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Invertebrate of the Week #7 – Sally Lightfoot Crab (Grapsus grapsus)

Sally Lightfoot Crab (Grapsus grapsus)
Sally Lightfoot Crab (Grapsus grapsus). Source: http://goo.gl/NtGs7z

This week we are showcasing a dashing little crustacean known colloquially as the Sally Lightfoot Crab (Grapsus grapsus).  Sally Lightfoot’s can grow to a maximum carapace size of ~8cm and are a common resident of rocky intertidal zones along BOTH the Atlantic and Pacific coastlines of the North and South America.  You may also spot them on islands near the American continents such as the Galapagos archipelago.

Sally Lightfoot Crab (Grapsus grapsus)
Sally Lightfoot Crab (Grapsus grapsus) on a rocky shoreline in the Galapagos archipelago. Source: Wikimedia Commons

These flashy crabs get their name from their remarkable speed and agility which comes in handy as they dash around the rocks in search of food.  If they happen to 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 as well as important scavengers of dead organisms and food remains.  They are also known to behave as opportunistic predators of green sea turtle hatchlings (Chelonia mydas) and masked booby chicks.

In terms of predators, Sally Lightfoot’s are on the menu for animals such as 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 crab often spend 2/3 of their time hiding among the rocks.

Sally Lightfoot Crab taking cover among the rocks in the intertidal zone.  Source: http://goo.gl/vZHjZX
Sally Lightfoot Crab taking cover among the rocks in the intertidal zone. Source: http://goo.gl/vZHjZX
Sally Lightfoot Crab  in the Galapagos archipelago.  Source: Wikimedia Commons http://goo.gl/GeKPCw
Sally Lightfoot Crab in the Galapagos archipelago. Source: Wikimedia Commons http://goo.gl/GeKPCw
References:
  • 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.

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