Some benthic foraminifera have the ability to incorporate functional chloroplasts from diatoms (kleptoplasty). Our objective was to investigate kleptoplast cellular organisation, functionality (O2 flux, C and N incorporation), pigment composition and photoprotection mechanism in one shallow water benthic foraminiferal species (Haynesina germanica). Different experimental strategies (light regimes, stable isotopes) and analytical methods (TEM observations, O2 microsensor, NanoSIMS, PAM fluorometry, reflectance and HPLC pigment analysis) were used.Haynesina germanica showed net oxygen production up to 1000 pmol.O2.cell-1.day-1. Its Fv/Fm (ratio informing about photosystem II functionality) slowly decreased from 0.65 to 0.55 in 7 days in darkness and quickly decreased to 0.2 under high light (70 µmol photons.m-2.s-1). Kleptoplast functional time was estimated between 11-21 days in darkness and between 7-8 days at HL. The H. germanica cells are able to assimilate 1) labelled bicarbonate( 13C) in some chloroplasts, lipid droplets, fibrillar vacuoles; and 2) ammonium (15N), in some chloroplasts, fibrillar vacuoles, nucleus, dense bodies, crystalline structures and unidentified organelles (NanoSIMS observations coupled to TEM). Pigment composition was similar to diatoms.A “functional” xanthophyll cycle was observed on H. germanica exposed to different short term light regimes. However, on long term experiments total pigment content decreases or d by more than 50% after 5 days of starvation and then slowly decreases over time (15 days). These results showed that Haynesina germanica kleptoplasts are able to be completely functional but only over a relatively short time. This strategy may be an advantage for this species if,continuous chloroplast resupply from food source.