SERIES: Invertebrate of the Week

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 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.

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 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.

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

Further Reading