Diogoul N. auteur aut IRD Brehmer Patrice auteur aut IRD Perrot Yannick auteur aut IRD Tiedemann M. auteur aut IRD Thiam A. auteur aut IRD El Ayoubi S. auteur aut IRD Mouget Anne auteur aut IRD Migayrou C. auteur aut IRD Sadio Oumar auteur aut IRD Sarré A. auteur aut IRD text conferencePaper eng text/pdf reformatted digital access The micronectonic organisms aggregate at specific depths and occur as scattering layer on echosounder records. They constitute an important component in the marine food web in direct contact with primary producers. We characterized the Senegalese water masses of the 'Petite côte' on physicochemical and biological criteria using an in situ data set collected during an acoustics survey. Then we described at fine scale spatial and temporal variation of micronektonic layers in relation with their environment. Two areas with different characteristics have been discriminated: the upwelling's cell area and the upwelling's offshore area more stratified, warm and sharply separated from the other area by a strong thermal boundary. The spatio-temporal variation of scattering layer's thickness of micronectonic is strongly influenced by depth and the time of the day. The continental shelf scattering layer's thickness increases with depth, but no variation is reported in longitudinal plane. In both areas nocturnal layers are thicker and deeper than diurnal ones. The hydrological structure of the water column also influence the micronectonic scattering layer. The scattering layer requires "stable" physical conditions which support vertical stratification. In the upwelling's area cell, the chlorophyll-a (CHL) concentration is correlated to scattering layer thickness during night time. In the upwelling's offshore area, sea temperature, water density and oxygen have a significant effect on the scattering layer's thickness during the nightime. However, during the daytime, CHL has a significant effect on the scattering layer's thickness. This correlation between CHL and scattering layer thickness in the upwelling's offshore area during day could be explained by an inverse diel vertical migration of a micronectonic group. On this basis we assume that trophic relationship between phytoplankton and micronecton operate during the day at the surface in this area. specialized AFRIQUE DE L'OUEST SENEGAL ATLANTIQUE 040 021 034 032 ICAWA : International Conference AWA, 4., Mindelo (CPV), 2017/11/13-17 51 Brehmer Patrice ed. edt IRD Diogoul N. collab. clb IRD Zenk C. collab. clb IRD Vareilles M. de collab. clb IRD Keenlyside N. collab. clb IRD Nascimento J.M. collab. clb IRD Ramos V. M. collab. clb IRD Sow B.A. collab. clb IRD Fock H. collab. clb IRD Schmidt J. collab. clb IRD Ekau W. collab. clb IRD Mbaye A. collab. clb IRD Fall. A. collab. clb IRD Monteiro I. collab. clb IRD Kouassi A.M. collab. clb IRD Silva O. collab. clb IRD Brochier Timothée collab. clb IRD Sall. M. collab. clb IRD Mayif M. collab. clb IRD Koné V. collab. clb IRD Gorgues Thomas collab. clb IRD Ferreira Santos C. collab. clb IRD Bamy I.L. collab. clb IRD Barry I. collab. clb IRD Sidibe M. collab. clb IRD Diadhou H. collab. clb IRD Dakar (SEN) SRFC/CSRP Marseille IRD 2019 https://www.documentation.ird.fr/hor/fdi:010078253 978-9553602-0-06 [F A010078243] https://www.documentation.ird.fr/hor/fdi:010078253 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers20-05/010078253.pdf IRD - Base Horizon / Pleins textes 2020-04-27 2025-12-10 fdi:010078253 fre