Speaking from more than 400 feet below the surface of the Indian Ocean, the president of the Seychelles made an impassioned plea on Sunday to protect the world’s seas.

Calling oceans the “beating blue heart of our planet,” the president, Danny Faure, said the sea had “a special relationship with all of us.”

Mr. Faure, dressed in salmon-colored shorts and a T-shirt with the Seychelles flag, gave his speech from a submersible craft that had dived to 406 feet off Desroches Island in the Seychelles, part of a series of scientific missions to explore and protect the Indian Ocean.

Marveling at the underwater beauty and biodiversity of his surroundings, Mr. Faure called for more protection for the ocean’s ecosystem.