Invasive Species

America's Least Wanted

When a plant or animal is introduced to a non-native area—where its presence is not "natural"— the effects are often devastating to the ecosystem.  The balance is upset, and without its natural predators the non-native species may "out-compete" the native species.  The native plants and animals, business, agriculture, and recreational activities may be negatively impacted.

Here are just a few examples of these "invasive species":

CHINESE MITTEN CRABS (Eriocheir sinensis)
Chinese mitten crabs, native to China's Yellow Sea, are now growing to HUGE populations in San Francisco Bay. These 3-inch crabs were 1st found in 1992. Today fishermen unintentionally catch thousands of these crabs every day! It is not clear exactly how they came to our coast, but now that they are here they are inhabiting the S.F. Bay & all the rivers in the surrounding areas. Even though they are considered a delicacy in China, this is not good news for many reasons. Chinese mitten crabs have parasites called flukes that live inside them. These parasites can be transferred to humans! Also, mitten crabs burrow into the mud causing erosion problems on the banks of rivers. Perhaps their worst crime is their destruction to fishing nets and catch that results in thousands of dollars worth of damage.

ZEBRA MUSSELS (Dreissena polymorpha)

Zebra mussels are tiny invertebrates (2-3 cm long). Who could imagine these small animals could cause so much damage! Native to Russia's Caspian Sea, they were probably brought to the U.S. in the ballast waters of large ships. Since invertebrates begin their lives as small floating plankton, ballast waters are filled with them & provide the perfect transportation to areas where they'll become an alien (non-native) species. These striped mussels were 1st found in the Great Lakes, but now inhabit many U.S., waterways. Zebra mussels can remove contaminants in the water & then concentrate them on the shores—shore birds eating these mussels may also be eating large amounts of contaminants! Also, these little mussels attach themselves to the insides of pipes from factories, water companies, & power plants. They clog the pipes (see photo), causing companies to spend huge amounts of money to have them removed.

IMPORTED RED FIRE ANTS (Solenopsis invicta)

Native to South America, imported red fire ants 1st invaded the southeastern U.S. in the 1930's, probably in soil used as ballast in cargo ships. They are now found in 11 states, including CA. These tiny invertebrates are more than just annoying pests—they've caused billions of dollars of damage to agriculture. Imported red fire ants have been compared to a "weed"—aggressive and adaptable. They are more aggressive than the black imported fire ants, which have been displaced by the red ants. Maybe more unsettling is their harmful effect on young birds, small mammals, amphibians & reptiles. Bobwhite quail chicks & horned lizards must compete for food (small insects) with the red fire ants—the ants win that
battle every time.

ICE PLANT (Cotula coronopifolia)

Ice plant is native to South Africa but came to the U.S. in the 1800's. Since that time, it has virtually taken over the wetland (salt marsh) areas in southern CA. This ecosystem is already threatened due to loss of habitat. The ice plant makes matters worse by out-competing native plants. Ice plant is very strong, often stronger than the native plants themselves. Because of this, ice plant wins when it comes to getting nutrients! Also, once ice plant dies it leaves behind so much salt that other native plants don't want to live there. All of this lessens the diversity of wetland plants. This means that endangered species like the Clapper Rail lose their homes. Over 90% of the southern CA wetlands have already been destroyed!

#1 LEAST WANTED: "EVIL ALGAE"(Caulerpa taxifolia)

Native to the Carribbean, a strain of this saltwater aquarium plant has devastated the Mediterranean. It is like "laying astro-turf on the ocean floor"—displacing everything in its path. The algae gives off toxins making it undesirable for fish, molluscs & sea urchins to eat. Unfortunately it was discovered right here in San Diego, probably after someone dumped the contents of their aquarium in the lagoon. Luckily immediate efforts to control & eradicate the algae have been successful, but as long as it is legal to posses and sell in CA, the threat remains. Click here to learn more about this "evil algae".

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