Large Megafauna in Oceans

I think the ocean would benefit from large peaceful grazing mobs like Whales, Whales Sharks, Sun Fish, and Manta Rays. Imagine the scene. Vibrant Visuals casting rays of light on the seabed as you search for treasure. You are running out of air. You swim for the surface and see a large graceful Manta swimming overhead. Ambience like that would be a small thing but bring more life to the desolate oceans.