Okhéania Series by Éric Corbeyran, Elsa Brants, Guillaume Lapeyre

The planet Oceania is covered with an ocean of vegetation. Humans navigate the green seas with futuristic ships. Teenagers Jon and Jasper spend most of their days surfing the vast waves of foliage, until one day, without warning, they're hit by a tsunami. Jon disappears beneath the leafy ocean surface and Jasper is picked up by a ship called the Poseidon. It is said that none return from the depths of this treacherous ocean. But the captain of the Poseidon tells a different story... moreThe planet Oceania is covered with an ocean of vegetation. Humans navigate the green seas with futuristic ships. Teenagers Jon and Jasper spend most of their days surfing the vast waves of foliage, until one day, without warning, they're hit by a tsunami. Jon disappears beneath the leafy ocean surface and Jasper is picked up by a ship called the Poseidon. It is said that none return from the depths of this treacherous ocean. But the captain of the Poseidon tells a different story. Will Jon and Jasper ever find each other? less

Pursued by the unrelenting Darianna, Jasper is accidentally catapulted into the depths of Okheania where he is miraculously welcomed by his friend Jon and Tania, the gentle savage girl. As the search intensifies, the trio encounters the group that abducted Helenia, the Imperator's daughter, who convinces Jon to help her get back to the surface...