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South à£à£Ö±²¥Ðã State University faculty members are fighting back against the state's most challenging invasive species.

Researchers in South à£à£Ö±²¥Ðã State University's College of Agriculture, Food and Environmental Sciences are on the front lines of South à£à£Ö±²¥Ðã's fight against invasive species. From aquatic invaders to terrestrial intruders, SDSU researchers are working to stop invasive species from wreaking havoc on the state's natural ecosystems and native wildlife.

Invasive carp

Formerly known as Asian carp, invasive carp are the largest aquatic invaders in South à£à£Ö±²¥Ðã's waters and can be found primarily in the James River and the Missouri River up to Gavin's Point Dam. While it is unlikely the fish will ever be completely eradicated, researchers are working to ensure these fish stay behind the rivers’ man-made dams. If these fish were to move above Gavin's Point and into Missouri River reservoirs, officials are worried the river's native walleye population could be severely threatened.

Alison Coulter is an SDSU assistant professor who has significant experience working on aquatic invasive species, both in South à£à£Ö±²¥Ðã and in Illinois. She explained the challenges that invasive carp present when introduced into new waterways.

"What we see from other places is that first, you see changes in the plankton and zooplankton, which overall can mean less food for your native species," Coulter said. "You will then have poorer feeding conditions for the native fish, and eventually that will affect the native fish populations."

To protect the state's native fish populations, SDSU assistant professor Dave Coulter is leading research into how flooding could allow invasive carp to spread around current barriers. Additionally, he is modeling how carp can survive and reproduce in new locations. All of this information will help resource managers identify where action will be needed to slow the spread of invasive carp.

Coulter and her graduate research assistant, Hannah Mulligan, have also been conducting an analysis on the live bait trade in the Missouri River basin. The live bait trade is one of the human-mediated pathways through which aquatic invasive species can spread, and Coulter and Mulligan’s work is identifying where the weak points in the system may be.

"Juvenile invasive fish may be inadvertently released by anglers, resulting in potential negative ecological, economic and social impacts," Mulligan said. "This work illustrates the need for preventative actions, including regulations, targeted and active monitoring, and educational and outreach materials near invasion fronts, to limit the risk of invasive species introductions."

Zebra mussels

Zebra mussels are small, fingernail-sized freshwater mussels that are native to Eastern Europe and Western Russia. They likely arrived in the United States’ Great Lakes in the 1980s through cargo ships from Europe. 

In South à£à£Ö±²¥Ðã, zebra mussels are a growing problem and have infested lakes throughout the state. Full-grown zebra mussels are usually less than one inch in size and will attach themselves to practically anything, including plants, rocks, docks, boats and pumping stations. They pose both an economic and environmental threat as they clog water intakes for power plants, cause issues for drinking water and impact agricultural irrigation systems. Zebra mussels also eat food like phytoplankton and small zooplankton that native fish rely on. Like other invasive species, zebra mussels throw the natural ecosystem completely out of balance and have even been linked to toxic algae blooms. ­­­

But maybe the most troubling issue with zebra mussels is how hard they are to contain. Larvae of zebra mussels are microscopic, so it’s nearly impossible to know when they are inadvertently being transported into new waterways by unsuspecting boaters and anglers.

Eradicating zebra mussels when they are already entrenched in a waterway is nearly impossible. That's why SDSU researchers are focused on informing and educating the public to slow or prevent further spread.

David Kringen is an SDSU Extension water resources field specialist. His work has been focused on developing and implementing educational programming and spreading public awareness on water-related issues and aquatic invasive species, like zebra mussels, in South à£à£Ö±²¥Ðã.

Coulter and her team have also been active in informing the public on all types of aquatic invasive species, including zebra mussels. In conjunction with South à£à£Ö±²¥Ðã Game, Fish and Parks and SDSU Extension, Coulter developed an aquatic invasive species middle school curriculum and activity guide aimed at educators looking to introduce their students to aquatic ecosystems and real-life problems caused by aquatic invasive species.

"Our goal is to create a culture in South à£à£Ö±²¥Ðã where the term 'aquatic invasive species' is commonly understood in households and the phrase 'Slow the Spread: Clean. Drain. Dry.' is at the tip of a person's tongue when asked what they can do to help," Coulter explained.

