Nutrient fluxes, oxygen consumption and fatty acid composition from deep-water demo- and hexactinellid sponges from New Zealand
Authors: Stratmann Tanja , Busch Kathrin , de Kluijver Anna , Kelly Michelle , Mills Sadie , Rossel Sven , Schupp Peter Josef 
Published: April 2024

Sponges are an important component of deep-water ecosystems enhancing eukaryotic biodiversity by hosting diverse endo- and epibiota and providing three dimensional habitats for benthic invertebrates and fishes. As holobionts they are important hosts of microorganisms which are involved in carbon and nitrogen cycling. While increasing exploration of deep-water habitats results in new sponge species being discovered, little is known about their physiology and role in nutrient fluxes. Around New Zealand (Southwest Pacific), the sponge biodiversity is particularly high, and we selected six deep-sea sponge clusters (Saccocalyx, Suberites, Tedania, Halichondria/ Dendoricella, Sceptrulophora, Lissodendoryx) for in-situ and ex-situ experiments. We investigated the biochemical composition of the sponges, measured oxygen consumption and inorganic nutrient fluxes, as well as bacterial and phospholipid-derived fatty acid (PLFA) compositions. Our aim was to assess differences in fluxes and fatty acid composition among sponge clusters and linking their bacterial communities to nitrogen cycling processes. All sponges excreted nitrite and ammonia. Nitrate and phosphate excretion were independent of phylum affiliation (Demospongiae, Hexactinellida). Nitrate was excreted by the Halichondria/ Dendoricella and Lissodendoryx clusters, whereas the Suberites, Tedania, and Sceptrulophora clusters consumed it. Phosphate was excreted by Sceptrulophora and Halichondria/ Dendoricella clusters and consumed by all other clusters. Silicon was consumed by all sponge clusters, except for Saccocalyx and Halichondria/ Dendoricella clusters. Oxygen consumption rates ranged from 0.17 to 3.56+-0.60 mmol O2 g C d-1. The PLFA composition was very sponge-cluster dependent and consisted mostly of long-chain fatty acids. Most PLFAs were sponge-specific, followed by bacteria-specific PLFAs, and others. All sponge clusters, except for Suberites, were low-microbial abundance (LMA) sponges whose bacterial community composition was dominated by Proteobacteria, Bacteroidota, Planctomycetota, and Nitrospinota. The Suberites cluster consisted of high-microbial abundance (HMA) sponges with Proteobacteria, Chloroflexota, Acidobacteriota, and Actinobacteriota as dominant bacteria. Based on the inorganic nitrogen flux measurements, we identified three types of nitrogen cycling in the sponges: In type 1, sponges (Dendoricella spp. indet., Lissodendoryx cluster) respired aerobically and ammonificated organic matter (OM) to ammonium, fixed N2 to ammonium, and nitrified aerobically heterotrophically produced ammonium to nitrate and nitrite. In type 2, sponges (Halichondria sp., Sceptrulophora, Suberites, Tedania clusters) respired OM aerobically and ammonificated it to ammonium. They also reduced nitrate anaerobically to ammonium via dissimilatory nitrate reduction to ammonium. In type 3, ammonium was microbially nitrified to nitrite and afterwards to nitrate presumably by ammonium-oxidizing Bacteria and/ or Archaea.