Purple shore crabs

Crabs come in many shapes and sizes, but they have a few things in common (usually). Ten jointed legs make them decapods, and their eyes are found on the ends of short stalks. When they grow, the species that have hard exoskeletons molt their old shells! Crabs can be found both in water and on land because they breathe through gills, which just have to stay moist while the crabs are on land.

Purple shore crab on a rock with kelp

Purple’s not the only hue

While their name seems self-explanatory, purple shore crabs don’t always grow up to have plum-toned shells. You may find some adults with colors ranging from yellow or olive green to reddish brown. Juveniles have an even wider range of color and pattern, but all ages have claws with reddish spots and white tips. And watch out—they pinch!


Diets and dangers

These grapsoid crabs (meaning they belong to the Grapsidae family) look for food during low tide at night on top of rocks and on nearby sandy beaches, feeding on green algae, snail eggs, little crustaceans and more. For their part, they’re eaten by scoters (a type of sea duck), fish and gulls.


Purple shore crab in green kelp bed

The long and short of it

You’ll find these crustaceans all the way from Yakobi Island, Alaska, in the north to Bahia de Tortuga, Mexico, in the south. Their shell, or carapace, can grow up to a width of 2.2 inches for males or 1.3 inches for females.


Keeping them in our waters

Like all marine life in our one world ocean, purple shore crabs need a healthy environment to thrive. You can help on your local shoreline by being careful to not disturb the creatures and habitats you find there while exploring. And helping keep pollutants, such as single-use plastics (straws, wrappers, cups, etc.), out of the ocean by purchasing sustainable, environmentally friendly products will contribute to our collective efforts to protect the purple shore crabs’ ecosystem.

Other Invertebrates


These sedentary creatures lock onto (or into) objects and animals and include more than 1,000 species.

Moon Jelly

Jellies have been around for hundreds of millions of years!

Sea Star

Sea stars don’t have brains but are still able to detect light!

Tide pool ecosystems

Tide pools are found on rocky beaches in the strip of land between high and low tide, called the intertidal zone.

Hermit Crabs

There are over 500 species of hermit crabs around the world.


You can see both warm- and cold-water corals at the Seattle Aquarium.