 |
|
 |
| ||
|
Familiar Strangers
When restoration managers in the 1970s imported cordgrass from Oregon's Humboldt Bay to Corte Madera Marsh, all cordgrass on the West Coast was believed to be of the same, native, species. The import spread rapidly, choking out native vegatation. Only much later was the grass found to be a Chilean species introduced into Humboldt Bay in the mid nineteenth century. Today it's found in three other Marin marshes and creekzones and even across the Bay in Point Pinole, where park managers have been forced to remove it with shovels and chemcals.
This incident illustrates the restoration pitfalls associated with so-called "cryptogenic" species, those whose status as native or introduced is unknown. Until recently, species were assumed to be native unless proven otherwise, according to the S.F. Estuary Institute's Andy Cohen, who says the Bay is filled with such species. Species distribution patterns led scientists to question this assumption. "Some distribution patterns make no sense whatsoever unless the species are exotic," he says, "We should not assume that a species is either native or introduced without evidence."
In a 1995 report on exotic species in the Bay, Cohen and James Carleton of Williams College list 123 cryptogenic species, including phytoplankton, crustaceans, insects, worms, sea squirts and sea anemones, but note that the number is actually much higher. "The large number of cryptogenic species suggests that there may be a much larger number of introduced species in the Bay than previously thought," says Cohen. He adds that there are some organisms, such as the common bay worm commonly identified as Capitella capitata, that appear to be a single species but may in fact be comprised of several, one or more of which may be introduced.
Cryptogenic species and the related "taxonomic complexity" pose big issues for Bay restoration, says Cohen. "We need to be honest about what we know and cautious about claiming benefits by creating habitats that will be occupied by cryptogenic species, as well as about creating habitats that encourage cryptogenic species." If the cryptogenic category had existed in the 1970s, the Corte Madera Marsh cordgrass incident would probably not have occurred.
Most of all, the uncertainty associated with these species argues for additional investigation of their origins, including the possible use of molecular genetics. "If restoring native species is part of the restoration agenda, then it's worth putting some effort into figuring out what's native and what's not," says Cohen.
Contact: Andy Cohen (510)231-9423
[ ABAG HOME | SFEP HOME ]
Copyright © 2002, San Francisco Estuary Project