Sargassum Swimming Crab

Blending in with the free-floating masses of orange-brown Sargassum seaweed that seasonally drift onto the beach at Padre Island National Seashore, Sargassum swimming crabs rely on their fantastic camouflage and ability to swim for survival. As with other swimming crabs, they come equipped with tiny swim paddles on their hind legs. They are, however, also capable of crawling on land. Sargassum swimming crabs aren’t alone in this fragile, complicated mini-ecosystem. There are as many as 70 species living in these floating masses. Their neighbors include larval crabs, shrimp, flatworms, hydroids, tiny fish, seahorses and nudibranchs. Sargassum swimming crabs both aggressively hunt and wait for prey to wander close enough to deliver an unsuspecting lethal jab. The crabs also feed on less complex invertebrates, such as hydroids and bryozoans, which also inhabit the seaweed. These layers of interdependence in their enable these crabs and other species to coexist and keep their shared Sargassum home in balance.