Description: Deep-sea sponge grounds are underexplored ecosystems that provide numerous goods and services to the functioning of the deep-sea. This study assessed the microbial diversity (by 16S rRNA gene amplicon sequencing) in embryos, juveniles and adults of Craniella zetlandica and Craniella infrequens, common and abundant representatives of deep-sea sponge grounds in the North Atlantic. For this study, in total 39 sponge individuals of the two sponge species were collected and analysed for their associated microbial community composition: C. zetlandica (8 adults, of which one was brooding, and 9 juveniles) and C. infrequens (8 adults, of which four were brooding, and 9 juveniles). We use the term 'juvenile' for small (i.e. mean diameter = 1 cm for C. infrequens; and maximal diameter = 0.3 cm for C. zetlandica), young individuals. For C. zetlandica, juveniles were sampled in September 2018 from an aquarium system (Bergen, Norway). C. zetlandica juveniles were smaller (and most likely younger) than the in situ sampled C. infrequens juveniles and therefore flash-frozen as a whole. Embryos of both sponge species were carefully picked out of the parent sponges with sterile spring steel forceps onboard the research vessel using a stereomicroscope. Ten whole embryos were pooled per adult sponge to account for the small biomass. Data such as presented here provide information on the recruitment of deep-sea sponge holobionts which is needed to develop integrated management tools of such vulnerable marine ecosystems.

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: Deep-sea sponge grounds are underexplored ecosystems that provide numerous goods and services to the functioning of the deep-sea. This study assessed the prokaryotic diversity in embryos, recruits, and adults of Craniella zetlandica and Craniella infrequens, common and abundant representatives of deep-sea sponge grounds in the North Atlantic. Our results reveal that symbiont transmission in the two Craniella sponge species likely occurs vertically, as highly similar microbial consortia have been identified in adults, embryos, and recruits. Moreover, transmission electron microscopy revealed high abundances of sponge-associated microorganisms, among which Chloroflexi (SAR202) were identified as common representatives by amplicon sequencing and fluorescence in situ hybridization (FISH). Equal diversity metrices, a similar overall prokaryotic community composition and a distinct dominance of the phylum Chloroflexi within all life stages are the key findings of our analyses. Information such as presented here provide understanding on the recruitment of deep-sea sponge holobionts which is needed to develop integrated management tools of such vulnerable marine ecosystems.

Description: In northern Chilean Patagonia the scleractinian cold-water coral Caryophyllia huinayensis (Cairns, Häussermann & Försterra 2005) occurs in depths from 16 m up to 265 m. Knowledge about ecological parameters and its response to environmental changes in the habitat are still rare. With global ocean warming and ongoing ocean acidification cold-water corals face possible harmful impacts. To predict the influence of these changes on C. huinayensis and other scleractinian cold-water corals growth rates, abundance, respiration rates and feeding strategies have to be known. Furthermore complex relationships within cold-water reefs need to be revealed. In order to quantify abundance frame based individual census have been carried out in two Chilean fjords. The frame based census showed that C. huinayensis can be abundant with up to 2211 ± 180 individuals per square meter and thrives on a temperature range of 9,5 to 16 °C. In the Comaufjord C. huinayensis is widespread along a natural pH gradient. Due to this natural horizontal pH gradient down to values of pH 7,4 the Comaufjord allows growth experiments in pH conditions that are predicted for the next century. For estimations of growth rates and the influence of changing water parameters on coral growth a cross transplantation experiment has been carried out. Individuals from pH 7.94 ± 0.03 and pH 7.76 ± 0.09 have been cross transplanted, respectively. With a growth rate of 3,39 ± 2,52 μmol CaCO3×cm-2×d-1 transplanted individuals under low pH conditions showed comparable growth rates with the control group under high pH conditions. Maximum growth of 3,2 mm in height and 2,1 mm in calice diameter indicate the ability of C. huinayensis for growing under pH conditions that have been suspected to be harmful for coral skeletons. Individual respiration rates have shown that oxygen consumption under conditions of pH 7,4 was increased by 250 % compared with the control group of pH 8,0. An increased energy demand under low pH conditions could indicate a physiological adaptation of C. huinayensis enabling this species to up-regulate internal pH in tissues where biologically induced calcification takes place. In vitro-feeding-experiments revealed a zooplankton uptake of two prey organisms per hour. Carbon uptake showed that the ingested food could not provide enough energy for important metabolic activities. Dissolved organic substances or other particulate matter might have an importance for nutrition of C. huinayensis. Also zooplankton-uptake might increase with higher in situ prey densities. The present study shows that the scleractinian cold-water coral C. huinayensis has the ability to cope with future acidified seawater. Deep-water coral biocenosis might face harmful impacts of a shoaling aragonite saturation horizon. Despite the potential of calcification under decreased seawater pH the dissolution of seawater-exposed aragonite structures will limit the future distribution of scleractinian cold-water corals in ocean depths.

