Stable isotopes and trophic positions of littoral fishes from a Mediterranean marine protected area |
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Authors: | Salvatrice Vizzini Antonio Mazzola |
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Institution: | (1) Department of Ecology, University of Palermo, via Archirafi 18, 90123 Palermo, Italy |
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Abstract: | Stable isotope analyses were employed to explore feeding and foraging habitats and trophic levels of littoral fishes in a
western Mediterranean Marine Protected Area (Egadi Islands, Sicily, Italy). Carbon and nitrogen stable isotope ratios were
measured in primary producers, invertebrates and fishes collected in December 2001 and January 2002. Fishes of the littoral
region of the Egadi Islands had isotopic signatures that fell into a wider range for δ
13C (about 6‰) than for δ
15N (about 3‰). Carbon isotope ratios were consistent with a food web based on mixed sources and two trophic pathways leading
to different fish species. Differences in the isotopic composition between islands were higher for benthivorous than for planktivorous
fishes. The overall picture gained from this study is of a isotopic distinction between planktivorous and benthivorous fishes,
resource partitioning facilitating the coexistence of similar species within the same ecosystem, and spatial variability in
the isotopic signatures and trophic level of fishes. Asymmetrical analysis of variance showed that estimated trophic levels
were lower in the area with the highest level of protection (Zone A) for only two out of the nine fishes analysed. As a consequence,
overall spatial differences do not seem to be a consequence of protection, since in most cases trophic levels did not change
significantly between zone A and zones C where professional fishing (trawling apart) is permitted, but of natural sources
of variation (e.g. variability in food availability and site-specific food preferences of fishes). However, the results of
this study suggest a different response at the species compared to the community level. |
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Keywords: | Stable isotopes Trophic level Food web Spatial variability Protection effects |
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