The invasion of non-native, or invasive species poses a serious threat to San Diego Bay's ecosystem. Invasive species are those that evolved elsewhere and whose introduction has or is likely to cause harm to the environment, the economy, or human health. Invasive species have arrived in San Diego Bay from all over the world, by intentional and accidental means. They are transported in the ballast water of international ships, arrive attached to boat hulls, introduced intentionally for fishery or mariculture, released as unwanted organisms by aquarists, or spread naturally through dispersal. The first introduction of invasive marine species into San Diego Bay may have come from the ships used by the early Spanish explorers. Some invasive species have been in their current ecosystem for so long that they were assumed to be natives until recent genetic analyses proved otherwise.
Invasive organisms can significantly change the structure and function of an ecosystem. Once introduced, they often grow and spread rapidly because they lack local predators and usually affect native species by competing for food and habitat space.
According to a 1999 study, the following invasive species are present in San Diego Bay: one species of marine algae, one marine protozoan, 47 marine invertebrates, and five marine fish. There are also 28 species of invasive coastal plants. In total, at least 82 non-native species are found in the Bay. This number is not as alarming when compared San Francisco Bay, which is often thought of as the most invaded ecosystem in the world, with at least 234 non-natives and a new species arriving every 12 weeks.
For a complete listing of the invasive species found in and around San Diego Bay, please see Table 2-26 of the San Diego Bay Integrated Natural Resources Management Plan.
Although not yet found in the San Diego Bay, Caulerpa taxifolia has a devastating potential. The marine seaweed Caulerpa taxifolia, also known as "killer algae," poses no threat to human health, but it could have devastating ecological and economic consequences for California if it is allowed to become permanently established. This non-native seaweed threatens California's coastal marine life by overgrowing and eliminating native seaweeds, seagrasses, reefs, and other communities. An overgrowth of this species in the Mediterranean is reported to have harmed tourism, devastated recreational diving, and had a costly impact on commercial fishing by altering the distribution of fish and inhibiting the establishment of juveniles. Historically, this species has been used as a popular aquarium plant in peoples' homes, and biologists believe that the Mediterranean outbreak may have been the result of irresponsible aquarium cleaning practices.
Caulerpa taxifolia has a brilliant (almost fluorescent) green color and grows in the form of flat, leafy (fern-like) fronds that extend upward from each main stem. Each stem can grow to nine feet in length and have up to 200 fronds. This algae can be found as individual plants or in dense blankets that may cover many acres. Do not be deceived by its attractive appearance!
If you're an aquarium enthusist, here are some tips for preventing a Caulerpa taxifolia invasion:
- If you see this seaweed for sale for your aquarium in a pet store, do not use it!
- Do not release any water, plants, or animals from a saltwater aquarium into a street, storm drain, creek, bay, lagoon, or the ocean.