MEPS prepress abstract  -  DOI: https://doi.org/10.3354/meps12443

Reef sponges facilitate the transfer of coral-derived organic matter to their associated fauna via the sponge loop

Laura Rix*, Jasper M. de Goeij, Dick van Oevelen, Ulrich Struck, Fuad A. Al-Horani, Christian Wild, Malik S. Naumann

*Email: laura.n.rix@gmail.com

ABSTRACT: The high biodiversity of coral reefs results in complex trophic webs where energy and nutrients are transferred between species through a multitude of pathways. Here, we hypothesize that reef sponges convert the dissolved organic matter (DOM) released by benthic primary producers (e.g. corals) into particulate detritus that is transferred to sponge-associated detritivores via the sponge loop pathway. To test this hypothesis, we conducted stable isotope (13C and 15N) tracer experiments to investigate the uptake and transfer coral-derived organic matter from the sponges Mycale fistulifera and Negombata magnifica to two common sponge-associated detritivores: ophiuroids (Ophiothrix savignyi and Ophiocoma scolopendrina) and polychaetes (Polydorella smurovi). Findings revealed that the organic matter naturally released by the corals was indeed readily assimilated by both sponges and rapidly released again as sponge detritus. This detritus was subsequently consumed by the detritivores, demonstrating transfer of coral-derived organic matter from sponges to their associated fauna and confirming all steps of the sponge loop. Thus, sponges provide a trophic link between corals and higher trophic levels, thereby acting as key players within reef food webs.