Presenter: Leila Hamdan (University of Southern Mississippi)

Description:
The seafloor contains complex ecosystems where habitat heterogeneity influences biodiversity of all organisms. Widespread natural, biological and geological features create hardbottom environments that select for distinct populations of micro- and macrofauna. While largely studied for macrobiological diversity, built habitats may also have a role in shaping microbiomes. Built habitat density on the seafloor is increasing as ocean sprawl expands in the continental shelf and slope. This may have widespread effects on benthic microbiomes. This study addresses the impact of one type of built habitat - shipwrecks, on microbiomes in the surrounding marine sediment. Sediment samples were collected along transects extending 2 to 1000 m away from nine historic shipwrecks in the northern Gulf of Mexico by remotely operated vehicle (push cores) or with a MC800 multicorer. Shipwrecks in the study spanned the early 19^th century to the mid 20^th century, were made of both wood and steel and were found at depths spanning 140 to 2050 m deep. 16S rRNA gene amplification was carried using universal bacterial and archaeal primers targeting the V6-V8 variable regions and sequenced on the Illumina MiSeq platform. We report elevated diversity and a predictable core microbiome in sediments extending ~ 300 m into the surrounding seabed. Supervised learning made predictions of microbiome proximity to the shipwrecks. The response of archaea was consistent across sites found at different depths (140 to 2050 m deep) and with different hull construction material, while bacteria showed greater between site variability. Built habitats have similar effects on deep-seabed archaea regardless of environmental context, and shape microbiomes in expected ways. These findings are of significance to revealing how built habitats impact microbial biodiversity in the Anthropocene.