Fig 1.
ROV-based images of the wood experiments.
Photos portray the condition of the wood experiments during the deployment and sample recovery in the (a–i) Eastern Mediterranean sea (Central Province) and the (j–k) Norwegian sea (HMMV). Pictures a, c, d, f, g, i, j, k reprinted with permission from MARUM, University Bremen, Germany. Pictures b, e, h reprinted from [14] under a CC BY license, with permission from PLOS ONE, original copyright 2013.
Table 1.
Location of wood experiments in the Norwegian and the Eastern Mediterranean deep sea, description of the benthic habitats and date of deployment and samplings events.
Table 2.
List of the most prominent and abundant fauna colonizing the wood experiments in the Norwegian and Eastern Mediterranean Sea.
Fig 2.
A close-up of wood logs colonized by wood-boring bivalves.
Photos depict prominent differences in the degradation of wood experiments by wood-boring bivalves in the Norwegian (a) and Eastern Mediterranean Sea (b). Burrows with calcareous linings built by Xyloredo ingolfia at the Norwegian Sea wood experiment are visible on the left panel (a). The right panel shows the burrows of Xylophaga spp., which produce large quantities of wood chips (see Fig 1).
Fig 3.
NMDS analysis revealing temporal variations in the bacterial community structure, based on ARISA.
The Eastern Mediterranean Sea NMDS analysis (a) includes samples derived from EMed-CP-wood#1, EMed-CP-wood#2, EMed-CP-wood#5, immersed for one and three years, EMed-CP-wood#6 submerged for one day and two years, and EMed-CP-wood#7 deployed for one day in the Central Province. The Norwegian Sea NMDS analysis (b) includes samples from NorS-HMMV-wood#1 immersed for two and three years. Samples are color coded according to immersion time. Convex hulls depict significant differences between the groups, as determined by the analysis of similarity (ANOSIM R = 1, Bonferroni corrected p < 0.01, see also S4 Table).
Fig 4.
Temporal variation in the taxonomical composition of bacterial classes during three years of submergence.
For the first two bars, data from all wood experiments (EMed-CP-wood#1, EMed-CP-wood#2 and EMed-CP-wood#5) of the Central Province in the Eastern Mediterranean immersed for one (Y1) and three (Y3) years, respectively, were pooled together.
Fig 5.
Spatial variations in the wood-associated bacterial community structure.
3D NMDS analysis (Bray-Curtis dissimilarity) (a) and percentage of shared 454 OTU0.03 (lower triangle) and ARISA OTUs (upper triangle) (b), depicting spatial variations in the structure of wood bacterial communities (immersed for 3 years) between wood experiments of different geographic regions i.e. Central Province, Amon Mud Volcano and the Håkon Mosby Mud Volcano. ARISA data used for the NMDS analysis includes samples of the following wood experiments: EMed-CP-wood#1-Y3, EMed-CP-wood#2-Y3, EMed-CP-wood#5-Y3, EMed-AMV-wood#3-Y3, EMed-AMV-wood#4-Y3 and the NorS-HMMV-wood#1-Y3). The complete 3D NMDS configuration is displayed in S4 Fig.
Fig 6.
Taxonomical comparison of bacterial communities at the class (a) and genus (b) level. Analysis reveal spatial variations in the wood-associated bacterial communities immersed for 3 years between experiments at the Central Province (CP), Amon Mud Volcano (Amon) and Håkon Mosby Mud Volcano (HMMV). (a) Depicts the five and (b) the ten most sequence-abundant classes and genera, respectively, given as percentages. For this analysis sample of wood experiments deployed in the same province were pooled together. See also S6 Table for more details.
Fig 7.
NMDS analysis depicting differences in the structure between wood and sediment bacterial communities.
Analysis were performed using Bray-Curtis dissimilarity based on the ARISA dataset. “At wood” (open symbols) and “Away wood” (closed symbols) samples changed with time in (a) EMed-CP-wood#1 and (b) EMed-CP-wood#5 experiments. Communities sampled after 1y of immersion are colored in black and communities after 3y in red. Different symbols of the sediment communities refer to the depth horizon sampled (circle = 0–1 cm, triangle = 1–2 cm, square = 4–5 cm and rhomb = 9–10cm), while wood samples are depicted with an asterisk. Note that topmost surface 0–2 cm “At wood” samples (open symbols) contained variable amounts of wood-chips mixed with sediment. NMDS plot (a) stress = 18% and NMDS plot (b) stress = 7.5%. Percentage of the shared ARISA OTUs between the wood and the sediment “At wood” and “Away wood” samples for the different immersion times is given in the tables below the NMDS panels. See S8 Table for associated results of the ANOSIM test.
Table 3.
Summary of biogeochemical measurements performed at wood-influenced (0.5 m–“At wood”) and reference sediments away from the wood experiments (> 10 m distance–“Away wood”) in the Eastern Mediterranean after one year of submergence (2007; [14]) and 3 years (2009, this study).
For comparison, data from surrounding seafloor sediments were included. The table combines information on the in situ Total Oxygen Uptake (TOU), in situ and ex situ Dissolved Oxygen Uptake (DOU), Oxygen Penetration Depth (OPD), total sulphide flux as determined ex situ with microsensors and ex situ average Sulphate Reduction (SR) rates integrated over 0–10 cm. n.d. = not determined.
Fig 8.
Microsensor measurements of oxygen concentrations at wood influenced sediments.
Measurements were performed at EMed-CP-At-wood#1 (a, b) and EMed-CP-At-wood#5 (c, d) sediments after 1 year (a, c) and 3 years (b, d). Oxygen measurement in (b) was performed in situ and in (a, c, d) ex situ. The sediment surface is indicated with dashed black line, denoting the boarder between the wood chip (brown color) and sediment layer (olive green color).