An Integrative Model of Carbon and Nitrogen Metabolism in a Common Deep-Sea Sponge (Geodia barretti)

• Published in: Frontiers in Marine Science
• Main Authors: de Kluijver, Anna, Bart, Martijn C, van Oevelen, Dick, de Goeij, Jasper M, Leys, Sally P, Maier, Sandra R, Maldonado, Manuel, Soetaert, Karline, Verbiest, Sander, Middelburg, Jack J
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Zenodo 2021
• Subjects: allometry; metabolic network model; sponge holobiont metabolism; production; biogeochemistry; chemoautotrophy; sponge ground; LIM; European Union (EU); Horizon 2020; Grant Agreement No 679849; Deep-sea Sponge Grounds Ecosystems of the North Atlantic: an integrated approach towards their preservation and sustainable exploitation; SponGES; North Atlantic
• Online Access: https://doi.org/10.3389/fmars.2020.596251

ABSTRACT Deep-sea sponges and their microbial symbionts transform various forms of carbon (C) and nitrogen (N) via several metabolic pathways, which, for a large part, are poorly quantified. Previous flux studies on the common deep-sea sponge Geodia barretti consistently revealed net consumption of dissolved organic carbon (DOC) and oxygen (O 2 ) and net release of nitrate (NO − 3 ). Here we present a biogeochemical metabolic network model that, for the first time, quantifies C and N fluxes within the sponge holobiont in a consistent manner, including many poorly constrained metabolic conversions. Using two datasets covering a range of individual G. barretti sizes (10–3,500 ml), we found that the variability in metabolic rates partially resulted from body size as O 2 uptake allometrically scales with sponge volume. Our model analysis confirmed that dissolved organic matter (DOM), with an estimated C:N ratio of 7.7 ± 1.4, is the main energy source of G. barretti. DOM is primarily used for aerobic respiration, then for dissimilatoryNO − 3 reduction to ammonium (NH + 4 )(DNRA), and, lastly, for denitrification. Dissolved organic carbon (DOC) production efficiencies (production/assimilation) were estimated as 24 ± 8% (larger individuals) and 31 ± 9% (smaller individuals), so most DOC was respired to carbon dioxide (CO 2 ), which was released in a net ratio of 0.77–0.81 to O 2 consumption. Internally producedNH + 4 from cellular excretion and DNRA fueled nitrification. Nitrification-associated chemoautotrophic production contributed 5.1–6.7 ± 3.0% to total sponge production. While overall metabolic patterns were rather independent of sponge size, (volume-)specific rates were lower in larger sponges compared to smaller individuals. Specific biomass production rates were 0.16% day –1 in smaller compared to 0.067% day –1 in larger G. barretti as expected for slow-growing deep-sea organisms. Collectively, our approach shows that metabolic modeling of hard-to-reach, deep-water sponges can be used to predict ...