by Neil Stalter | Zoom Out Mycology
It can be a little weird to look at a plant, insect, or animal and think “I wonder where that came from?” but that can actually be one of the most important questions to ask for environmentalists! Whether a certain species is native to your area or “invasive” meaning that it came from somewhere else, can be fundamentally important to how ecosystems change and evolve over time.
Before we get into that though, it’s important to understand exactly what an “invasive species” is, and why we should care. There are four types of species that are not native to the area in which they live: Introduced, Exotic, Alien, and Invasive species. “Invasive” species are those that are both non-native while also having a negative effect on the ecosystem or economy that they have invaded. Potatoes, for example, are an introduced species that started in South America, and eventually spread to Europe and North America (1), but don’t have a negative effect (can you imagine a world with no French fries?). This means that potatoes are non-native and introduced, but not invasive because they don’t have a negative effect, and instead provide an economic benefit to the places they were introduced. On the other hand, there are a lot of weeds that are invasive species that can prevent us from effectively growing our crops! Species like Giant Hogweed have invaded and can cause major damage for our farmers and gardeners.
What negative effects an Invasive species can have depends a lot on the species in question. Often times, these species that are introduced to a new area, whether by boat, farming, gardening, or by accident, lack any predators in the new areas they find themselves in. Ecosystems need time to evolve to keep all of the species that live in them in check. Wolves have had a lot of time to evolve and hunt deer and buffalo, but they would struggle to hunt as effectively if all of a sudden, elephants took the place of those buffalo they were used to hunting. This is a dramatic example that probably would never happen, but it’s a useful way to describe how these ecosystem dynamics can change when a new species arrives. These invasive species can then take over entire ecosystems unchecked, causing immense damage. In fact, it is estimated that the spread of invasive species has contributed to the decline of 42% of the listed threatened and endangered species, and the damage done by them has cost the US an estimated $120 billion (2). Much of this cost is due to damage to agriculture, but these invasive species can have profound negative effects on ecosystems where the cost is harder to calculate, like lakes. To best describe invasive species and the damage they can do, I’ll tell you about three invasive species that each are very different from each other, but each pose a very significant threat to ecosystems in the US and around the world: Zebra Mussels, Varroa Mites, and the Emerald Ash Borer. Stay tuned until the end of the article for some suggestions about what you can do to help combat this problem and stay educated!
Zebra Mussels are an invasive freshwater mussel that were originally native to Eastern Europe. After hundreds of years spreading through Europe, they recently reached the US Great Lakes in 1988, when it is suspected that a shipping barge with infested bilge water dumped mussels and their larva into the Lake St. Clair. (3) You’ll find that this is a common story; it only takes one seemingly small contamination to start a full blown infestation. Since the initial contamination, these mussels have spread like wildfire through the US, attaching to boats and traveling down rivers like the Mississippi. They reached all the way down to Southern California in 2008. (4)
These small mussels populate water bodies with unbelievable speed, and can completely cover lakes and reservoirs in just one season. The effects they have on the lakes they invade are immediately obvious. They latch onto docks, infrastructure, and the stones on the lake bottom. They also can grow on top of native mussels and clams, and rob them of nutrients, completely outcompeting them and driving them toward extinction. In fact, sometimes several thousand mussels can be found attached to native clams. Zebra mussels threaten over 30 native mussel and clam species, some of which are already endangered, with extinction. Zebra mussels have also been implicated in the decline of crawfish and snail species. (5) These mussels also feed on certain algae and can increase water clarity dramatically. This can sound like a benefit, but this increased clarity leads to sunlight penetrating further into the water, allowing the growth of more weeds that are both no fun to swim in, and can change the landscape of the lake ecosystem. They also do not eat blue-green algae, which are responsible for the harmful algae blooms (HABs) which are becoming more prominent in the US and which we will discuss more in another article soon!
