Coral spawning is a critical time of year for conservation scientists. In 2016 and 2017, the Great Barrier Reef suffered massive coral bleaching events that damaged two thirds of the reef. Coral bleaching occurs when pollutants or abnormally warm water prompt coral to expel the algae that live symbiotically in their tissues, and which provide the polyps food through photosynthesis. When conditions don't improve, the algae don't return, and the corals eventually starve to death.

One study published by the United Nations this summer predicted all the world's corals could die off in 30 years if nothing is done to curb globally warming waters. This could have far-reaching impacts, because corals aggregate to become some of the world's largest living organisms, and they provide critical habitat to a host of marine life, from fish to invertebrates.

Words by Sarah Gibbens

Shot on assignment for National Geographic 2017