Benthic foraminiferal species tolerance for hydrothermal activity: a case of study from the Lucky Strike vent field

Abstract. Hydrothermal vent fields represent dynamic environments hosting rich ecosystems. At the Mid-Atlantic Ridge, the Lucky Strike (LS) vent field has been the focus of multiple biological studies. While ecological studies have been focusing on microbial and macrofaunal communities, some groups still remained out of the scope. We present here the first ecological study of benthic foraminifera inhabiting soft sediments in the peripheries of hydrothermal edifices at LS. A total of fifteen blade cores were analyzed. We combine microhabitat environmental descriptors with faunal density and diversity of benthic foraminifera (living & fossil) to investigate the impact of hydrothermal activity on their ecology. The far periphery, ~150 m away from vents, harbors a community of diverse foraminifera feeding on pre-degraded organic matter characterized by a phytoplankton detrital signal. Communities located at intermediate distance (~ 50 m) from venting showed the presence of opportunistic species likely feeding on chemosynthetic microorganisms. Finally, environments closer to active sites (few meters) showed very low abundance of living individuals, as the presence of harsh environmental conditions may limit foraminiferal growth. Unexpectedly, the presence of widespread iron-oxidizer bacterial biofilms was associated to the dissolution of all biogenic carbonate content raising questions on their impact on regional carbon budget.