Signage warning the public of invasive zebra mussels (Source:

Signage warning the public of invasive zebra mussels (Source:

Invasive species are species that are not native to a location, have the ability to spread throughout an area, and cause harm to the ecological environment they invade (Mack et al. 2000). Marine ecosystems are particularly susceptible to invasive species. Many species that attempt to invade a new area do not survive the transportation, while others cannot handle the conditions of the new environment (Mack et al. 2000). Those that are able to overcome these hurdles and colonize a new environment are deemed invasive. The majority of marine invasive species are found in the tidal and subtidal zones (Bax et al. 2003).

Methods of Introducing Marine Invasive Species to a Novel Water Body

A large ship expelling ballast water (Source:

A large ship expelling ballast water (Source:

Nonindigenous species can be introduced to a location through a variety of vectors. Several of these vectors are associated with large shipping or cargo vessels. Shipping transports more than 80% of the world’s trade, dumping about 12 billion tons of ballast water per year in the process (Bax et al. 2003). Ballast water is pumped into the ballast tank of a ship to provide stability and maneuverability. When released after travel, novel organisms in the ballast water are introduced into new environments and can disrupt the native species.

In addition to ballast water, hull fouling (a process in which organisms attach themselves to the hull of the ship and are transported to a new location) also occurs with large international shipping vessels. Increased numbers of nonnative species present in fouling communities can alter filtering rates, harming the ecosystem, as well as alter water clarity, potentially causing economic hardship as well (Sorte et al. 2010). Although techniques such as anti-fouling paints and increased shipping speeds have reduced the effect of hull fouling, it still contributes to the transport of marine invasive species (Bax et al. 2003).

An example of hull fouling on a recreational boat (Source:

An example of hull fouling on a recreational boat (Source:

Recreational boating also contributes to the issue of hull fouling. Murray et al. (2011) reasoned that it is the largest unregulated vector responsible for the introduction of numerous marine invasive species. Dive studies in various marinas in British Columbia revealed numerous nonindigenous species found in the hull fouling communities of recreational boats, implying that recreational boating is a major vector contributing to the spread of marine invasive species (Murray et al. 2011). Other agents of introduction not associated with shipping include unintentional transport through importation of mariculture species, as well as intentional introduction of various exotic species for mariculture (Bax et al. 2003). Mariculture is the cultivation of marine organisms for food and other products. By importing these news species for the purpose of mariculture, humans are introducing species to novel environments and contributing to the spread of invasive species.

A graph showing increasing global ocean heat content from the 1960's through present day (Source:

A graph showing increasing global ocean heat content from the 1960’s through present day (Source:

Research has shown that factors such as increasing temperature due to climate change and the creation of new habitats facilitate the likelihood that an introduced species will become invasive. Sorte et al. (2010) hypothesized that ocean warming associated with climate change facilitates the ability of a species to successfully invade. They found that introduced species were more tolerant of rising temperatures than native species (Sorte et al. 2010). With warming climate trends, invasive species are more likely to become dominant over native species (Sorte et al. 2010). A study by Bax et al. (2003) claims that factors that either modify or construct new habitat may also facilitate invasion. With increased population, trade, and tourism in coastal communities, the establishment of novel man-made environments increases, providing species with new habitats for colonization (Bax et al. 2003).

Marine invasive species can have biological, as well as social and economic impacts as well. The marine invasive species that inflict the most risk can displace native species, alter community structure and food webs, and disrupt other processes in the marine environment, such as nutrient cycling and sedimentation (Molnar et al. 2008). Marine invasive species negatively affect human health and decrease economic production by altering fisheries products, tourism, and marine infrastructure (Bax et al. 2003). Although occurring much less frequently, marine invasive species can also positively affect the economy by creating employment opportunities through marine species management programs and aquaculture (Bax et al. 2003). It is evident that marine invasive species pose a significant risk to local marine communities; however, if the issue fails to be addressed, invasive species could have significant global consequences as well (Mack et al. 2000).


Bax, N., Williamson, A., Aguero, M., Gonzalez, E., and Geeves, W. 2003. Marine  invasive alien species: a threat to global biodiversity. Marine Policy 27: 313 –         323.

Mack, R.N., Simberloff, D., Lonsdale, W.M., Evans, H., Clout, M., Bazzaz, F.A. 2000.   Biotic invasions: causes, epidemiology, global consequences, and control. The    Ecological Society of America 10(3): 689 – 710.

Molnar, J.L., Gamboa, R.L., Revenga, C., Spalding, M.D. 2008. Assessing the global         threat of invasive species to marine biodiversity. Ecological Society of America     6(9): 485 – 492.

Murray, C.C., Pakhomov, E.A., Therriault, T.W. 2011. Recreational boating: a large          unregulated vector transporting marine invasive species. Diversity and Distributions 17: 1161 – 1172.

Sorte, C.J.B., Williams, S.L., Zerebecki, R.A. 2010. Ocean warming increases threat of      invasive species in a marine fouling community. Ecology 91(8): 2198 – 2204.