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The actual food of macroconsumers grazing on leaves or ingesting detritus of Posidonia oceanica seagrasses: a delta13 C study
Dauby, P.; Coulon, P. (1993). The actual food of macroconsumers grazing on leaves or ingesting detritus of Posidonia oceanica seagrasses: a delta13 C study. Belg. J. Zool. 123(Suppl. 1): 14-15
In: Belgian Journal of Zoology. Koninklijke Belgische Vereniging voor Dierkunde = Société royale zoologique de Belgique: Gent. ISSN 0777-6276, more
Peer reviewed article  

Also published as
  • Dauby, P.; Coulon, P. (1993). The actual food of macroconsumers grazing on leaves or ingesting detritus of Posidonia oceanica seagrasses: a delta13 C study, in: Chardon, M. et al. (Ed.) Third Belgian Congress of Zoology, 5-6 November 1993. Belgian Journal of Zoology, 123(Suppl. 1): pp. 14-15, more

Available in Authors 
Document types: Conference paper; Summary

Keyword
    Marine

Authors  Top 
  • Dauby, P., more
  • Coulon, P.

Abstract
    The grazers Paracentrotus lividus (Echinoid), Idotea baltica (Isopod) and Sarpa salpa (Teleost), and the detritivorous Holothuria tubulosa are among the only macroconsumers observed feeding on Posidonia seagrasses material in the Mediterranean. A question however remains: do these animals actually assimilate the organic matter of this tough plant or do they preferentially feed on its epiphytes? The analysis of stable carbon isotope ratios in animal tissues allows to elucidate the origin of organic carbon because delta13 C of the two plant groups are well distinct (between -14 and -11%) clearly showing that this isopod assimilates seagrass carbon (this is confirmed by laboratory feeding experiments). The viscera of the Paracentrotus sea urchin present a mean delta13 C of -17.8 %, giving evidence of an epiphyte-based dietary. Sarpa delta13 C values range from -16.4 (gut wall) to -18.6% (liver), showing that this fish, though it obviously ingests Posidonia blades, preferentially assimilates epiphytic carbon; it is worth noticing that Sarpa also feeds on large seaweeds growing beside the seagrass bed. The sea cucumber Holothuria, eating sediments within the bed (whose delta13 C averages -15.5%, intermediate between Posidonia and epiphytes) has tissue delta13 C values close to its food source (except for the hema1 systgem; -17.9%); values for faeces are slightly more enriched in delta13 C than food, indicating a preferential assimilation of epiphytic carbon. In conclusion, it appears that Posidonia carbon plays a minor role in the diet of the seagrass bed macroconsumers and that inconspicuous epiphytic algae, despite their apparent small standing stock, constitute the main carbon source for herbivores.

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