Abstract
Favia fragum is a Caribbean coral exhibiting high abundance on shallow reefs and scarcity at depth. Light quality and quantity may contribute to this vertical zonation. We studied the effects of light spectrum and irradiance on recruitment, survival and growth of F. fragum . A larval settlement experiment with four different light treatments (white or blue light, each at 75 or 750 μmol quanta m −2 s −1 ) was performed for a 5-day period. Subsequently, settled larvae were cultured under these four light conditions for 10 weeks to monitor survival, growth and photosynthetic yield. After, we measured zooxanthellae densities, chlorophyll a and green fluorescent protein (GFP) to understand settler photoacclimation potential. Settlement shifted to sheltered microhabitats with elevated irradiance under white light only. Settler survival after 10 weeks was 70–100%. Growth was lowest under low irradiance for cryptic settlers. Highest growth rates were found in corals that settled in exposed locations under low irradiance levels, irrespective of light spectrum. Cryptic settlers photoacclimated to low irradiance locations through increased chlorophyll a production, although this was accompanied by reduced growth and symbiont densities. GFP production was highest under high blue light. The elevated production of chlorophyll a and GFP under extreme light environments might have negatively affected net energy available for coral growth. F. fragum can recruit, survive and grow well under both high irradiance white and low irradiance blue light, reflecting shallow and deep reef conditions, respectively. Thus, light conditions do not seem to explain the vertical zonation of this species.