Northern kelp crab
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''Pugettia producta'', known as the northern kelp crab or shield-backed kelp crab, is a species of
crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...
in the family
Epialtidae Epialtidae is a family of crabs, containing the subfamilies: * Epialtinae MacLeay, 1838 * Pisinae Pisinae is a subfamily of crabs in the family Epialtidae, comprising the following genera: * '' Acanthophrys'' A. Milne-Edwards, 1865 * '' Ana ...
.


Distribution

Found along the Pacific Coast of North America from southern Alaska to northern Mexico.


Description

Upper
carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...
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.


Sexual Dimorphism

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.


Behavior

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 zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...
s in beds of
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
or eelgrass. They may also be found under rocks or shelters at extreme low tides within the intertidal zones. Northern kelp crabs are
herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
s 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 Red algae, or Rhodophyta (, ; ), are one of the oldest groups of eukaryotic algae. The Rhodophyta also comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majority ...
. Whereas in the winter, they are more
carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...
, eating small
mussel Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and Freshwater bivalve, freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other ...
s,
barnacle A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in eros ...
s, bryozoans, and hydroids. This seasonal
adaptation In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...
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.


Predation

Northern kelp crabs are predated by a few different animals in different stages of life. Adults are frequently eaten by
cabezon Cabezón is the Spanish word for "stubborn" or "big-headed". In Chile, cabezon means intelligent. Cabezon or cabezón may refer to: Fish species * Cabezon (fish) (''Scorpaenichthys marmoratus''), a species of fish in the family Cottidae * '' Cach ...
, gulls,
sea otter The sea otter (''Enhydra lutris'') is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between , making them the heaviest members of the weasel family, but among the small ...
s and staghorn sculpins. Sea otters are significant
predators Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
for the northern kelp crab within kelp forests. As pelagic larvae (
zoeae Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult, in which the hard exoskeleton is shed to allow the animal to grow. The ...
) they are eaten by velella velella or the by-the-wind sailor. The northern kelp crab can be parasitized by
heterosaccus californicus ''Heterosaccus'' is a genus of barnacles in infraclass Rhizocephala. Like other taxa in this group, they parasitize crabs. Geoffroy Smith circumscribed the genus in 1906; he initially only included ''H. hians''. Smith circumscribed a genus distin ...
( rhizocephalan sacculinid barnacle) that exhibits as a brown mass extending from the crab's underbelly. Once the crab has been
parasitized Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
, it will only molt one more time. During this molt the
barnacle A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in eros ...
then pushes its reproductive sac through the crabs molt-softened carapace. This damages or destroys the crabs male reproductive organs and which leads males to exhibit some female characteristics. These parasite-damaged males may become hermaphroditic and produce both eggs and sperm. Parasite-damaged females may have a faster development of mature characteristics.


Reproduction and Lifecycle

Adult crabs migrate to waters as deep as 75m to mate. They join together, feed, then mate. Females may carry eggs during most parts of the year but are rarely seen in the south Puget Sound in May, September, and October. These
clutches A clutch is a mechanical device that engages and disengages power transmission, especially from a drive shaft to a driven shaft. In the simplest application, clutches connect and disconnect two rotating shafts (drive shafts or line shafts). ...
may be from 34,000 to 84,000 eggs. Eggs change color as they age. They begin bright orange, change to red as they mature and hatch when they are a gray-ish purple color. This maturating and development may take anywhere from a month to nearly a year. This crab has a terminal molt which may end up covered with barnacles, limpits or bits of algae.


Human Consumption

Northern kelp crabs are not attractive for human consumption. They are difficult to purposely catch and bear very little meat.  Their chelipeds are large and adept. They have an aggressively strong pinch.


References


External links

* iNaturalist
Northern Kelp Crab
* WoRMS taxon details
Pugettia producta
Majoidea Crustaceans of the eastern Pacific Ocean Crustaceans described in 1840 {{crab-stub