“The long-jawed mudsucker is not a sexy fish,” admits UC Davis marine biologist Susan Anderson. No argument there. Gillichthys mirablis has a face only another mudsucker could love: beady little eyes and a huge mouth whose gape extends back to the gill covers. It’s small (8 inches long) and sedentary, spending its whole life on one patch of mudflat. This is one fish whose name will never be bestowed on a fast car or a major league sports franchise.
As homely and obscure as it is, though, there’s good reason to pay attention to the mudsucker. Anderson and other scientists in the Pacific Estuarine Ecosystem Indicator Research Consortium are using these fish as sentinels to monitor carcinogens, endocrine disrupters, and other nasty substances in San Francisco Bay and other coastal waters.
Mudsuckers are members of the huge (1,900 species) and diverse goby family, which includes the smallest known vertebrates. They inhabit shallow mud-bottomed tidal sloughs in bays and estuaries from Bahia Magdalena in Baja California north to Tomales Bay. Tolerant of high salinities and temperatures, they even thrive in our bay’s salt evaporation ponds and the Salton Sea. Mudsuckers retreat into burrows in the mud during low tides; when stranded, they can survive by gulping air and wriggling across the flats to the nearest water. They’ve been known to live out of water for 6 to 8 days if kept moist.
In spawning season, December through June in the Bay Area, male mudsuckers dig special breeding burrows and defend them from rivals, long jaws wide open in impressive threat displays. Females may lay up to 27,000 eggs, which the males guard for the 10 to 12 days required for hatching. Larval mudsuckers feed on plankton; as they mature, they settle to the bottom and switch to a diet of algae, smaller fish, and small crustaceans.
This lifestyle exposes the mudsucker to whatever contaminants are in the local sediment. To assess the effects, the PEEIR group samples fish from five study sites: Stege Marsh in Richmond, China Camp on the Marin side of the North Bay, Walker Creek and Toms Point on Tomales Bay, and Carpinteria Marsh in Santa Barbara County. They’ve also moved mudsuckers from relatively clean sites to polluted sites to see what biological changes result.
And if you want a polluted site, you can’t do much better than Stege Marsh with its 128-year history of abuse. Mercury fulminate for blasting caps was produced there beginning in 1877, sulfuric acid from 1897. Stauffer Chemical, which branched out into other industrial and agricultural chemicals, closed up shop in 1982, by which time AstraZeneca was cranking out herbicides and pesticides. That operation ended in 1988, leaving a toxic legacy of 160 or more hazardous substances: PCBs, volatile organic compounds, heavy metals, and more. The property is now owned by developers who capped the contaminated muck and plan to build high-rise housing on top of it, a scheme that Henry Clark of the West County Toxics Coalition calls “one of the worst projects I have ever seen proposed in this area.”
Stege Marsh still has a remnant population of the endangered California clapper rail, and it still has long-jawed mudsuckers. But they’re not healthy fish. Anderson’s group has found fish with damaged livers and female mudsuckers with ovarian tumors. Equally alarming is the evidence for chemical damage to the fishes’ reproductive systems, with contaminants playing the role of estrogens: male mudsuckers with both ovaries and testes, or with high levels of the eggshell protein choriogenin. These abnormalities were common at Stege, less so at Carpinteria, rare or absent at the Marin sites.
Endrocrine disrupters are insidious things, mimicking hormones or shutting down normal hormonal activity. You may have read Theo Colborn’s pathbreaking book Our Stolen Future, or followed the coverage of UC-Berkeley biologist Tyrone Hayes and his work on biochemically warped frogs. Biologists have been finding reproductive anomalies in wildlife all over the globe, from alligators in the Everglades to polar bears in the Arctic, that appear to result from exposure to PCBs, dioxin, DDT, and other chemicals.
Mudsuckers are handy proxies because of their hardiness and limited home ranges (about a 32-foot radius from the burrow for an adult). It’s also easy to tell the sexes apart: males have bigger mouths. The PEEIR group uses nonlethal sampling to test males and juveniles for eggshell proteins that indicate their hormonal systems are out of whack. They also measure estrogenic chemicals in the sediment around the mudsuckers’ burrows, using a bioassay based on, of all things, the firefly luciferase gene. Interestingly, endrocrine-disruption effects were found at two sites where sediment toxicity was low or nonexistent. Makes you wonder.
The mudsucker is just one part of PEEIR’s portfolio of indicator species, along with shore crabs, clams, cordgrass, and pickleweed. Abnormal embryo development in the crabs, for instance, has been linked to heavy metal exposure. Anderson says this kind of integrated science—multiple species, multiple sites, field studies linking ecology with toxicology—is the wave of the future. That overworked canary in the mine shaft is going to have lots of company.