Host influenced geochemical signature in the parasitic foraminifer Hyrrokkin sarcophaga

Here, we present element to Ca ratios (Mg/Ca, Sr/Ca, Na/Ca and Mn/Ca) and stable isotope data (δ18O, δ13C) of the parasitic foraminifer Hyrrokkin sarcophaga, collected from two different host organisms, Desmophyllum pertusum - a cold-water coral commonly found in cold-water coral reefs and Acesta excavata - a bivalve associated with cold-water coral reefs. Our results reveal that the geochemical signature in H. sarcophaga is influenced by the host organism. Sr/Ca ratios are 1.1 mmol mol-1 higher in H. sarcophaga that infest D. pertusum, which could be an indication that dissolved host carbonate material is utilised in shell calcification. Similarly, we measured 3.1 ‰ lower δ13C and 0.3 ‰ lower δ18O values in H. sarcophaga that lived on D. pertusum, which might be caused by the direct uptake of the host’s carbonate material with a more negative isotopic composition. Moreover, we observe higher Mn/Ca ratios in foraminifera that lived on A. excavata but did not penetrate the host shell compared to specimen that did. H. sarcophaga is therefore, unlikely to be a reliable indicator of paleoenvironmental conditions using Sr/Ca, Mn/Ca, δ18O or δ13C unless the host organism is known and its geochemical composition can be accounted for. Still, these results provide interesting insights in the calcification process of these specialized foraminifera.