What is the menu today in a subantarctic kelp food web from the Kerguelen Islands? Phytodetritus, phytoplankton and phytobenthos; not living kelp.

• Published in: Marine Biology
• Main Authors: Le Bourg, Baptiste, Saucède, Thomas, Charpentier, Anouk, Lepoint, Gilles, Michel, Loïc N.
• Other Authors: Freshwater and Oceanic Sciences Unit of reSearch (FOCUS), Laboratory of Oceanology, Université de Liège-Université de Liège, Institut méditerranéen d'océanologie (MIO), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS), Biogéosciences UMR 6282 (BGS), Université de Bourgogne (UB)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Environnement Profond (LEP), Etudes des Ecosystèmes Profonds (EEP), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Research funded by the Belgian Science Policy Office (BELSPO) as part of the vERSO and RECTO projects (www. recto verso proje cts. be; contract nr. BR/132/A1/vERSO and BR/154/A1/RECTO), and by a PhD scholarship from the Belgian Fund for Research Training in Industry and Agriculture (FRIA).
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2022
• Subjects: Benthic communities; Food web; Kelp forests; Mixing models; Stable isotopes; [SDE.BE]Environmental Sciences/Biodiversity and Ecology; Kerguelen; Kerguelen Islands
• Online Access: https://hal.science/hal-03774825; https://doi.org/10.1007/s00227-022-04105-z

17 pages International audience Kelp forests dominated by Macrocystis pyrifera are widely distributed in coastal waters from boreal, temperate and subantarctic regions. This widespread distribution may result in regional differences in food web structure and functioning. In temperate northern regions, where most studies on kelp forest benthic food webs have been conducted, kelp grazing is a well-documented phenomenon and can lead to the overgrazing of M. pyrifera by sea urchins when their predators (e.g., sea otters) are absent. In contrast, little is known about their counterparts in subantarctic areas. The present study aimed to reconstruct the benthic food web of a kelp forest dominated by M. pyrifera in a subantarctic environment using stable isotope analysis. Stable carbon (δ13C), nitrogen (δ15N) and sulfur (δ34S) isotope ratios were measured from food sources (macrophytobenthos, suspended particulate organic matter SPOM, and sediment) and consumers (sponges, bivalves, gastropods, sedentary and mobile polychaetes, arthropods and echinoderms) which were sampled in a kelp forest of the Kerguelen archipelago. Mixing models highlighted two interconnected trophic pathways which were either supported by SPOM and resuspended macrophytobenthos detritus (bentho-pelagic), or by live micro/macrophytobenthos (phytobenthos-based). No major prey were highlighted for several consumers, indicating the existence of potential supplementary trophic pathways. No consumer relying primarily on living M. pyrifera was highlighted by the mixing models. The investigated kelp forest is hence a complex ecosystem supporting multiple trophic pathways, and direct consumption of M. pyrifera is limited. Nonetheless, M. pyrifera and other macrophytobenthos species may constitute a pool of detritus supporting several trophic pathways.