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Spawning brain coral (Lobophyllia sp.). Hard coral releasing sperm and eggs (gametes) into the water. Once released, the gametes fuse during fertilisation to form planula larvae. The planula swims towards light, where the larvae drift and grow before swimming down to locate a surface on which to establish a new colony. They grow into a coral polyp before developing into a coral head by asexual growth, creating new polyps. Corals reproduce simultaneously according to the tide flow and the moon. Photographed off Sangalaki Island, in the Sulawesi Sea, Indonesia. (KEYSTONE/SCIENCE PHOTO LIBRARY/MATTHEW OLDFIELD, SCUBAZOO/SCIENCE PHOTO LIBRARY)