Horizontal and vertical small-scale patterns of protist communities at the Atlantic deep-sea floor

Spatial distribution patterns of protists in the deep sea are not yet understood and due to the remoteness of the deep-sea biome this is a challenging task. Here, we investigated the structure and dispersal of protist communities in abyssal sediments at three sites in the Caribbean Sea (15?53.21?N/68?55.73?W), the northwestern Atlantic (23?33.23?N/48?05.04?W) and the central Atlantic Ocean (10?20.38?N/36?57.76?W), focusing especially on small horizontal (-1 m) and vertical (1 cm) spatial scales. High-throughput sequencing of the V9 SSU rDNA, revealed diverse protist communities dominated by diplonemids and dinoflagellates. Only 12% of OTUs were shared between the three deep-sea regions (4000?5134 m deep), indicating patterns of protistan distribution at large spatial scales in deep-sea sediments. The analyses of sediment samples taken from cores of the same MultiCorer deployment, separated by -1 m, showed differences in the community structure, indicating a distinct microbial eukaryotic diversity even at a local horizontal scale. At a vertical scale, in different sediment depth layers (upper 2 mm layer, 1 cm, 2 cm, 3 cm) of the same core, only 4?11% of OTUs were shared. We could show, that already at small spatial scales protist communities varied strongly, indicating an underestimated complexity of deep-sea microbial food webs.

Automated summary

The study revealed significant differences in spatial distribution of deep-sea protists, with only a small percentage of species shared between different deep-sea regions. Even at small spatial scales, there were large variations in protist communities, indicating an underestimated complexity of deep-sea microbial food webs.