This week we are showcasing a dashing crustacean known colloquially as the Sally Lightfoot Crab (Grapsus grapsus).
Sally Lightfoots can grow to a maximum carapace size of ~8cm and are a common resident of rocky intertidal zones along the Atlantic and Pacific coastlines of North and South America. You can also find them on outlying islands such as the Galapagos archipelago.
These flashy crabs get their name from their remarkable speed and agility as they dash around the rocks in search of food. Should they not be quick enough to dodge the surf and get caught in the powerful splash of a crashing wave, they will flatten their bodies as close to the rock as possible and use their extremely strong legs to grip the surface.
G. grapsus are voracious grazers of algae and important scavengers of dead organisms and other detritus. They are known to be opportunistic predators of green sea turtle hatchlings (Chelonia mydas) and masked booby chicks.
In terms of predators, Sally Lightfoots are on the menu for octopuses, Kemp’s Ridley sea turtles, moray eels, and various birds such as the Galapagos Lava Heron (Butorides striata sundevalli). With so many animals finding them appetizing, it’s no wonder that these crabs spend 2/3 of their time hiding among the rocks.
Further Reading
- Grapsus grapsus – Encyclopedia of Life
- Johnson, Markes E., Paul M. Karabinos, and Victor Mendia. “Quaternary Intertidal Deposits Intercalated with Volcanic Rocks on Isla Sombrero Chino in the Galápagos Islands (Ecuador).” Journal of Coastal Research 26.4 (2010): 762-768.
- Davis, Christopher. “Marine Invertebrates of Bermuda: Sally Lightfoot Crab (Grapsus grapsus).” The Cephalopod Page. 6 Jul. 2011. http://www.thecephalopodpage.org/MarineInvertebrateZoology/Grapsusgrapsus.html
- Gianuca, Dimas and Carolus Maria Vooren. “Abundance and Behavior of the Sally Lightfoot Crab (Grapsus grapsus) in the Colony of the Brown Booby (Sula leucogaster) in the São Pedro and São Paulo Archipelago.” Investigaciones Marinas 35.2 (2007): 121-125.
- Shapiro, Leo. “Grapsus grapsus (Linnaeus, 1758).” EOL Species Rapid Response. 6 Jul. 2011. http://eolspecies.lifedesks.org/pages/15872
- Vinueza, L. R., G. M. Branch, M. L. Branch, and R. H. Bustamante. “Top-Down Herbivory and Bottom-Up El Niño Effects on Galápagos Rocky-Shore Communities.” Ecological Monographs 76.1 (2006): 111-131
- Kensley, B. F. “The Occurrence of Grapsus grapsus tenuicruistatus (Herbst) at the Tsitsikama Coastal National Park (Decapoda, Brachyura, Grapsidae.” Koedoe 13 (1970): 127-130.
- Johnson, Garland E. “An Ethological Study of the Rock Crab, Grapsus grapsus (Family Grapsidae) with Emphasis on Behavior Variations during Ontogeny and with Habitat.” American Zoologist 5.4 (1965): 632.