Kleptoplastic foraminifera: a trophic strategy of life

Foraminifera are single-celled organisms, and part of protists. They are present in all types of environments, though most foraminifera are marine benthic and are found from the deep ocean to the intertidal zone. Thus, foraminifera are subjected to various environmental stresses, (natural or anthropogenic). Because of their rapid response to stresses and their strong resistance, foraminifera are studied as paleo-environmental indicators. However, little is currently known about their biology, and specifically their metabolism and physiology. Some foraminifera species are notably known to retain, in their cytoplasm, chloroplasts from diatom preys. This phenomenon is called kleptoplasty. It has been shown that kleptoplasts remain intact and photosynthetically functional from a few days to several weeks, depending of the foraminiferal species and abiotic factors as light. In order to better understand this life strategy and the advantages provided to foraminifera by kleptoplasty in a coastal mudflat environment, we study metabolism of kleptoplastic and non-kleptoplastic species.

The “Mudsurv” (Mudflat survey, OSUNA) project initiated in 2016 a monitoring of the foraminiferal fauna and sediment geochemistry of Bourgneuf Bay (French Atlantic Coast). The main foraminiferal species observed were: Ammonia sp. T6, Elphidium oceanense and a kleptoplastic specie, Haynesina germanica. We therefore set up a monthly monitoring of respiration and photosynthesis of those kleptoplast and non-kleptoplast foraminifera species. The oxygen production or consumption is measured by microelectrodes in light and darkness. Preliminary results suggest a seasonality of photosynthesis in kleptoplast foraminifera. A second approach, using gas chromatography-mass spectrometry (GC-MS)-based experiments, provided us with the first’s foraminifera metabolomes highlighting kleptoplast species metabolic specificities.