Recent coral reef bleaching, though being global and becoming chronic, is still poorly understood today. Bleaching of corals and large foraminifers involves basically the loss of their photosynthetic symbionts and/or their pigments. Though the cause is unclear, temperature, irradiation and C0₂ are assumed to be primary factors for the symbiosis rupture. In order to establish a monitoring of the vitality of the symbiotic associations, we investigated in three genera of coral reef and temperate foraminifers the behaviour of the photosynthetic apparatus of their symbionts in hospite, by means of the JlP-test. By this screening test that we widely use for studies of land plant stress, many samples can be analysed quickly as it needs a measuring time in vivo of only 1 to 5 seconds. We measured the fast polyphasic fluorescence kinetics O-J-l-P of the symbionts by a Plant Efficiency Analyser (PEA) with a 10μs time resolution and 12 bit signal resolution. The measurements can be conducted continuously even on a single cell in a test tube, as well as on the reef. The behaviour of photosystem II of the photosynthetic apparatus, being at different physiological states established by different light conditions and culture temperature, was quantified through a constellation of functional and structural parameters provided by the analysis of the fluorescence transients according to the JlP-test. We moreover induced by strong light, at each physiological state, a State-1 to State-2 transition and again followed the response of the photosynthetic apparatus by the JIP-test. The aim was to investigate whether and how adaptive processes are revealed as regulating the different parameters, in an attempt to get an insight into the capacity of foraminifers for adaptation under different conditions. We observed that the various parameters undergo modifications that differ concerning both their extent and their degree of elasticity, thus indicating that different survival strategies are employed in response to stress. We here witnessed that low light pronouncedly protects the photosynthetic apparatus against the mild warming, and in a lesser extend against the strong light stress, by reducing in some parameters the extent of their deformations and by increasing in others the elasticity of their deformations. The final goal was to correlate adaptability and resistance to bleaching and establish a rapid and easily handled test for the biomonitoring of symbiotic associations in situ. This would offer an access to the understanding of the causes of bleaching and possibly serve in foreseeing the future of reefs. A mapping of vitality in terms of performance and behaviour criteria is also proposed, which can serve for the comparison of whole reef ecosystems, or of organisms among an ecosystem, upon any environmental stress and for monitoring the general impact of global changes.