Why Aquatic Invasive Species are a problem
For as long as plants and animals have been around, species have moved around the planet. For most of history, species distributions were limited by the distance a population could crawl, fly, swim, walk, or get blown in the wind. In more recent times, humans have helped a wide variety of species move far beyond their native ranges. In fact, many of the plants and animals important to agriculture in Massachusetts originated from some other part of the world. However, with human travel and trade, some undesirable species have come along as well. These species arrive both intentionally and unintentionally and threaten the Commonwealth’s natural history and economy.
But what makes one species invasive and not another? We define Aquatic Invasive Species (AIS) as nonindigenous or cryptogenic species that threaten the diversity or abundance of native species or the ecological stability and/or uses of infested waters. These species are invasive and threatening when they are introduced to new environments that lack the physical or biological constraints present in the native environment. Because it is difficult to predict which species will be invasive, we look at the track records of foreign species in ecosystems similar to those in Massachusetts to indicate which species should be considered potential invaders. Although the majority of introduced species will never become established populations, some will pose a great threat to native ecosystems and economies.
Invasive species threaten the biodiversity of Massachusetts when they displace species that naturally occur here. This can occur when the invasive species has a more effective defense against predators (or no predators at all), faster growth, higher reproductive success rates, or the ability to out-compete native species for food and habitat. Plant species like purple loosestrife (Lythrum salicaria) form dense mats in wetlands and crowd out native aquatic plant species. Although not yet widespread in Massachusetts, hydrilla (Hydrilla verticillata) is known to become so abundant that it alters the physical and chemical characteristics of lakes and impacts the survival of fish and other species. In Florida, it has become the most abundant aquatic plant in public waters since it was introduced in the 1950s. When hydrilla has occupied a majority of the water column, fish are often smaller and weigh less. Hydrilla may even contribute to fish kills.1
A new species competing for scarce resources can stress endangered species and may contribute to extinction. Furthermore, dramatic changes in the characteristics of an ecosystem can damage important ecosystem services like water purification, flood mitigation, and nutrient cycling. This loss of ecosystem function can have great implications for local species and human communities.
The negative economic impacts of invasive species are significant and diverse as well. The commercial seafood industry in Massachusetts produced almost $1 billion 2 in output in 2004. Recreational fishing led to $494 million 3 in retail sales in 2001 according to American Sportfishing Association estimates. Even though no one has put an exact number on economic losses in Massachusetts due to AIS, it is clear that when invasive species disrupt these industries, the Commonwealth’s economy suffers overall.
The European green crab (Carcinus maenas) is an example of a species that has impacted the Massachusetts economy. Introduced in the mid-1800s, this crab has a voracious appetite for commercially valuable shellfish. Since being introduced it has become one of the most abundant crabs in our coastal waters and it competes with native fish, birds, and humans for the same food. Because it eats clams, oysters and other mollusks, the seafood industry has been impacted by the resulting ecological change. Other economic impacts from AIS can include biofouling, which occurs when animals like the zebra mussel (Dreissena polymorpha) or Asian clam (Corbicula fluminea) grow to such densities that they impair industrial water intakes. Furthermore, AIS can lead to a loss of recreational, property, and commercial values.
To help manage species that have already established themselves in Massachusetts, prevent new species from arriving, and respond to new introductions, the AIS Working Group was formed to develop a management plan and guide future efforts.
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