We found several of these super cool crustaceans while tidepooling in California. Like other members in their family, they have very tough exoskeletons to protect them from predators.
These crabs belong to a large group called “Spider Crabs.” They generally have long legs with relatively small body. Their carapace (back shell) somewhat resembles a five-pointed sheriff’s badge; it is smooth and is longer than it is wide.
This species is usually dark brown. Kelp Crabs, as their name implies, are typically associated with their namesake plant and they are colored much like kelp. Their legs end in sharp points, which are used to cling to slippery surfaces.
These creatures are herbivores most of the time. During the Summer they nip off bits of brown algae such as kelp, rockweed and sea cabbage, as well as several types of red algae. When the algae die back during Winter, they turn to an animal diet, including small mussels and barnacles.
Kelp Crabs are found in rocky intertidal areas, kelp beds and around structures such as pier pilings. In the Fall, adults move to deeper water where they congregate, feed and mate. They use kelp beds not only for food, but also as shelter against predators such as Sea Otters.
These creatures will sometimes attach pieces of kelp to the points on their carapace, saving them to eat later. While these long-legged invertebrates look delicate, they are stronger than you may think and are able to give forceful pinches with their front claws.