Sediment interfaces; ecotones on a microbial scale

Author(s): Borchers, M. R.; Colwell, F. S.; D'Angelo, G.; Thurber, A. R.; Graw, M. F.
Author Affiliation(s): Primary:
Oregon State University, College of Earth, Ocean, and Atmospheric Science, Corvallis, OR, United States
Volume Title: AGU 2015 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2015; American Geophysical Union 2015 fall meeting, San Francisco, CA, Dec. 14-18, 2015. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Ecotones - transitions between different biomes - often support greater faunal diversity than the adjacent ecological systems. For subseafloor microorganisms, defined geological and chemical gradients have been shown to affect population sizes and community structure, but the role that sediment interfaces play is still unclear. Here, we test the hypothesis that zones of transition between two distinct sediment types increase microbial diversity and change community composition. Concurrently, we explore those factors that drive deep-subsurface microbial community structure (e.g., depth, interstitial water chemistry, methane concentrations, clay content). Samples from IODP Expedition 349 - South China Sea Tectonics - had interfaces of either ash/clay or turbidite/clay boundaries sampled, DNA extracted, and the 16S rRNA gene analyzed on an Illumina MiSeq platform. Initial analyses reveal that microbial communities in sediment samples are distinct from communities in drilling fluid, indicating that contamination is unlikely. In four of the eight complete interfaces currently analyzed we found an increase in diversity (based on the chao1 index), in certain cases doubling the diversity of the adjacent rock types. The pattern was not uniform across all interfaces. While some posit that ecotones provide a mixing of the two adjacent communities, we were surprised to find an abundance (mean = 392 OTUs) of unique microbial taxa within the ecotone itself when compared to adjacent sediment (mean=282 unique OTUs). Thus while diversity was not uniformly increased in ecotones, the interface led to divergent microbial communities that were not simply mixtures of those adjacent. We will discuss the ability of abiotic factors in explaining the among ecotone variance that we observed. Our investigation helps to characterize the factors that drive microbial community structure of the subseafloor while highlighting the need to focus on habitat heterogeneity at a scale pertinent to bacteria and archaea in studies of microbial ecology.
Year of Publication: 2015
Research Program: IODP2 International Ocean Discovery Program
Key Words: 07 Marine Geology and Oceanography; Cores; Ecology; Expedition 349; International Ocean Discovery Program; Marine sediments; North Pacific; Northwest Pacific; Pacific Ocean; Sediments; South China Sea; West Pacific
Coordinates: N125500 N183400 E1170100 E1145500
Record ID: 2016053220
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