Sargassum Swimming Crab

Organisms / Invertebrates / Arthropods

Portunus sayi

Bahia Honda State Park, Bahia Honda Key (24.661N, 81.270W)

March 18, 2008

Photograph by Michael Martins

Descriptive Information

Field Marks: The pattern of the white spots on its back. Three sharp spines on its wrist point toward the claw.
Size: 2.5 cm.
General Habitat: Only lives on sargassum seaweed that is sometimes washed up on shore.
Range:

Field Observations
We saw the Sargassum Swimming Crab in the intertidal zone at Bahia Honda State Park during low tide (the tide was rising quickly). It washed up with the waves, and we noticed it on the rocks. We quickly snapped a picture then tried to catch it. While we were trying to catch it, a wave came and hid it momentarily in the surf. We then saw it swim under a rock, and after another wave came, there was no sign of the crab. It had a unique pattern of organgish brown with white spots on its back, which made it easily identifiable. The crab was about a 2.5 cm wide and when it was first spotted it was walking sideways on the rock. We noticed that its hind legs were flippers, which make it easy for the crab to swim. There was a lot of Sargassum Sea Weed on the beach and in the water that day, which made it a good habitat for the crab. The crab had one prominent spine on the left and one on the right side of its body. There were also little spines that reached from the large spine to its eyes on both sides.

References
Kaplan, Eugene H. Peterson Field Guide to Southeastern and Caribbean Seashores. Boston: Houghton Mifflin Company, 1988.

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