Story highlights David Doubilet: Rising temperatures in the Great Barrier Reef are causing immediate coral bleaching and could ultimately cause sea levels to rise and endanger green sea turtles

The water could submerge Raine Island, where the turtles travel to safely lay their eggs in the sand, he writes

David Doubilet began taking underwater photographs at the age of 12 and is a contributing photographer for National Geographic . He has won many awards and has produced several books, including "The Kingdom of Coral: Australia's Great Barrier Reef." He is a member of the Academy of Achievement, International Diving Hall of Fame, Honorary Fellow of the Royal Photographic Society and a Rolex Ambassador. The views expressed in this commentary are solely those of the author.

(CNN) Hold your pinky nail out in front of you. Now divide your nail into quarters. This is the size of one of the most remarkable animals in the world -- the coral polyp. The life of this tiny creature represents a biological process that helps produce geological fact in the form of coral reefs. These minute organisms are the building blocks of The Great Barrier Reef, which at 1,400 miles long is the largest living structure on Earth -- visible even from space.

David Doubilet

Some of my most memorable moments in the sea have occurred in this remarkable ocean ecosystem. One mid-October night in the Australian spring our team, led by Dr. Peter Harrison, sank beneath the surface off Heron Island into a dark world that that resembled a galaxy of stars created by many different species of reef-building corals that release their eggs and sperm into a warm sea with precision timing in a single night. These bundles of eggs and sperm combine to eventually produce coral larvae. The morning sea is coated with oily pink coral spawn, and a tangy coralline odor, unlike any other smell in the world, hangs in the humid air, evidence of millions of years of evolution and one of the most intricate mass spawning events in the world.

Today, this living structure is facing an uncertain future in a warming sea.

Acropora millepora release egg and sperm bundles that rise to the surface, creating a sea that resembles a starry night in the waters off Heron Island.

Sequential coral bleaching events in 2016 and 2017 have affected nearly 900 miles of the reef. Thermal stress causes the coral polyp to lose its symbiotic algae, which provides valuable nutrients and gives coral its color. If temperatures return to normal quickly, coral can recover with time. But these unprecedented back-to-back bleaching events give the already stressed coral little time to recover. The reef is literally in hot water, living under the Damoclean sword of ocean acidification and rising sea levels.

The Great Barrier Reef may be located in Queensland, Australia, but it really belongs to the world as the most well-known of all corals reefs on our planet. I am confident that even the most landlocked of Americans in the heartland know what it is and vaguely where it is.

Read More