What Is a Kelp Crab?


Kelp crabs are a group of five crab species belonging to the genus pugettia. They are small to medium-sized oceanic crustaceans in the spider crab family. These small crabs belong to the same family as the world's largest crab, the Japanese spider crab, which can grow to over 12 feet across. The species in this group include the northern, spined, graceful, cryptic and Venice kelp crabs.


Kelp crabs tend to be small in size, just a few inches across at most, depending on species. All species posses a common shovel-shaped body which is broadest at the head and pointed at the tail. Color is highly dependent on the species' diet with the shell's pigment coming from the crab's food. This adaptation means they can camouflage amid the algae on which they feed. The shells of kelp crabs tend to be spiny, as do their legs.

Habitat and Range

Kelp crabs are native to the Pacific Ocean along the shorelines of North and South America. Some species can be found ranging from Alaska to Mexico and all tend to have large home ranges. These small crabs are found in dense kelp beds and inter-tidal pools. They mainly live in shallow waters but can be found at depths of up to 240 feet. The ability for kelp crabs to adapt to changes in temperature is the main reason they are so wide ranging.

Diet and Predators

Kelp crabs are nocturnal and will hide in the shade of kelp and vegetation by day. At night they come out to feed on a wide array of plants and shellfish. Bull kelp, sea cabbage and rock weed are among the vegetation favored by the small crabs. Small muscles, barnacles, algae and other microscopic organisms are also included in the diet. Using camouflage and hiding during the day, the crabs avoid many predators, but they do fall prey to kelp fish, halibut and cling fish.

Life Cycle

As kelp crabs grow, they molt their shells to grow a new one. The last time the crabs do this is when they reach sexual maturity. The mating season varies with species and range. After mating, eggs begin to develop on the underside of the female's body. Females produce thousands of eggs per season which can hatch within a few months. When the eggs hatch, the offspring are fully-formed minuscule crabs and receive no further parental care.

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