5 Invasive Species You Should Know

A ship flushes and refills its ballast task in mid-ocean to prevent marine organisms from moving from one port to another.

Credit: Smithsonian Environmental Research Center

Regardless of what continent you live on, the waters that surround it are home to marine invaders. The ocean is teeming with plants and animals willing and able to move beyond their native habitats. Often all they need is a ride. Enter: humans. Some invaders hitchhike on ship hulls or inside ballast tanks, others are introduced through the aquarium trade. However they move, invasive species can alter ecosystems, food webs, and economies. The Smithsonian Environmental Research Center’s Marine Invasions Lab travels the globe to better understand the movement and impacts of invasive species. They highlight a daily invader on their website; we asked them to introduce us to five. 



Filip Nuyttens, World Register of Marine Species


1. Green Crab (Carcinus maenas) 

This European crab has been carried by ships in ballast water and is sold as fish bait in much of the world. It now has established populations on both coasts of North America, in southern South America, Australia, South Africa, and Japan. It is a predator of many forms of shore life, including worms and mollusks. In some areas, the crab’s voracious appetite has affected the commercial shellfish industry.





Antoine N'Yeurt, Moorea Biocode Project


2. Killer Algae (Caulerpa taxifolia)

A strain of this green seaweed, native to the Indian and Pacific Oceans, has escaped public and private aquariums in California, Japan, Australia, and Monaco. It has spread widely in the Mediterranean, replacing native plants and depriving marine life of food and habitat. In California, it was eradicated at considerable cost using toxic chemicals. 






Marco Faasse, World Register of Marine Species


3. Sea Walnut (Mnemiopsis leidyi) 

This ctenophore (a stingless jellyfish-like animal) is native to the east coast of North and South America. In 1982, it was discovered in the Black Sea, where it was transported by ballast water. It subsequently spread to the Caspian Sea. In both places it multiplied and formed immense populations. The sea walnuts contributed to the collapse of local fisheries because they feed on zooplankton that the commercial fish also consume. Mnemiopsis leidy has also been discovered in the Mediterranean, Baltic, and North Seas.





Smithsonian Environmental Research Center

4. Veined Rapa Whelk (Rapana venosa) 

A large marine snail with a beautiful shell, Rapana venosa is native to the northwest Pacific, from Vladivostok, Russia to Hong Kong. In 1946 it was discovered in the Black Sea and later spread to the Mediterranean Sea. In 1998, it was found in the Chesapeake Bay where it was probably transported in the ballast water of ships. It is also established in European coastal waters from Norway to Spain, and in the Rio de la Plata estuary in South America. This animal, a predator on bivalve mollusks, severely reduced shellfish in the Black Sea, but is now fished and sold to Asian countries as food. Its role as a predator in the Chesapeake Bay is being studied, and it is expected to colonize other parts of the east coast.




D. Jude, Univ. of Michigan, NOAA

5. Zebra Mussel (Dreissena polymorpha)

This bivalve mollusk is native to the Caspian Sea, lagoons of the Black Sea and their inflowing rivers. It lives in fresh and brackish water and cannot tolerate full seawater. In the 18th and 19th centuries, it spread through European canals, reaching the Baltic Sea and many European river estuaries. In 1988, it was discovered in the Great Lakes and has spread to many rivers and lakes in eastern and central North America. The mollusk has fouled power plants, water purification facilities, ships, and littered beaches with decaying mussels and sharp shells. Large populations have devoured plankton and decreased the food available for commercial and game fish. It is abundant in the fresh, tidal parts of the St. Lawrence and Hudson Rivers, and has been discovered at the head of Chesapeake Bay.

Algae, Mollusks, Crabs, Ctenophores

Related Video

Researching Invasive Species Near the Panama Canal

If you want to study invasive species in the ocean, the Panama Canal offers a lot to explore. The ships passing through can inadvertently transport plants,...

In this video, get a first-hand look at Smithsonian researchers as they test new methods of removing invasive species from the water in ballast tanks. 


Smithsonian Institution

Busy shipping areas, like the Port of Oakland, are especially vulnerable to invading species that can be carried in ballast water.

Credit: Monaca Noble, Smithsonian Environmental Research Center

More Information

Join Citizen Science Efforts to Combat Invasive SpeciesNational Ballast Water Information Clearinghouse (NBIC)Marine Invasions Research Lab, Smithsonian Environmental Research CenterGlobal Invasive Species Database