Cancer productus
"Red Rock Crab"
Described by Randall, 1839.
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Kingdom: Animalia
Phylum: Arthropoda
Class: Malacostraca
Order: Decapoda
Family: Cancridae
Genus: Cancer
Species: Cancer productus
Introduction:
Cancer productus or more commonly known as the Red Rock Crab is a species of crab that belongs to the phylum Arthropoda. This phylum is home to many widespread and fascinating creatures, such as insects, spiders, scorpions, lobsters, and crabs. The Red Rock Crab is only one of many crab species found on the Pacific Northwest and is often caught by people to eat. Despite being a common and well-known species, the Red Rock Crab is full of many interesting surprises that simply cannot be ignored.
Description:
The Red Rock Crab is a medium sized crab with a red, serrated carapace. This carapace can range from 20 cm - 5 inches in length and can vary in color in juveniles. This variation in carapace color in juveniles is expansive. Some young are white, while others can have more diverse patterns such as having dark red spots or even zebra-like stripes. It is likely that these juveniles have this wide variation of carapace colors because of pressure from predation.
It has the typical crab body shape. It has ten legs, two of which are its pincers. The pincers are black at the tip, which is something that both fisherman have used in the past to identify its species. Another distinct feature of their claws is a lack of serration on the ventral side of the claw. They only have serration on the dorsal side of the claw. These crabs have small, black eyes above their mouth that help them detect predators and hunt in the ocean.
Habitat and Diet:
The Red Rock Crab has a wide range. It can live up North to as far as Alaska and can span down to the much warmer Baja California. It is typically found in the intertidal zone of the ocean, at around 70 meters deep. They inhabit rocky beaches, as they allow the crab more protection from predators.
The Red Rock Crab is not a particularly picky eater. It is a predator and has been recorded to prey on barnacles, soft shelled mussels, and smaller crab species. The Red Rock Crab is also known for occasionally scavenging on dead fish. While it is not as commonly caught by fishermen as other crab species, its meat is described to have a sweet flavor.
It was found in a study done in 1999 by Smith, et al, that these crabs do have a specific pattern when it comes to hunting mussels. Smith's team did an experiment to see if the depth of the clam in sand would influence whether or not the crab would forage for it or not. They did this by having three tanks, one with 5 cm of sand, one with 10 cm of sand, and 15 cm of sand. They would bury the mussels in the sand and then let the crabs into the tank to see if they would forage or not. They found that the deeper the mussel, the less likely the crab would forage, as the expenditure of energy would be too great for the energy it would gain by catching the mussel. This foraging is not only affected by something such as depth of prey in a substrate. In another study done by Robles, et al, Red Rock Crabs were found to have a preference for foraging areas. This species prefers to forage at intertidal zones with high water, little to no wave action, at night. This foraging varied with different age groups, with female crabs being the most common with these ideal conditions.
Behavior:
These crabs show off a variety of interesting behaviors that may be a surprise to some. Firstly, they vary the type of hunting and eating strategies depending on their prey. With barnacles, they smash them with their big claws to get the meat inside. As discussed previously, they will dig into the substrate for mollusks and will actively hunt more mobile prey such as smaller crab species. Red Rock Crabs also display a burying behavior. This burying behavior is used as both a defensive measure against predators and as a resting behavior for the crab. According to a study done by Ian McGaw in 2005, this burying is done differently from another crab species, Cancer magister . This is likely due to the two crab species having a similar range and being sympatric species.
These crabs have a few interesting mating behaviors as well. Red Rock Crabs mate from October to June, when the female crabs are soft-shelled. The male crabs guard the female crabs from danger and other males until they molt. These crabs will then go their separate ways, the males going to shallow waters and the females into deeper waters. It is suspected that female crabs do this to help with the development of their eggs and as potential predator evasion.
Fun Facts:
It was discovered in the Ian McGaw experiment, when buried under substrate, that Red Rock Crabs can stay underground for up to 50 hours. These crabs are quite literally able to stay underwater and under sand for over two days! They are able to do this by changing the physiology of their vents and gills, which they use to help them breath.
Red Rock Crabs, when paired with the sea star Evastarias troschelii, were discovered to actually lower the mortality rate of a shared prey species, a bivalve called Mytilus trossulus. This lower mortality rate is likely to be because of mutual avoidance from the two predator species. It was shown that the two predators would kill less of the bivalves if they were sharing a habitat than if they were alone with their own species.
Red Rock Crabs can control their own heartbeats. Not only that, but they also experience periods of acardia. This means that they will experience times where they have no heartbeat for anywhere from 15 - 300 seconds.
We just recently discovered a neuroendocrine system in the Red Rock Crab on its ganglion! Function isn't known (Yet...).
Works Cited:
McGaw IJ. Burying behaviour of two sympatric crab species: Cancer magister and Cancer productus. scimar [Internet]. 2005Sep.30 [cited 2021Nov.11];69(3):375-81. Available from: https://scientiamarina.revistas.csic.es/index.php/scientiamarina/article/view/266
C. Robles, D. A. Sweetnam & D. Dittman (1989) Diel variation of intertidal foraging by Cancer productus L. in British Columbia, Journal of Natural History, 23:5, 1041-1049, DOI: 10.1080/00222938900770951
Here is the link to "Foraging behaviour of an excavating predator, the red rock crab (Cancer productus Randall) on soft-shell clam (Mya arenaria L.)": https://www.sciencedirect.com/science/article/pii/S0022098198001579
Here is the link to "Juvenile colour polymorphism in the red rock crab, Cancer productus: patterns, causes, and possible adaptive significance": https://www.sciencedirect.com/science/article/pii/S094420061000022X
Daniel I. Messinger, Kimberly K. Kutz, Thuc Le, Derek R. Verley, Yun-Wei A. Hsu, Christina T. Ngo, Shaun D. Cain, John T. Birmingham, Lingjun Li, Andrew E. Christie; Identification and characterization of a tachykinin-containing neuroendocrine organ in the commissural ganglion of the crab Cancer productus. J Exp Biol 1 September 2005; 208 (17): 3303–3319. doi: https://doi.org/10.1242/jeb.01787
"Emergent effects of two rocky intertidal predators on prey: Interaction of crabs and sea-stars may reduce mussel mortality": https://www.sciencedirect.com/science/article/pii/S0022098121000320
McGaw, I. J., Nancollas, S. J. (2021). Patterns of heart rate and cardiac pausing in unrestrained resting decapod crustaceans. J. Exp. Zool, 335, 678– 690. https://doi.org/10.1002/jez.2533
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