On the inner continental shelf (depth < 50 m close to the shore) of South Brittany (France) dense settlements of Haploopsspp., tube dwelling crustacean amphipods, have been reported over the last decades. Their key-role as bio-engineer species, on the sediment dynamics and ecological niches is still poorly known. Recently, the perfect overlap of Haploopssettlements on pockmarks field on three different sites along the French Atlantic coast arose the hypothesis that a link exists between the release of methane through active pockmarks and the presence of these organisms. The aim of the present study is to explore the foraminiferal faunas associated to these complex ecosystems and eventually the role of Haploops settlements as source of heterogeneity compared to the adjacent muddy substrates. 

Foraminiferal assemblages (>125 µm) of three replicated cores collected inside the Haploops settlement in the adjacent muddy facies and inside a small pockmark crater (where the Haploops are scarce), were analyzed. 

The three facies have a common species pool, but display major differences in terms of absolute abundances and biodiversity. The Haploops facies shows less dense and highly diverse faunas, compared to the assemblages in the bare muddy facies, where the assemblages are largely dominated by the species Elphidium selseyense. 

Compared to Haploops settlements, the pockmark facies exhibits similar abundances but a lower diversity. The main difference with Haploops facies concerns rare species, only present in the tube cover. Our results highlight a positive impact of Haploops ecosystems on the total diversity of the study area.