Biogeochemical characteristics and microbial response to indicate degradation of organic matter around Pair-summit Seamounts in the Tropical Western Pacific Ocean

Abstract

The ecological knowledge of seamounts has accumulated plentifully in recent years. However, there are few studies on the distribution and degradation pattern of organic matter in seamounts morphology by using microorganisms and nutrients as indicators. In this research, we investigated the dynamic distribution of nutrients, particulates and microbial communities of the summits, flanks and base in the M5 Pair-summit Seamount, aiming to better understand the distribution and degradation pattern of organic matter around the seamount. The results indicate that TOC concentration presented a gradual decrease from summit to base, and obtained the lowest value at Base1 (0.65 mg L−1). Illumina Hiseq high-throughput sequencing analysis shows that Firmicutes (38.86%) and Bacteroidetes (6.86%) on the seamount Base1 obtained the highest relative abundance, which were related to the degradation of organic matter caused by denitrification. The distribution of organic matter and composition of microbial communities formed disparity due to the morphology of seamounts. In addition, shallow seamounts and deep seamounts exhibited a high degree of temporal and spatial specificity. Summit1 produced organic matter from phytoplankton, with the highest TOC content (1.23 mg L−1), dominated in microorganisms of Cyanobacteria (18.06%), and an upwelling of nutrients due to the “seamount effect”. However, Summit2 utilized nitrifying bacteria Taumarchaeota to degrade organic matter. This research suggests that the unique topographic features of seamounts is essential to sustain the surrounding microbial composition and hydrodynamics, which can further promote the study of seamount ecological environment.