I don't think Arkada hit upon this in their guide/video.

But since I've gotten to know these damned crabs pretty good after a day of speedrunning this game again I can go into detail for newer players, or my fellow crappy gamers.

There are 3 kinds of crabs in this world, and I only like 1 of 'em.

Is your crab jumping up and down like he just doesn't care/claws raised to the sky? That one is an attack crab. He will damage you.

Is your crab shaking side to side like he's doing the macarena? That is an item grab crab. He lives only to mug you. I hate him. However if he is underwater he is just there for the vibes. He cannot hurt you.

Is your crab looking particularly depressed? If his claws are laying down on the ground on either side of him, he is an attack crab at rest. He snipped one too many times and needs to have a break. This guy is harmless and you can swim right past him. (though, he may have a second burst of energy at any moment)

If you are ever unsure, just spin attack through them.

Speaking of spin attacks, use them whenever you think you might get hurt by something. There is a solid chance your will be able to just clip through it without getting stunned. Jellyfish are a great example of this. As Arkada mentioned in their guide, only their heads have hit boxes. So you know, if you see a head coming up and you don't really want to move for it, just spin attack through it. This is also possible to do with some of the burning ship debris though it is significantly harder so you might have to take the L on that one.