Persisting Natives of San Francisco Bay

The elusive blue mud shrimp maintains healthy populations by burrowing to hide from predators.

Hailed as one of the most livable cities in the country, San Francisco has long attracted new inhabitants from around the world. However, humans aren't the only organisms that have flocked to the Bay area over the years - many invasive marine species such as green mitten crabs have made a home in the Bay, cramping and threatening many natives.

One species that is apparently safe for now is the native blue mud shrimp. With a range from Southern Alaska to Baja California, male and female pairs construct permanent burrows in mud flats of estuaries and intertidal zones. By fanning the water with their pleopods (feathered feet), the shrimp generate a constant supply of water currents to carry in food. Hairs on the shrimp's first two leg pairs strain the detritus and plankton they need to survive. Marine predators of blue mud shrimp are sturgeon, large croakers and striped bass, but commercial bait collectors with suction devices are even more effective at vacuuming the shrimp from their burrows.

In 2000, scientists and educators at the California Academy of Sciences started a project called San Francisco Bay:2K to document the Bay's current invertebrate species and determine what percent of its inhabitants are now invasives. Nearly two hundred species have been identified - about 90% of which are not native. One of the most challenging to collect has been the enduring native blue mud shrimp.

Blue Mud Shrimp (Upogebia pugettensis) can range from 65mm to 150mm in length. They were first described scientifically in 1852.
Photo: Pam Schaller.

Since its introduction in 1989, the green crab (Carcinus maenas) has spread rapidly along the West Coast. A voracious predator, it consumes many native species, including juvenille Dungeness crabs. Photo: Chris Brown.