Thanks to globalization, there’s a variety of aquatic plants and animals available in the aquarium trade that has never been seen before. While this means more gorgeous tanks and ponds than ever, it also brings a new threat: invasive species. You’ve probably heard about the snakehead, a predatory fish native to Asia that can travel short distances on land, leading it to populate New England, or maybe your rose bushes have been chewed up by Japanese beetles. Those are both invasive species, introduced to the US accidentally in the case of Japanese beetles, and purposefully as food stock in the case of snakeheads. Animals are not the only living things that can become problems when introduced to lands not originally their own. Aquatic plants can also cause destruction when introduced to rivers, lakes, or oceans. Following are the three most common invasive plants found in the aquarium trade. After learning about the damage they can cause, we’ll learn how to prevent it.
A common trait all of these plants have is their ease of care, which lends itself to their success in environments they should not be in. Anacharis is possibly the easiest plant on this list. It requires medium light (perfect for lakes) and doesn’t even need to be planted in the substrate to thrive and grow. Floating anacharis will grow roots along its stem, drawing nutrients directly from the water column. Anacharis can be propagated by breaking the stems into pieces, which is great news for a plant that humans try to physically remove from waterways. Any pieces left behind can immediately begin to repopulate.
Problem: Anacharis grows faster than many native aquatic plants and can block out light and rob them of nutrients, out-competing them. Anacharis can also form thick floating mats that prevent recreation like swimming, rowing, fishing, and boating. An unsuspecting boater can get a nasty surprise when their propeller gets tangled in a mass of anacharis.
An admittedly gorgeous ornamental pond plant, water hyacinth has a dark side. Like anacharis, it can form massive, acres in width patches, blocking light from lower levels of the water and making recreation difficult if not impossible. Its light blocking effect doesn’t just slow down growth of other aquatic plants. Preventing light from reaching those plants prevents them from photosynthesizing, which prevents them from producing oxygen. Additionally, just the hyacinths’ presence on the water surface decreases the area for gas exchange. What we end up with is a body of water that is oxygen starved and full of dying fish. Waterfowl can’t land on hyacinths. Their habitat is effectively destroyed when lakes and rivers are clogged with floating plants. The density of hyacinth patches slows down any water movement at the surface, enabling algae growth and mosquito breeding (and remember, all the fish that might eat the larvae are already dying from a lack of oxygen). Hyacinths are also excellent at reproduction, employing two strategies: budding, and seeds. During their active growing season, hyacinths grow “daughter plants,” small hyacinths that grow off of the original plant until they are large and established enough to grow on their own, and then break off and begin growing and budding on their own. Hyacinths can also reproduce sexually, producing seeds. Seeds are the insidious sleeper cells. They can begin growing within a few days, or lie dormant for years in case of unfavorable conditions like droughts. Once the environment is more conducive to growth, the seeds will sprout and begin the invasion all over again. The main weaknesses of water hyacinth are herbicides and cold winters, which have prevented their spread into the northern half of the US.
Can any plant sound less threatening? Water lettuce? C’mon. How dangerous can soggy Romaine be? Don’t be fooled: this plant is nearly as bad as water hyacinth. It is another floating plant that clogs up rivers and lakes, out-competing native plants, lowering oxygen concentrations, creating mosquito nurseries, and stealing habitats. Additionally, it’s invaded Hawaii, where some of their most important crops are grown at least partially underwater, like taro and rice, and is becoming a noxious weed. Another layer of difficulty in controlling water lettuce is its inedibility. Very few animals are willing to eat it, because it is full of needle-like crystals made of calcium oxalate. Eating water lettuce would lead to a severe itchy burning sensation in your mouth and throat, as well as damage to your GI tract. Only two animals can really make a dent: the hippo, and the manatee. Unfortunately, it would be a logistics nightmare to deploy them in the battle against water lettuce. And finally, to add insult to injury… it’s pretty ugly.
What Can I Do About It?
An ounce of prevention is worth a pound of cure. Avoid using invasive species in your aquariums and ponds. There are so many species available in the trade that you can almost always find a safer alternative, one that would not be able to survive in the wild in your area. If you can’t find a suitable alternative, or you just fell in love with an invasive plant, there are some things you can do to be safe. First, NEVER release ANYTHING from your tank or pond to the outdoors. Never dump captive plants into a stream, river, pond, etc. Second, make sure you dispose of the plants safely. Let them dry out completely before throwing them out, or freeze them solid. In both cases, you’ll want to put them into a bag (preferably sealed) when disposing of them. Third, and this is more for pond owners, prevent natural spread of plants outside your pond. Ensure that a flood won’t mix local waters with your pond, enabling escape of plants or animals. Build stone walls around your pond, or build your pond on higher ground. Keep wildlife out of your pond. Plants, seeds, or plant fragments can stick to fur or feathers and be carried to other areas. Fourth, help slow the spread of already escaped plants. Whenever you go swimming, fishing, boating, rafting, etc. make sure you clean off anything that went into the water. Plants can stick to boats and water toys and be inadvertently taken from an infested pond to a clean one.
Do you have any questions? Comments? Ideas on better ways to protect native waterways? Send them in to firstname.lastname@example.org. I’d love to hear from you!