Exploring the microbial communities of ferromanganese concretions and pockmarks in the Gulf of Finland

Abstract

Ferromanganese concretions are aggregates of precipitated minerals, of which the mechanism of formation is not clear. They are found in aquatic environments and may be formed by abiotic and/or biotic processes. Pockmarks are depressions in the seafloor that can be caused by groundwater breaking through it during a process called submarine groundwater discharge. This work was conducted to assess the bacterial community composition of ferromanganese concretions and pockmark sediments using molecular biology methods and comparing them to seawater and other sediment samples from the Gulfs of Finland and Riga, and Väinameri. The concretion microbiome was significantly different from all the other sample types, as was the sediment microbiome from one pockmark site. Both microbiomes were distinguished by a high abundance of bacteria from the phylum Patescibacteria, which may be involved in the formation of concretions. Pockmark sediments from a different site resembled sediments not affected by groundwater, signifying the inactivity of this pockmark. Different layers of sediment cores were homogenous in their microbial community composition, pointing to the occurrence of sediment resuspension.