Point Reyes Light - November 7, 2002

Spartina invades Tomales Bay

By Ivan Gale

A fast-spreading and highly adaptive exotic plant has been found in West Marin’s bay shores and lagoons and poses a serious threat to the area’s fragile ecosystems.

Spread of species

Experts believe the spread of non-native species of Spartina, commonly known as cordgrass, could cause damage to Tomales Bay, Drake’s Bay, and Bolinas Lagoon similar to Humbolt Bay, where it now covers 85 percent of the bay and surrounding marshes.

Should the exotic cordgrasses establish itself, it could squeeze away indigenous plants and the habitats they provide for native birds and animals, as well increase sedimentation by clogging waterways.

"This is potentially one of the greatest threats to Tomales Bay," said Catherine Caulfield, executive director of the Environmental Action Committee of West Marin. "Once they [Spartina plants] get a foothold, they’re very hard to eradicate."

A native California cordgrass known as Spartina foliosa has been co-opted by four hardier, exotic species. Experts said the plants slowly spread after taking root on the West Coast from discarded dry ballast or after being used for packing material during the 19th century. Other plants were introduced more than a century later in the 1970’s for erosion control in the San Francisco Bay.

Species spread

Together, the four non-native species have separately spread to more than 500 acres throughout the Bay Area.

Biologists have discovered and recently removed 64 individual plants in Tomales Bay, five colonies of plant in Drake’s estero, and one plant from the Bolinas Lagoon.

Particularly startling however is that fact that almost all of the plants identified recently are actually hybrids, the result of cross-pollination within the five different species.

When non-natives hybridize, explains Katy Zaremba, a Stinson Beach resident and biologist for the California Coastal Commissions’ Invasive Spartina Project (ISP), the younger generations are reproductively superior to natives and parents, and can reproduce and spread in dramatic fashion.

"They can occupy lower and higher elevations in the marshes, and it’s very easy to establish and out compete natives," she said.

The new cordgrasses are so adaptive that Zaremba said she considers them an "ecosystem engineer" because of the plants’ ability to engineer or change the structure of marshes and mudflats.

Threat to animals

Some studies have shown the spread of non-native Spartina causes decreased abundance of shorebirds, reduces food for migratory waterfowl, restricts fish to narrow channels, and limits access to open water.

Experts said West Marin plant species that might be "out-competed" are salt grass, California sea blite, soft bird’s beak, and pickleweed, which provides habitat for the salt marsh harvest mouse.

Since non-native cordgrasses are physically denser and taller and grow lower in the marsh plain, they have the potential to devastate the tidal flow, environmental experts said.

The plants’ denser stands slow the flow of water which deposits more sediment trapped in the water.

Katie Etienne, a biologist for Audubon Canyon Ranch, said the invasion of channel margins could also deplete the foraging and nesting habitat for the California clapper rail, a federally and state endangered bird.

The hardy cordgrass plants can be spread by land, sea, and air. Seeds or roots can propagate in the soil next to a parent plant or, be spread by the tides or by birds. Pollen can also float in the air and pollinate other species, accelerating hybridization.

Despite this, Etienne is quick to warn concerned bay enthusiasts not to pull up Spartina but to alert Katy Zaremba and her staff at the ISP.

Easily confused

Non-natives species are easily confused with native cordgrass to the untrained eye, and the fast-spreading plant can easily evade efforts to eradicate lest every seed and portion of the rootstock be removed. Etienne said the plant will stimulate growth if only the top is pulled, by putting more energy into the root system.

Alerting ISP staff, Etienne explained, allows biologists to map the location of clumps, which would be included in their monitoring.

Point Reyes Light Cover | News | Coastal Traveler