Investigating the influence of temperature on respiration rates of the benthic foraminifer Nonionella sp. T1

With the warmest year on record and heating of oceans all over the world, it is of increasing interest how marine organisms adapt to these changing conditions. Benthic foraminifera are important components of marine ecosystems, contributing to biogeochemical cycling and serving as indicators of environmental change. Gaining knowledge of their role in energy and nutrient flows leads to a better understanding of ecosystem functioning. In this study we investigated oxygen respiration rates of the potentially invasive benthic foraminifer Nonionella sp. T1 originating from sediments within the Gullmar Fjord and cultivated in artificial sea water (ASW) in the laboratory at the University of Vienna. Nonionella sp. T1 was incubated at two different temperatures: 12 °C closely resembling natural fjord conditions and 20 °C simulating thermal stress to the foraminifers. Additionally, the influence of light on this species’ oxygen consumption was tested because it is known to harbour kleptoplasts (= functioning chloroplasts from algal food source), but little information exists about kleptoplast potential photosynthetic activity. Prior to the experiment, foraminifers were fed with the living diatom Phaeodactylum tricornutum, which is also used as food source for the culture. A non-invasive method was used to analyze oxygen respiration rates. The method involved placing an Oxygen Sensor Spot in a small, 2.5 ml airtight glass vial filled with ASW alongside the foraminifera. Oxygen concentrations under dark and light conditions and at 12 °C and 20 °C, respectively, were documented using an Oxygen Microsensor. We used a large number (n = 100, triplicates) of cleaned, living specimens. Respiration rates are given in µmol O₂/h calculated for biovolume (µm³) which was assessed for each individual using photo microscopy. The measured oxygen respiration rates under dark conditions at 12 °C fall within the upper range of previously observed foraminiferal respiration rates. Lower respiration rates during light exposure indicate oxygen production which is likely related to the activity of kleptoplasts. The pending results of the experiment at 20 °C will show if respiratory activity of Nonionella sp. T1 will increase with temperature and if the efficiency of oxygen production of their kleptoplasts is temperature-dependent.