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Title: A wolf in sheep"s clothing: carnivory in dominant sea urchins in the Mediterranean
Author: Wangensteen Fuentes, Owen S. (Simon)
Turon Barrera, Xavier
García Cisneros, Álex
Recasens, Mireia
Romero, Javier (Romero Martinengo)
Palacín Cabañas, Cruz
Keywords: Eriçons de mar
Biologia de poblacions
Mediterrània (Mar)
Biologia marina
Sea urchins
Population biology
Mediterranean Sea
Marine biology
Issue Date: Nov-2011
Publisher: Inter-Research
Abstract: Arbacia lixula and Paracentrotus lividus are the dominant sea urchins in the Mediterranean sublittoral, where they are key structuring species due to their grazing activity. It has been commonly accepted that competition between both species is minimized by specializing in different algal foods. A. lixula is considered to feed mainly on encrusting coralline algae, while P. lividus prefers fleshy macroalgae. We used stable isotope analysis to test if these species occupy different trophic positions at 3 locations in the western Mediterranean and one in Macaronesia. Our results show unambiguously that A. lixula always occupies a higher trophic level than P. lividus, with a δ15N comparable in some locations to strict carnivores such as Actinia schmidti or Marthasterias glacialis. A temporal monitoring at one locality showed that this signature of a higher trophic level is consistent throughout the year. These results are incompatible with the current belief of an herbivorous diet for A. lixula and suggest that it must be considered an omnivore tending to carnivory in Mediterranean ecosystems, feeding at least partially on sessile animals such as Cirripedia, Hydrozoa or Bryozoa. A parallel analysis of gut contents showed a predominance of vegetal items in both species, although A. lixula consistently had a higher abundance of animal components than P. lividus. Our results challenge the validity of using gut content observations alone for characterizing the trophic behaviour of omnivorous marine invertebrates that feed on a variety of food sources with different digestibility.
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It is part of: Marine Ecology Progress Series, 2011, vol. 441, p. 117-128
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ISSN: 0171-8630
Appears in Collections:Articles publicats en revistes (Biologia Evolutiva, Ecologia i Ciències Ambientals)

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