You will often find this crab in seaweed or kelp because that is what it eats.
Look for a smooth olive colored shield shaped shell (carapace) that helps them camouflage. Adults can have some red or yellow.
Kelp crabs have slender legs and are more delicate looking than other crabs.
Kelp crabs tend to move more slowly so are easy to observe. Other than tiny shore crabs, this crab is usually more tolerant to careful handling. Just watch the claws!