The Hostile Takeover of San Francisco Bay

May 1, 2009
Sejal Choksi
by Sejal Choksi

San Francisco Bay is known throughout the world for its majestic natural beauty, and San Francisco Baykeeper works every day to protect the health of the birds, fish and other aquatic animals that make the Bay so special. But the Bay isn’t just lovely to behold – it is also an active end point along an international shipping route that contributes to a significant portion of California’s trillion-dollar economy.

More than 7,000 container ships transit the Bay every year, making shipping both an important part of the Bay Area’s industrial economy and a source of pollution to our waterways. The constant cycle of ships traveling between San Francisco Bay and ports around the world has serious environmental consequences for our local ecosystem. For example, heavy ship traffic can lead to serious environmental accidents, such as the collision and resulting oil spill from the Cosco Busan container ship in 2007. A dynamic shipping industry can also create pollution from the building, breaking down and maintenance of large vessels.

A less obvious but equally serious consequence of supporting shipping in the Bay is the introduction of invasive species to our ecosystem. Exotic species are introduced into the Bay in several ways – in boat motors, on the bottom sides of sailboats, and from the aquaculture industry. But by far the most significant source of invasive species is the ballast water of container ships. Ballast water is taken on board an empty ship at port in order to provide vessel stability for an ocean voyage. When the ship reaches its destination, it discharges ballast water  containing tiny stowaways – the larvae of exotic marine organisms – in and around the local ports.

When these exotic plants and animals enter Bay waters, they are able to thrive, often outcompeting native species and dominating the ecological community. Scientists estimate that approximately one new exotic species comes to the San Francisco Bay every 14 weeks, so it is no surprise that the Bay is home to 240 invasive species comprising 97% of the total number of Bay organisms. Invasive species are successful because they can tolerate a range of environmental conditions and eat many different types of food. When they reach their new environment, individuals can grow and reproduce quickly in the absence of their natural predators, eventually establishing themselves as a large and virulent population.

Invasive species wreak havoc on the Bay’s ecosystem. The pervasive overbite clam, Corbula amurensis, is suspected to have entered the San Francisco Bay as larvae discharged with a ship’s ballast water. Now the tiny clam can be found in huge numbers – 19,000 clams per square meter in some regions of the Bay. Because it can tolerate a variety of temperature and salinity conditions, it has truly thrived, to the detriment of the Bay. The invasive clam consumes phytoplankton at a rapid rate and limits the base of the food web, making San Francisco Bay a less productive ecosystem. It also assimilates contaminants in the water more readily than other clam species. As a result, the clams themselves actually become toxic and can poison the fish and ducks that feed on them.

Invasive species may come to the Bay as just a few tiny individuals, but it is nearly impossible to eliminate them once they have taken hold of the ecosystem. The best way to protect the Bay from the damage of more invasive species is to regulate the ships that carry them. In July 2008, San Francisco Baykeeper won a legal victory to prevent the spread of invasive species in our waterways. The U.S. Court of Appeals for the Ninth Circuit ruled that the U.S. Environmental Protection Agency (EPA) must regulate ship discharges, including ballast water discharges containing invasive species, that pollute U.S. waters under the Clean Water Act.

But EPA’s regulation alone won’t be enough. The invasive species problem is severe, and the shipping industry must be closely monitored and regulated. Baykeeper supports the implementation of mandatory ballast water treatment, which will effectively kill any organisms in ballast water before they can enter the Bay ecosystem. We are also working with local agencies, lawmakers and scientists to ensure that regulations improve under the Clean Water Act.

The Bay’s native critters will always share their home with invaders, but with better management of ballast water and invasive species, we can close the Golden Gate to new invaders and end the cycle of environmental damage. To learn more about Baykeeper’s efforts to limit the spread of invasive species please visit

Join us to hold polluters accountable and defend the Bay DONATE NOW >