Purple shore crabs live in the shallow intertidal waters of the Pacific Northwest. They can be found in water less than 1 meter deep. They prefer rocky coastlines where they can hide under the rocks.
Their shells are usually a deep purple, although they can be from green to brown in color. The claws are the same color as the shell, with raised, darker purple spots and white tips. Size is an accurate method of judging the age of these creatures. They grow very slowly, reaching only 1 cm by the end of their first year. By the end of the second year, most have reached up to 3 cm. It takes a full three years for them to reach an adult size of 5 cm.
Purple shore crabs start their lives as eggs that are glued to the underside of their mother’s body. After hatching, the tiny larvae float to the surface of the water and live as plankton. After several molts, the larvae begin to look more like crabs. As they grow and gain weight they become heavier, and they sink to the bottom. After several more molts, they become juvenile crabs. They look exactly like adults except much smaller. Males reach sexual maturity by 7 months but females do not until they are around a year old.
The purple shore crab can be found under stones and among seaweeds on all the shores of the Pacific Northwest Coastal Region, this crab is the first crab that most children learn about. I can remember even at a very young age, turning over rocks at the beach and watching the shore crabs scurry off to new hiding places, you can hear their small claws on the gravel.
Purple Shore Crabs are omnivores who feed on algae, live prey, and will scavenge dead prey. They, in turn, are eaten by various animals and birds.