Contributions of stable-isotope data to elucidating food webs of Mediterranean rocky littoral fishes |
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Authors: | J K Pinnegar N V C Polunin |
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Institution: | (1) Department of Marine Sciences and Coastal Management, University of Newcastle, Newcastle upon Tyne NE1 7RU, UK e-mail: j.k.pinnegar@ncl.ac.uk Tel.: +44-191-2226661, Fax: +44-191-2227891, GB |
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Abstract: | The food webs of rocky infra-littoral ecosystems in the Mediterranean have been little studied. In this investigation stable
isotopes and dietary data were compared in an attempt to describe features of the food webs concerned. δ13C and δ15N were determined for plants, invertebrates and fishes from the Bay of Calvi, Corsica. Dietary data were derived from the
literature. δ13C of plants ranged from –8.59‰ to –33.74‰, of benthic invertebrates from –17.0‰ to –20.52‰, of planktonic invertebrates from
–20.08‰ to –22.34‰ and of fishes from –16.27‰ to –19.59‰. δ15N was generally greater at higher trophic levels. δ15N of plants was 0.95–2.92‰, of benthic invertebrates 1.69–6.54‰, of planktonic invertebrates 3.51–6.82‰ and of fishes 4.63–9.77‰.
13C enrichment tended to be associated with benthic food chains and 13C depletion with planktonic chains. Stable-isotope data suggested more varied diets for many species than implied by gut-contents
data. Omnivory and trophic plasticity were widespread, and many consumers fed lower down the food chain than previous studies
had suggested. Both stable-isotope and gut-contents analysis resolved differences between fishes feeding on planktonic and
benthic prey and indicated that the herbivorous fish Sarpa salpa fed on a diet substantially different from that of other fishes. Zooplankton were important in the diets of several consumers
(both primary and secondary), as was plankton derived detritus. One species of fish previously identified as planktivorous
was shown to feed largely on benthic organisms, whilst several species of benthic invertebrates may feed on plankton-derived
detritus. Although herbivores seemed to obtain most of their C from macroalgae, δ15N data suggested that many of these animals supplemented their intake of N, although gut-contents analysis did not provide
evidence for such uptake. The isotopic data have elucidated several features of the food web which we would not otherwise
have detected.
Received: 26 April 1999 / Accepted: 24 September 1999 |
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Keywords: | Stable nitrogen isotope ratio Stable carbon isotope ratio Trophic level Gut contents Corsica |
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