Kelp Crab

Pugettia producta

Kelp Crab

Pugettia producta

Other Common Names
Northern kelp crab
Shield-backed kelp crab

Sandy Coast

Other Common Names

Northern kelp crab
Shield-backed kelp crab

At the Aquarium

Sandy Coast

Appearance

The squarish carapace of this crab is smooth and longer than it is wide, reaching widths up to 3.7” in males and 3.1” in females. The color can vary from green, to brown, to red, and often has a dark red underside. These crabs have relatively long, slender legs that end in sharp points, which are good for climbing.

Habitat

Adults are found in kelp beds and forests. Juveniles can be found in tide pools covered with surfgrass or algae.

Diet

Primarily algae, but if algae is not available they may eat barnacles, mussels, hydroids, and bryozoans.

Life History

At sexual maturity, this crab undergoes a terminal molt. A female carries a mass of anywhere from 34,000 to 84,000 yellow to reddish-orange eggs under her abdomen for as short as one month in warmer waters and several months in northerly latitudes. The eggs hatch into tiny zoea larvae.

IUCN Status

Not Evaluated

Ecosystem & Cultural Importance

Northern kelp crabs feed on bull kelp directly and somewhat voraciously. However, as omnivores, they also feed on herbivorous snails that feed on kelp, helping maintain ecosystem balance. These crabs are important to food webs, serving as prey for a variety of fishes, larger crabs, and sea otters.

Alaska to Baja California, Mexico

You might come across a kelp crab while tidepooling in surfgrass beds. If you do uncover one of these crabs, be sure to place the grass back, as this protects it from the sun!

The particular color of a kelp crab is dependent on the exact type of algae they eat, thus providing them with camouflage that matches their environment.
There is sexual dimorphism in this crab: males have larger chelipeds and shorter legs than females.
Juveniles will sometimes place a bit of seaweed on their rostrum for later snacking, but adults lack the gripping setae for this.

Citations & Other Resources

Animal Diversity Website: https://animaldiversity.org/accounts/Pugettia_producta
A snail’s Odyssey Website
Dobkowski, Katie. “The role of kelp crabs as consumers in bull kelp forests—evidence from laboratory feeding trials and field enclosures.” PeerJ 5 (2017): e3372.
Invertebrates of the Salish Sea website: https://inverts.wallawalla.edu/Arthropoda/Crustacea/Malacostraca/Eumalacostraca/Eucarida/Decapoda/Brachyura/Family_Majidae/Pugettia_producta.html
Puget Sound Museum of Natural History website: https://www.pugetsound.edu/puget-sound-museum-natural-history/exhibits/marine-panel/kelp-crab
Scholars Bank Website: https://scholarsbank.uoregon.edu/xmlui/bitstream/handle/1794/12731/P_producta_2015.pdf?sequence=3

Kelp Crab

Kelp Crab

Other Common Names

At the Aquarium

Appearance

Habitat

Diet

Life History

IUCN Status

Ecosystem & Cultural Importance

Citations & Other Resources

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