All of the damage that Zebra Mussels do to the ecosystem, as well as the damage they can do to power creation and drinking water infrastructure by attaching to and damaging pipes and water intakes, has been estimated to be about $5 billion from 1993-1999. And that number has only increased since then. The damage they do is so intense and widespread that it can be hard to estimate as they spread through the US. They are also incredibly sharp, and once they invade a lake you like to visit and swim in, they can almost ruin that experience. Swimming in a lake with Zebra Mussels can be dangerous unless you’re wearing water-shoes, as they can cut your feet without shoes! In fact, I have a scar on my chest from jumping into one of the many important lakes in my life, and getting cut by one of them. The damage Zebra Mussels do is three fold: they hurt the ecosystem, they hurt the economy that relies on the freshwater body (including both power creation and drinking water), and they make the lake much harder to enjoy on a sunny summer day! It is up to us to help make sure these mussels don’t enter any more lakes by taking precautions I will talk more about at the end of the article.
Invasive species don’t just affect water ecosystems, but can also have a profound effect on our agriculture too. One such species is the Varroa Mite, sometimes referred to (appropriately) as the “Varroa Destructor.” These are very small insects or “mites” that latch onto honeybees, almost like ticks, and act as parasites, using their nutrients and infecting their hives. They originated in Japan and Eastern Russia, but through overseas trade of agricultural products and honeybees (6). Since their initial spread in the 1960s, Varroa mites have infected every continent (with the exception of Australia) and have even spread to islands like Hawaii and New Zealand. These pests have quickly become a worldwide agricultural issue, since honeybees play such an integral part not only in the honey industry, but in the market of nearly every cultivated crop in the world.
These pests were spread completely by accident, and yet they have had an almost immeasurably negative effect on the economies and food production of countries around the globe. Varroa mites reproduce by breeding where the bees lay their larva. These mites then feed on the bee larva, using precious resources created by the bees and killing the larva in the process. Eventually these mites outcompete the entire bee colony, and reproduce faster than the bees can, killing the entire colony (7). The adult mites also feed on the nutrients that adult honeybees gather while out foraging. All this to say, these mites are exacerbating and already dire honey bee mortality crisis in both the US and around the world. Bees are fundamentally important to both natural and agricultural ecosystems by pollinating plants, allowing them to effectively reproduce over longer distances. Without bees, it is not an exaggeration to say we would be facing a worldwide food crisis. Though it is nearly impossible to estimate the economic impact these mites have had, it is in the order of billions of dollars – killing hundreds of thousands of bee colonies. Though invasions of this magnitude seem harrowing, we as consumers have the power to prevent future invasions like this, as well as slow the effects of Varroa mites and similar species. Invasive species like this mite can have immediate and tangible effects on our lives, whether it’s not seeing honey or apples in the grocery store as often, or local farmers going out of business because of the collapse of local bee colonies. Invasive species, like many modern sustainability issues, are finally beginning to get the attention that they deserve.
Emerald Ash Borer
Last, but not least, is the Emerald Ash Bore (EAB), which is a small green beetle that is originally from Eastern Asia, and was accidentally introduced into the US in June of 2002, likely through the transport of firewood or ashwood used for stabilizing cargo ships (8). These beetles selectively infect and kill Ash trees, of which there is a huge population in North America. There are 8 billion ash trees in the US, and the EAB has already killed tens of millions. The remaining trees are all at risk as this small bug rushes through North America. In particular danger is the national forest resources of the USDA Forest Service in the Western US. The states with the largest national forests have largely not been invaded yet, but the spread of this insect has not stopped. These forests provide a huge economic and recreational asset to the US, and protect ecosystems, including endangered species, that live in them. The EAB could harm these important environments irreparably.
