Shield back kelp crab

Description

Pugettia producta, known as the northern kelp crab or shield-backed kelp crab, is a species of crab in the family Epialtidae. Found along the Pacific Coast of North America from southern Alaska to northern Mexico. Upper carapace typically dark brown, olive, or olive brown. Underside surface tends to be more vibrant having colors such as red, yellow or orange. Younger crabs may be lighter olive brown or reddish brown. The carapace is a badge like shape similar to a police officer's badge or shield; hence the secondary name shield-backed crab. Carapace is curved and smooth, with a slick texture. The front of the crab has a protrusion called a rostrum, extending the carapace and used in feeding. They have large chelipeds used for defense and feeding. The northern kelp crab is part of the spider crab family and exhibits the long many jointed hairless legs associated with the family. Their long legs and shield-like carapace are key identifying factors. Male crabs tend to be slightly larger than female crab at about 93mm (4 in) across the carapace. Females tend to be 7.8 cm (~3in). Female crabs exhibit a broader back and smaller chelipeds than males Northern kelp crabs are known for their association with kelp and their similar coloration. Their long many-jointed legs have evolved to help them climb bull kelp and also provide help climbing man-made pilings. These crabs are also common in lower intertidal zones in beds of algae or eelgrass. They may also be found under rocks or shelters at extreme low tides within the intertidal zones. Northern kelp crabs are herbivores with seasonal preferences. In the summer months when algae is prevalent, they eat nearly exclusively algae. They eat kelp, rockweed, sargassum and some types of red algae. Whereas in the winter, they are more carnivorous, eating small mussels, barnacles, bryozoans, and hydroids. This seasonal adaptation is an evolutionary advantage when preferred food is scarce. The northern kelp crab can be differentiated from similar species like the decorator crabs by its two rows of hooked setae right behind its rostrum. The northern kelp crab sometimes attaches bits of kelp and seaweed to these hooked setae to store as food for later. The northern kelp crab does not decorate its carapace as other majid crabs do.