Corals stressed by heat and other environmental conditions can bleach, or kick out their life-giving algae companions. (Credit: sabangvideo/Shutterstock)

It’s been said time and time again that climate change is killing coral reefs. Rising ocean temperatures cause bleaching, which damages huge chunks of coral ecosystems from Australia to the southern United States.

But heat isn’t the only reason reefs are dying. Nitrogen runoff from human activities could be damaging corals around the wo