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Hudspith M, van der Sprong J, Rix L, Víg D, Schoorl J, de Goeij JM
Quantifying sponge host and microbial symbiont contribution to dissolved organic matter uptake through cell separation
Sponge-microbe symbioses underpin the functioning and ecological success of sponges from shallow to deep seas. Sponges can consume dissolved organic matter (DOM), which is generally considered a microbially-mediated process. But what is the role of host and symbiont in DOM processing? Here, we quantified DOM uptake by sponge cells and microbial cells of the coral reef sponges Haliclona vansoesti and Scopalina ruetzleri, which host only sparse symbiont communities. Sponge cells were responsible for the vast majority (99 %) of DOM uptake. Over time, DOM-derived nitrogen was transferred from sponge cells to microbial symbionts, indicating that symbionts recycle nitrogenous waste products of the host. Therefore, sponges that lack abundant symbionts likely ‘drink’ precious sugars, whereas symbionts help retain nutrients in an otherwise food-poor environment.