Coral reefs

A coral reef is built by colonies of tiny animals, coral polyps, held together by the calcium carbonate they lay down.¹ Inside the polyps live microscopic algae, zooxanthellae, that provide the coral with nutrients.¹ Together they have built structures that cover less than 0.1% of the ocean yet shelter at least a quarter of all marine species.¹

Why they matter

Reefs support fisheries and tourism and protect shorelines, services estimated to be worth billions of dollars a year.¹

Under pressure

Rising ocean heat, acidification, overfishing and nutrient pollution are all taking a toll,¹ and shallow tropical reefs have declined by half since 1950.¹ A coral that loses its algae turns white, or bleaches, and can die unless conditions recover in time.¹

What we do

Knowing whether a reef is recovering means measuring coral cover, survey after survey. Our coral reef work segments every coral colony in underwater photos and separates hard from soft coral, turning hours of manual annotation into a repeatable measurement.