In this Sept. 6, 2017 photo provided by the National Oceanic and Atmospheric Administration (NOAA), fish swim on a reef at Pearl and Hermes Atoll in the Northwestern Hawaiian Islands. In 2016, government researchers were on a routine survey of Pearl and Hermes Atoll when they found small clumps of seaweed they'd never seen before. Last summer, they returned to find algae had taken over huge areas of the reef with seaweed nearly 8 inches (20 centimeters) thick and killing the coral underneath. Jacob Asher / NOAA via AP