Diversity and abundances of foraminifera in living sponges of the Norwegian-Greenland Sea

Abstract

Foraminifera nourishing on fresh organic matter often exhibit an epibiotic or even an epizoic lifestyle. This study investigates the colonization of sponges by foraminifera. For this purpose, 12 siliceous sponges of different genera (Asconema, Geodia, Lissodendoryx and Schaudinnia) and order Haplosclerida were collected in 2018 with a ROV in water depths of 223 to 625 m in the Norwegian-Greenland Sea. Sponges were stained with a Rose Bengal/ethanol mixture to allow a differentiation between foraminifera that had been recently alive and empty tests. Each sponge sample contained 3–42 dead and 1–10 living foraminiferal individuals per cm3 and summarizing up to 78 different taxa on one single sponge (Geodia phlegraei). Even on Geodia barretti, which is able to release barrettin (an alkaloid) to avoid colonialization by other organisms, living foraminiferal individuals (1 ind./cm3) were observed. The highest foraminiferal densities (living and dead individuals) were recorded on Haplosclerida sp. (49 ind./cm3) and Geodia sp. (45 ind./cm3). The lowest densities of foraminifera were found on G. barretti (3–14 ind./cm3) and on Lissodendoryx complicata (9 ind./cm3). The foraminiferal diversity ranges from 7.04 to 17.38 for Fisher α and from 2.40 to 3.33 (Shannon-Wiener (H)S). The highest diversity was found on G. phlegraei and the lowest one on L. complicata. This study is highlighting the ecosystem engineering role of sponges providing niche habitats for a high number of foraminifera.