Vitality and stress adaptation of the symbionts of coral reef and temperate foraminifers probed in hospite by the fluorescence kinetics OJIP

Recent coral reef bleaching, though being global and becoming chronic, is s till poorly understood today. Bleaching of corals and large foraminifers in volves basically the loss of their photosynthetic symbionts and/or their pi gments. Though the cause is unclear, temperature, irradiation and CO2 are a ssumed to be primary factors for the symbiosis rupture. In order to establi sh a monitoring of the vitality of the symbiotic associations, we investiga ted in three genera of coral reef and temperate foraminifers the behaviour of the photosynthetic apparatus of their symbionts in hospite, by means of the JTP-test. By this screening test that Eve widely use for studies of lan d plant stress, many samples can be analysed quickly as it needs a measurin g time in vivo of only 1 to 5 seconds. We measured the fast polyphasic fluo rescence kinetics O-J-I-P of the symbionts by a Plant Efficiency Analyser ( PEA) with a 10 mu s time resolution and 12 bit signal resolution. The measu rements can be conducted continuously even on a single cell in a test tube, as well as on the reef. The behaviour of photosystem If of the photosynthe tic apparatus, being at different physiological states established by diffe rent light conditions and culture temperature, was quantified through a con stellation of functional and structural parameters provided by the analysis of the fluorescence transients according to the JIP-test. We moreover indu ced by strong light, at each physiological state, a State-1 to State-2 tran sition and again followed the response of the photosynthetic apparatus by t he JTP-test. The aim was to investigate whether and how adaptive processes are revealed as regulating the different parameters, in an attempt to get a n insight into the capacity of foraminifers for adaptation under different conditions. We observed that the various parameters undergo modifications t hat differ concerning both their extent and their degree of elasticity, thu s indicating that different survival strategies are employed in response to stress. We here witnessed that low light pronouncedly protects the photosy nthetic 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 deformati ons. The final goal was to correlate adaptability and resistance to bleachi ng and establish a rapid and easily handled test for the biomonitoring of s ymbiotic associations in situ. This would offer an access to the understand ing of the causes of bleaching and possibly serve in foreseeing the future of reefs. A mapping of vitality in terms of performance and behaviour crite ria is also proposed, which can serve for the comparison of whole reef ecos ystems, or of organisms among an ecosystem, upon any environmental stress a nd for monitoring the general impact of global changes.