Some Effects of Light on Coral Growth

Abstract

The rate of coral growth under varied light regimes was tested using 45Ca uptake while temperature was held constant. Pocillopora damicornis and Acropora formosa, respectively, were used in Hawaii and Enewetak under natural and artificial light conditions. Light intensity and spectral distribution patterns were determined for all experiments. Pocillopora damicornis was tested under different natural light conditions and total darkness. Light enhances calcification within limits. Calcification was shown to have a negative regression with light at 380 nm when that light was partitioned from visible light (400-800 nm), thus indicating longwave ultraviolet inhibition. Acropora formosa held for 6 hr of pretreatment under natural light conditions during the day or in the dark at night calcifies faster during the day than at night. This testing, which was conducted for 20 min under either dark or light conditions, did not show a statistically significant difference between dark or light testing conditions. This same species was pretreated for 4 hr with dark, low light, and high light intensities at the same time of the day; then the samples were immediately tested for calcification rate for 20 min under dark conditions. Those pretreated under high light calcified faster than those pretreated under low or dark conditions, indicating a light-dependent lag effect.