Invasive species in Great Lakes
Over 180 non-indigenous species have invaded the Great Lakes since 1840, and Ricciardi (2006) estimated that one new species invades them every 28 weeks. Non-indigenous species (e.g. plants or animals) are defined as species that adversely affect the habitats they invade economically, environmentally or ecologically. In other terms, any species, including its seeds, eggs, spores, or other biological material capable of propagating that species, that is not native to that ecosystem and whose introduction does or is likely to cause economic or environmental harm or harm to human health. Nonnative species have many vectors, including many biogenic ones, but most species considered “invasive” are transferred by association with human activity. Natural range extensions are common in many species, but the rate and magnitude of human-mediated extensions in these species tend to be much larger than natural extensions, and the distances that species can travel to colonize are also often much greater with human agency (Cassey et al. 2005).
Most non-indigenous species in the Great Lakes are from the Baltic, Azov and Caspian Sea, or from other regions in Eurasia (MacIsaac et al. 2001). These invaders threaten biodiversity, the ecosystem, and human health (Mack et al. 2000). According to Ricciardi (2006) the Great Lakes basin is one of the most influenced ecosystems, by invasive species, in the world. Invasive species survive well in a newly introduced environment due to the ability to reproduce both asexually as well as sexually, their fast growth, their rapid reproduction and high dispersal ability, their phenotypic plasticity (the ability to alter one’s growth form to suit current conditions) and their tolerance to a wide range of environmental conditions (generalist), in addition to their ability to live off of a wide range of food types (generalist), and/or association with humans (e.g., Kolar & Lodge 2001, Reichard & Hamilton 2002, Tilman 2004).
Transportation of Invasive Species to the Great Lakes
The major vector for invasions into the waters of the Great Lakes is ballast water from ships that is discharged upon arrival (e.g., Mills et al. 1993, Ricciardi 2001, Holeck et al. 2004). For example, 65% of all invasions recorded since opening the St. Laurence Seaway in 1959 were caused by ballast water release (Ricciardi 2006). In order to preclude the arrival of new organisms that could potentially threaten the Great Lakes, prevention is the most cost-effective approach. Since 1993, the United States has forced ships entering the St .Lawrence Seaway with ballast water on board to exchange the water in a mid-ocean (Ballast Water Exchange) (e.g., Locke et al. 1993, Murphy et al. 2004). Nevertheless, the rate of invasion has not decreased (Costello et al. 2007). Recognizing the problem and to strengthen local controls, the International Maritime Organization (IMO) proposed an international regulation for ballast water performance. Their criteria for suspended particles in dischargeable ballast water are:
Regulation D-2 Ballast Water Performance Standard – Ships conducting ballast water management shall discharge less than 10 viable organisms per cubic metre greater than or equal to 50 micrometres in minimum dimension and less than 10 viable organisms per milliliter less than 50 micrometres in minimum dimension and greater than or equal to 10 micrometres in minimum dimension; and discharge of the indicator microbes shall not exceed the specified concentrations.