Before he became a Hollywood star, Leonardo DiCaprio dreamed of becoming a marine biologist.

“As a kid, I always had a fascination with the ocean and its wildlife,” DiCaprio said at this year’s State Department Our Ocean Conference. “In fact, the first philanthropic dollar I ever contributed was to save the wild manatee in Florida.”

DiCaprio still loves the sea. An avid scuba diver, DiCaprio focuses much of his philanthropic work on protecting ocean life. In the past year, his Leonardo DiCaprio Foundation has pledged $10 million to support ocean conservation causes.

DiCaprio recognizes the role oceans play in sustaining billions of people. Overfishing threatens the world’s fish stocks and the ocean’s biodiversity.

DiCaprio’s first contribution to philanthropy went toward saving manatees. (© AP Images)

“We have systematically devastated our global fisheries through destructive practices like bottom trawling…literally scraping up everything in their path, permanently destroying abundant underwater forests teeming with every imaginable form of wildlife,” DiCaprio said.

Even as overfishing destroys marine life habitats, carbon dioxide pollution is harming coral reefs. DiCaprio has seen firsthand how coral reefs are vanishing faster than rainforests in places like Australia’s Great Barrier Reef.

“What once had looked like an endless underwater utopia is now riddled with bleached coral reefs and massive dead zones,” DiCaprio said.

DiCaprio is not alone in urging citizens to protect the sea. Groups like the World Wildlife Fund and the U.S. National Oceanic and Atmospheric Administration work to conserve the oceans.

“If we don’t do something to save our oceans now, it won’t be just the sharks and the dolphins that will suffer,” DiCaprio concludes. “It will be all of us, including our children and our grandchildren.”

DiCaprio, an avid diver, offers extensive evidence of the importance of protecting oceans: