Zebra mussels (Dreissena polymorpha)
They are about the size of a dime and can greatly impact the water quality of the waterbody they infest.
Zebra mussels (Dreissena polymorpha) are small mussels with, you guessed it, zebra-like striping on their shells. Unlike native freshwater mussels that nestle in the soft sediments in streams and reservoirs, zebra mussels can attach to submerged hard substrates. The fibers the zebra mussels use to do this are particularly robust, making them difficult to remove.
Spawning may begin when water temperatures reach 53°F. Zebra mussel infants, called veligers, can be free-swimming for up to a month until they settle on to a substrate and attach.
Zebra mussels were first described in the lakes of southeast Russia, with natural distributions in the Black and Caspian Seas. It is likely that shipping activities in the early 1800’s allowed zebra mussels to begin spreading into Great Britain, the Netherlands and the Czech Republic. It is thought that discharge from the ballast tanks of transoceanic ships is responsible for the invasion into the Great Lakes (1988) in the United States. Because boats and boat trailers were not properly cleaned, drained and dried leaving the Great Lakes, zebra mussels spread rapidly into other water bodies and major waterways. The first detection of zebra mussels in Texas occurred in Lake Texoma in 2009.
According to Texas Parks and Wildlife, 21 lakes across five river basins are classified as infested with zebra mussels.
To date, the U.S. Geological Survey calculates the economic impacts of zebra mussels in the United States to be about $5 billion.
In waters infested with zebra mussels, intake pipes for power plants, irrigation, industry, and drinking water facilities must undergo constant maintenance so that zebra mussels do not clog the pipelines. Veligers can settle out into coolant systems of boats and grow into passage clogging adults, ultimately causing overheating and destruction. Floating docks and other structures can also be weighed down beyond their designed maximum weight by excessive growth.
Zebra mussels are prolific filter feeders. They filter large volumes of water every day, as much as 2.5 gallons per mussel is possible, removing nutrients, algae, zooplankton, and other particulates from the water column.
They do have a positive effect on water clarity. However, this increased clarity often results in excessive plant growth in waterbodies. Initially, the increase in plant growth can create habitat for game and forage fish, leading to a temporary increase in quality and quantity of fish. Long-term, the decrease in available suspended particulates caused by zebra mussels exceptional filtering ability will result in a deficit in microzooplankton and algae that often forms the base of the food web for larval fish, thus damaging a waterbody’s fishery.
Additionally, zebra mussels will attach to any hard surface they settle on including native mussels. Excessive growth on and around native mussel beds can suffocate them over time.
The shells are razor-sharp and can cause trouble for beaches and swimming areas in two ways:
- direct attachment to rocks, retaining walls, buoys, and other hard substrates around recreational areas, and
- as they die and wash up on shore, replacing sand and smooth rocks with jagged, sharp, broken shell material.
What you can do to help prevent the spread of zebra mussels:
Clean: Inspect your boat, trailer and gear. Remove all plant material and mud.
Drain: Remove all water from the boat, as well as the motor, bilge, live wells and bait buckets.
Dry: Open all compartments and allow the boat and trailer to dry for at least a week or more before going into another body of water.
If the boat cannot be dried for a week, it is recommended that the boat be washed with high pressure and soapy water.
If your boat has been stored in water with zebra mussels, the Texas Parks and Wildlife Department said it needs to be decontaminated before moving. Call (512) 389-4848 for guidance. Report any suspected new growth in uninfected lakes to the Texas Parks and Wildlife Department so appropriate treatments can be applied before things get out of hand.
The Brazos River Authority’s environmental team, in cooperation with the Texas Parks and Wildlife Department, has taken an active role in the surveillance and monitoring of BRA System reservoirs for zebra mussel infestations. Learn more about that here.
Zebra mussels are one of the invasive species monitored in the Brazos River basin. Others include feral hogs and nutria. Invasive species can also include plants. The most common invasive plants in Texas are hydrilla, giant salvinia, water hyacinth, kudzu, alligator weed, Chinese Tallow Tree, and salt cedar.