MEPS 335:123-131 (2007)  -  doi:10.3354/meps335123

Meadows of the seagrass Posidonia oceanica are a significant source of organic matter for adjoining ecosystems

L. Cardona1,2,*, M. Revelles1, M. Sales3, A. Aguilar1, A. Borrell1

1Department of Animal Biology, Faculty of Biology, University of Barcelona, 08029 Barcelona, Spain
2Department of Experimental and Health Sciences, Faculty of Biology and Health Sciences, University Pompeu Fabra, 08003 Barcelona, Spain
3Centre d’Estudis Avançats de Blanes, CSIC, Camí Santa Bárbara s/n, 17300 Blanes, Spain

ABSTRACT: Stable isotopes of carbon and nitrogen were used to assess the relevance of 4 primary carbon sources (the macroalga Cystoseira balearica, decaying blades of the seagrass Posidonia oceanica, seagrass epiphytes and pelagic particulate organic matter [POM]) for consumers inhabiting 3 adjoining subtidal habitats in the Western Mediterranean: seagrass meadows, unvegetated sandy patches and the overlying pelagic ecosystem. MANOVA and ANOVA revealed statistically significant differences between the δ13C signal of decaying blades of P. oceanica (–13.0 ± 0.6‰), epiphytes (–19.7 ± 0.4‰) and a third group including POM (–23.1 ± 0.3‰) and C. balearica (–22.7 ± 0.8‰). However, these primary sources did not differ in their δ15N signals (average: 1.0‰; range: 0.8 to 1.2‰). IsoSource mixing model software was used to calculate the contribution of each primary source to the carbon assimilated by each animal species. Nested ANOVA showed that the 3 trophic webs differed in the average contribution of the decaying blades of P. oceanica to the carbon assimilated by animals. The average contribution was 46.0 ± 14.0% for meadow-dwelling species, 18.3 ± 6.0% for sand-dwelling species and 12.8 ± 3.0% for pelagic species, once zooxanthellae-bearing jellyfish were removed from the analysis. However, IsoSource provided solutions for all the pelagic species and for half the sand-dwelling species that do not use decaying blades of P. oceanica as a carbon source. Conversely, IsoSource identified the decaying blades of P. oceanica as a relevant carbon source in all the solutions calculated for 3 different sand-dwelling species and in all of the meadow-dwelling species. Thus, we conclude that organic detritus from P. oceanica is a relevant carbon source for species inhabiting seagrass meadows and for those sand-dwelling species living close to the meadows, but not for species exploiting deeper and more distant unvegetated patches.

KEY WORDS: Detritus · Export · Seagrass meadows · Stable-isotope analysis

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