Description: This is the first study on the interactions between foraminifera and sponges. Although Cibicides and Hyrrokin are regarded as parasites on siliceous sponges, it is not yet clarified whether foraminifera specifically colonize sponges or are accidentally sucked in during the pelagic stage. To better elucidate these relationships, 12 sponges of different genera were examined and their foraminiferal communities analyzed. In 2018, the sponges for this study were collected with a ROV in water depths of 223 to 625 m in the Norwegian-Greenland Sea. Sponge parts were preserved in ethanol (96 %) and stained with Rose Bengal (2g l-1) to allow a differentiation between the living and dead foraminiferal fauna. Each sponge sample contained several hundred live and dead foraminiferal individuals of up to 60 different species. Even on Geodia baretti, which is able to release barettin to avoid colonalisation of other organisms, few foraminiferal individuals were observed. On all sponges, the most abundant genus was Cibicides, with Cibicides lobatulus and Cibicides refulgens as the most common taxa. Other very common species were Discorbinella bertheloti or Epistominella nipponica. Also, Hyrrokkin sarcophaga was found on different sponges and following its lifestyle, penetrating the sponge surfaces. The fact that besides adult foraminifera splendid juvenile stages were found indicate that foraminifera reproduced while inside the sponges. This reproduction might be stimulated/triggered by enhanced food availability by the pumping sponge. In summary, sponges are a special habitat for a high number of foraminiferal taxa. Their interaction ranges from parasitic lifestyle up to reproduction purposes. All these aspects highlight the importance of foraminifera-sponge interactions.

Description: Foraminifera nourishing on fresh organic matter often exhibit an epibiotic or even an epizoic lifestyle. This study investigates the colonization of sponges by foraminifera. For this purpose, 12 siliceous sponges of different genera (Asconema, Geodia, Lissodendoryx and Schaudinnia) and order Haplosclerida were collected in 2018 with a ROV in water depths of 223 to 625 m in the Norwegian-Greenland Sea. Sponges were stained with a Rose Bengal/ ethanol mixture to allow a differentiation between foraminifera that had been recently alive and empty tests. Each sponge sample contained 3–42 dead and 1–10 living foraminiferal individuals per cm3 and summarizing up to 78 different taxa on one single sponge (Geodia phlegraei). Even on Geodia barretti, which is able to release barrettin (an alkaloid) to avoid colonialization by other organisms, living foraminiferal individuals (1 ind./cm3) were observed. The highest foraminiferal densities (living and dead individuals) were recorded on Haplosclerida sp. (49 ind./cm3) and Geodia sp. (45 ind./cm3). The lowest densities of foraminifera were found on G. barretti (3–14 ind./cm3) and on Lissodendoryx complicata (9 ind./cm3). The foraminiferal diversity ranges from 7.04 to 17.38 for Fisher α and from 2.40 to 3.33 (Shannon-Wiener (H)S). The highest diversity was found on G. phlegraei and the lowest one on L. complicata. This study is highlighting the ecosystem engineering role of sponges providing niche habitats for a high number of foraminifera.