Diversité structurelle et fonctionnelle des peuplements sablo-vaseux de Bretagne sud : Impact de l'expansion d'Haploops nirae

This thesis aims here, based on the case of the Bay of Concarneau, to understand the impact of the development of dense populations of the tubiculous amphipod Haploops nirae on the structural and functional diversity of sandy-mud communities of South Brittany. The study of Haploops communities was developed on various levels of organization of life, from the specific role of Haploops nirae to functional role of Haploops community in the ecosystem passing through the description of the community composition and its role on the biodiversity. Our results suggest firstly that the functional role of Haploops nirae alone (filtration pressure, secondary production) is potentially important. Moreover, the physical changes induced by Haploops were found to have important consequences on the composition of species assemblages and species diversity. In contrast, the study of the functional diversity addressed by biological traits analysis (BTA) and secondary production at the community scale reveals that the functional consequences of Haploops occupation in an ecosystem are generally low. In addition, the analysis of the trophic functioning of benthic communities from the Bay of Concarneau (through the use of stable isotopes) showed low incidence of Haploops occupation on the functioning of the benthic food web. Although Haploops communities are not characterized by profound functional changes, trophic flows to higher trophic levels, however, are likely to be affected by the presence of Haploops.