Not all new species introduced to an area are invasive, but those that are can have a negative effect on the ecology and biological diversity of a region as the invasive species tend to outcompete and at times eradicate their native counterparts. Here are six notorious invasive species. These range from plants originating in China to fish weighing upwards of 50 pounds. We look at their origins, why they’re invasive and what we can do to contain or eradicate them.
How did it get here? The Alabama (or Coosa) bass (Micropterus henshalli) isn’t your typical invasive species in the sense that its origins aren’t too far away from where it’s currently thriving. The Alabama bass was recently classified as a unique species from the spotted bass (Micropterus punctulatus) and it made its way from the Alabama-Coosa-Tallapoosa river basin in Northwest Georgia and Alabama to adjacent river basins, such as the Mississippi. Anglers are likely responsible for most of this movement, whether intentionally or by accident. Some of the invasive species you’ll read about below come from all over the world, whereas the Alabama bass is closely linked to the spotted bass. So close, in fact, that the only sure fire way to tell the difference is to count the scales or do a genetic analysis.
Why is it considered invasive? Basically the Alabama bass is taking over the neighborhood by dominating the gene pool. Through active mating and genetic swamping, the Alabama bass is eradicating some native species. At the current rate of population growth, native bass species in some rivers and lakes are incapable of thriving due to Alabama bass saturating the fisheries.
What can be done to manage this species? One current hope is to stock the native species to full capacity, giving them a competitive advantage when it comes to population growth. This method is unproven, however. Some natural resource management agencies are removing bag limits on Alabama bass outside of their native range, but there are too few anglers to help curb the population this way. The only way to keep the Alabama bass from taking over is to prevent their spread into new basins where they currently do not reside.
How did it get here? Remember when we said some species came from around the world? The Chinese privet (Ligustrum sinense) is a perfect example. Imported from China and Europe in the mid-1800s, the Chinese privet was originally intended to be an ornamental plant as it can be pruned into a dense hedge.
Why is it considered invasive? Remember how we said Chinese privet could be pruned into a dense hedge? Well, that density can be very detrimental to the surrounding plants that cannot tolerate the shade. The Chinese privet is a bit of a sun hog, and the native plants trying to grow beneath it suffer the consequences and begin to die off while the Chinese privet thrives. Another tool used by the Chinese privet is its own seeds. Area birds consume the purple fruit and distribute the seeds, facilitating expansion of the Chinese privet.
What can be done to manage this species? The Chinese privet is very difficult to eradicate if there are nearby seed sources. It can be controlled, however, with careful herbicide use. Some effective methods include applying glyphosate to foliage or freshly cut stumps, particularly during the growing season, which begins just after the beginning of spring. Another method is to uproot seedlings, which can be easily accomplished in moist soil.
Hydrilla verticillata (Hydrilla)
How did it get here? There are two biotypes of the submerged aquatic plant Hydrilla verticillata—monoecious, which has both male and female flowers on the same plant, and dioecious, which has male and female flowers on separate plants. The former originated in Korea while the latter came from southern India. The dioecious version was introduced via the aquarium plant trade in southern Florida in the late 1950s. By the 1970s it had spread all over Florida. The current hypothesis is that unsuspecting aquarium owners dumped contents of their aquariums with the Hydrilla plants in nearby water bodies, thus beginning the spread. Only a small fragment of a Hydrilla plant is needed to begin an entire colony.
The monoecious type was introduced farther north, in the Mid-Atlantic States and in the Potomac River Basin. It has since spread to many parts of the northeastern and southeastern U.S. The monoecious version is thought to have hitched a ride with boats and boat trailers, going from one body of water to the next. This helped it spread quickly over a wide range.
Why is it considered invasive? Hydrilla takes a page out of the Chinese privet playbook—it shades and outcompetes important native submersed plants such as pondweeds and coontails, blanketing the surface of the water with thick mats, resulting in altered water chemistry and dissolved oxygen levels. It does so quickly, too, as it can grow an inch each day. Hydrilla slows water flow and can clog culverts, water control intakes, and pumping stations with its thick floating mats. It also interferes with hydroelectric power generation by clogging intakes. Hydrilla also interferes with boating, swimming, and fishing.
