Dive Dry with Dr. Bill

034: Sheep Crab

During the Avalon Harbor Cleanup sponsored in part by the Catalina Conservancy Divers, I had an opportunity to dive Avalon Bay to videotape those involved in the event. While I obtained some good footage of divers collecting trash (and valuables) from the bottom, it was a chance encounter with a sheep crab that provided some of my best footage that day. Despite some 500 dives in the Casino Dive Park alone, I have yet to see a sheep crab there but others have. Therefore the sheep crab was a welcome subject for my camera (of course no sooner did I write this column than they started appearing in numbers in the Dive Park!).

The sheep crab is a member of the spider crabs. Its scientific name Loxorhynchus grandis means large bent nose. The body may be more than 6" wide and there are older collected specimens measuring nearly 11" across. The eight long legs and two claws add substantially to its size (sometimes surpassing 18 inches across). Males have much longer claws than the females.

The body is covered with spines and tubercles. Unlike some of its relatives (the masking crab for example), adults do not camouflage their body by covering it with other organisms. However the young individuals may blanket themselves with barnacles, bryozoans, hydroids and algae to give them greater protection from potential predators. It is reported that the name "sheep" crab came from the wool-like algae covering the shells of some individuals.

Sheep crabs can be found from Point Reyes in northern California to Punta San Bartholeme in Baja California. They frequent sandy as well as rocky bottoms from depths of about 10-500 feet. Young crabs are even seen in the intertidal zone.

The adult crab I encountered during the Cleanup was ambling awkwardly across the sandy bottom. At first it ignored me completely, but as I approached more closely it took notice. The crab assumed a defensive posture, sitting back on its rear and waving the single remaining claw at me to keep me at bay. Apparently it had lost one claw previously and had yet to regrow it. On videotape the crab appeared quite humorous, throwing roundhouse "punches" at me (but landing none). It reminded me of a clumsy, overweight and half blind boxer who couldn't judge the distance to his opponent well. Good thing... the claws are capable of delivering a strong pinch that can be painful.

Mating in southern California apparently occurs in spring and early summer. When they mate, the male and female wrap each other up with their long legs in a loving embrace. The eggs hatch into planktonic larvae which drift for a while in the plankton before settling to the bottom. The young crabs molt their external shells about once a year as they grow, but stop shedding their exoskeleton after they mature.

Good thing this pugilistic crab was no Mike Tyson, so my ear (and other body parts) were safe. After all, they are carnivores and scavengers and have been known to tear apart and feed on starfish, clams and octopus. Of course I'm a lover, not a fighter... and I could probably use the sheep crab's eight arms and two claws!

© 2003 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays.

Image caption: Sheep crab: the Mike Tyson of the underwater world (note this one is
missing its left claw so it can only throw right hooks)

This document maintained by Dr. Bill Bushing.
Material © 2003 Star Thrower Educational Multimedia