Absorption and Utilization of Radiant Energy by Light- and Shade-Adapted Colonies of the Hermatypic Coral Stylophora pistillata

The specific absorption coefficient for chlorophyll a (k_c) was measured in zooxanthellae from light- and shade-adapted colonies of the hermatypic coral, Stylophora pistillata from the Red Sea. These data, together with measurements of photosynthetic rates and irradiance, were used to compare the quantum yields of photosynthesis in these corals. Quantum yields varied from 0.10 CO₂ per quantum at low light to less than 0.001 CO₂ per quantum at maximal irradiances. Shade-adapted corals had higher pigment content, which allowed them to have twice as much light harvesting capability as light-adapted corals. In all cases, however, the quantum yield of the light-adapted corals was higher by a factor of about 1.5.