Examples of Invasive species in San Fransisco Bay
Asian clams are eating up the food sources of baby salmon and striped bass.
Chinese mitten crabs accumulate on top of federal water pumps in the Delta, 20,000 are scooped off the screens each day.
European green crabs are eating into commercial oyster production at Tomales Bay, north of San Fransisco.
Amur River clam (Potamocor-bula amurensis), is the most abundant organism in many areas of the San Fransisco Bay.
Hydrozoans, (Maeotias inexspectata & Blackfordia virginica), feed excusively on small crustaceans, copepods, and crab zoea larvae.
New Zealand carnivorous sea slug, Black Sea jelly fish, Japanese gobies, dozens of Asian zooplankton species and hundreds more have been introduced by ballast water and are projected to spread rapidly.
Introduction of species
In the United States, one of the ecosystems most severely affected by biological invasions can be found in California. San Francisco Bay, an estuary protected from the harsh elements of the Pacific Ocean, has been quietly robbed of its unique identity over the past hundred and thirty years. The bay once had rich fishing waters for prized catch such as oysters, shrimp, Pacific salmon and Dungeness crab. Today, the natives of the bay are greatly outnumbered by more recent arrivals.
The bay has endured a number of assaults. In 1899, after the completion of the transcontinental railroad, trains brought live oysters to the bay for cultivation. The oysters were unable to adapt to their new home, but other organisms that traveled with the oyster clusters thrived. As California's population grew, and demands on the land increased, agriculture runoff and industrial pollution introduced harmful chemicals into the bay waters.
San Francisco is a thriving international port, receiving shipments from locations around the world, including stowaway organisms in Ballast water. In 1985, a species of clam native to Asia appeared in the upper region of the bay. These clams, while still in their larval form, most likely hitched a ride in the ballast tank of a freighter. Today, the floor of the bay is carpeted with these creatures, with more than 10,000 clams per square meter in some places. To complicate an already complex situation, another invader was found in southern San Francisco Bay in 1990. The European green crab, a small but voracious crab with a hearty appetite for clams and mussels, has since spread throughout the bay. The rapid growth of the Asian clam population is an environmental concern because of the implicit negative impact on native shellfish and other invertebrates.
There are now more than 200 non-indigenous species of organisms in the San Francisco Bay. Sea slugs from New Zealand and jellyfish from the Black Sea are just a few of the recent arrivals that have joined the alien menagerie in the bay. There is a biological roulette game in progress with an outcome that has affected, and will continue to affect, the ecology of the entire bay.
San Francisco Bay is not the only American body of water now inhabited
by alien invaders. Inland waters have been found to be vulnerable as well.
Non-indigenous zebra mussels in the Great Lakes have cost millions of dollars
in damage, clogging intake pipes of utilities and industries, devastating
native clam populations, and severely disrupting the freshwater lake ecosystems.
By
the year 2000, the price tag for dealing with the mussel will reach hundreds
of millions of dollars. These one-inch-long invaders first appeared in the
mid-1980s, transported from the Black Sea in the ballast water of ships.
Despite precautions, they are still spreading, making their way into the
major waterways of North America.