Effects of light intensity and spectral composition on the growth and physiological adaptation of Acroporid corals

Light affects physiological aspects of coral growth. However, it is unclear how light conditions (photoperiod, intensity, and spectrum) influence growth physiology. We examined the effects of various light conditions on skeletal growth promotion and the physiological mechanisms responsible for growth in Acroporid corals. Acroporid corals (Acropora tenuis, A. muricata, and A. intermedia) were reared for 2 months under various photoperiods (hours of light/dark = 8:16, 12:12, and 16:8) and light intensities (100 and 200 mu Em(-2) s(-1)). Growth was greater in all coral species under longer photoperiods and at higher light intensities. Next, we used a photoperiod of 16:10 (hours of light/dark) and 200 mu Em(-2) s(-1) light of three spectral composition from a light-emitting diode. The growth of A. tenuis and A. intermedia increased with increasing wavelength. The symbiotic algae density increased as the photoperiod increased. Symbiotic algae density and chlorophyll content were affected by the light spectrum but were not associated with the degree of growth. Therefore, changes in light conditions can induce coral growth without changing symbiotic algae density or chlorophyll content. Real-time quantitative polymerase chain reaction analysis revealed that the level of carbonic anhydrase mRNA changed with coral growth, suggesting that light accelerates coral calcification via photosynthesis by algal symbionts.

Automated summary

Light conditions (photoperiod, intensity, and spectrum) affect coral growth. Longer photoperiods and higher light intensities promote coral growth. Changes in light spectrum affect symbiotic algae density and chlorophyll content, but not growth. Light accelerates coral calcification through photosynthesis by algal symbionts.