Bay Crossings Article

Oddball Creatures of San Francisco Bay

Deb Self
From the September 2012 edition of Bay Crossings

One fish has lights on its stomach and wakes up houseboaters. Another gets a crab to give it dinner and a worm to build its house. They’re among the more than 35 species of native fish that depend on San Francisco Bay.

During early summer, the sleep of Sausalito houseboaters can be disturbed by the rumbling midnight mating hums of the plainfin midshipman (Porichthys notatus). Also called a toadfish, it has two types of male competing for one type of female.

Type 1 toadfish males, a foot long and eight times larger than females, build a nest in tidal mud under a rock. Type 1 males then use their stomach bladders to hum advertisements of their nest, hoping to draw a female to lay eggs. The loud humming can last up to an hour. Females sometimes answer with short grunts or growls.

Once a female lays her eggs in a Type 1 male’s nest, a Type 2 male, who is about the same size as the females, quickly sneaks in. He fertilizes the eggs before the Type 1 male gets a chance. Type 1 males then guard the bright gold eggs under the rock for about three weeks, until they hatch.

The "midshipman" in this fish’s name comes from its photophores—light-emitting organs similar to those of fireflies, used in mating displays and possibly to confuse predators. The midshipman’s underside has hundreds of photophores in rows, which reminded the marine biologist who coined the name of a British naval uniform’s buttons.

Plainfin midshipmen are an important food for seals, sea lions and migrating eagles. During the seasons when they are not spawning as threesomes in the Bay, toadfish live as deep as 1,200 feet in the ocean.

Another oddball native Bay fish is the little arrow goby (Clevelandia ios), a year-round resident at the bottom of the Bay’s shallow areas. Less than two inches long, the goby puts pieces of food too large to swallow in front of a crab, then waits to eat scraps that float its way as the crab dines. Arrow gobies also forage on their own for small green algae, young shrimp and shrimp eggs.

Gobies themselves often end up in the bellies of terns and great blue herons, as well as bigger fish. But gobies also manage to escape their predators—and keep from drying out at low tide—by hiding in the burrows of several bottom-dwelling creatures, including the fat innkeeper worm.

Resembling a paler and plumper version of a banana slug, the fat innkeeper worm (Urechis caupo) digs a U-shaped burrow in the Bay’s muddy bottom, and does not seem to mind the arrow gobies as they move in and out. The innkeeper worm lives in the burrow’s bottom full time, eating plankton and keeping the burrow’s two entrances clear of mud. The water-filled burrow holes, two to three inches deep, are the perfect place for a goby to find shelter.

These oddball creatures are vital parts of the San Francisco Bay’s ecosystem, but they’re threatened by pollution to the Bay, including trash that washes down to the shoreline from city streets. One way you can help make the Bay healthier for all its wildlife is by volunteering at California’s annual Coastal Cleanup Day on September 15. Baykeeper is hosting a cleanup at India Basin State Park in San Francisco. See you there!


Saturday September 15, 9 am – noon

India Basin State Park, Hunters Point Blvd. at Hawes St., San Francisco

Please pitch in with Baykeeper to remove trash and debris from San Francisco’s India Basin State Park during Coastal Cleanup Day on Saturday, September 15. Coastal Cleanup Day is California’s largest single effort to remove debris that has accumulated on beaches and inland shorelines over the past year. Tens of thousands of volunteers turn out annually to help make our state’s shores safer and cleaner for both people and wildlife. Please wear comfortable shoes, clothes you don’t mind getting dirty and sun protection. Click here for more information.