Ocean Matters

Marine Exotic Species


Exotic Threats

Exotic species are a serious threat to marine ecosystems. An exotic or non-native species is an organism that invades an area where it does not naturally belong. Left on their own, exotic species can do incredible damage to marine ecosystems where they out-compete native species. We look at how exotic species move from one place to another and what can be done to stop them.

Transfer of Marine Exotic Species

There are two major ways that marine exotic species get transferred to the ocean. The first method involves people bringing plants and animals with them when they move from one place to another. If the species is able to reproduce, it can eventually establish itself in a new ecosystem. The introduction of Scotch Broom, a plant that grows on land, into British Columbia in the nineteenth century is an example of an exotic species that has quickly become a weedy menace. Rarely are marine exotic species introduced this way but.

Most marine exotic species are transferred to new places through the ballast water of ocean freighters.  Freighters are huge ships with hollow interiors for transferring cargo from place to place. Once these freighters unload their cargo they need to take on extra weight in the form of ballast water to ensure a safe stable ride to the next port. Unfortunately, ballast water often contains thousands of unwanted stowaways in the form of exotic species. When the freighters travel to their next port the critters in the ballast water go along for the ride. Once at the port, the ships dump their ballast water in preparation for taking on new cargo. During the dumping of the ballast water these critters find their way into a new ecosystem where they can breed and perhaps take over.

Above a freighter dumping its ballast water is shown. Any exotic species held in this ballast water find their way into a new ecosystem where they can possibly breed and out-compete the native species. Image used with permission from MIT Sea Grant Center for Coastal Resources. Picture taken by David L. Smith.



Reasons Why Exotic Species are Dangerous

Exotic species are dangerous because they can out-compete native species for food and interbreed with native organisms, diluting the gene pool. Fortunately, many exotic species cannot survive in their new homes because the habitat conditions are not right for them.

Stopping the Transfer of Marine Exotic Species

There are ways to combat the transfer of exotic species from freighters. The first method is to install filters on the freighters to sieve out some (perhaps even most) of the organisms that would otherwise end up in the ballast tanks. The second method is for freighters to exchange their ballast water in the open ocean to minimize species introduction in coastal waters. Most organisms cannot survive being dumped into the open ocean waters. The problem with the second method is that freighter captains do not like to exchange ballast water in the open ocean because it could destabilize the freighter. If a freighter destabilizes it could have unforeseen navigation problems and possibly sink. Using both methods can minimize but not eliminate the chance for species introduction. If we can stem the tide of incoming exotic species it may be possible to reduce their negative impacts on marine ecosystems.

For more information go to:
University of British Columbia E-Fauna website
Monterey Bay National Marine Sanctuary
Action BioScience

to Ocean Matters Headlines

OceanLink Home | OceanNews | Deep Sea Science | Biodiversity
Students in Action | Ocean Matters | Career Info | Links