Puget Sound crawling with crabs, and that’s a good thing

Living in the Puget Sound-area, you likely know a lot about crabs — even if your knowledge is just limited to what they look like and your favorite ways to eat them.

But crabs are far more than those dishes you love: creamy artichoke and crab dip, crab cakes or as cooked whole crabs that you crack open with a mallet and pick clean of sweet white meat.

They are an interesting part of ocean life, and they play an important role in the marine food web.

Crabs belong to the group of animals known as crustaceans, which includes lobsters and shrimp. People are not the only ones who like to eat crabs. Seagulls, fish, seals, otters, octopuses and lots of other animals snack on them.

For protection, most types of crabs grow a hard outer shell, or exoskeleton. The shell is made of a material called chitin, the same stuff that makes the exoskeletons of insects like preying mantises, and the colorful scales of butterfly wings. Crab exoskeletons are tough but flexible enough to form the varying shapes of crab body parts.

Growing is a tricky business. That outer shell doesn’t get larger once it hardens. So, a young crab must shed its shell in order to get bigger — a process called molting. A new exoskeleton forms underneath the shell, but stays soft until the crab is able to pop open its old shell and crawl out of it. Then, the new covering can swell with seawater to reach a bigger size. Hardening up again can take six weeks, so crabs need to be very good at “hide and seek.” Lots of animals will try to eat them while their new shells are still soft, even other crabs.

Have you ever wanted to do more things at once and wished you had an extra pair of arms or legs? If you were a crab, you’d have 10 legs, as well as two pinching claws to use as hands. Of course, you would need to learn to coordinate your other eight legs so you could get where you need to go.

Crabs move sideways. How good is your crab walk? Try it out by sitting on the floor with your knees bent and feet in front of you. Put your palms on the floor behind you and lift your bottom up into the air. Now, try to walk sideways on your hands and feet. How fast can you go? Imagine if you had eight legs to coordinate.

Not only do crabs walk sideways, but they also breathe backwards. Like fish, they breathe underwater using gills. But, while fish take water in through their mouths and out through gill slits on the sides of their bodies, crabs go backwards. They take water in through feathery gills in their “armpits,” or holes where their pincers connect to their bodies, and back out through their mouths. By bubbling air through water they hold in their gills, some species of crabs can keep breathing out on land.

Tide pools and rocky beaches are great places to study crabs. You might feel like a giant walking through an alien city as you wander around at low tide. Watch your steps — all sorts of tiny, colorful and strange animals feed in the shallow water and hide in the sand and mud.

Gently turn over the larger, barnacle-encrusted rocks to release a tiny crab flurry. There, waving their claws and hurrying sideways are lots of shore crabs. Look for shells that are purple, green, gray, white or spotted. Some might be as small as your fingernail. These miniature crusty creatures are not babies, though. They stay small and hidden their whole lives, growing only to about the size of a Thin Mint Girl Scout cookie. Be sure to take extra care when replacing the shelter rocks so you don’t squish any crabs.

Whether hiding beneath rocks on beaches, crawling sideways across the seafloor or spicing up our restaurant menus, crabs are a big part of Puget Sound life. The crusty decapods deserve our protection so we can watch and enjoy them for a long time to come.

This story was originally published March 11, 2016 at 10:35 AM with the headline "Puget Sound crawling with crabs, and that’s a good thing."