Metadata and NCBI-Accession numbers of 16S data for seawater and Craniella sponges from the North Atlantic Ocean and an aquarium experiment in 2017 and 2018

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.