Invasive species, also known as exotics, are plants, animals, insects, and aquatic species introduced into non-native habitats.
Often, invasive species travel to non-native areas by ship, either in ballast water released into harbors or attached to the sides of boats. From there, introduced species can then spread and significantly alter ecosystems and the natural food chain as they go. Another example of non-native species introduction is the dumping of aquarium fish into waterways.
Without natural predators or threats, these introduced species then multiply.
Invasive species also put water conveyance systems at risk. Water pumps and other infrastructure can potentially shut down due to large numbers of invasive species.
Invasive Species in California
Since the arrival of Western settlers, California has been troubled by invasive species. In one prominent example, eucalyptus from Australia has thrived across the state.
The state’s waterways are also home to some of the densest concentrations of invasive species in the world. This is the case in San Francisco Bay, with its busy ship traffic from around the globe, and the Sacramento-San Joaquin Delta.
In the past decade, invasive species threats have included trout and bass in Lake Tahoe, water hyacinth in the Delta, and quagga mussels in reservoirs along the lower Colorado River and in the Colorado River Aqueduct that carries water to Southern California.
Invasive aquatic vegetation in the Delta includes Brazilian waterweed, water hyacinth, and water primrose. Invasive vegetation has increased exponentially in recent years, clogging about 17,400 acres of waterways across the Delta, according to the U.S. Geological Survey.
Delta invasives alter water flows, water temperature and the amount of oxygen and nutrients in the water. They disrupt sediment transport and turbidity — how clear or cloudy the water is — which in turn affects the quality of habitat for fish, such as smelt. Decreasing turbidity makes young smelt more vulnerable to predators. Sediment transport also is important because its deposition across marsh plains protects against predicted sea level rise.
Total eradication of these invasive plants from Delta waterways is unlikely because they have spread too widely, according to USGS.
And a large rodent native to South America known as nutria began causing concern after invading the Delta. Nutria has a propensity to devour every bit of vegetation in sight and destabilize levees by burrowing into them.
Along the Colorado River, once thriving cottonwoods have been crowded out by tamarisk, salt cedar and other exotic plants that erode beaches and degrade wildlife habitat.
In response, the Lower Colorado River Multi-Species Conservation Program was launched in 2005 to balance use of the river with the conservation of native species and their habitat. The MSCP, which works toward the recovery of species listed under the Endangered Species Act, includes actions such as densely planted riparian conservation areas to reduce invasive species competition with native species.
California adopted legislation in 1999 requiring ballast water management. In 2006, the State Lands Commission issued regulations setting ballast discharge standards and deadlines. Under the current plan, ships must meet the ballast standards by 2020.
In 2017, the State Lands Commission adopted regulations for ballast water management. Among other things, they required arriving vessels of a certain tonnage to discharge only the minimal amount of ballast water essential for operations and to minimize or avoid uptake of ballast water in areas with known infestations of invasive species.