Fabien Cousteau — ocean explorer, documentary filmmaker, and grandson of Jacques-Yves Cousteau — looks like he feels at home with his sandy hands patting down the fragile roots of a baby mangrove plant. He holds a propagule, the seed of a red mangrove plant, as he explains the crucial role that these plants play in preserving Florida’s coast, and how they are threatened by human development.

“We can all be better stewards of the planet,” he said of Florida’s fragile ecology and urban expansion. “We need to think about living with the planet rather than on it.”

Cousteau was at John U. Lloyd State Park in Broward County earlier this week with his global nonprofit, Plant-a-Fish, which partners with local communities all over the world to help restore fragile aquatic ecosystems. The organization’s Florida initiative is working with South Plantation High School, among others, to plant and preserve the mangroves that have been devastated by beachfront development.

Elisabeth Jacobi is a marine science teacher at South Plantation and the program manager for Plant-A-Fish in Florida. In the two years that the program has been up and running, her students have planted more than 1,000 mangroves at the state park , and are raising an additional 20,000 plants in their school’s nursery.

“It’s important to get the schools involved because the minds of the youth are not yet corrupted,” she said in reference to the challenges facing other conservation movements. “They’re not thinking about the political side or the financial side yet. They just want to help.”

Jacobi was accompanied by her student Julia Sheffer, 17, who participated in Plant-A-Fish’s mangrove planting day last year. Julia said she has “always had a passion for the ocean,” and wants to study marine science in college. Jacobi’s two young sons ran around the sandy shore lined with long roots and leafy branches, asking their mother when they could go plant more mangroves.

Cousteau explained that these plants are often bulldozed to improve a property’s ocean view, but they are “integral nurseries for countless species.” He said he loves snorkeling through mangroves because they are home to “miniatures of everything,” where the offspring of these aquatic animals spend the first few years of their lives. The plants also serve as natural protection for housing developments that sit in beautiful but precarious coastal areas.

“Mangroves are especially important in storm-prone areas because they provide a barrier to hurricanes and prevent erosion and run-off,” Cousteau said. “They are essential to fish, but also to people.”

The tide was rising as he spoke, slowly submerging the fragile mangroves he had just planted. A heron landed nearby and stuck its long neck out to catch a small fish swimming in the long roots of the more mature plants. Cousteau admired the display of wildlife that call these waters home, and said that he worries about their future.

Florida has lost 65 to 70 percent of its wetlands in the last 15 years, according to Cousteau, and raising awareness about their importance and vulnerability is a significant part of Plant-A-Fish’s mission in Florida.

On a global scale, his nonprofit understands both the words “plant” and “fish” in the broadest possible sense. It began with a project on the Hudson River in New York to plant oysters and then expanded to Florida to plant mangroves. It also has projects in El Salvador to save sea turtles and in the Maldives to focus on coral reefs. More mangrove projects in Nicaragua and Haiti are in the planning stages, under Jacobi’s direction.