users with a user-friendly, free executable program

Switching off the sun to observe the twilight zone spatial dynamics across Saint-Paul and New-Amsterdam Islands, Southern Indian Ocean [résumé]

ICES. Working Group of Fisheries Acoustics, Science and Technology (WGFAST), Somone, SEN, 25-/04/2022 - 28/04/2022Information on micronekton (> 1 cm organisms) is globally scarce in the open ocean, and its ver-tical and horizontal distribution in relation to oceanographic structures is poorly known. The complex biodiversity composing micronektonic functional groups lead to even more challenging interpretations of their spatial dynamics. Advanced generations of echosounders emit simulta-neously several acoustic signals (multi-frequency device), allowing a finer view of the micron-ektonic community. While data becomes more abundant and complex, it is crucial to develop statistical tools aiming to objectively extract key components of its variability. In this study, we analyse data recorded onboard the R/V Marion Dufresne from an EK80 echosounder emitting at 18, 38, 70, 120 and 200 kHz. We developed a Multivariate Functional Data Analysis method to identify patterns in micronekton structures across Saint-Paul and New Amsterdam economic exclusive zone, at the boundary between vast oceanic domains. This approach proposes an ob-jective method to analyse the vertical backscatter distribution and quantify temporal and spatial modes of variability in multivariate acoustic data. By filtering the temporal mode, we uncovered a latitudinal acoustic pattern in concordance with hydrological features and biological samples distribution. Such methods could be implemented at a global or local scale and allow 3-D mod-elling of micronekton structuring