Spatio-temporal variations of archaeal communities in the Wocan hydrothermal plume-influenced zone, Carlsberg Ridge, northwest Indian Ocean

Abstract:

[Objective] Hydrothermal plumes exchange matter and energy with background seawater during the processes of buoyant rising and non-buoyant lateral migration. Due to the dynamic variability of both hydrothermal activity and ocean currents, the pattern, physico-chemical parameters, and microbial communities of hydrothermal plumes experience spatio-temporal variations. However, due to the lack of long-term monitoring and time-series sampling of hydrothermal plumes, the diversity and spatio-temporal variations of microbial communities, especially archaea, remain unclear.[Methods] From July 2018 to June 2019, a mooring system with two sediment traps (one for collection of hydrothermal plume samples 300 m above seafloor and the other for collection of near-bottom water 40 m above seafloor) and a turbidity sensor (150 m above seafloor) was deployed at 300 m southeast of the active Wocan-1 hydrothermal field for 18 months. We employed 16S rRNA gene high-throughput sequencing to study the diversity and spatio-temporal variations of archaeal communities in the samples on the monthly scale.[Results] The abundance of hydrothermal plume-associated archaea including Thermoplasmata, Methanosarcinia, and Methanobacteria increased when turbidity anomalies were higher. Spatially, the archaeal community structures in the hydrothermal plume and near-bottom water were similar at the phylum and class levels but showed differences at the order level. The relative abundance of Thermoplasmata was generally higher in the plume, whereas ammonia-oxidizing archaea and Methanosarcinia were more abundant in the near-bottom water. [Conclusion] Both the hydrothermal plume and the near-bottom water from 300 m southeast of the Wocan-1 hydrothermal field were affected by hydrothermal fluids, with the plume layer being more significantly affected. The near-bottom layer was affected by re-suspended sediments in addition to hydrothermal fluids. Dynamic changes of hydrothermal contributions and re-suspension of sediments were probably the main factors responsible for the spatial and temporal heterogeneity of archaeal communities. This study gives insights into the structure and spatio-temporal evolution of the archaeal community in the hydrothermal-influenced zone on a monthly scale.