Factors controlling the expansion behavior of Favia favus (Cnidaria : Scleractinia): Effects of light, flow, and planktonic prey

Colonies of the massive stony coral Favia favus were exposed to different f low speeds and levels of light, and to the addition of zooplankton prey. Th e relative importance of each factor in controlling polyp expansion behavio r was tested. The coral polyps fully expanded when they were exposed to low Light intensity (0-40 mu mol m(-2) s(-1)) and high flow speed (15 cm s(-1) ), regardless of prey presence. They also partially expanded under low and medium light (40-80 mu mol m(-2) s(-1)) at medium flow speed (10 cm s(-1)). The corals expanded their polyps only when they were exposed to Light leve ls below compensation irradiance (I-com: light level at which photosynthesi s = respiration), which was determined to be about 107 +/- 24 mu mol m(-2) s(-1). The results presented here indicate that high flow, low light, and the pres ence of pIanktonic prey induce coral expansion. There is a hierarchy of res ponse to these stimuli, in which light level and flow speed are dominant ov er prey presence. Coral response to these three factors is probably due to the relative importance of gas exchange and zooplankton prey.