Background Readings

Biodiversity: Invasive Species


The cost of controlling aquatic invasive
species in the U.S. is estimated to be $120
billion per year!


Zebra mussel, Dreissena polymorpha, an invasive
freshwater mussel recently found in the Susquehanna
watershed. Photo credit: USGS Nonindigenous Aquatic
Species Program.


Golden Alga, Prymnesium parva, cells. Photo
Credit: Dr. John LaClaire, University of
Texas at Austin.

Invasive species are a growing threat to the biodiversity of Pennsylvania’s aquatic ecosystems. They can compete with native plants and animals for food and space; interfere with recreational boating and fishing activities; and choke waterways, irrigation ditches for agriculture, and industrial water intakes. Once they become established in a stream, lake, or river, it is often very costly and very difficult to remove them.

They can be spread by natural dispersal, recreational boating and fishing, or by transport of water or sediments. Since “frac water” is generally collected from surface waters and trucked to the well site, there is a potential risk of transporting invasive species from infested waters to areas where they have not yet been introduced.

What's the big deal about a few non-native species?

Did you know that freshwater mussels are considered the most imperiled species in North America? Over 30 species have gone extinct in the past 100 years (WPC, 2009). In the Susquehanna watershed, only 14 species of native mussels remain. Three of those species are listed as rare or endangered.

Currently, only a few of the 12,000 lakes and 84,000 miles of streams in Pennsylvania are infested with invasive mussels. Zebra mussels have been found in the Lower Susquehanna sub-basin, but are not yet widespread (map). However, since one single female can release over 1 million eggs, introduction of just a handful of zebra mussels could ultimately wipe out native mussel populations in the Susquehanna watershed.

Another invader, the golden alga (Prymnesium parvum), can’t even be seen with the naked eye. While “golden algae” sounds innocent enough (and perhaps even lovely to look at), it can be a toxic enemy to freshwater fish and invertebrates. Normally found in brackish waters (waters having a salinity of 0.5 to 30 parts per thousand), the algae formed massive blooms, devastating entire populations of fish, mussels, and salamanders along a 34-mile stretch of Dunkard Creek in 2009. Scientists pinpointed the cause of the algal bloom as the release of waste water with higher than normal concentrations of total dissolved solids from a treatment plant upstream. However, no one is sure how this brackish species of algae found its home in a freshwater creek.

Because of the high risk that zebra mussels and other invasive species pose to the native biodiversity of Pennsylvania’s freshwater streams, lakes, and river, the natural gas industry is committed to preventing introductions of non-native species through their drilling operations. Jason de Wolfe, former environmental affairs manager for Chief Oil and Gas Company, discusses the natural gas industry’s approach to preventing the spread of invasive species like the zebra mussel during hydraulic fracturing operations. Read more about industry’s actions to safeguard Pennsylvania’s waters in his essay.

Background Reading: (Each reading opens a separate window.)

  1. Zebra Mussel and Quagga Mussel Fact Sheet, Pennsylvania Sea Grant.

  2. Mid-Atlantic Panel on Aquatic Invasive Species.

  3. Biology of Golden Alga, Texas Parks and Wildlife Department.

  4. “Toxins Tied to Fish Kills may have Hitchhiked”, by Don Hopey, October 4, 2009, Pittsburgh Post-Gazette.

  5. “EPA pins killing of Dunkard Creek on mine discharges”, by Don Hopey, December 3, 2009, Pittsburgh Post-Gazette.

Discussion Questions:

  1. If you look at the current USGS map of zebra mussel distribution in Pennsylvania, New York, and West Virginia, which watersheds have the highest occurrence of zebra mussel sightings? How does this compare to drilling activity in Pennsylvania or your state? Visit the USGS Zebra Mussel and Quagga Mussel Information Resource page for additional maps.

  2. Can you think of ways to prevent the transport of invasive species in water trucked to the well drilling sites?