Figure 3.

Effect of dark/light periods and CA inhibitors on the log enrichment (percentage ¹³C¹⁸O₂) of C_i in the medium during assays of Symbiodinium sp. Assays were conducted in a water jacketed cuvette (28°C) connected to a mass spectrometer. Freshly isolated cells were added to the cuvette (final concentration of 0.125 μg Chl a mL⁻¹) containing 4 mL of CO₂-free media (25 mm BTP, pH 8.0, and 428 mm NaCl) and H¹³C¹⁸O₃⁻ (1 mm) that had achieved chemical equilibrium. After 3 min of darkness, the cuvette was illuminated at a photon flux density of 500 μE m⁻² s⁻¹ for 3 min, followed by another 5 min of darkness, as indicated by the bar at the top of the graph. Where appropriate, the CA inhibitors AZA (▿; final concentration 50 μm) or EZA (+; final concentration 500 μm) were added prior to the addition of the cells. Data are presented as log enrichment as per the formula detailed in “Materials and Methods.”