Nitrogen and phosphorus recycling mediated by copepods and response of bacterioplankton community from three contrasting areas in the western tropical South Pacific (20° S)
<p>Zooplankton play a key role in the regeneration of nitrogen and phosphorus in the ocean through grazing and metabolism. This study investigates the role of the organic and inorganic nitrogen and phosphorus compounds released by copepods on biogeochemical processes and on the microbial c...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-10-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/15/6019/2018/bg-15-6019-2018.pdf |
| Summary: | <p>Zooplankton play a
key role in the regeneration of nitrogen and phosphorus in the ocean through
grazing and metabolism. This study investigates the role of the organic and
inorganic nitrogen and phosphorus compounds released by copepods on
biogeochemical processes and on the microbial community composition during
the OUTPACE cruise (18 February–3 April 2015) at three long-duration
stations (LD). Two LD stations were located in the Melanesian Archipelago
region (MA; LD A and LD B) and one in the South Pacific Gyre (SG; LD C),
which represent oligotrophic and ultra-oligotrophic regions respectively. At
each station, on-board microcosm experiments were performed with locally
sampled organisms, comprising a mix of epipelagic copepods fed with their
natural food and then incubated along with wild microbial assemblages. In
the presence of copepods, ammonium and dissolved organic nitrogen showed a
significant increase compared to a control in two situations: in ammonium
concentration (rate: 0.29 µmol L<sup>−1</sup> h<sup>−1</sup> after 4 h of
incubation) in LD C and in dissolved organic nitrogen concentration (rate:
2.13 µmol L<sup>−1</sup> h<sup>−1</sup> after 0.5 h of incubation) in LD A.
In addition, during the three experiments, an enhanced remineralization
(ammonification and nitrification) was observed when adding copepods compared
to the controls. A shift in the composition of the active bacterial community
was observed for the experiments in LD A and LD B, which were mainly characterized by an
increase in Alteromonadales and SAR11, respectively, and linked with changes
in nutrient concentrations. In the experiment performed in LD C, both groups
increased but at different periods of incubation. Alteromonadales increased between 1
and 2 h after the beginning of the experiment, and SAR 11 at the end of
incubation. Our results in near in situ
conditions show that copepods can be a source of organic and inorganic
compounds for bacterial communities, which respond to excretion pulses at
different timescales, depending on the initial environmental conditions and
on their community composition. These processes can significantly contribute
to nutrient recycling and regenerated production in the photic zone of
ultra-oligotrophic
and oligotrophic oceanic regions.</p> |
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| ISSN: | 1726-4170 1726-4189 |