Hellboy: [Offering a beer.] Here. Drink up.
Abe Sapien: Oh, no, my body is a temple.
Hellboy: Well, now it's an amusement park.
Hellboy: Can't.Smile...Without you.
Abe Sapien: I like this song, you know.
Hellboy: Yep I'm gonna need a beer too.
Prince Nuada: We die and the world will be poorer for it.
Johann Krauss: Nice baby.
Baby: I'm not a baby. I'm a tumor.
Hellboy: I know; I'm ugly!
Chosen answer: Why not wear it? It's clearly something that's useful to him, even if it's apparently not particularly essential. It may simply just make him more comfortable, like a human wearing a scarf in cold weather - allowing him to breathe the water that he prefers rather than air. There's never any mention that Abe can only survive for a limited time out of the water; equally, there's no suggestion that he's particularly vulnerable to atmospheric microbes. It's part of his equipment that he uses when he wishes to, that's all.
Tailkinker ★