The EAB started its spread in Michigan, but has infected every state east of South Dakota except Mississippi and Florida. The one major aspect that prevents its unchecked spread, apart from the incredibly important work some organizations like the USDA are doing, are the colder climates in much of the north and western US. To put into perspective just how much damage these beetles do, in Ohio alone, the total cost of remediation following Ash borer infestation is estimated to range anywhere from $1.7 - $7.6 billion (9). And that’s not even taking into account the costs of protection against the spread and further infection of these beetles. I know at my home in Western New York, we have a giant beautiful ash tree that we rely on for shade on our deck and in our yard. Now, since the ash borer invasion into New York, we have had to chemically treat this giant beautiful tree every couple of years to prevent the ash borer from killing it. Our tree that clearly has been growing for at least a hundred years is now all of a sudden at risk of dying because of these beetles. The risk that this species presents to our forests absolutely deserves an article of its own, but it’s important to understand just how different invasive species can be, and how they’re effects can be so significant that it can very literally change your daily life.
What You Can Do
The damage that these invasive species can do can seem almost impossible to face sometimes, and their ability to spread is astounding. But invasive species are not new, and there is a long history of plants and animals being moved from place to place without being aware of the consequences. As an example, the wild boar found across the southern US are actually an invasive species that were brought to the US in the 1500s by explorers of the “New World” as a food source (10). Now, over 500 years later, they have become a part of not only the ecosystem, but the culture of the south. As long as people have been moving from place to place, and bringing plants and animals with them, there have been invasive species. What’s beginning to change however, is that the world gets “smaller” every year. As it gets easier and easier for people to travel around the world and for goods to be traded from country to country (this is what is often referred to, in part, as “Globalization”), more and more species will also move around the globe. Not all of these will be bad. In fact, some might improve ecosystems! The monarch butterfly was introduced to Australia, where they help combat the invasive milkweed (11). The milkweed is native to North America, and was introduced to Australia. To help combat it, Australia introduced its natural predator, the monarch butterfly, with very good results!
So what can we do to help stop and prevent the spread of invasive species? Well sometimes, it depends on the species. For example, with Zebra Mussels, one of the single best ways to prevent their spread is to “Clean, Drain, and Dry” your boat when you remove it from a lake or river. This is also incredibly important to do to prevent the spread of other aquatic invasive species I wasn’t able to mention in this article. On land, when you’re planting gardens and doing landscaping, make sure you use native species! Each region of the US has beautiful plants native to that area that would be a great addition to your rain garden (http://www.zoomoutmycology.com/blog/when-it-rains-it-pours). So when you’re planting in your garden, look online to make sure your plants aren’t coming from overseas! Similarly, support local farmers! By minimizing the distance that your food is travelling, you’re also minimizing the risk that any stowaway species are hitching a ride on your veggies while they travel to you. Plus, you’re minimizing your carbon footprint and supporting your local economy! Buying local is truly one of the most sustainable practices average folks can take up. Finally, make sure you stay informed! Reading this article is a great first step, but each invasive species requires different practices to help prevent its spread. Look up what invasive species are in your area, and some of the things you can do to help!
You can also look up certain species on the USDA’s National Invasive Species Information Center here: https://www.invasivespeciesinfo.gov/index.shtml. On each page you can learn more about each species, and what you can do to help.
As with all environmental problems, the risks that invasive species pose can be significant, and complicated to solve. However, that doesn’t mean we’re powerless! Though the world economy is changing, and more and more goods, people, and species travel across the oceans, by being constantly careful and vigilant we can prevent unintended invasion of new species into faraway places. Invasive species can impact your daily life, and by helping to keep plants and animals in their native environment, you can help protect ecosystems around the world!
Zoom Out Mycology’s Environmental Awareness blog strives to explain and expose environmental topics and concerns to a wide audience. Our team consists of a diverse group of scientists, policy experts, and engineers that help describe the science behind environmental issues that you see in the news and experience in your daily life. We hope that this knowledge will help all of our readers embrace a healthy and sustainable lifestyle! If you are interested in being a guest contributor, please email us at: firstname.lastname@example.org