California Coast & Ocean

In California's coastal and nearshore waters, areas known for exceptional species abundance and biodiversity are rapidly being turned into virtual monocultures by alien species from as far away as Asia. Most of these invasive organisms arrive in ballast water carried by ships, but many also ride in or are spread by attaching to hulls. The state is attempting to curtail further invasions, but some battles may already be lost.

The first step, in 1999, was to adopt legislation that prohibits oceangoing vessels from dumping or taking in ballast water within state waters. "The rules [established] boil down to ships being required to discharge ballast water at least 200 nautical miles from shore," according to Andy Cohen, environmental scientist at the San Francisco Estuary Institute. Next, in 2003, the Legislature passed the Marine Invasive Species Act, which renewed the 1999 law and expanded the initial program to include shipping within California waters, and also required a study of "fouling species," organisms that attach to hulls.

Ballast water is seawater that vessels take on board as they leave port, to help maintain balance and trim. Some ships dump this water before entering a port, to reduce the depth of the vessel's draft. Before the return journey, they take in more water. These operations, which had often been performed in or near ports, are now prohibited in state waters.

Because seawater, especially along the coast, is a living soup of tiny plants and animals and their spores, eggs, and larvae, multitudes of organisms are transported from port to port in ballast water, and this can have calamitous consequences for local ecosystems.

Non-indigenous species occur everywhere along the California coast, but the greatest numbers are found in large ports that handle international shipping. Well over 250 alien species have become established in San Francisco Bay, along with many others whose point of origin has not been determined, according to Cohen. In surveys he conducted in 2004 and 2005, he found that in some parts of the bay, nonindigenous species have completely taken over.

Ocean life has always been transported by travelers, but modern shipping has greatly increased the problem. Studies show that from 1850 to 1960 about one new species became established in San Francisco Bay every year. Since 1960 that rate has quadrupled.

Some imported species fail to survive, others fit into a new ecosystem with little effect. Some, however, explode in numbers, usually because the predators, competitors, and diseases that kept their populations in check where they came from are absent in their new habitat. Such highly successful invaders can alter entire ecosystems, devouring natives and driving them to extinction, disrupting food webs, or even changing environmental conditions on which natives rely for survival.