What can be done to manage this species? Many environmental agencies conduct annual surveys to identify, map and assess the degree of Hydrilla spread. This is usually followed by an application of EPA-approved aquatic herbicides to the infested areas. The problem with Hydrilla is how quickly it grows. Once it invades a system, the goal becomes less about eradication and more about containment. Stakeholders can assist with containment by inspecting their boats and trailers and removing any Hydrilla fragments before entering or leaving water bodies.
Egeria densa (Egeria)
How did it get here? Egeria densa is native to Brazil and coastal Uruguay. Much like Hydrilla, Egeria came to America through the aquarium trade; its first reported arrival was in 1893 in the Long Island, NY area. As with Hydrilla, Egeria was most likely dumped into water sources by unknowing aquarium owners, allowing it to traverse waterways.
Why is it considered invasive? Egeria densa, as its name suggests, can be very dense. It can also rapidly expand its biomass, outcompeting native vegetation. This creates monospecific stands, which leads to less biodiversity. Egeria can fill waterways with its thick growth pattern and hinder recreational use such as fishing, swimming and boating. Egeria densa also blocks out sunlight to the water column leading to dissolved oxygen deficits.
What can be done to manage this species? Management typically comes down to containment as once Egeria becomes established it can be difficult to eradicate. Targeted use of EPA-approved aquatic herbicides to keep the crop to the lowest feasible levels is usually the course of action. The use of herbicides begins in May and is sustained until early fall. As with Hydrilla, stakeholders can help by checking boats and trailers for any fragments and removing before entering and leaving any water bodies.
How did it get here? The flathead catfish (Pylodictis olivarisis) is native to the Mississippi River basin, however the fish has been transferred east of the Appalachian Mountains, outside of its natural range. Flatheads are excellent table fare and can reach large (regularly exceeding 50 pounds) sizes quickly. This makes them incredibly popular with anglers, which is why the fish were transferred in the first place.
Why is it considered invasive? Do you remember the schoolyard bully? Well, that’s what the flathead catfish is to the native species. They are voracious predators and have decimated native redbreast sunfish (Lepomis auritus) populations in many areas. Redbreast fisheries are virtually nonexistent in many rivers where flatheads have become established.
What can be done to manage this species? There are few options on the table for controlling flathead catfish. Some states are using electrofishing to actively remove adult flathead catfish from the population. This technique cannot fully eradicate flatheads from a river, but it has proven effective in reducing the average size of adult flatheads, providing some respite for redbreast sunfish survival. This technique must be implemented annually or the fish community will quickly revert. The only way to eradicate flathead catfish would be by using a piscicide such as rotenone. However this is not a viable option in most scenarios, as it would also kill all non-target fish species.
How did it get here? Ah yes, there couldn’t be a list about invasive species without talking about Kudzu (Pueraria montana). Originally planted as a landscape ornamental in Philadelphia in 1876, by the early 1900s Kudzu was being promoted for livestock forage as well as being promoted by the U.S. Soil Conservation Service for controlling soil erosion.
Why is it considered invasive? Anyone who lives in the Deep South knows all too well why Kudzu is considered invasive. It takes over everything, blanketing the area in a sea of green leaves. Like Chinese privet, Kudzu throws shade all over native species. However, Kudzu is an even greater threat because it can climb and shade out the tallest trees, often resulting in significant economic loss through timber damage. And the resulting snags can be hazardous to people living nearby when they eventually fall. The ecological damage Kudzu inflicts can be very serious when it threatens the existence of rare plants and sensitive natural communities.
What can be done to manage this species? Persistence pays off when dealing with Kudzu. The longer a stand has been established, the larger the root system will be. This means the resistance to control will be higher, making the job of containment and removal more difficult. One key to removal and containment is to target Kudzu stands with herbicides during the growing season. However applications must typically be repeated in successive years as the large roots re-sprout; Kudzu is nothing if not stubborn. Make sure to employ herbicides well in advance of the winter season to give them enough time to penetrate the root system. Perhaps a more ”green” method is to employ persistent grazing to help control and eventually eliminate patches.
Southern Company takes an active role helping control, contain and eliminate invasive species. Through its Longleaf Stewardship Fund and the FiveStar and Urban Waters Restoration Program, Southern Company has awarded several grants to recipients around the South with the goal of combating invasive plants and wildlife, among other objectives. The aforementioned invasive species are just a few of the nuisances faced in the region. With the help of conscientious stakeholders as well as organizations such as Southern Company doing their part, we can help keep native species thriving in our neighborhoods.