Living benthic foraminiferal assemblages of a transect in the Rockall Trough (NE Atlantic)

Acknowledgments The authors would like to thank the captain and the crew of the RRS Discovery cruise DY051 for their work and ship time. Many thanks go to C. Baal for his support with the SEM. Funding Information: This study was undertaken with financial support from the NERC grant ( NE/I023465/1 ) to U. Witte.Peer reviewedPublisher PD

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

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

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

The change in metabolic activity of a large benthic foraminifera as a function of light supply

Abstract We studied metabolic activity of the symbiont-bearing large benthic foraminifer Heterostegina depressa under different light conditions. Besides the overall photosynthetic performance of the photosymbionts estimated by means of variable fluorescence, the isotope uptake (13C and 15N) of the specimens (= holobionts) was measured. Heterostegina depressa was either incubated in darkness over a period of 15 days or exposed to an 16:8 h light:dark cycle mimicking natural light conditions. We found photosynthetic performance to be highly related to light supply. The photosymbionts, however, survived prolonged darkness and could be reactivated after 15 days of darkness. The same pattern was found in the isotope uptake of the holobionts. Based on these results, we propose that 13C-carbonate and 15N-nitrate assimilation is mainly controlled by the photosymbionts, whereas 15N-ammonium and 13C-glucose utilization is regulated by both, the symbiont and the host cells

Assimilation of Particular Organic Matter and Dissolved Organic or Inorganic Compounds by Cribroelphidium selseyense (Foraminifera)

Marine carbon and nitrogen processing through microorganisms’ metabolism is an important aspect of the global element cycles. For that purpose, we used foraminifera to analyze the element turnover with different algae food sources. In the Baltic Sea, benthic foraminifera are quite common and therefore it is important to understand their metabolism. Especially, Cribroelphidium selseyense, also occurring in the Baltic Sea, has often been used for laboratory feeding experiments to test their effect on carbon or nitrogen turnover. Therefore, foraminifera were collected from the Kiel Fjord and fed with six different algal species in two qualities (freeze-dried algae vs. fresh algae, all 13C- and 15N-labeled). Also, labeled dissolved inorganic C and N compounds and glucose were offered to the foraminifera to test direct assimilation of dissolved compounds (carbon and nitrogen) from the water column. Our experiments showed that after 15 days of incubation, there were highly significant differences in isotope labeling in foraminifera fed with fresh algae and dry algae, depending on algal species. Further, different algal species led to different 13C and 15N enrichment in the studied foraminifera, highlighting a feeding preference for one diatom species and an Eustigmatophyte. A significant carbon assimilation from HCO3– was observed after 7 days of incubation. The N assimilation from NH4+ was significantly higher than for NO3– as an inorganic N source. The uptake of glucose showed a lag phase, which was often observed during past experiments, where foraminifera were in a steady state and showed no food uptake at regular intervals. These results highlight the importance of food quality on the feeding behavior and metabolic pathways for further studies of foraminiferal nutrition and nutrient cycling