I have spent a lifetime exploring the world's ocean and, as the son of Jacques Cousteau, I already had a head start. Even so, I continue feel awe at the magnitude, scope and surprising fragility of this world of water. For example, 80 percent of the biosphere — the life of our planet — is found in the deep sea, making the abyss the largest habitat on Earth and still containing unimaginable surprises.

Yet while 72 percent of our planet is covered by water, much of its vitality today is threatened. Ninety percent of the world's large predatory fish are now gone, while pollution and habitat destruction have touched virtually every major body of water.

But we are at the frontier of a clear understanding of how to stop the damage as we restore and protect these vital areas and resources, and we have before us the opportunity to protect a truly unique marine ecosystem. Currently, President Bush is considering the creation of several new marine national monuments, including one that encompasses part of the Mariana Trench in the western Pacific. It's crucial to make our voices heard on why it's so important that we protect these underwater treasures while we still can.

I have visited many stunning locales above and below the waves, and the roughly 100,000 square miles of water in the proposed marine monument off the coast of the Northern Mariana Islands is a natural marvel. The proposed monument area contains the deepest part of the ocean and the deepest location on Earth, as well as a significant cross-section of the Ring of Fire — the planet's most volcanically active region.

The combination of the deepest water in one of the most geologically active zones creates a unique and extraordinary ecosystem that is supplemented with undersea volcanic structures called seamounts. Because of the unprecedented size of the proposed monument, the seamount ecosystems would be insulated from any effect of future local development and would continue to provide zones of biodiversity for the region and the ocean's overall health. This area also holds a kaleidoscope of marine life. In 2007, the first survey of whale and dolphin populations conducted in the Marianas region reported 19 species of migratory cetaceans. Sharks, which have plummeted by 90 percent from their historic numbers, exist in the area in some of the highest densities seen in the Pacific.

The uninhabited islands of Maug, Asuncion and Uracus also serve as an oasis and breeding grounds for birds. Off the coasts of the islands, corals thrive, fed by nutrients from the deep ocean and carried in a rich food web to the seabirds of the sky. Sadly, though, signs of trouble are already apparent.

The Mariana Trench, relatively untouched now, is under threat from increasing populations and development in Asia that pose an imminent risk to the health of this remarkable region. Without protection, we could lose a fascinating and vital habitat, one of the world's most undamaged natural wonders.

I have witnessed, time and again, that every creature, no matter how small, plays a role in making an ecosystem healthy and rich, whether we fully understand its importance or not. The biodiversity seen in this proposed Marine National Monument in the Marianas is rare and delicate.

The proposed monument would complement local protections in the region but would provide broader and deeper safeguards for every link in this complex chain — birds, seamounts, predatory fish and corals.

People around the world may be more familiar with the Grand Canyon or Yosemite, but not all national treasures lie above the waves. An opportunity now exists for us to protect the ocean's deepest canyon and the sea life that surrounds it as a one-of-a-kind region, by declaring it a Marine National Monument.

In my travels, I've been able to see firsthand how dependent we are on the health of our marine surroundings, and am convinced that when we protect the ocean, we protect ourselves. We must seize this unique moment and opportunity while there is still time to save these natural treasures. If we make our voices heard during the assessment and public comment period for this historic conservation proposal we might yet be able save these treasures for generations yet to see their first ocean waves.

Jean-Michel Cousteau is president of the Ocean Futures Society. He wrote this commentary for McClatchy-Tribune News Service.