Skeleton growth of the hydrocoral Millepora complanata Lamarck in relation to light

The daily length increment of the skeleton of the distal growing edge of Millepora complanata from Discovery Bay, Jamaica, was measured by laser diffraction. The individual variation in growth rates between adjacent and morphologically comparable parts of the same colony was pronounced. There was a significant correlation between length increment rate and light intensity. When daytime light intensities were high the length increment rates were slightly, but significantly, larger during night than during day. A few measurements are also reported for Millepora alcicornis.