The hydrothermal vent community of a new deep-sea field, Ashadze-1, 12°58′N on the Mid-Atlantic Ridge

Abstract

Ashadze-1 (12° 58′N 44° 51′W, 4080 m) on the Mid-Atlantic Ridge (MAR) is the deepest known active hydrothermal vent field. The first observations on this site were numerous clear and black smokers and surprisingly few known symbiotic species dominant in other vent areas on the MAR. The species most abundant at Ashadze-1 are those usually found at the periphery of hydrothermal communities: sea-anemones Maractis rimicarivora and chaetopterid polychaetes Phyllochaetopterus sp. nov. This study comprised site mapping and faunal sampling and Ashadze-1 was completely mapped by using the remote operated vehicle ‘Victor 6000’ and a new high resolution tool available for deep-sea research. A photo-mapping survey was carried out with a long range optical black and white camera. Digitization of substrata and sea-anemones visible on the images was performed by GIS. Spatial distribution of Ma. rimicarivora was distinguished by high densities of 32 ind.m −2 on the western side of the main smoker area. Submersible sampling operations allowed taxonomic identification within a 200 × 110 m area. Carbon, nitrogen and sulphur isotopic ratios were measured in four dominant species to identify their trophic position. The present paper gives the complete maps and describes the faunal community of the Ashadze-1 vent field. The results obtained led us to consider this site as an ecosystem in its declining stage. Finally we compare the similarities of this community to other hydrothermal communities on the northern MAR.