Crabs of the Pacific Northwest come in a wide variety of shapes and sizes. They are also known as decapods because they have ten legs. Their first pair of legs is modified into claws. On a dive I always get a kick out of finding an umbrella or butterfly crab. These interesting small animals have all their legs tucked underneath and can easily be overlooked, often mistaken as a piece of shell litter.
It is amazing how well camouflaged and hidden crabs can be in their environment. The graceful decorator crab offers a prime example of blending in and not being seen. This crab actually attaches pieces of kelp or small anemones to itself in order to disappear from sight. I recall getting very close to take a photo once, and all of a sudden right in front of my face a small piece of kelp moved! It was only then that I truly appreciated how well the graceful decorator crab can disappear and blend into the reef.
Crabs cannot easily grow longer and larger like most animals because of their hard shells. Long before molting or shedding its old exoskeleton takes place, a crab will reabsorb some of the calcium carbonate from its shell. A new softer shell develops below the old one, and this may take several weeks. A day before the molting process happens a crab will absorb ocean water, making it swell or puff up. This swelling causes the old exoskeleton to crack along a seam around its body. The actual process of molting where the crab sheds its old shell takes about fifteen minutes.
There are two varieties of crab in the Pacific Northwest that people enjoy eating with the main one being the dungeness crab, and to a lesser extent the smaller red rock crab.