Effects of short-term illumination on calcification of the coral Galaxea fascicularis

Time course of enhancement of calcification of the coral Galaxea fascicularis in light and decay of light-enhanced calcification in darkness were studied. The hourly rates of calcification and of photosynthesis/respiration of isolated polyps of G. fascicularis were measured successively in light or in darkness using the alkalinity anomaly technique. Corals were kept in darkness for 15-19h before experiments. Calcification rate during 50min incubations in light was about four times higher than that during previous incubation in darkness. Light-enhanced calcification did not decrease abruptly when the coral was returned to darkness but decayed gradually to about 46%, 3h after illumination was terminated. The rate of light-enhanced calcification increased gradually when corals were incubated in light. The photosynthetic uptake of CO2 by corals held in light was 3.7 times faster than CO2 uptake due to calcification. Dark respiration increased after 50min incubation in light. The slow decay of light-enhanced calcification in darkness suggests that there is an internal pool of substances which enhance calcification, and that accumulation of the substances might sustain high rates of calcification in darkness.