U.S. Fish and Wildlife volunteers and workers photographed, for the first time, cauliflower coral spawning in a reef off the Northwestern Hawaiian Islands.

“The spawning event was spectacular,” said Fish and Wildlife Service volunteer Lindsey Kramer. She was diving at Shark Island, a large uninhabited atoll about 500 miles northwest of Oahu, when she and other workers witnessed the spawning on May 19-20.

She said one or two coral colonies would begin to spawn and the neighboring colonies would follow. Gray, smoke-like puffs of coral sperm and eggs were ejected from each coral in waves, until the water became a hazy gray. The out-going tide washed the spawning materials away within a few minutes, and the entire event lasted only about 10 minutes across the entire lagoon.

Cauliflower coral is a common, reef-building species found throughout the Hawaiian islands, but its spawning had never before been documented in the Northwestern Hawaiian Islands.

“Most species of corals that spawn reproductive material only do so once a year, so documenting that window of time is important for understanding the species’ potential vulnerability to environmental disturbance,” said Jean Kenon, a Fish and Wildlife Service biologist.

Knowing where and when coral reproduce helps scientists understand and develop strategies to mitigate the impacts of global climate change, marine debris and invasive species, Fish and Wildlife Service officials said.