Do underwater animals need special protection from the water?

Chris Smith put this to marine biologist Kate Feller...

Kate - Well, fish are not made of iron so they don’t rust as metal would corrode. However, most creatures have some sort of mechanism for turning over the external surface of their body in order to cope with harsh environment which you live in, including humans. We shed skin cells that turn into dust that we have to dust from our homes.

Chris - There’s 40,000 skin cells a second apparently.

Kate - Yeah, tons. So we have mechanisms…

Chris - Fish do the same thing?

Kate - Yeah. So fish will shed skin cells. Crustaceans and arthropods actually they go through more dramatic changes. They’ll go through what’s called the molt, where they literally gro a new exoskeleton and just pop out of the old one. So a soft shell crab is when you’re harvesting crabs that are at that in between phase where they’ve just popped out of the old exoskeleton and they haven’t hardened up into their new one. They basically will grow a new one and there’ll be a soft leathery surface that they’re very vulnerable until it has a chance to deposit the hard materials that make it that hard crab surface.

Chris - But that’s literally just replacing your surface, but what about suppressing things like microbes because they grow really well in wet, damp, gooey places?  So these animals are continuously in contact with a damp environment that’s bringing things in that could infect them, so do they have other adaptations to fend that off?

Kate - Yeah. A lot of aquatic creatures will have a mucus layer over the surface of their body. Mantis shrimp actually are super slimy and sometimes in my experiments I need to glue something to them and it doesn’t work very well because it just comes off. They’re just so covered in this layer of slime that presumably has mechanisms of defence against microbes and infection, much like we have mechanisms of defence against that.