Dissolved organic matter fluxes and fatty acid composition from shallow-water and deep-water demo- and hexactinellid sponges from New Zealand

Abstract

Sponges are an important component of shallow- and deep-water ecosystems enhancing eukaryotic biodiversity via diverse endo- and epibiota and by providing three dimensional habitats for benthic invertebrates and fishes. Sponge biodiversity is particularly high in the waters around New Zealand (Southwest Pacific), where we collected two shallow- and two deep-water sponge species (Tedaniasp.,Suberea meandrina,Farrea raoulensis,Artemisinasp.) forex-situincubation experiments to detect whether these sponges may process dissolved organic matter.We assessed the biochemical and phospholipid-derived fatty acids (PLFAs) and measured dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) fluxes. Changes in fluorescent dissolved organic matter (FDOM) over time were analyzed and the results were linked to the bacterial communities of the sponge holobiont.Dried sponge tissue consisted of 17.5 ± 3.75% organic (org.) C and of 4.34 ± 1.02% total nitrogen (TN) with a natural stable isotope composition of -19.0 ±0.25‰ for δ13org. C and of 10.2 ±2.43‰ for δ15TN. None of the DOC fluxes was significant and only the release of TDN byTedaniasp. was significantly different from 0 μmol TDN g org. C-1d-1. We detected the presence of four fluorophores in the FDOM pool: 2 tryptophan- and protein-like fluorophores (C1, C2), 1 humic-like fluorophore (C3), and 1 tyrosine-like fluorophore (C4). The maximum fluorescence intensity Fmaxof C1 decreased significantly inS. meandrinaincubations, whereas Fmaxof C2 grew in the same incubations. Fmaxof C3 increased inTedaniasp. incubations, in which Fmaxof C4 decreased. In comparison, Fmaxof C4 inS. meandrinarose.The PLFA composition of sponge tissue was dominated by long-chain fatty acids, saturated fatty acids, and monosaturated fatty acids and most PLFAs were sponge- and bacteria-specific. The bacterial community of the demospongesArtemisinasp.,S. meandrinaandTedaniasp. consisted mostly of Proteobacteria and Chloroflexota, whereas the dominating bacteria phylum of the hexactinellidF. raoulensiswas Proteobacteria.We proposed that the holobionts ofS. meandrinaandTedaniasp. contain bacteria that are involved in the transformation and degradation of DOM. InS. meandrina, Chloroflexota and Poribacteria may degrade tryptophan-like fluorophores to a chemically modified tryptophan-like and protein-like fluorophore, while producing a tyrosine-like fluorophore. InTedaniasp., Chloroflexota may contribute to the release of significant amounts of TDN by producing humic-like fluorophores, while degrading tyrosine-like fluorophores.Farrea raoulensismay not take up DOM due to a lack of Poribacteria and Chloroflexota or may use colloidal instead of truly dissolved DOC.