Invasive beetles

In July, SDSU professor John Ball confirmed the dreaded — but expected — reality: emerald ash borer had made its way to Brookings County. The diminutive green beetle, which was first confirmed in South à£à£Ö±²¥Ðã by Ball in 2018, is an exterminator of ash trees and has wiped out the tree through much of the eastern and midwestern United States.

"Once detected in a community, emerald ash borer spread and kills most ash trees within five to 10 years," Ball explained.

But Ball and his team of forestry specialists have been preparing for the emerald ash borer invasion since the early 2000s. First, they confirmed how many trees were at risk in the state, which was a lot, to say the least. Then, they began working to figure out what management techniques were available. They provided early communities most at risk of invasion — towns near the Minnesota/Iowa border — with tree management plans. Eventually, they conducted and published research on different methods that could save ash trees even after infestation. 

When emerald ash borer finally did come to South à£à£Ö±²¥Ðã in 2018, the state was well prepared, thanks in no small part of the work of Ball, the South à£à£Ö±²¥Ðã Department of Agriculture forest health specialist, and his team.

Unfortunately, the reality of emerald ash borer is that most, if not all ash trees, will be lost. The dangers that the beetle presents are real, as infected ash trees become brittle and are prone to falling at any moment. In places like Michigan, this has created extreme safety hazards that have resulted in injuries and death. To prevent similar issues, most ash trees must be cut down as a preventative measure.

The loss of ash trees isn't a complete negative, however. According to Ball, towns are now planting a more varied tree population. This will protect against total loss from future invasions.

"We are learning from our past mistakes," Ball said.

Ball's research has found that some ash can be saved, especially those in urban settings where ash trees make up around 30% of total tree population. Applying an insecticide through a trunk injection can protect the tree from emerald ash borer.

While emerald ash borer will never be eradicated from the state, specific techniques are slowing the spread. According to Ball, quarantines on firewood movement in counties where emerald ash borer is present will give researchers more time to figure out long-term solutions to this problem.

Woody encroachment

North America’s grasslands are one of the most endangered ecosystems in the world and have been under constant attack since settlers first arrived in the 1800s. While a good chunk of native grasslands has been lost to row crops and infrastructure, invasive trees, like the eastern redcedar, are threatening what little remains.

SDSU professors Lan Xu and Alexander Smart have been studying the impacts of eastern redcedars on South à£à£Ö±²¥Ðã's grasslands for a number of years. The reasons eastern redcedars have been successful in encroaching on grasslands, they say, is because of shelterbelts — which are almost always full of eastern redcedars — and fire suppression.

Fires were natural to grasslands and, because they happened every three to four years, would wipe out woody invasive species before they able to take hold and spread, Xu explained. Even though they were planted in shelterbelts, fires would keep eastern redcedars at bay. But as more people began settling, fires became rarer. This caused the eastern redcedar to spread from riverbanks, where they are most commonly found, to what was once pristine grasslands.

Like other invasive species, the ramifications of eastern redcedars and other invasive woody species are far-reaching. Because of their dense canopies, eastern redcedars prevent native plants from growing and create excellent protection for predators, who feed on birds , like pheasants, and small mammals. Previous research has shown that when eastern redcedars become present, native species populations decrease substantially.

To combat against this spread, Xu and a number of her current and former students have been conducting research on the various aspects and problems that eastern redcedars present. The issue is complex, and solving it will not be simple, nor easy. However, Xu and Smart have investigated a biological control to attack the eastern redcedar. Goats, they have learned, can combat the invasive tree by stripping it of its bark. Because of their four-chamber stomach, goats are able to digest woody plant matter and are known to strip bark off the trees not just for nourishment, but for "fun." While this could be an issue in some places, it could be a solution in South à£à£Ö±²¥Ðã and other places where grassland is being encroached upon.

In 2021, Smart's control study showed promising signs that goats will consume bark off the trunks and branches, killing the tree. While there is more to learn about this biological control, initial signs show this could be a promising tool in combatting against woody invaders and saving what remains of one of the continent's most precious ecosystems.