There's evidence that global warming is affecting corals in some of the reef flats of American Samoa.
The acting chief marine biologist at the Department of Marine and Wildlife Resources says coral bleaching goes up during the summer months.
Doug Fenner, who has been monitoring coral reefs for the last four years, says coral is a live organism and the inner part of the coral gets hurt if it gets too hot.
Dr Fenner says the first thing that happens in the heat is that coral loses its colour, as the colour is from tiny plant cells inside them.
He says the problem arises when the plant cells leave.
"The plant cells provide food when the sun hits them so when they leave the corals don't have as much food to eat and then if gets a little hotter and the temperature needed turns them white then it actually kills them."
The Acting Chief marine Biologist at the Department of Marine and Wildlife Resources, Doug Fenner.