Fig. 2.
Maximum quantum yields of fluorescence (Fv/Fm, dimensionless) and electron-transfer rates (τ, μs) from the primary electron acceptor in PSII, QA, to the secondary quinone, QB, for all clones of zooxanthellae. Fluorescence parameters were derived from measurements with a custom-built fast repetition-rate fluorometer (14, 24). All cultures were grown in F/2 medium; cultures were incubated for up to 224 h (to verify resilience and nonreversibility of thermally damaged cultures) under a 10/14-h light/dark cycle at 26 and 32°C for each species tested. Maximum quantum yields of photochemistry (Fv/Fm) of the thermally tolerant clones averaged 0.57 ± 0.05 at 26°C and 0.55 ± 0.01 at 32°C; the corresponding electron-transfer rates (τ) were 318 ± 24 and 341 ± 9 μs. In heat-sensitive clones, the maximum quantum yields averaged 0.50 ± 0.07 at 26°C and 0.31 ± 0.03 at 32°C; the corresponding electron-transfer rates were 304 ± 54 and 200 ± 46 μs.