Trophic niche of two co-occurring ophiuroid species in impacted coastal systems, derived from fatty acid and stable isotope analyses

M Guillou,C Quéré,Sf Dubois,F Pernet,A Blanchet-Aurigny

doi:10.3354/meps11169

Abstract

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 525:127-141 (2015) - DOI: https://doi.org/10.3354/meps11169 Trophic niche of two co-occurring ophiuroid species in impacted coastal systems, derived from fatty acid and stable isotope analyses Aline Blanchet-Aurigny1,*, Stanislas F. Dubois1, Claudie Quéré2, Monique Guillou3, Fabrice Pernet2 1IFREMER, Laboratoire d’Ecologie Benthique, Département Océanographie et Dynamique des Ecosystèmes, Centre de Bretagne, BP70, 29280 Plouzané, France 2IFREMER, Laboratoire de Physiologie Fonctionnelle des Organismes Marins, LEMAR UMR CNRS IRD 6539, Centre de Bretagne, BP70, 29280 Plouzané, France 3Institut Universitaire Européen de la Mer, Université de Bretagne Occidentale, LEMAR UMR CNRS IRD 6539, place Nicolas Copernic, 29280 Plouzané, France *Corresponding author: ablanche@ifremer.fr ABSTRACT: The trophic niches of 2 common co-occurring ophiuroids, Ophiocomina nigra and Ophiothrix fragilis (Echinodermata, Ophiuroidea), in 2 contrasting coastal systems of Brittany (France) were investigated. We used a combination of fatty acid biomarkers derived from neutral lipids and stable isotopic compositions to explore the contributions of oceanic versus continental inputs to the ophiuroids’ diet. We investigated 2 different systems with an inshore versus offshore comparison. We sampled potential food sources and surveyed organisms every 2 mo for 1 yr. Spatio-temporal variations in stable isotopes and fatty acid profiles of the ophiuroids were generally low compared to interspecific differences. Fatty acid markers showed that both ophiuroids relied on diatom inputs. However, a more δ15N-enriched isotopic composition as well as a more balanced plant- versus animal-derived fatty acid composition in O. nigra suggest that a broader range of food sources are being used by this species irrespective of location or sampling time. The positive correlation between the 18:1n-9/18:1n-7 fatty acid ratio and δ15N values indicates a higher trophic position for O. nigra (suggesting an omnivorous feeding mode), whereas O. fragilis appears to be more herbivorous. Moreover, the low polyunsaturated/saturated fatty acid ratio associated with elevated bacterial fatty acid markers indicates that O. nigra preferentially consumes detritus, while O. fragilis relies more on fresh phytoplankton-derived material. Both stable isotope and fatty acid analyses suggest that terrestrial inputs do not contribute significantly to the diet of these ophiuroids. However, phytodetritus derived from decomposing green macroalgae contributed to the diet of O. nigra in the Bay of Douarnenez. KEY WORDS: Echinoderm · Feeding ecology · Ophiocomina nigra · Ophiothrix fragilis · Trophic markers · Green algae Full text in pdf format Supplementary material PreviousNextCite this article as: Blanchet-Aurigny A, Dubois SF, Quéré C, Guillou M, Pernet F (2015) Trophic niche of two co-occurring ophiuroid species in impacted coastal systems, derived from fatty acid and stable isotope analyses. Mar Ecol Prog Ser 525:127-141. https://doi.org/10.3354/meps11169 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 525. Online publication date: April 09, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Highlights

Echinoderms often exhibit high population density fluctuations — called ‘outbreak’ or ‘die-off’ events — in coastal and deep water ecosystems, where they play key structural and functional roles.Such events are often facilitated by anthropogenic factors and the life history traits of the echinoderms, and could trigger dramatic changes in the marine ecosystem structure (Uthicke et al 2009).Mar Ecol Prog Ser 525: 127–141, 2015In European coastal waters, benthic assemblages are often dominated by dense populations of benthic suspension-feeders as well as opportunistic depositfeeders which can take advantage of the high primary production (Hily 1991, Carvalho et al 2011)
We aimed to investigate the trophic niche of the 2 ophiuroid species O. nigra and O. fragilis, using stable isotope and fatty acid biomarkers
Stable isotope values of potential food sources and both ophiuroid species are presented in Table S1 in the Supplement at www.int-res.com/articles/suppl/ m525p127_supp.pdf

Summary

Introduction

Echinoderms often exhibit high population density fluctuations — called ‘outbreak’ or ‘die-off’ events — in coastal and deep water ecosystems, where they play key structural and functional roles.Such events are often facilitated by anthropogenic factors (e.g. nutrient inputs, over-fishing) and the life history traits of the echinoderms (adult feeding mode, high fecundity, high longevity, larval type), and could trigger dramatic changes in the marine ecosystem structure (Uthicke et al 2009).Mar Ecol Prog Ser 525: 127–141, 2015In European coastal waters, benthic assemblages are often dominated by dense populations of benthic suspension-feeders as well as opportunistic depositfeeders which can take advantage of the high primary production (Hily 1991, Carvalho et al 2011). The Land’s End of Brittany (France) hosts dense populations of both Ophiocomina nigra and Ophiothrix fragilis (Echinodermata, Ophiuroid) (Abildgaard), which occur either in mixed or monospecific beds across a wide range of sedimentary features (Hughes 1998) This species assemblage is reported to be stable over time and is usually dominated by O. fragilis (Hily 1991), recent investigations in Brittany revealed long-term density changes and spatial shifts in O. nigra and O. fragilis beds between 1987 and 2011 (Blanchet-Aurigny et al 2012a, Guillou et al 2013). O. nigra is more mobile at the sediment−water interface and commonly consumes a variety of deposited material (Vevers 1956), or behaves as a scavengerous species, foraging on detritus or carrion (Nagabhushanam & Colman 1959)

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