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What Is An Invasive Species?
The United States Department of Agriculture maintains the National Invasive Species Information Center (NISIC). They define an invasive species as a species that is:
“Non-native (or alien) to the ecosystem under consideration AND whose introduction causes or is likely to cause economic or environmental harm or harm to human health.”
In the United States alone, there are around 4,300 species of invasive plants and animals. There is not one area of the country where invasives are not present; however some areas are more heavily affected than others. It is important for those who enjoy the outdoors to know about the issues caused by invasive species.
How Does a Species Become Invasive?
You may ask why invasive species have become such a widespread problem. The answer is: people. We are the sole culprit behind most introductions of invasive species. Lots of animals are introduced into new habitats because they end up as stowaways in shipping crates, ballast water, or a traveler’s belongings. Others are set free from holding equipment due to natural disaster or human error.
These previous methods of introduction are all unintentional. However, many invasive species were introduced on purpose. Sometimes animals are introduced to combat native nuisance animals (cane toads for agricultural pest control). Others get introduced because exotic pet or home aquarium owners cannot handle certain animals anymore, and release them into the wild – but not their native habitat (Burmese pythons in Florida).
We must remember that not every species that is introduced into a new environment will survive. Those that become invasive have special adaptations: they are tolerant of varying environmental conditions, they can reproduce quickly, and can consume a wide variety of food. These traits also make them very difficult to eradicate.
What You Can Do
The most important thing you can do is to prevent future introductions of invasive species. Although large scale control or eradication is often unrealistic, there are many actions you can take to help combat invasives and the problems that they cause:
See the “Links” page for more details on local organizations and volunteer opportunities.
Nancy Balcom is the Associate Director of the Connecticut Sea Grant. She is an expert on invasive species in Connecticut. Have a look at her answers to some interesting invasive species questions!
What problems do invasive plants raise? How do they affect local habitats?
How are invasive plants introduced?
If I see an invasive plant or animal, should I kill it?
Why is it so hard to eradicate invasive species?
I have an exotic pet, not native to this area and do not wish to care for it anymore - I do not want to release it to the wild. What can I do?
Indo-Pacific Lionfish (Pterois volitans)
These voracious and venomous predators, native to Indo-Pacific reefs, now have established populations over almost the entire western Atlantic Ocean. They can be found off the coast of Bermuda, the Caribbean, Gulf of Mexico, and the entire eastern seaboard of the United States as far north as Rhode Island. The reason for their success – and the reason for concern – is their incredible appetite and hunting skill. In the Caribbean they are known to prey on at least 40 different species of fish. This intense predation has put stress on many fish species in the areas they have invaded.
The exact method of lionfish introduction is not known, but the most likely culprit is the aquarium trade – lionfish are a popular ornamental fish, and research shows the most likely cause to be home aquarium owners in Florida releasing them to the wild. Some even theorize that Hurricane Andrew had a significant impact, by shattering tanks and flushing the animals into Floridian waters. You are probably aware that we house lionfish at Mystic Aquarium. These beautiful fish are lovely additions to the Aquarium; what we must keep in mind is that in their native habitat they are in a perfect balance with the ecosystem – but in the Atlantic, their existence is not naturally controlled.
There is a very unique control effort happening with lionfish. Many organizations host “lionfish derbies”, where fishermen and divers venture out and try to catch as many lionfish as possible. They then market the flesh for locals to eat. Although poisonous in their barbs, the flesh of lionfish is quite palatable and some believe that developing the taste and popularity of eating lionfish will help decrease the impacts they have on native ecosystems.
Common Reed (Phragmites australis)
This plant is a common fixture of marsh habitats around much of the eastern United States, and it may surprise you to know it is an invasive species. Although some species of Phragmites (pronounced frag-MIGHT-ees) may have been native to this area, a different variety – one from Europe – has emerged as a threat to native ecosystems.
The fact that this organism is a plant may deceive you. They can seriously disturb ecosystems in a number of ways. They grow in thick strands, and serve as physical barriers to animals wanting to access water. In fact, Phragmites marshes have less diversity and abundance of aquatic animals due to their presence. They degrade the habitat for birds as few can use them for nesting. Phragmites grows tall (perhaps 20 feet) and can shade other plants, which need the sun to grow and produce. They decompose slowly and become serious fire hazards. All these effects may seem subtle, but our local marshes that are not adapted to cope with the effects Phragmites has, and overall ecosystem health has suffered.
Asian Shore Crab (Hemigrapsus sanguineus)
These animals are now extremely common along rocky intertidal habitats here in the Northeast. After the introduction in 1994, densities of the native flatback mud crab (Eurypanopeus depressus) decreased by 95%, and common periwinkle (Littorina littorea) density decreased by 80%. Their invasive abilities are extraordinary; even another invasive crab, the European green crab (Carcinus maenas) has been displaced by the Asian shore crabs. Their introduction is likely due to ballast water.
The Asian shore crabs prey on a wide variety of molluscs and crustaceans, especially juveniles. One main reason for their abundance here is the lack of natural parasites that regulate their population in their native range. In addition, many animals here are not accustomed to feeding on them. Research has shown that these crabs are here to stay – large scale eradication is simply not possible. Scientists will continue to monitor and research the impacts that these animals have on native populations of molluscs and crustaceans.
If you have more questions, the US Fish and Wildlife Service has an extensive Frequently Asked Questions page with lots of useful information.
Access the National Invasive Species Information Center! This site has lots of info, including species profiles and identification guides.
The US Fish and Wildlife Service has advice for preventing the spread of invasives, based on the outdoor activities that you enjoy!
Check out a local group, the Connecticut Invasive Plant Working Group!
Check out an NPR article discussing the lionfish invasion. Read about how their invasion has been so deadly – relentless predators, and resistant to local parasites!
The Burmese python invasion of the Florida Everglades has captured the attention of the national media. Have a look at some of these articles, discussing the spread of these animals and their impacts.
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