This past year's El Niño is to blame for the death of coral reefs on Christmas Island, says a University of Victoria biologist.

"It looked like a ghost town. The structure is still there, all the buildings are still standing but there is no-one home. Meaning all the corals are dead," says Julia Baum.

Coral reef dead near Christmas Island bleaching

Three dead corals with a bleaching coral in the foreground. (Kristina Tietjen/University of Victoria)

Baum was part of a team of scientists that recently returned from a month long scuba diving expedition of coral reefs near Christmas Island in the Pacific Ocean. 

The team found only 5 per cent of the corals were alive after months of intense heat from El Niño. 

"The coral has already died, moved past the bleaching phase and is covered by bright algae," she said. 

Coral Reef Christmas Island dying

A bleaching coral, seen on the left, is surrounded by mostly dead reef. (Danielle Claar/University of Victoria)

When corals 'bleach' it is a sign they are sick, but if the water temperatures come down quickly, they can regain their colour. 

In the case of Christmas Island, the water temperature did not drop quickly enough and essentially the corals starved to death. 

Baum says there is no way for coral reefs to come back to life. This then affects the fish population that relies on corals for food and habitat. 

Coral reef Christmas Island before bleaching

Site of coral reef near Christmas Island before bleaching. (Kieran Cox/University of Victoria)

Christmas Island coral reef bleaching

Same site of coral reef after bleaching caused by warm water temperatures. (Danielle Claar/University of Victoria)