Colorful Crabs: Meet the Grapsids

by Joseph DeSisto

A Sally Lightfoot crab (Grapsus grapsus) from the Galapagos Islands. Photo by Anne Dirkse.

A Sally Lightfoot crab (Grapsus grapsus) from the Galapagos Islands. Photo by Anne Dirkse, licensed under CC 4.0.

The creature above is a Sally Lightfoot crab (Grapsus grapsus) from the Galapagos Islands, off the Pacific coast of South America. Found along the Pacific coast of the tropical Americas from Mexico to Peru, and on many offshore islands, these crabs get their name from their agility and speed on land (although why they should be called “Sally” is beyond me). On the Galapagos, where the Sally Lightfoot is especially common, their majestic red, yellow, and blue colors contrast beautifully with the black lava that makes up the shore.

They share the space with marine iguanas, and both species are abundant. While iguanas venture into the water to graze on seaweed, the crabs forage for food on land. Sally Lightfoots also eat seaweed but, being smaller and more nimble than their reptilian neighbors, can subsist on the smaller fragments that grow and are washed up between the tides.

Marine iguanas and Sally Lightfoot crabs share the rocky shores of the Galapagos Islands. Photo by D. Gordon E. Robertson.

Marine iguanas and Sally Lightfoot crabs share the rocky shores of the Galapagos Islands. Photo by D. Gordon E. Robertson, licensed under CC 3.0.

Sally Lightfoots belong to the family Grapsidae, which includes around 41 species of relatively large crabs, most of which are found along shorelines. Many are algae eaters, but like all crabs they are resourceful and will scavenge on small invertebrates and detritus.

Despite being called “shore crabs,” grapsids can live in a variety of habitats. These can include freshwater streams, mangrove swamps, and even drifting seaweed in the open ocean. Although many are accomplished land-lovers, they nonetheless have gills and so must remain moist in order to breath.

You might think it’s hard to beat the striking colors of the Sally Lightfoot, and you would probably right, but there are several other beautiful grapsids that deserve some limelight. So without further ado, here is the Sally Lightfoot’s Atlantic cousin, Grapsus albolineatus:

Grapsus albolineatus. Photo by S. Karthikeyan.

Grapsus albolineatus. Photo by S. Karthikeyan, licensed under CC 3.0.

And here’s the purple Leptograpsus variegatus from Australia, looking just a little sheepish:

Leptograpsus variegatus from Australia. Photo by Benjamint, licensed under CC 3.0.

Leptograpsus variegatus from Australia. Photo by Benjamint, licensed under CC 3.0.

Finally, my personal favorite, the striped shore crab Pachygraspus crassipes from the northern Pacific shores of North America and East Asia:

Pachygraspus crassipes. Photo by Matt Knoth, licensed under Creative Commons 2.0.

The striped shore crab, Pachygraspus crassipes. Photo by Matt Knoth, licensed under CC 2.0.

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