Diurnal carbon-14 partitioning between zooxanthellae and the coral animal tissue of intact Seriatopora hystrix colonies

Abstract

At various times throughout the light period of a day, freshly harvested Seriatopora hystrix colonies in seawater were labeled with H¹⁴CO ^-₃ for 20 min and then washed thoroughly with fresh seawater. The labeled colonies were left in fresh seawater, and at time intervals (some as long as 27h) samples were removed, separated into zooxanthellae and coral animal tissue, and the radioactivity in the two fractions determined. In 30 to 60 min after initiating the experiments, the zooxanthellae retained 75 to 82% of the total label. Zooxanthellae labeled early in a day lose label throughout the day and near sunset retain about 55% of the total label in the colony. Colonies labeled in the last 1 to 2 h of daylight retain 65 to 73% of the label in the zooxanthellae. At night the zooxanthellae retain almost all of their ¹⁴C-labeled materials regardless of the labeling hour of the previous day. A loss of carbon at night from the zooxanthellae occurred only when the colonies were labeled in the last 1 to 2 h of daylight; the loss was approximately 5% over the night period. The next day, after several hours of light, ¹⁴C-labeled material again moved from the zooxanthellae to the animal tissue. We conclude that in the intact coral as much as 45% of the newly fixed carbon moves from the zooxanthellae to the animal tissue each day, but that little net carbon movement between these two organisms occurs at night.