Invasive creatures have infested Texas waters, from the zebra mussel to the armored catfish. When you think of invasive species, you might think of those critters, but the designation also includes plants.
Named for the Greek mythical 9-headed serpent, hydrilla is a perennial aquatic plant that can produce an entirely new plant from a stem fragment, according to the United States Fish and Wildlife Service. The USFWS lists hydrilla as a noxious weed and as the world’s “worst invasive aquatic plant.”
The plant grows in freshwater and is often found submerged in bodies of water. The Texas Invasive Species Institute said that the plant forms long, branching stems that reach the water’s surface. The plant is covered in small leaves, in 4-8 whorls.
Hydrilla is native to Asian countries and was believed to have been brought to the United States as an aquarium plant. It was first discovered in the United States in the 1960s and has since spread to over 30 states.
What makes hydrilla such a threat is the way it forms thick mats at the surface. The Texas Invasive Species Institute said that hydrilla changes pH levels in the waters it invades, restricts native plant growth, blocking out needed nutrients for other aquatic life and more. The plant is described as extremely competitive and resilient and has even clogged waterways.
Hydrilla’s spread has been successful in part because of unknowing human assistance. Hydrilla can spread from just a tiny fragment. Boaters have spread the weed in the past, carrying a small piece of the plant from one body of water to another, creating the next infestation.
Management of hydrilla has been difficult. The USFWS said that once hydrilla infests a body of water, it is costly to get rid of it. The plant can grow rapidly in a wide variety of water conditions. The USFWS said that the plant has no natural predators or diseases to limit the population or spread.
In Texas, it is illegal to possess or transport the plant. In the Brazos River basin, issues with hydrilla have existed at Lake Stillhouse Hollow in the past. Drought and freezes have knocked the plant out naturally, but other places haven’t been so lucky.
The USFWS said that millions of dollars are spent a year on eradication of the plant such as physical controls like water level drawdowns, chemical controls like herbicides and biological controls such as leaf-mining flies and tuber-feeding weevils.
Though hydrilla poses a major threat, other invasive plants are also lurking beneath the surface.
Water hyacinth is a large aquatic plant native to the Amazon basin. The plant floats on water and can spread from fragmentation and seed production. The peak flowering time for this invasive species is late summer and early fall, according to the Texas Invasive Species Institute.
The plant can produce thousands of seeds a year and can be viable for up to 30 years, according to the USFWS. The plant is one of the fastest-growing with the ability to double its population in just two weeks.
What makes water hyacinth a pest is its ability to grow into thick layers over water.
These thick layers can shade out other aquatic plants and can negatively impact the dissolved oxygen levels. The USFWS said that these thick layers of hyacinth can also interfere with boat navigation and recreational activities. Not only could it cause these issues for those wanting to spend time on water bodies, it can also affect lake levels by evapo-transpiration, which is when water evaporates from a lake surface and lost through plant leaves as vapor.
In the Brazos River basin, hyacinth was an issue for Lake Limestone in 2002 and 2003. Starting off as a pest for the upper portion of the reservoir, it migrated into the Navasota River below the dam. It was cleared naturally and no complaints or photos of the plant were seen after late 2003.
Water hyacinth is often used in water gardens and was introduced in the United States in the late 1800s. The USFWS said that the plant is sold in nurseries for use in water gardens and home ponds.
The BRA works to prevent the spread of invasive species by supporting Texas Parks and Wildlife’s public outreach campaign. The BRA also performs routine observations by environmental services staff that identify exact species, assess threats to reservoirs, and treat if needed.
The biggest threat to our ecosystem when invasive species are introduced would be the reduction of natural biodiversity, reduced food source for native wildlife, low dissolved oxygen problems and much more, according to BRA Environmental Services Manager Tiffany Morgan.
“Many invasive, aquatic plant species have the ability to rapidly reproduce, and many can reproduce vegetatively, meaning a new plant can grow from a fragment of the parent plant. This is why it is important not to mow over plants at the water’s edge or run your boat through them,” said Morgan. “Don’t dump your aquariums into Texas waterways. This is one of the primary ways, along with hitchhiking on boats, invasives are introduced in our system.”
Prevention is key to stop the spread of invasive plants such as hyacinth and hydrilla. Such as the phrase for the prevention of zebra mussels, the USFWS said that boaters should keep these points in mind:
- Avoid boating through mats of hydrilla or hyacinth.
- Clean any mud or plant fragments from all parts of your boat, as well as your gear like boots and waders before you leave a water body.
- Drain all of the water from your boat before leaving the area.
- Dry your boat after each use.
- Never release your aquarium or water garden plants into any body of water
To view where hydrilla has spread, click here.