Microenvironment and photosynthesis of zooxanthellae in scleractinian corals studied with microsensors for O2, pH and light

During experimental light-dark cycles, O9 in the tissue of the colonial scleractinian corals Favia sp. and Acropora sp reached >250 % of air saturation after a few minutes in light. Immediately after darkenmg, 0; was depleted rapidly, and within 5 mm the 0; concentration at the tissue surface reached 680 nm). The scalar irradiance spectra exhibited bands of chlorophyll a (chl a ) (675 run), chl c (630 to 640 nm) and pendinin (540 nm) absorption and a broad absorption band due to chlorop h y l l ~ and carotenoids between 400 and 550 nm. The shape of both action spectra and photosynthesis vs irradiance (Pvs I) curves depended on the choice of the light intensity parameter. Calculations of mi-ha1 slopes and onset of light saturation, Ik, showed that P vs Eo curves exhibit a lower initial slope and a higher 4 than corresponding Pvs Ed curves. Coral respiration in light was calculated as the difference between the measured gross and net photosynthesis, and was found to be >6 times higher at a saturating irradiance of 350 pEm m 2 s 1 than the dark respiration measured under identical hydrodynamic conditions (flow rate of 5 to 6 cm ssl).