Donovan is trying to pick up a girl he met before. He once was on a beach at sunset with her but she's not his girlfriend. He wants her to be. He's trying to impress her.

He says Superman or Green Lantern don't have anything on him. He's a superhero himself. What does he base that on?

He can make like a turtle and dive for her pearls in the sea.

That's what the whole song is about. He's telling her that he's fantastic in bed, a superhero, because he can make like a turtle and dive for her pearls in the sea.

Use your imagination. You should be able to figure it out.

In case you didn't figure it out, he's telling her that he will be a Superman about going down on her and blow her little mind.