Coral reefs are so colourful because of tiny algae living inside the coral—these algae also help feed the coral.

Coral reefs—like the staghorn coral pictured here—are home to roughly 25% of all marine species, despite covering less than 1% of the seafloor. These ecosystems not only support ocean biodiversity but also protect coastlines and drive economies through tourism and fishing. But coral reefs are in crisis. Warming oceans, pollution and overfishing have put over 70% of coral reefs at risk—a figure expected to rise in the coming years.