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. 2015 Jun;9(6):1306-18.
doi: 10.1038/ismej.2014.217. Epub 2014 Dec 12.

Spatial scales of bacterial community diversity at cold seeps (Eastern Mediterranean Sea)

Petra Pop Ristova  1 , Frank Wenzhöfer  1 , Alban Ramette  2 , Janine Felden  1 , Antje Boetius  1
Affiliations

Spatial scales of bacterial community diversity at cold seeps (Eastern Mediterranean Sea)

Petra Pop Ristova et al. ISME J. 2015 Jun.

Abstract

Cold seeps are highly productive, fragmented marine ecosystems that form at the seafloor around hydrocarbon emission pathways. The products of microbial utilization of methane and other hydrocarbons fuel rich chemosynthetic communities at these sites, with much higher respiration rates compared with the surrounding deep-sea floor. Yet little is known as to the richness, composition and spatial scaling of bacterial communities of cold seeps compared with non-seep communities. Here we assessed the bacterial diversity across nine different cold seeps in the Eastern Mediterranean deep-sea and surrounding seafloor areas. Community similarity analyses were carried out based on automated ribosomal intergenic spacer analysis (ARISA) fingerprinting and high-throughput 454 tag sequencing and were combined with in situ and ex situ geochemical analyses across spatial scales of a few tens of meters to hundreds of kilometers. Seep communities were dominated by Deltaproteobacteria, Epsilonproteobacteria and Gammaproteobacteria and shared, on average, 36% of bacterial types (ARISA OTUs (operational taxonomic units)) with communities from nearby non-seep deep-sea sediments. Bacterial communities of seeps were significantly different from those of non-seep sediments. Within cold seep regions on spatial scales of only tens to hundreds of meters, the bacterial communities differed considerably, sharing <50% of types at the ARISA OTU level. Their variations reflected differences in porewater sulfide concentrations from anaerobic degradation of hydrocarbons. This study shows that cold seep ecosystems contribute substantially to the microbial diversity of the deep-sea.

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Figures

Figure 1
Figure 1
Overview maps of all three investigated cold seep regions, including seep and non-seep sites in the Eastern Mediterranean Sea (a) the Amsterdam MV (b), the Pockmark area (c), and Amon MV (d). The main sampling and measurement sites are depicted with symbols, that is, push core and multicore sampling (green triangles), benthic chamber incubations (yellow squares) and microprofiler measurements (black circles).
Figure 2
Figure 2
Underwater photographs of reduced seep habitats investigated in this study: Upper panel (a, b, c) photographs were taken at the Amon MV and lower panel (d) photographs at the Amsterdam MV and (e, f) at a Pockmark seep. (a) Center of the Amon MV characterized by gassy sediments and patchy bacterial mats, (b, c) a lateral mud flow with extensive bacterial mats at the outer rim of the volcano. (d) Typical methane-seeping habitat marked by black sediment patches encountered at the Amsterdam MV. Overview (e) and a more detailed photo (f) of a bacterial mat habitat at the Pockmark cold seep.
Figure 3
Figure 3
Plots of porewater concentration profiles at methane-seeping, reduced sites (a–c; Pock_seep_1) and at nearby non-seep sites from the Pockmark region (d–f; Pock_non-seep_1). (a, d) Depth profiles of total sulfide (closed circles) and sulfate concentrations (open circles); (b, e) DIC concentration (open circles) and alkalinity (closed circles); (c, f) in situ oxygen concentration determined with microsensors, the insert in panel (c) shows the same profile at higher depth resolution. Further detailed geochemistry plots of all regions can be found in the Supplementary Figures S1–S5.
Figure 4
Figure 4
Non-metric multidimensional scaling analysis depicting differences in the bacterial community structure between seep (black symbols) and non-seep sites (red symbols) of three cold seep regions, as derived from ARISA-based data. Convex hulls depict significant differences between the groups, as determined by analysis of similarity (R=0.8, Bonferroni's P=0.001). Pooled (0–5 cm) samples per site were used to calculate Bray–Curtis dissimilarity matrix.
Figure 5
Figure 5
Non-metric multidimensional scaling analysis plots (based on Bray–Curtis dissimilarity) depicting differences in the bacterial community structure between different seep regions, as calculated from depth-pooled ARISA (a) and 454 MPTS (b), as well as depth-unpooled ARISA data (c). Seep sites are colored according to the seep region: Amsterdam MV sites in red, Amon MV sites in black, and Pockmark sites in green. Different sites within the same seep region are depicted with different symbols. Convex hulls in (c) depict significant differences between the groups, as determined by analysis of similarity (R=0.3–0.6, Bonferroni's P⩽0.003).
Figure 6
Figure 6
Plot depicting positive relation between beta-diversity (derived from ARISA) and differences in sulfate (a), sulfide (b) and DIC concentrations (c). Solid line represents a LOWESS curve (locally weighted scatterplot smoothing).
Figure 7
Figure 7
OTU accumulation curves, based on the 454 MPTS (a) and ARISA (b) data. Arrow indicates the number of seep sites needed to recover 95% of the observed OTUs.
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