Harris Mudcrab
(Rhithropanopeus harrisii)

Description: This small crab (max. size 20 mm) has white-tipped claws, one of which is bigger than the other. There are four spines on either side of the eyestalk; there is no prominent frontal notch (indentation in the front of the carapace between the eyes). Coloration is brown to olive green, and the legs bear sparse patches of hair. Two similar native species differ from this invader: H. nudus has red-spotted claws and hairless legs, while H. oregonensis has only three spines and a pronounced frontal notch.

Habitat: The Harris mud crab is primarily found in brackish waters, but also occurs in fresh water environments. It can be found in shallow water with muddy or sandy substrates.

Origin: East Coast of North America.

Invaded Areas: San Francisco Bay, Central Valley, various bays in Oregon; Europe.

Concerns: First discovered in California in 1937, the Harris mud crab has invaded much of San Francisco Bay's brackish waters and adjacent freshwater areas of the Central Valley. Because it may be a more aggressive and active predator than its native counterparts, this crab could outcompete them. Its tolerance of broad salinity conditions gives it the potential to spread widely through Californian coastal and inland waters.