Predators
The Leafy Seadragon isn't necassarily hunted. It gets eaten because of its SIZE. There are predators that are trying to consume other organisms in the area and the Leafy Seadragon is sucked into its mouth. There are also fish that, when opening their mouth, accidentally suck the Leafy Seadragon into its mouth. And, despite not eating them, HUMANS also kill Leafy Seadragons (fishing nets, pollution, etc.)!
Prey
Since the Leafy Seadragon lacks both teeth and a stomach, they eat almost constantly. They swallow their food (mysid shrimp is most preffered, other crustaceans, plankton, and larval fishes) whole, and they create suction in the process, pulling the food into its tiny mouth.