Coral Gas: Oxygen Production in Millepora on the Great Barrier Reef

Large volumes of a gas consisting of 69 percent molecular oxygen and 31 percent molecular nitrogen with trace amounts of carbon monoxide, carbon dioxide, and methane have been found trapped inside skeletons of the common hydrozoan Millepora. Volumes were low in the morning and reached a maximum by late afternoon. The oxygen was probably produced by the endolithic (boring) algae, with which the Millepora skeletons are very heavily infested. Oxygen production by endolithic algae in Millepora and in other substrates could influence estimates of reef productivity based on measurements of dissolved gases.