Research ArticleAPPLIED ECOLOGY

Effects of a deep-sea mining experiment on seafloor microbial communities and functions after 26 years

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Science Advances  29 Apr 2020:
Vol. 6, no. 18, eaaz5922
DOI: 10.1126/sciadv.aaz5922
  • Fig. 1 Photographs of the sampling sites.

    (A) DEA plough track (photo credit: ROV Kiel 6000 Team, GEOMAR), showing the different microhabitat samples; (B) EBS track [photo credit: Ocean Floor Observation System (OFOS), Alfred-Wegener Institute (AWI)]; and (C) the Reference (photo credit: ROV Kiel 6000 Team, GEOMAR). (D to F) Schematic representation of the sampling design (A) and different microhabitats observed (photo credit: Autun Purser).

  • Fig. 2 CT scan results of representative sediment cores from different microhabitats.

    (y axis ± 2 cm) showing (A) bioturbation channels (green), manganese nodules (yellow), and cracks (black/dark-gray), and (B) middle layer of the CT showing the sediment densities (x-ray attenuation) with higher densities appearing lighter.

  • Fig. 3 Sediment characteristics of the different microhabitats.

    Boxplots show the median (horizontal line), interquartile ranges (box limits), range (whiskers), outliers (circles), and individual data points (dots). Significant differences from the reference are indicated with an asterisk (test statistics in table S1). The colors represent the different sampling sites: reference station (green); outside the DEA tracks (yellow); DEA track furrows, ridges, and subsurface patches (orange); fresh EBS track (red); and subsurface, i.e., at 14 to 16 cm bsf (gray). (A) Oxygen penetration depth (blue bar) and MnO2-rich brown layer depth (brown bar). (B) Average x-ray density (▬) and porosity at the top centimeter (󠇅■) (n = 3). (C) TIC concentrations of the top centimeter (n = 3 for EBS; others n = 9). (D) Nitrite (NO2) profiles of the cores outside the tracks, the subsurface patches, and the EBS track (n = 3).

  • Fig. 4 Biological processes and bacterial and other organic biomass.

    (A) Inorganic carbon uptake into TOC [dark CO2 fixation (DCF)], (B) dissolved oxygen uptake (DOU), and (C) potential beta-glucosidase activity as an example of potential extracellular enzyme activities (EEA) measured. Boxplots show the median (horizontal line), interquartile ranges (box limits), range (whiskers), outliers (circles), and individual data points (dots). For the station color code, see Fig. 3. Significant differences from the reference are indicated with an asterisk (test statistics in table S1). (D) Cell numbers based on AODC counts. (E) TOC (gray bar) and chlorophyll a (green bar) values at the top centimeter. Boxplots show the median (horizontal line), interquartile ranges (box limits), range (whiskers), outliers (circles), and individual data points (dots). Significant differences (Kruskal-Wallis test, P < 0.05) from the reference were indicated with an asterisk (test statistics shown in table S1). For the station color code, see Fig. 3.

  • Fig. 5 Biplots showing different community structures and environmental variables.

    (A) NMDS plots, using Bray-Curtis dissimilarities and relative untransformed OTU abundances (stress = 0.06). The colors and symbols indicate the microhabitats and sampling sites, respectively [legend of (A) valid for (A) to (C)]. The locations of the sample points relative to each other indicate their similarity. The closer the points are together, the more similar the samples are based on their community structure. (B) Redundancy analyses using different sediment characteristics to separate different sampling sites (sediment characteristics scale 5× reduced). (C) Redundancy analyses using different sediment characteristics to separate the different reference stations.

  • Fig. 6 Synthesis of the observed disturbance gradient.

    (A) Schematic representation of increasing degree of impact from left to right, i.e., green to red color. (B) Schematic summary of the differences between the different disturbance levels. (C and D) Overview of biogeochemical activity per area (C) and per cell numbers (D). Light yellow fields indicate more activity, while orange and red colors represent less activity. The distribution of relatively more and less activity can be seen in the color key histogram on top. The activity is summarized as the median of the z-scaled values (mean = 0, standard deviation = 1). Asterisks indicate significant differences from the reference sites (Kruskal-Wallis, P < 0.05; table S1).

  • Table 1 Median values (upper line) and interquartile ranges or min and max (lower line) of measured biogeochemical variables in the top centimeter of each station and at 14 to 16 cm bsf (subsurface).

    Because of only one replicate for nutrients in the EBS track, no ranges are given. TN, total nitrogen; TOC, total organic carbon; TIC, total inorganic carbon; Chla, chlorophyll a; Phaeo, phaeopigments; NO2, nitrite; NO3, nitrate; NH4+, ammonium; Fe2+, ferrous oxide; TA, total alkalinity.

    ParameterUnitReferenceOutsideFurrowRidgeSubsurface
    patch
    EBS trackSubsurface
    X-ray densityHU294314326315384390416
    292–296296–328310–339314–326363–385NA392–433
    Porosity0.930.930.920.910.920.890.88
    0.93–0.930.93–0.930.92–0.920.91–0.920.91–0.92NA0.87–0.88
    TNμgN mgSed−11.31.31.31.21.20.91.1
    1.2–1.41.0–1.41.2–1.31.2–1.31.1–1.30.9–0.90.9–1.1
    TOCμgC mgSed−19.19.18.98.28.39.27.7
    9.0–9.48.4–9.98.5–9.57.4–8.38.1–8.48.9–9.47.0–7.8
    TICμgC mgSed−100.21.31.656.75.9
    0–0.40–0.90.4–3.21.2–1.83.8–5.75.9–7.15.8–7.4
    Chlaμg ml−10.090.090.070.040.050.070.02
    0.07–0.10.07–0.090.06–0.10.04–0.060.04–0.060.08–0.080.02–0.03
    Phaeoμg ml−10.230.210.190.130.170.230.1
    0.17–0.250.15–0.270.16–0.230.11–0.140.15–0.190.22–0.240.08–0.11
    Chla, relative%26252724232522
    24–2923–3022–2822–3122–2524–2718–23
    NO2μM1.31.21.20.80.60.20.2
    1.3–2.11.0–1.51.1–1.20.4–1.00.6–2.3NA0.2–0.3
    NO3μM46.24241.940.242.137.944.8
    43.8–50.240.3–42.640.7–42.339.3–73.839.8–43.0NA43.8–72.2
    NH4+μM14.612.29.511.18.59.815.2
    8.9–40.26.1–16.47.6–12.35.7–12.97.9–16.5NA43.8–72.2
    Fe2+μM00.30.200.20.10
    0–0.10.2–0.30.14–0.480–0.20.2–0.2NA0–0.1
    TAmeq liter−12.12.32.32.22.32.22.4
    2.1–2.22.3–2.32.3–2.32.2–2.22.2–2.3NA2.4–2.4

Supplementary Materials

  • Supplementary Materials

    Effects of a deep-sea mining experiment on seafloor microbial communities and functions after 26 years

    T. R. Vonnahme, M. Molari, F. Janssen, F. Wenzhöfer, M. Haeckel, J. Titschack, A. Boetius

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    • Figs. S1 to S8
    • Tables S1 and S2

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