U.S. Department of the Interior

U.S. Geological Survey

Quagga Mussel Risk Assessment

Theodore Kennedy
Outline

 Background: life cycle, ecological impacts in 

eastern US

 Risk of attaining high densities in the CRe

 Risk of ecological impacts in the CRe
Life Cycle

• Larval life stages 

are free-floating

• Time to settlement

is 1-4 weeks

• Populations in rivers

therefore require an 

upstream lake/reservoir

From

http://ucanr.edu/sites/WAEMA

P/Quagga_and_Zebra_Mussel

s/Eurasion_Mussels_101___C

haracteristics_of_an_Extreme_

Invader/Reproduction_and_Life

_Cycle/
Ecological Impacts of Quagga 

Mussel

Before Invasion

• Native/endangered mussels

• Water column food web prominent 

• Benthic food webs present

After Invasion

Zebra mussel density of ~1000/m2

• Native mussels declined/extirpated 

• Water column food web declined

• Benthic food webs increased

http://www.caryinstitute.org/educators/teaching-materials/changing-hudson-project
Ecological Impacts of Quagga 

Mussel

http://www.caryinstitute.org/educators/teaching-materials/changing-hudsonproject
Ecological Impacts—Summary

http://www.lmvp.org/Waterline/spring2006/zebramussels1.htm
Outline

 Background: life cycle, ecological impacts in 

eastern US

 Risk of attaining high densities in the CRe

 Risk of ecological impacts in the CRe
Risk of attaining high densities

Larval transport

 Larvae are fragile and easily killed in 

turbulent flow

 90% of larvae alive at a lake outlet stream, but only 

40% alive 18km downstream (Horvath and 

Lamberti 1999)

 Rapids will likely be a significant source of 

mortality

 Prediction: Downstream decline in abundance
Risk of attaining high densities

Larval transport—Glen Canyon

RM -4.8 to -3.1 RM -14 to -13

Yard unpublished data; preliminary, do not cite
Risk of attaining high densities

Suspended sediment

 Adult mussels filter feed on suspended 

organic matter (algae and detritus)

 Mussel growth is negatively affected by 

suspended sediment

 Lab studies

 growth declined sharply when suspended 

sediment >1 mg/L

 growth was negative when suspended sediment 

>100 mg/L
Risk of attaining high densities

Suspended sediment

growth negative

growth declines sharply

Sediment data from gcmrc.gov; lines of declining and negative growth derived from:

Madon, S.P., Schneider, D.W., Stoeckel, J.A., and Sparks, R.E., 1998, Effects of inorganic sediment and 

food concentrations on energetic processes of the zebra mussel, Dreissena polymorpha: implications for 

growth in turbid rivers: Canadian Journal of Fisheries and Aquatic Sciences, v. 55, no. 2, p. 401–413. 
Outline

 Background: life cycle, ecological impacts in 

eastern US

 Risk of attaining high densities in the CRe

 Risk of ecological impacts in the CRe
Risk of ecological impacts

 Magnitude of impact will depend on mussel 

density and filtration rate

 Key question: how much water can be filtered 

as water travels through Glen and Grand 

Canyon?
Risk of ecological impacts

~10% of water filtered ~6% of water filtered

Kennedy, T.A., 2007, A Dreissena risk assessment for the Colorado River 

ecosystem: U.S. Geological Survey Open-File Report 2007-1085, 17 p. 
Conclusions