Foraminifera-sponge interactions – commensalism to parasitism in the Norwegian-Greenland Sea

This is the first study on the interactions between foraminifera and sponges. Although Cibicides and Hyrrokin are regarded as parasites on siliceous sponges, it is not yet clarified whether foraminifera specifically colonize sponges or are accidentally sucked in during the pelagic stage. To better elucidate these relationships, 12 sponges of different genera were examined and their foraminiferal communities analyzed. In 2018, the sponges for this study were collected with a ROV in water depths of 223 to 625 m in the Norwegian-Greenland Sea. Sponge parts were preserved in ethanol (96 %) and stained with Rose Bengal (2g l^-1) to allow a differentiation between the living and dead foraminiferal fauna.

Each sponge sample contained several hundred live and dead foraminiferal individuals of up to 60 different species. Even on Geodia baretti, which is able to release barettin to avoid colonalisation of other organisms, few foraminiferal individuals were observed. On all sponges, the most abundant genus was Cibicides, with Cibicides lobatulus and Cibicides refulgens as the most common taxa. Other very common species were Discorbinella bertheloti or Epistominella nipponica. Also, Hyrrokkin sarcophaga was found on different sponges and following its lifestyle, penetrating the sponge surfaces. The fact that besides adult foraminifera splendid juvenile stages were found indicate that foraminifera reproduced while inside the sponges. This reproduction might be stimulated/triggered by enhanced food availability by the pumping sponge.

In summary, sponges are a special habitat for a high number of foraminiferal taxa. Their interaction ranges from parasitic lifestyle up to reproduction purposes. All these aspects highlight the importance of foraminifera-sponge interactions.