REEF REHAB A coral fluoresces purple (left), perhaps as a sunscreen defense for colorless polyps, in a photo taken September 12 of a bleached reef near Okinawa, Japan.
© XL Catlin Seaview Survey/Underwater Earth
Coral reefs are bustling cities beneath tropical, sunlit waves. Thousands of colorful creatures click, dash and dart, as loud and fast-paced as citizens of any metropolis.