Biology Reference
In-Depth Information
placement of the native organisms in the bay with exotic organisms is
probably the biggest threat we face, outweighing the threat from pollution,
fishing, and climate change,” says Andrew Cohen.
At this point, San Francisco Bay will never go entirely native—it would
be impossible to rid the bay of its established invaders. Any attempt would
involve poisoning the entire bay, and eradicating all of the natives in the
process.
But parts of the bay ecosystem still sustain a fair number of their origi-
nal native species. Some locales, habitats, or taxonomic groups may be
completely dominated by exotic organisms, but others are not. For exam-
ple, says Cohen, the nonanadromous fishes that most people catch with
their fishing poles from bay piers are largely natives. Likewise, zooplank-
ton communities in the Central and South Bay are much less altered than
their counterparts in the fresher, lower-salinity waters around Suisun Bay.
In terms of fish, the northern reaches of the delta retain more of the natu-
ral mix of species than southerly waters. So parts of the estuary ecosystem
are still worth defending from invaders.
A Few Bad Actors
The delta's longest lived and most expensive invaders are exotic plants that
clog waterways, snag propellers, and block fish passage. Perhaps the most
familiar of these is the water hyacinth, Eichhornia crassipes. he hyacinth
was
introduced into the United States in 1884 as an ornamental plant for
water gardens, where its floating, showy, lavender-blue flowers attracted
many admirers. Able to double in size every 10 days in hot weather, water
hyacinth is the world's fastest growing plant. Recent surveys indicate that
by early summer, California's infestation can cover up to approximately
4,000 acres of the Sacramento-San Joaquin Delta.
To clear a path for boaters, the state Department of Boating and Water-
ways sprays the hyacinth with herbicides every year. The treatment kills
about half of the hyacinth mass, but costs millions of dollars. Similar con-
trol programs are undertaken by the state Department of Food and Agri-
culture to kill hydrilla, purple loosestrife, giant salvinia, and alligatorweed,
among other aquatic and wetland weeds. But the most insidious plant in-
vader, likely introduced via an emptied aquarium, is Egeria densa . Also
known as Brazilian elodea, this aquatic plant now infests approximately
12,000 acres of submerged delta habitat. Egeria changes the architecture of
shallow water ecosystems, erecting walls between deepwater and intertidal
habitat.
 
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