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Invasive species

The arrival of non-native species, species that do not naturally occur in a certain area, is not a new problem for the Chesapeake Bay. Researchers at the Marine Invasion Research Laboratory at the Smithsonian Environmental Research Center (SERC) have reconstructed the pattern of invasions over the past four centuries, beginning with European colonization. The researchers have now identified approximately 160 species that are nonindigenous to the Chesapeake Bay, and scores of other species that are of unknown origin.

Today, the global movement of ships has increased the distribution of species all over the world. Non-native species don't just swim across the ocean; they can conveniently ride with large cargo vessels that are crossing the ocean from port to port.

"All aboard!"

When cargo ships are not carrying a load, they need to carry other weight in order to remain stable and be able to adjust the balance of the ship for optimal steering and propulsion. So after ships deliver their cargo at a port and head home, they fill up enormous tanks on the ship with water from the port or coastal region.

Researchers are taking a sample of the ship's ballast waterPicture: Researchers taking a sample of the ship's ballast water.

With the ballast water, as it is called, the ships also pump up the animals and plants that are in the water. When the ships then get to the next port to load cargo, they release the water (with the animals and plants in it), either in the port or along the coast. As a result, the ships pick up, transport, and release marine organisms around the world.

Researchers at SERC's Marine Invasion Research Laboratory measure the supply and fate of these foreign species in the Chesapeake Bay and elsewhere in the United States. SERC researchers examine many different aspects of the big journey of these organisms from their origin to the waters of the Chesapeake Bay.

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Researchers at SERC's Marine Invasion Research Laboratory examine many different aspects of the big journey of the invasive species from their origin to the waters of the Chesapeake Bay and elsewhere in the country. Picture: Researchers at SERC's Marine Invasion Research Laboratory examine many different aspects of the big journey of the invasive species from their origin to the waters of the Chesapeake Bay and elsewhere in the United States.

The researchers, for example, track where the ships are coming from, what percentage of the animals and plants survive the trip, which creatures can actually reproduce after they arrive in the Chesapeake Bay, and how many new invasions are discovered.

Although the effects of many introductions remain unmeasured, it is clear that invasive species can have significant economic and ecological impacts, as well as human-health consequences. Invaders like the zebra mussel in the U.S. Great Lakes, toxic dinoflagellates in Australia, and the oyster parasite MSX in the Chesapeake Bay have had tremendous ecological and economic impacts.

Is there a way to stop this worldwide transport?

The only effective way at the moment to reduce the risk of introducing more invasive species is called "ballast water exchange."

Ballast water exchange means that ships on their way to the next port release the coastal water they pumped up and replace it with open-ocean water. Although this measure is not perfect, it at least reduces the number of potentially invasive species in the ballast tanks and replaces them with oceanic organisms that are less likely to survive in the near-shore waters of the next port where the ship will dock.

Although alternate methods to treat ballast water are not yet available, the researchers at SERC are carrying out extensive laboratory and field tests to examine the many possible treatments.

A ship is exchanging its coastal ballast water with water from the open ocean to reduce the chance of transporting any invasive species to the next port.

Picture: A ship is exchanging its coastal ballast water with water from the open ocean to reduce the chance of transporting any invasive species to the next port.

(Pictures courtesy of SERC's Marine Invasion Research Laboratory.)

References and further reading

For more information about invasive species and ballast water exchange, visit the web pages of the SERC Marine Invasion Research Laboratory.