Microzooplankton diversity and potential role in carbon cycling of contrasting Southern Ocean productivity regimes

Type Article
Date 2021-07
Language English
Author(s) Christaki Urania1, Skouroliakou Ioli-Dimitra1, Delegrange Alice1, 2, Irion Solène1, Courcot Lucie1, Jardillier Ludwig3, Sassenhagen Ingrid1, 4
Affiliation(s) 1 : Univ. Littoral Côte d'Opale ULCO, CNRS, Univ. Lille, UMR 8187, LOG, Laboratoire d'Océanologie et de Géosciences, 62930 Wimereux, France
2 : Institut national supérieur du professorat et de l'éducation, Académie de Lille – Hauts de France, 59658 Villeneuve d'Ascq, France
3 : Unité d'Ecologie, Systématique et Evolution, Université Paris-Sud, CNRS, AgroParisTech, Université Paris-Saclay, Rue du doyen A. Guinier bât. 360, 91405 Orsay Cedex, France
4 : Department of Ecology and Genetics/Limnology, Uppsala University, Norbyvägen 18D, 75236 Uppsala, Sweden
Source Journal Of Marine Systems (0924-7963) (Elsevier BV), 2021-07 , Vol. 219 , P. 103531 (16p.)
DOI 10.1016/j.jmarsys.2021.103531
WOS© Times Cited 6
Keyword(s) Dinoflagellates, Ciliates, Microscopy, Metabarcoding, Dilution experiments, Southern Ocean, Microzooplankton, Diversity

Microzooplankton play an important role in aquatic food webs through their multiple interactions with other organisms and their impact on carbon export. They are major predators of phytoplankton and bacteria while being preyed on by higher trophic levels. Microzooplankton diversity (Dinoflagellates, DIN and Ciliates, CIL), community structure, interaction with phytoplankton and its potential in channeling carbon to higher trophic levels were studied in contrasting productivity regimes (off- and on-plateau, the latter been naturally fertilized by iron) around the Kerguelen islands in the Southern Ocean (SO). DIN and CIL diversity was sampled in late summer (February–March 2018; project MOBYDICK) and at the onset-of the bloom (KEOPS2 cruise), and assessed by Illumina sequencing of 18S rDNA amplicons and microscopic observations. The diversity obtained by the two approaches could be compared at a relatively high taxonomic level (i.e., often to family level). In particular for DIN, relative abundances and ranking of dominant taxa differed between sequencing and microscopy observations. CIL were always recorded at considerably lower abundances than DIN, the median of their abundances across stations and seasons being 350 and 1370 cells L−1, respectively. During late summer, DIN and CIL biomasses were about 1.5 times higher on- than in off-plateau waters, while community composition was spatially similar. The most abundant DIN at all stations and during both seasons were small Gymnodinium (<20 μm). During late summer, ciliates Lohmaniella oviformis (<20 μm) and Cymatocylis antarctica (20-40 μm) dominated on- and off-plateau, respectively. Dilution experiments suggested significant grazing of microzooplankton on phytoplankton as phytoplankton net growth (k) was lower than microzooplankton grazing (g) at all stations (mean k = 0.16 ± 0.05 d−1, g = 0.36 ± 0.09 d−1) in late summer. Despite having great potential as a phytoplankton grazer, microzooplankton occurred at low biomass and showed little temporal variability, suggesting that they were controlled by copepod predation. Microzooplankton are a key component of the SO as an intermediate trophic level mediating carbon transfer from primary producers to higher trophic levels.

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Christaki Urania, Skouroliakou Ioli-Dimitra, Delegrange Alice, Irion Solène, Courcot Lucie, Jardillier Ludwig, Sassenhagen Ingrid (2021). Microzooplankton diversity and potential role in carbon cycling of contrasting Southern Ocean productivity regimes. Journal Of Marine Systems, 219, 103531 (16p.). Publisher's official version : https://doi.org/10.1016/j.jmarsys.2021.103531 , Open Access version : https://archimer.ifremer.fr/doc/00689/80068/