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Auteur (up) Annasawmy, P.; Ternon, J.-F.; Lebourges-Dhaussy, A.; Roudaut, G.; Cotel, P.; Herbette, S.; Menard, F.; Marsac, F. doi  openurl
  Titre Micronekton distribution as influenced by mesoscale eddies, Madagascar shelf and shallow seamounts in the south-western Indian Ocean: an acoustic approach Type Article scientifique
  Année 2020 Publication Revue Abrégée Deep-Sea Res. Part II-Top. Stud. Oceanogr.  
  Volume 176 Numéro Pages 104812  
  Mots-Clés biological production; circulation; community composition; deep-scattering layer; diel vertical migration; Diel vertical migration; dynamics; Madagascar shelf; mesopelagic fish; Mesoscale eddies; Micronekton; mozambique channel; Multi-frequency; myctophid fishes; Seamount; South-western indian ocean; zooplankton  
  Résumé An investigation of the vertical and horizontal distributions of micronekton, as influenced by mesoscale eddies, the Madagascar shelf and shallow seamounts, was undertaken using acoustic data collected during two research cruises at an unnamed pinnacle (summit depth similar to 240 m) thereafter named “MAD-Ridge”, and at La Perouse seamount (similar to 60 m) in the south-western Indian Ocean. MAD-Ridge is located to the south of Madagascar, in an “eddy corridor”, known both for its high mesoscale activity and high primary productivity. In contrast, La Perouse is located on the outskirts of the Indian South Subtropical Gyre (ISSG) province, characterised by low mesoscale activity and low primary productivity. During the MAD-Ridge cruise, a dipole was located in the vicinity of the seamount, with the anticyclone being almost stationary on the pinnacle. Total micronekton acoustic densities were greater at MAD-Ridge than at La Perouse. Micronekton acoustic densities of the total water column were lower within the anticyclone than within the cyclone during MAD-Ridge. Micronekton followed the usual diel vertical migration (DVM) pattern, except within the cyclone during MAD-Ridge where greater acoustic densities were recorded in the daytime surface layer. The backscatter intensities were stronger at the 38 kHz than at the 70 and 120 kHz frequencies in the daytime surface layer at MAD-Ridge cyclonic stations. These backscatter intensities likely correspond to gas-filled swimbladders of epi- and mesopelagic fish actively swimming and feeding within the cyclone or gelatinous organisms with gas inclusions. Our findings evidenced that the distributions of micronekton and DVM patterns are complex and are influenced significantly by physical processes within mesoscale eddies. The mesoscale eddies' effects were dominant over any potential seamount effects at the highly dynamic environment prevailing at MAD-Ridge during the cruise. No significant increase in total micronekton acoustic densities was observed over either seamount, but dense aggregations of biological scatterers were observed on their summits during both day and night.  
  Auteur institutionnel Thèse  
  Editeur Lieu de Publication Éditeur  
  Langue English Langue du Résumé Titre Original  
  Éditeur de collection Titre de collection Titre de collection Abrégé  
  Volume de collection Numéro de collection Edition  
  ISSN 0967-0645 ISBN Médium  
  Région Expédition Conférence  
  Notes WOS:000556810400001 Approuvé pas de  
  Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 2836  
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