Corals are able to conserve and recycle inorganic nutrients due to their photosynthesizing symbionts, the zooxanthellae. However it has been demonstrated that sponges are the main producers of considerable amounts of ammonium, nitrate and nitrite in coral reefs contributing to a far greater extent to the recycling of nitrogenous nutrients than corals. The present study examined if sponges and corals are competing for nutrient sources or if sponges support corals in terms of nutrient supply. The study investigated if sponges have an influence on the “well-being” of corals by releasing additional nutrients. For this purpose corals and sponges were incubated separately and together in either artificial seawater or artificial seawater enriched with cyanobacteria and nutrients (ammonium and nitrate). Changes in dissolved inorganic nutrients, in total nitrogen (TN) and in dissolved and total organic carbon (DOC/TOC) were measured and compared between the different treatments. Before and after each incubation, the photophysiological response of the coral symbionts was measured with pulse amplitude modulated (PAM) fluorometry. An accumulation of nitrate was detected when sponges alone were incubated in water enriched with cyanobacteria and nutrients. This accumulation was not found in incubations of corals alone or corals and sponges together. Besides, the maximum quantum yield (MQY) of the coral symbionts was significantly higher in the presence of a sponge. These results indicate that corals may directly benefit from the additional nutrients released by the sponges.