FN Archimer Export Format PT J TI Meso-zooplankton structure and functioning in the western tropical. South Pacific along the 20° parallel south during the OUTPACE survey (February-April 2015) BT AF Carlotti, François Pagano, Marc Guilloux, Loïc Donoso, Katty Valdés, Valentina Grosso, Olivier Hunt, Brian P. V. AS 1:1;2:1;3:1;4:1;5:2,3;6:1;7:1,4,5,6; FF 1:;2:;3:;4:;5:;6:;7:; C1 Aix Marseille Université, Université de Toulon, CNRS, IRD, OSU PYTHEAS Mediterranean Institute of Oceanography, MIO, UM 110, 13288, Marseille, Cedex 09, France Millennium Institute of Oceanography (IMO), Universidad de Concepción, Concepción, Chile Programa de Doctorado en Oceanografía, Departamento de Oceanografía, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Concepción, Chile Institute of the Oceans and Fisheries, University of British Columbia, Vancouver, V6T 1 Z4, British Columbia, Canada Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, British Columbia, 15 Canada Hakai Institute, Heriot Bay, British Columbia, Canada, C2 UNIV AIX MARSEILLE, FRANCE UNIV CONCEPCION, CHILE UNIV CONCEPCION, CHILE UNIV BRITISH COLUMBIA, CANADA UNIV BRITISH COLUMBIA, CANADA INST HAKAI, CANADA IN DOAJ IF 3.951 TC 11 UR https://archimer.ifremer.fr/doc/00435/54683/56101.pdf https://archimer.ifremer.fr/doc/00435/54683/56102.pdf https://archimer.ifremer.fr/doc/00435/54683/60825.pdf https://archimer.ifremer.fr/doc/00435/54683/60826.pdf LA English DT Article CR BIOSOPE FLUPAC NECTALIS-1 NECTALIS-2 OUTPACE BO L'Atalante Alis AB This paper presents results on the spatial and temporal distribution patterns of mesozooplankton in the western tropical South Pacific along the 20 °S south visited during austral summer (February–April 2015). By contributing to the interdisciplinary OUTPACE (Oligotrophy to UlTra-oligotrophy PACific Experiment) project (Moutin et al., 2017), the specific aims of this study dedicated to mesozooplankton observations were (1) to document the responses of zooplankton in terms of species diversity, density and biomass along the transect, and (2) to characterize the trophic pathways from primary production to large mesozooplanktonic organisms. Along a West-East transect of 4000 km from New Caledonia to the French Polynesia, 15 short-duration stations (SD-1 to SD-15, 8 hours each) dedicated to a large-scale description, and three long-duration stations (LD-A to LD-C, 5days each), respectively positioned (1) in offshore northern waters of New Caledonia, (2) near Niue Island, and (3) in the subtropical Pacific gyre near the Cook Islands, were sampled with a Bongo Net with 120 μm mesh size net for quantifying mesozooplankton abundance, biomass, community taxonomy and size structure, and size fractionated content of δ15N. Subsequently, the contribution of Diazotroph Derived Nitrogen (DDN (%) to zooplankton δ15N (ZDDN) values at each station was calculated, as well as an estimation of zooplankton carbon demand and grazing impact and of zooplankton excretion rates.  The mesozooplankton community showed a general decreasing trend in abundance and biomass from West to East, with a clear drop in the ultra-oligotrophic waters of the subtropical Pacific gyre (LD-C, SD-14 and SD-15). Higher abundance and biomass corresponded to higher primary production of more or less ephemeral blooms linked to complex mesoscale circulation in the Coral Sea and between the longitudes 170–180 °W. Copepods were the most abundant group (68 to 86 % of total abundance), slightly increasing in contribution from west to east while, in parallel, gelatinous plankton decreased (dominated by appendicularians) and other holoplankton. Detritus in the net tow samples represented 20–50 % of the biomass, the lowest and the highest values being obtained in the subtropical Pacific gyre and in the Coral Sea, respectively, linked to the local primary production and the biomass and growth rates of zooplanktonic populations.  Taxonomic compositions showed a high degree of similarity across the whole region, however, with a moderate difference in subtropical Pacific gyre. Several copepod taxa, known to have trophic links with Trichodesmium, presented positive relationships with Trichodesmiumabundance, such as the Harpacticoids Macrosetella, Microsetella and Miracia, and the Poecilostomatoids Corycaeus and Oncaea. At the LD stations, the populations initially responded to local spring blooms with a large production of larval forms, reflected in increasing abundances but with limited (station LD-A) or no (station LD-A) biomass changes.  Diazotrophs contributed up to 67 and 75 % to zooplankton biomass in the western and central Melanesian Archipelago regions respectively, but strongly decreased to an average of 22 % in the subtropical Pacific gyre (GY) and down to 7 % occurring in the most eastern station (SD-15). Using allometric relationships, specific zooplankton ingestion rates were estimated between 0.55 and 0.64 d−1 with the highest mean value at the bloom station (LD-B) and the lowest in GY, whereas estimated weight specific excretion rates ranged between 0.1 and 0.15 d−1for NH4 and between 0.09 and 9.12 d−1 for PO4. Daily grazing pressure on phytoplankton stocks and daily regeneration by zooplankton were as well estimated for the different regions showing contrasted impacts between MA and GY regions. For the 3 LD stations, it was not possible to find any relationship between the abundance and biomass in the water column and swimmers found in sediment traps. Diel vertical migration of zooplankton, which obviously occurs from observed differences in day and night samples, might strongly influence the community of swimmers in traps. PY 2018 SO Biogeosciences SN 1726-4170 PU Copernicus GmbH VL 15 IS 23 UT 000452661500001 BP 7273 EP 7297 DI 10.5194/bg-15-7273-2018 ID 54683 ER EF