Pelagic food web structure in high nutrient low chlorophyll (HNLC) and naturally iron fertilized waters in the Kerguelen Islands region, Southern Ocean

Type Article
Date 2021-12
Language English
Author(s) Hunt Brian P.V.1, 2, 3, Espinasse Boris4, Pakhomov Evgeny A.1, 2, 3, Cherel Yves5, Cotté Cedric6, Delegrange Alice7, 8, Henschke Natasha2
Affiliation(s) 1 : Institute for the Oceans and Fisheries, University of British Columbia, Vancouver, British Columbia, Canada
2 : Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, British Columbia, Canada
3 : Hakai Institute, Heriot Bay, British Columbia, Canada
4 : Department of Arctic and Marine Biology, UiT The Arctic University of Norway, Tromsø, Norway
5 : Centre d'Etudes Biologiques de Chizé (CEBC), UMR 7372 CNRS- La Rochelle Université, 79360 Villiers-en-Bois, France
6 : Sorbonne Université, CNRS, IRD, MNHN, Laboratoire d'Océanographie et du Climat: Expérimentations et Approches Numériques (LOCEAN-IPSL), Paris, France
7 : Institut National Supérieur du Professorat et de l'Éducation (INSPÉ) - Académie de Lille Hauts-de-France, Site d'Outreau10, rue H. Adam, 62230, Outreau, France
8 : Laboratoire d'Océanologie et de Géosciences - LOG UMR CNRS 8187, Maison de la Recherche en Environnement Naturel 32, Avenue Foch, 62930 Wimereux, France
Source Journal Of Marine Systems (0924-7963) (Elsevier BV), 2021-12 , Vol. 224 , P. 103625 (10p.)
DOI 10.1016/j.jmarsys.2021.103625
WOS© Times Cited 6
Keyword(s) Zooplankton, Micronekton, Food web, Size structure, Stable isotopes, Southern Ocean, Kerguelen plateau

The Kerguelen Plateau is a region of natural iron fertilization in the Southern Ocean, within the typically iron limited High Nutrient Low Chlorophyll (HNLC) waters of the eastward flowing Antarctic Circumpolar Current. Between 26 February and 19 March 2018, the MOBYDICK expedition investigated pelagic ecosystem dynamics in the Kerguelen Island region on the northern plateau during the post-phytoplankton bloom period. The survey specifically targeted sampling at two stations in the HNLC waters to the west of the Kerguelen Plateau, and in the iron enriched waters on and to the east of the plateau. A combination of WP2, WP3 and Mesopelagos midwater trawl were used to sample the mesozooplankton (125 μm to ≤10 mm), macrozooplankton (10–30 mm) and micronekton (> 30 to 200 mm) communities. Stable carbon (δ13C) and nitrogen (δ15N) isotopes were measured across representative samples of taxa from all stations. Trophic positions was estimated using a Bayesian isotope mixing model (tRophicPosition), that uses both the δ13C and δ15N values of baselines and consumers. Meso/macrozooplankton trophic positions (TPs) were ~ 2.4 on the plateau and > 0.6 TPs higher at the upstream HNLC stations. This provides empirical evidence for shorter food chains on the diatom dominated plateau and longer food chains in the HNLC region dominated by pico and nanophytopklankon. Meso/macrozooplankton TPs were also elevated downstream of the plateau, though to a lesser extent than in the upstream region, likely reflecting the effect of downstream iron transport, supporting elevated phytoplankton production in the downstream region. There was a consistent increase in trophic position between meso/macrozooplankton and micronekton of ~0.6 at all stations. Food chain length was therefore determined by the composition of the trophic levels below micronekton. Similar trophic structure at the two upstream HNLC stations, on either side of the northern branch of the Polar Front, indicated that food chain length was robust to the differences in community composition, and supports the critical role of size structured trophic interactions in determining food web properties.

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Hunt Brian P.V., Espinasse Boris, Pakhomov Evgeny A., Cherel Yves, Cotté Cedric, Delegrange Alice, Henschke Natasha (2021). Pelagic food web structure in high nutrient low chlorophyll (HNLC) and naturally iron fertilized waters in the Kerguelen Islands region, Southern Ocean. Journal Of Marine Systems, 224, 103625 (10p.). Publisher's official version : , Open Access version :