Species Spotlight: The Blackclaw Crestleg Crab

January 07, 2017 Posted by: Michael Ready
Guest Post: Michael Ready is a nature photographer based in San Diego, California. From vanishing amphibians to bioluminescent squid, Ready seeks to reveal the diversity of life and particularly its smaller and lesser-known forms. While possessing a background deeply rooted in natural history, Ready’s vision is divergent from typified nature photography. With an eye for rich colors, abstract patterns, and compositional mystery, the resulting images bring a sense of wonder and connection to the wild -- and to the idea that nothing is outside of nature. For more of Mike’s work, please visit: http://www.michaelready.com/
 
 Wonders abound in the intertidal. Having been enchanted by tide pools and the life therein since I was old enough to lose my balance on an algae covered rock, I’ve become quite familiar with many of the inhabitants of these rich ephemeral puddles. But even after many awkward slips and falls (I lost count), it’s still not unusual, and it is always a joy, to come across something new. Just recently, while exploring the intertidal of Cabrillo National Monument, I added a new armored wonder to my life list. During the extreme ebb of the tide, what appeared to be a tiny piece of bright orange plastic caught my eye. Upon closer inspection, I was thrilled to discover that it was not a man-made remnant, but a stunning orange and white crab. More specifically, a juvenile blackclaw crestleg crab, a species I had yet to observe.
 
Photo of a Blackclaw Crestleg crab
 
The intertidal of Cabrillo National Monument is home to over 35 species of crustaceans. Of those, twelve are brachyurans, or true crabs. The blackclaw crestleg crab (Lophopanopeus bellus bellus) (Rathbun, 1900), sometimes called the blackclaw pebble crab, is an inhabitant of the lower intertidal and shallow subtidal waters of the Eastern Pacific. It occurs from the Aleutian Islands of Alaska down to the central coast of Baja California, and shares part of its range with a very similar and closely related subspecies called Lophopanopeus bellus diegensis.
 
The brilliant young crab pictured here is just over one centimeter across. But even full grown, the blackclaw is a relatively small species of crab. Males reach only 34mm and females 24mm, measured across the carapace. The bright orange color of this individual is almost unreal and threw me off at first glance, but the species can be quite variable in hue. Carapace colors range from rusty orange to brown, grey, green, purple, or sometimes calico patterned.
 
Photo of a Blackclaw Crestleg crab
 
Blackclaws are omnivorous. Although they are known to graze on several types of algae, the blunt morphology of their claws designates them as “shell-breaking” crabs. Their strong and stout chelipeds give them the ability to predate on hard-shelled prey items like mussels, barnacles, and even other crabs. They are also thought to be significant predators of young abalone. For their size, they are not only formidable but also quite prolific. Females can release as many as 36,000 eggs per brood, and they spawn two times each year! The first brood is produced and released during the months of December through April, and the second between May and August.
 
The blackleg crestclaw crab may be new to my seashore naturalist eyes, but this species has been around for quite while. In fact, fossils of Lophopanopeus date back to the Pleistocene, over 2.5 million years ago. So, the next time you are out in the lower intertidal zone take a closer look in the crevasses and among the tangled holdfasts of algae. You just might behold one of these fascinating and ancient crustaceans. 
 
Sources:
Abbott, Donald Putnam, Haderlie, E.C. Intertidal Invertebrates of California
Stanford University Press, 1980. 609-611
 
Behrens Yamada, S., Boulding, E.G., Claw morphology, prey size selection and foraging efficiency in generalist and specialist shell-breaking crabs. Journal of Experimental Marine Biology and Ecology 220, 1998. 191 – 211
 
Campos, Ernesto, Rosa de Campos, A. Range extensions of decapod crustaceans from Bahia Tortugas and vicinity, Baja California Sur, Mexico. California Fish and Game, vol. 75, no. 3. 1989. 174-177
 
Griffiths, Allison M. ,Gosselin, L. Ontogenetic shift in susceptibility to predators in juvenile northern abalone, Haliotis kamtschatkana Journal of Experimental Marine Biology and Ecology, Volume 360, Issue 2, 2008. 85–93
 
Menzies, Robert James. A revision of the brachyuran genus Lophopanopeus. Vol. 4. University of Southern California Press. 1948.
 
Species Spotlight is an ongoing feature of the Cabrillo Field Notes Blog where we highlight the fur and feathered (and sometimes scaled and squishy) friends that call Cabrillo National Monument home. If there is a particular critter you would like to learn more about from our Natural Resources Rangers, please leave us a photo or name in the comments and we will do our best to investigate. 
 

Rocky Intertidal, Natural Resources, Species Spotlight




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Last updated: January 7, 2017

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