@article{fdi:010067597,
  title = {{C}ontribution and pathways of diazotroph-derived nitrogen to zooplankton during the {VAHINE} mesocosm experiment in the oligotrophic {N}ew {C}aledonia lagoon},
  author = {{H}unt, {B}. {P}. {V}. and {B}onnet, {S}ophie and {B}erthelot, {H}. and {C}onroy, {B}. {J}. and {F}oster, {R}. {A}. and {P}agano, {M}arc},
  editor = {},
  language = {{ENG}},
  abstract = {{I}n oligotrophic tropical and subtropical oceans, where strong stratification can limit the replenishment of surface nitrate, dinitrogen ({N}-2) fixation by diazotrophs can represent a significant source of nitrogen ({N}) for primary production. {T}he {VAHINE} ({VA}riability of vertical and trop{HI}c transfer of fixed {N}-2 in the south-w{E}st {P}acific) experiment was designed to examine the fate of diazotroph-derived nitrogen ({DDN}) in such ecosystems. {I}n austral summer 2013, three large ( similar to a{E}uro parts per thousand a{E}uro-50a{E}uro-m(3)) in situ mesocosms were deployed for 23 days in the {N}ew {C}aledonia lagoon, an ecosystem that typifies the low-nutrient, low-chlorophyll environment, to stimulate diazotroph production. {T}he zooplankton component of the study aimed to measure the incorporation of {DDN} into zooplankton biomass, and assess the role of direct diazotroph grazing by zooplankton as a {DDN} uptake pathway. {I}nside the mesocosms, the diatom-diazotroph association ({DDA}) het-1 predominated during days 5-15 while the unicellular diazotrophic cyanobacteria {UCYN}-{C} predominated during days 15-23. {A} {T}richodesmium bloom was observed in the lagoon (outside the mesocosms) towards the end of the experiment. {T}he zooplankton community was dominated by copepods (63a{E}uro-% of total abundance) for the duration of the experiment. {U}sing two-source {N} isotope mixing models we estimated a mean similar to a{E}uro parts per thousand a{E}uro-28a{E}uro-% contribution of {DDN} to zooplankton nitrogen biomass at the start of the experiment, indicating that the natural summer peak of {N}-2 fixation in the lagoon was already contributing significantly to the zooplankton. {S}timulation of {N}-2 fixation in the mesocosms corresponded with a generally low-level enhancement of {DDN} contribution to zooplankton nitrogen biomass, but with a peak of similar to a{E}uro parts per thousand a{E}uro-73a{E}uro-% in mesocosm 1 following the {UCYN}-{C} bloom. q{PCR} analysis targeting four of the common diazotroph groups present in the mesocosms ({T}richodesmium, het-1, het-2, {UCYN}-{C}) demonstrated that all four were ingested by copepod grazers, and that their abundance in copepod stomachs generally corresponded with their in situ abundance. {N}-15(2) labelled grazing experiments therefore provided evidence for direct ingestion and assimilation of {UCYN}-{C}-derived {N} by the zooplankton, but not for het-1 and {T}richodesmium, supporting an important role of secondary pathways of {DDN} to the zooplankton for the latter groups, i.e. {DDN} contributions to the dissolved {N} pool and uptake by nondiazotrophs. {T}his study appears to provide the first evidence of direct {UCYN}-{C} grazing by zooplankton, and indicates that {UCYN}-{C}-derived {N} contributes significantly to the zooplankton food web in the {N}ew {C}aledonia lagoon through a combination of direct grazing and secondary pathways.},
  keywords = {{NOUVELLE} {CALEDONIE} ; {PACIFIQUE} ; {NOUMEA} {LAGON}},
  booktitle = {},
  journal = {{B}iogeosciences},
  volume = {13},
  numero = {10},
  pages = {3131--3145},
  ISSN = {1726-4170},
  year = {2016},
  DOI = {10.5194/bg-13-3131-2016},
  URL = {https://www.documentation.ird.fr/hor/fdi:010067597},
}