These may or may not represent Lobophyllia hataii and in fact may not all be the same species. These are moderately common on lagoon, seaward and pinnacle reefs. If all of these are indeed one species, it is clearly a variable one.
Like some other coral species, some colonies show up underwater with bright red color in water deep enough that the red from sunlight has already been filtered out. Apparently proteins in the coral absorb sunlight in the bluish spectrum and re-emit at red wavelengths, making the coral appear red to the naked eye. The light level, however, is pretty low, so if you shine a flashlight on it or take a photo with a flash unit providing light, the red color is completely washed out, usually leaving brown. Only taking a photo with available light, as in a couple of examples below, does the red show up. The photo immediately below was taken with flash.
Same coral colony shot with a video camera with a color correcting filter but no external light.
Photo with a flash unit.
Photo of same colony with no flash unit. When you look at it underwater without lights, it looks red.
Created 23 April 2020
Updated 9 June 2023