An invasive species is one that causes ecological and/or economic harm to its new environment (NOAA 2014), and at any given moment there are some 10,000 being transported in ballast tanks ( Bax et al 2003). Lucky for us most of these potential  invaders die before they reach their final destination because of the dark and dirty conditions of the ballast tanks or the conditions in their new environment are not suitable for them (Bax et al 2003). Over the last few years the amount of invasive species has been accelerating (Roman 2010). However this increase is not just in one area, it has been seen in the number of plant, animal, protist, and microorganism species (Roman 2010).  To combat this problem, first is getting the knowledge out there. Answering questions like: how do they spread, what is so bad about them, and how can we manage the problem.

There are many different ways that an invasive species can be introduced. The most common ways (also known as pathways or vectors) are intentional importing (like stocking of fish into streams for sport fishing), escape from captivity, the transportation of aquaculture stock (shellfish, fish, or algae), on the hulls of ships, and the opening of channels and canals (Roman 2010, Lovell and Stone 2005).  However, boats and ballast water are generally the primary pathway that invasive species are introduced into a new habitat (Roman 2010, Bax et al 2003). Shipping carries more than 80% of the world’s trade, that can equate to over 12 billion tonnes of ballast water moved every year which could result in millions of new invasive species (Bax et al 2003).

You are probably wondering what can be the problem with introducing species into an ecosystem. Invasive species can wreak havoc on an ecosystem in many ways. To respond to that, not all species that get introduced into an ecosystem end up  becoming invasive (Bax et al 2003). In fact, most simply become part of the background flora and fauna (Bax et al 2003). However, for  those that do become invasive affect the ecosystem in many different ways. One such way is they will outcompete the native population for resources such as food, nutrients, and even sunlight. This causes a decrease in biodiversity in an area because the native species just can’t compete with the invaders.

Another way is that  invasive species do not always just affect the ecosystem. These invaders can also negatively affect the economy in the area. They can cause damages to commercial and recreational fishing, human health, and commercial facilities (Roman 2010). Since some invasive species are pathogens and parasites this can cause lots of problems for the aquaculture and fishing industries. Since stocks can be moved and stocked all over the world, their parasites and path

Green crab eating a clam. (Courtesy of ferrebeekeeper).

Green crab eating a clam. (Courtesy of ferrebeekeeper).

ogens can wreak havoc on the native stocks and decrease yields  which in turn means diminished profits for the people in the industry (Bax et al 2003). For example, polydorid polychaetes that bore into oysters and abalone have been introduced into Californian and Hawaiian stocks (Bax et al 2003).  These introductions can even lead to a collapse of an industry as seen in the impact that the Green Crab (Carcinus maenas) is having on clam and other bivalve industries in North America (Bax et al 2003).

What can be done to slow down, stop, prevent, and even get rid of the vectors that can lead to these possibly devastating invasions? Currently the vectors that are receiving the most attention are ballast water and transporting these species (Bax et al 2003). Since no single vector is completely to blame for an invasion, Bax et al suggests that more comprehensive management solutions need to be considered and used (2003). There are more than 50 national and international laws and regulations are in place to restrict the transport of nonnative species (Roman 2010). Most of these focus on one vector, but this not always effective. The most cost-effective policies are those that are more focused on prevention rather than removal as removal are not always successful (Roman 2010). For example, in 1993, more than 30,000 Northern Pacific seastars (Asterias amurensis) were removed from shallow waters in the Tasmanian Southern coast; in 2001, there were more than 140 million (Roman 2010).  Eradication can be effective and less costly if the invaders are caught in the early stages of an invasion since the distribution is more localized (Roman 2010).

As previously stated, most introduced species do not become a problem but merely become part of the background. For those that do become a problem, they can wreak havoc on the ecosystem. They outcompete the native species for food, space, and nutrients. They even can change the way the ecosystem is structured! They can negatively affect the economy and health of the surrounding areas by introducing new pathogens and parasites that the native species do not have a way to fight off. With the increase in shipping travel and the lack of real ways to prevent or decrease the amount of species being introduced, we need to be more aware of the damages we can cause to an ecosystem whether intentional or not. The first step is awareness, now take it and run with it.


Bax,  Nicholas, Williamson, Angela, Aguero, Max, Gonzalez, Exequiel, Geeves, Warren. “Marine invasive alien species: a threat to global diversity.” Marine Policy. 2003. 27:313-323.

Lovell, Sabrina, Stone, Susan. “The Economic Impacts of Aquatic Invasive Species: A Review of the Literature.” National Center for Environmental Economics U.S. EPA. January 2005.

Roman, Joe. “Aquatic Invasive Species.” Encyclopedia of Earth. 2 July 2010.

“What Is an Invasive Species.” National Oceanic and Atmospheric Administration. 2014.

NA. “Green Crabs”. Ferrebeekeeper. ND.