There are thousands of coral reefs. Maybe 10,000's. No one actually knows how many there are, let alone where they are.
They are usually in tropical waters. But also in waters that are warm both north and south of the tropics. But then again, I have found small patches of coral in cold waters, not big enough to be called a reef, but growing in cold water.
itsaboat mate...Life is just a boat and then ya marry one !