ALBERT

Description: Seamounts represent ideal systems to study the influence and interdependency of environmental gradients at a single geographic location. These topographic features represent a prominent habitat for various forms of life, including microbiota and macrobiota, spanning benthic as well as pelagic organisms. While it is known that seamounts are globally abundant structures, it still remains unclear how and to which extend the complexity of the seafloor is intertwined with the local oceanographic mosaic, biogeochemistry and microbiology of a seamount ecosystem. Along these lines, the present study aimed to explore whether and to which extend seamounts can have an imprint on the microbial community composition of seawater and of sessile benthic invertebrates, sponges. For our high-resolution sampling approach of microbial diversity (16S rRNA gene Amplicon sequencing) along with measurements of inorganic nutrients and other biogeochemical parameters, we focused on the Schulz Bank seamount ecosystem, a sponge ground ecosystem which is located on the Arctic Mid-Ocean Ridge. Seawater samples were collected at two sampling depths (mid-water: MW, and near-bed water: BW) from a total of 19 sampling sites. With a clustering approach we defined microbial micro-habitats within the pelagic realm at Schulz Bank, which were mapped onto the seamount's topography, and related to various environmental parameters (such as suspended particulate matter (SPM), dissolved inorganic carbon (DIC), silicate (SiO4−), phosphate (PO43−), ammonia (NH4+), nitrate (NO32−), nitrite (NO2), depth, and dissolved oxygen (O2)). The results of our study reveal a seamount effect (sensu stricto) on the microbial mid-water pelagic community up to approximately 200 m above the seafloor. Further, we observed a strong spatial heterogeneity in the pelagic microbial landscape across the seamount, with planktonic microbial communities reflecting oscillatory and circulatory water movements, as well as processes of bentho-pelagic coupling. Depth, NO32−, SiO4−, and O2 concentrations differed significantly between the determined pelagic microbial clusters close to the seafloor (BW), suggesting that these parameters were presumably linked to changes in microbial community structures. Secondly, we assessed the associated microbial community compositions of three sponge species along a depth gradient of the seamount. While sponge-associated microbial communities were found to be mainly species-specific, we also detected significant intra-specific differences between individuals, depending on the pelagic near-bed cluster they originated from. The variable microbial phyla (i.e. phyla which showed significant differences across varying depth, NO32−, SiO4−, O2 concentrations and different from local seawater communities) were distinct for every sponge-species when considering average abundances per species. Variable microbial phyla included representatives of both, those taxa traditionally counted to the variable community fraction, as well as taxa counted traditionally to the core community fraction. Microbial co-occurrence patterns for the three examined sponge species Geodia hentscheli (demosponge, HMA), Lissodendoryx complicata (demosponge, most likely LMA), and Schaudinnia rosea (Hexactinellida, most likely LMA) were distinct from each other. Over all, this study shows that topographic structures such as the Schulz Bank seamount can have an imprint (seamount effect sensu lato) on both, the microbial community composition of seawater and of sessile benthic invertebrates such as sponges by an interplay between the geology, physical oceanography, biogeochemistry and microbiology of seamounts.

Description: This is community, environmental, and nutrient data collected from two ROV video transects and two respective CTD casts taken of Sognefjord during a SponGES cruise with the RV G.O. Sars and ROV Ægir 6000 in July 2017.

Description: In 2014, two experimental Agassiz trawls were conducted on the Schulz Bank; one at the summit (568–670 m depth) and one on the southwestern flank (1,464 m depth). The 3-m-wide Agassiz trawl, with a 1 cm mesh size in the cod-end, was towed along the seafloor for 676 m on the summit and 441 m on the flank, resulting in a disturbed area of 2,028 and 1,323 m2, for the summit and flank, respectively. Towing speed was maintained at around 2 knots and the initial and final position were recorded. In August 2018, the two trawl marks and four additional control transects (one on either side of the trawl mark) were surveyed while onboard the R/V G.O.Sars. Video recordings were taken along the trawl marks and control transects with the ROV AEGIR6000. Control transects were located 50 m to the east and west of each trawl mark and were performed parallel to the mark.

Description: In 2014, two experimental Agassiz trawls were conducted on the Schulz Bank; one at the summit (568–670 m depth) and one on the southwestern flank (1,464 m depth). The 3-m-wide Agassiz trawl, with a 1 cm mesh size in the cod-end, was towed along the seafloor for 676 m on the summit and 441 m on the flank, resulting in a disturbed area of 2,028 and 1,323 m², for the summit and flank, respectively. Towing speed was maintained at around 2 knots and the initial and final position were recorded. In August 2018, the two trawl marks and four additional control transects (one on either side of the trawl mark) were surveyed while onboard the R/V G.O.Sars. Video recordings were taken along the trawl marks and control transects with the ROV AEGIR6000. Control transects were located 50 m to the east and west of each trawl mark and were performed parallel to the mark.