Sponges (Porifera) and eukaryotic, unicellular plankton: A case study on Aplysina aerophoba, Nardo 1886 in the Northern Adriatic

Sponges (Porifera), in general, are pumping water through their bodies. This water contains planktonic eukaryotic and procaryotic organisms as well as particulate and dissolved organic matter as potential food source. We analyzed the eukaryotic unicellular plankton fraction from water surrounding sponges of the species Aplysina aerophoba, Nardo 1886, from sponge tissue, as well as from water expelled from those sponges. We found sponges without any remnants of plankton in their tissue, as well as specimens which incorporated high numbers of remnants of organisms after planktonic “blooms”. In laboratory experiments, sponges were not showing any uptake of plankton from their surrounding water. Sponges are generally considered as inner filter feeders. However, our results indicate that eukaryotic unicellular plankton organisms are not the main food resource of the common sponge A. aerophoba. This raises the question if filter feeding is actually the main characteristic of the poriferan lifestyle.