Biology Reference
In-Depth Information
Brazilian plants and Black Sea Jellyfish—continue to arrive and settle in
San Francisco Bay. Some do little harm or never gain a foothold in the
local ecosystem, but others can wreak havoc and spread quickly from the
point of introduction. A single individual of these species may produce
thousands of seeds, yield masses of larvae, or reproduce from bits of roots
and stems. Whatever their origin, they aren't likely to find their natural
predators in their adopted home.
Bay Area locals first noticed how devastating a bioinvasion could be as
early as 1913, when the wood-boring Naval Shipworm arrived from the
Atlantic Ocean. The worm (actually a clam), riddled 50 major wharves,
ferry slips, and other structures in the North Bay with its thumbtack-top-
sized holes. Other exotic organisms had already arrived in Gold Rush
ships, and locals had begun farming eastern oysters and introduced
Striped Bass and American Shad for sport fishing. But the Shipworm was
one of the first exotics to cause significant damage to human property
around the bay.
Scientist Jim Carlton was the first to raise the alarm about bioinvasions
in the Bay Area in the 1970s. Carlton, a marine ecology professor, came
from Williams College in Massachusetts. By 1998, he and local scientist
Andrew Cohen had identified a total of 234 exotic species and 125 crypto-
genic species (of unknown origin) that had established themselves in the
bay-delta ecosystem. According to their work, the rate of invasions had
accelerated from an average of one new species every 55 weeks between
1851 and 1960 to one every 14 weeks between 1961 and 1995.
As the most invaded estuary in the world, San Francisco Bay is now
struggling not only with the Overbite Clam from Asia but also with Large-
mouth Bass from the Mississippi eating the young of endangered salmon
and Atlantic cordgrass hybridizing with its Pacific cousin (see p. 268,
“Weeding by Satellite”). Meanwhile, upstream reservoirs, islands, rivers,
and creeks are being choked out by invasive plants, and suffering from
aquarium keepers dumping their former charges into the water.
Whereas the oysters and bass that early entrepreneurs ordered for
aquaculture purposes traveled by rail, most accidental introductions have
arrived by ship. Vessels taking up ballast water in one port and discharging
it in another have delivered thousands of hitchhikers to San Francisco Bay,
not to mention whole colonies of barnacles, mussels, limpets, and other
species clamped to their hulls. Recreational boats also carry hitchhikers
on travels from inland lakes and rivers to launch ramps in California.
Fishing gear, surfboards, kayaks, and wetsuits often harbor exotics as well.
The young larvae of many aquatic organisms are too small for the human
eye to detect.
It took until the 1990s for concerned legislators to pass the first of a
series of federal and state laws to regulate ballast water releases and to edu-
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