ALBERT

Description: This study shows the microbial community composition over Haas Mound, one of the most prominent cold-water coral mounds of the Logachev Mound Province (Rockall Bank, NE Atlantic), outlining distribution patterns both vertically from the seafloor to the water column and laterally across the mound and coupling this to mound topography and hydrography. Samples were collected in 2012 and 2013 from biotopes that were partially chosen based on high definition video surveys that were conducted prior to sampling and included overlaying water (400 m depth and 5+10 m above the bottom (m ab)) collected with a CTD/Rosette system and near-bottom water, sediment, Lophelia pertusa mucus, and L. pertusa skeleton samples collected with a box-core. Furthermore, temperature and current measurements were obtained at two sites at the summit and foot of Haas Mound to study near-bed hydrodynamic conditions. Community composition was determined by next generation Roche 454 sequencing yielding high-resolution records of 16 S rRNA genotypes, improving our understanding of deep-sea microbial consortia. With the methods we employed we were able to report for the first time Archaea in association with L. pertusa. The pattern of similarities between samples visualized by multi-dimensional scaling (MDS), indicates a strong link between the distribution of microbes and specific biotopes. All biotopes share a number of taxa, but biotopes are distinct on basis of relative abundances and a small number of unique taxa. Similarity in microbes indicates that water is well-mixed at 400 m depth, but less so at 5 + 10 m above the bottom, where microbial communities differed between summit, slope and off mound. Even more variability was observed in the near-bottom water samples, which group according to sampling station. Likely the coral framework prevents the near-bottom water in between the branches to be vigorously mixed with the water overlaying the reef. The microbial consortium on Haas Mound appears strongly linked with the surrounding environment, making cold-water coral communities sensitive to outside environmental influences.