Description: Video showing release of embryos (em) from a Craniella zetlandica specimen upon sampling by remotely operated vehicle at 225 m depth in Stjernsund, Northern Norway (70.2707 °N, 22.4778 °E). The footage was recorded on 2018-08-13 at 10:50 UTC by ROV Ægir (University of Bergen) during the research cruise GS2018108 onboard RV G.O. Sars (dive identifier GS2018108-78-ROV-52).

Description: Connectivity is a fundamental process driving the persistence of marine populations and their adaptation potential in response to environmental change. In this study, we analysed the population genetics of two morphologically highly similar deep-sea sponge clades (Phakellia hirondellei and the 'Topsentia-and-Petromica (TaP)' clade) at three locations in the Cantabrian Sea. Sponge taxonomy was assessed by spicule analyses, as well as by 18S sequencing and COI sequencing. The corresponding host microbiome was analysed by 16S rRNA gene sequencing. In addition we set up an oceanographic modelling framework, for which we used seawater flow cytometry data (derived from bottom depths of CTD casts) as ground-truthing data.

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: Pteropods are important organisms in high-latitude ecosystems, and they are expected to severely suffer from climate change in the near future. In this study, sedimentation patterns of two pteropod species, the polar Limacina helicina and the subarctic boreal L. retroversa, are presented. Time series data received by moored sediment traps at the Long-Term Ecological Research (LTER) Observatory HAUSGARTEN in eastern Fram Strait were analyzed during the years 2008 to 2012. Results were derived from four different deployment depths (~200, 1,250, 2,400, and 2,550 m) at two different sites (79° N, 04°20' E; 79°43' N, 04°30' E). A species-specific sedimentation pattern was present at all depths and at both sites showing maximal flux rates during September/October for L. helicina and in November/December for L. retroversa. The polar L. helicina was outnumbered by L. retroversa (55-99 %) at both positions and at all depths supporting the recently observed trend toward the dominance of the subarctic boreal species. The largest decrease in pteropod abundance occurred within the mesopelagic zone (~200-1,250 m), indicating loss via microbial degradation and grazing. Pteropod carbonate (aragonite) amounted up to ~75 % of the total carbonate flux at 200 m and 2-13 % of the aragonite found in the shallow traps arrived at the deep sediment traps (~160 m above the seafloor), revealing the significance of pteropods in carbonate export at Fram Strait. Our results emphasize the relevance and the need for continuation of long-term studies to detect and trace changes in pteropod abundances and community composition and thus in the vertical transport of aragonite.