Quantifying rates of oxygen production and consumption in the benthic foraminifer Amphistegina lobifera at different temperatures

Abstract The benthic foraminifer Amphistegina lobifera Larsen 1976 is a major carbonate producer and an invasive species in the Mediterranean Sea, where its thermal tolerance contributes to its expansion. This study investigates A. lobifera ’s short-term response in respiration rate and photosynthetic activity across a temperature range of 16–36 °C following an acclimation period of 24 h. Oxygen consumption and production were recorded using non-invasive oxygen sensor spots, allowing for continuous measurements with minimal disturbance to the specimens. Results show a significant influence of temperature on respiration rates and photosynthetic activity. Oxygen consumption was at a minimum at 16 °C and increased with temperature, peaking at 32 °C before slightly decreasing at 36 °C. Photosynthetic rates followed a unimodal response, with peak oxygen production at 24 °C and a sharp decline at 36 °C. At this upper threshold respiration exceeded photosynthesis, indicating a decoupled response by the holobiont and its endosymbionts. As short-term thermal stress significantly influenced the holobiont’s metabolism, A. lobifera may seasonally or diurnally shift from net oxygen producer to net consumer. Given its high abundance in coastal benthic environments, this metabolic plasticity may affect benthic communities, that already suffer increasing thermal stress by globally heating waters. The study emphasises the need for further research on short-term thermal responses in benthic foraminifera and their role in oxygen cycles under ongoing climate change.