Cah. Biol. Mar. (2011) 52 : Trophic and biotic interactions in Laminaria digitata beds: which factors could influence the persistence of marine kelp forests in northern Brittany? Catherine LEBLANC1,2*, Gauthier SCHAAL3,4,5*, Audrey COSSE1,2, Christophe DESTOMBE3,4, Myriam VALERO3,4, Pascal RIERA3,4, Philippe POTIN1,2 (1) UPMC Université Paris 6, UMR7139, Marine Plants and Biomolecules, Station Biologique, Roscoff, France Fax: +33 (0)2 98 29 23 24. E-mail:
[email protected] (2) CNRS, UMR7139, Marine Plants and Biomolecules, Station Biologique, Roscoff, France (3) UPMC Université Paris 6, UMR 7144, Laboratoire Adaptation et Diversité en Milieu Marin, Station Biologique, Roscoff, France (4) CNRS, UMR 7144, Laboratoire Adaptation et Diversité en Milieu Marin, Station Biologique, Roscoff, France (5) Present address: Department of Zoology and Entomology. Rhodes University. BP94 Grahamstown. 6140 South Africa * These authors contributed equally to this work Abstract: In this paper, we first reviewed the trophic ecology studies carried out on Laminaria digitata beds, at two rocky areas of Northern Brittany (France), Batz Island and Ar Pourven, displaying contrasted ecological conditions. The general trophic structure did not vary between the two sites, with a wide diversity of filter-feeders and predators, and only 14% of grazers. The results of stable isotope analyses allow drawing a simplified model for the food web associated to L. digitata beds. Kelp-derived organic matter is channeled into two distinct trophic pathways, the particle feeding-based and the grazing-based, which are coupled with higher trophic levels. The L. digitata detritic pathway contributes most to the diet of filter-feeders inhabiting sheltered sites.