California Aquatic Invasive Species

Caulerpa prolifera

Caulerpa prolifera is native to European waters, the Mediterranean Sea, and warmer waters of the Gulf of Mexico and the eastern Atlantic Ocean, including south Florida. It was discovered in Newport Beach, CA in 2021. It can grow quickly, choking out native aquatic plants and harming marine life through habitat loss. A similar species, Caulerpa taxifolia, was eradicated in California in 2006, six years after if first became established. Species of Caulerpa can reproduce and spread by fragmentation, where pieces of algae break off and can take root in new areas, potentially outcompeting native algae and sea grasses.

Eichornia crassipes and Egeria densa

Waterweeds include a long list of non-native plants that have been introduced to California over the past fifty years, often through commercial sales. Among the most widely know is Water Hyacinth (Hydrilla verticillata), considered to be one of the worst invasive aquatic plants in the world. Native to South America, it has infested freshwater regions of California since the 1950s, likely through the aquarium trade. Similar to other waterweeds, such as Curly Pondweed (Potamogeton crispus), they can spread via vegetative structures that break off and create entire new plants. Heavy infestations of waterweeds decrease fishing stocks and restrict boating, which reduce recreational opportunities of infested waterways and the economies they support. Other problem species include Brazillian waterweed (Egeria densa), Alligator weed (Alternanthera philoxeroides) and Water primrose (Ludwigia spp.)

Spartina alterniflora x S. foliosa

The Army Corps of Engineers introduced Atlantic cordgrass (Spartina alterniflora) to San Francisco Bay in the 1970s for marsh mitigation. This non-native hybridized with the native Pacific cordgrass, Spartina foliosa, creating a much more invasive hybrid than the parent invader. Hybrid Spartina (S. alterniflora x foliosa) aggressively covered lower tidal mudflats in the 1980s and 1990s, displacing the native Pacific cordgrass and turning open mudflat habitat used by shorebirds to a non-native monoculture, eliminating foraging habitat for shorebirds by reducing the abundances of key invertebrates. Eradication of invasive Spartina in the San Francisco Bay Area has since resulted in a 95% decrease from peak levels.

Driessena bugensis and Driessena polymorpha

The quagga mussel (Driessena bugensis) and zebra mussel (Driessena polymorpha), known together as Eurasian mussels, are originally from Ukraine and were first detected in California in 2007 and 2008 and have since spread to canals, rivers, and lakes around the state. Although they measure under 5 cm long, they can cause major ecological harm by modifying aquatic habitats and pose a threat to the environment and to California's water supply. They reproduce rapidly and in high densities, competing for space with native species. They filter phytoplankton out of huge volumes of water which can change the physical and biological properties of an ecosystem. Eurasian mussels also cause significant economic harm by damaging boat engines, clogging pipes, covering infrastructure such as docks, dam gates and irrigation channels, and reducing the recreational and economic value of lakes.

Lithobates catesbeianus

American Bullfrogs (Lithobates catesbeianus) are a large species of frog native to Central and Eastern United States. They prefer shallow, slow moving or stagnant freshwater pools and ponds but have been found in the shorelines of lakes and rivers. They have been known to not only out-compete native species for food and habitat, but have been documented as predators of native California birds, fish, reptiles, amphibians, and invertebrates. Additionally, they are linked to the introduction of the deadly chytrid fungus, a disease known to have caused population declines and extinction of amphibian populations around the world.

Menidia auden and M. beryllina

Invasive silversides, Mississippi (Menidia audens) and inland (M. beryllina) areare small, 10 cm long fish native to the southern watersheds of the Mississippi River region. Intentionally introduced in 1967 to the Blue Lakes and Clear Lake in California to control insects, Silversides are now found throughout Northern California and have spread to Southern California via the California Aqueduct. In Clear Lake, they displaced native fishes, including Hitch (Lavinia exilicauda), the Sacramento Blackfish (Orthodon microlepidotus), and contributed to the extinction of the Clear Lake Splittail (Pogonichthys ciscoides). They also consume eggs and juveniles of native fishes in the Sacramento-San Joaquin Delta where they are a threat to the highly endangered Delta Smelt (Hypomesus transpacificus).

Myocastor coypus

Nutria (Myocastor coypus) is a large, aquatic rodent reaching 1/2 meter in length and weighing up to 10 kgs. They were first found in California in 2017 and have since been confirmed in several counties including San Joaquin, Stanislaus, Merced, Fresno, Mariposa, and Tuolumne. Nutria are exceptional herbivores that consume large amounts of wetland vegetation, up to 25% of their body weight daily. In regions where they have been introduced they have devastated marsh and wetland habitats through their consumption and burrowing and in some cases, converting vegetated marsh lands to unvegetated open water habitats.