Spatial patterns and co-occurrence networks of microbial communities related to environmental heterogeneity in deep-sea surface sediments around Yap Trench, Western Pacific Ocean.

Microbial communities are a large component of abyssal and hadal benthic environments, especially in deep-sea areas like Yap Trench, they provide a continuous source of nutrients and energy in their unique ecosystems. However, due to sampling difficulties, these microbial communities are relatively understudied. In the summer of 2017, sediment samples were collected from 21 stations around Yap Trench in the Western Pacific Ocean (mostly in the West Caroline Basin), at depths ranging from 3156 to 7837 m. Sediment samples from deep water depths and shallow water depths differed in organic matter content, median grain size, silt-clay content, and biodiversity. The structure of the microbial communities in the surface sediments had distinct relationships with environmental factors and their co-occurrence networks exhibited a clear spatial pattern. In addition, for both prokaryotes or eukaryotes, a combination of variables including silt-clay content, organic matter content, median grain size, and depth had the greatest impact on community structure. It was notable that fungi played important roles in the co-occurrence networks of deep water depth sediment samples while bacteria dominated those of shallow water depth samples. The differences in structure and ecological niches in the different networks were due to differences in sediment texture and organic matter content. Since clay had a positive effect on the diversity of bacteria, it had an indirect positive effect on fungi, leading to differences in biodiversity among different groups. More organic matter meant more nutrients were available for the growth and reproduction of microbes, which led to fewer niche overlaps. This study conducted an extensive and systematic sequencing survey of surface sediments around Yap Trench in the Western Pacific Ocean, providing insight into microbial responses to environmental heterogeneity in deep-sea benthic ecosystems.

Author Correction: Pore water pressure responses in silty sediment bed under random wave action.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Pore water pressure responses in silty sediment bed under random wave action.

We studied pore water pressure responses in silty seabed under random wave action through a series of experiments in a wide wave flume. Unlike previous experiments involving regular waves, we focus on random waves including wind-induced short waves and long waves so as to gain further insights into seabed responses and liquefaction risks posed by random waves. In particular, the study investigated how the secondary long waves that were induced by incident short wave groups affected the seabed responses. The test results revealed that these long waves could cause much larger seabed responses than the short waves (eight times larger in our flume tests). Although they had smaller wave heights than the short waves, the long waves were found to contribute much more significantly to the cumulative pore pressure than previously recognized. The likely reason is that the long waves are disproportionally effective in generating cumulative excess pore pressure, confirming qualitatively some of the earlier theoretical predictions. One of the implications from these research findings is that the existing design methods when applied to random waves could grossly underestimate liquefaction potential in silty sediment bed if either spectrum-based mean wave parameters or significant wave parameters were used.