Differential recycling of coral and algal dissolved organic matter via the sponge loop
Rix, L.; de Goeij, J.M.; Van Oevelen, D.; Struck, U.; Al-Horani, F.A.; Wild, C.; Naumann, M.S. (2017). Differential recycling of coral and algal dissolved organic matter via the sponge loop. Funct. Ecol. 31(3): 778-789. dx.doi.org/10.1111/1365-2435.12758
1. Corals and macroalgae release large quantities of dissolved organic matter (DOM), one ofthe largest sources of organic matter produced on coral reefs. By rapidly taking up DOM andtransforming it into particulate detritus, coral reef sponges are proposed to play a key role intransferring the energy and nutrients in DOM to higher trophic levels via the recently discoveredsponge loop. DOM released by corals and algae differs in quality and composition, butthe influence of these different DOM sources on recycling by the sponge loop has not beeninvestigated.2. Here, we used stable isotope pulse-chase experiments to compare the processing of naturallysourced coral- and algal-derived DOM by three Red Sea coral reef sponge species: Chondrillasacciformis, Hemimycale arabica and Mycale fistulifera. Incubation experiments were conductedto trace 13C- and 15N-enriched coral- and algal-derived DOM into the sponge tissueand detritus. Incorporation of 13C into specific phospholipid-derived fatty acids (PLFAs) wasused to differentiate DOM assimilation within the sponge holobiont (i.e. the sponge host vs. itsassociated bacteria).3. All sponges assimilated both coral- and algal-derived DOM, but incorporation rates weresignificantly higher for algal-derived DOM. The two DOM sources were also processed differentlyby the sponge holobiont. Algal-derived DOM was incorporated into bacteria-specificPLFAs at a higher rate while coral-derived DOM was more readily incorporated into spongespecificPLFAs. A substantial fraction of the dissolved organic carbon (C) and nitrogen (N)assimilated by the sponges was subsequently converted into and released as particulate detritus(15–24% C and 27–49% N). However, algal-derived DOM was released as detritus at a higherrate.4. The higher uptake and transformation rates of algal- compared with coral-derived DOMsuggest that reef community phase shifts from coral to algal dominance may stimulate DOMcycling through the sponge loop with potential consequences for coral reef biogeochemicalcycles and food webs.
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