Effect of the relative hardness of water on crayfish abundance and size
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Effect of the Relative Hardness of Water on Crayfish Abundance and Size. Sarah Deel Chris Brassell Ben Wade Jeff Rosemond. Crayfish Collected during the experiment. Introduction. Freshwater Crayfish naturally inhabit most all the continents.

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Effect of the relative hardness of water on crayfish abundance and size

Effect of the Relative Hardness of Water on Crayfish Abundance and Size

Sarah Deel

Chris Brassell

Ben Wade

Jeff Rosemond


  • Freshwater Crayfish naturally inhabit most all the continents.

  • The US is home to two families (Reynolds and Souty-Grosset2012).

    • Astacidae

    • Camvaridae


  • Crayfish play an important role in trophic structure (Edwards et al. 2009).

  • The amount of Ionic Calcium in water is critical to crayfish growth and survival. (Stelxer and Burton 2011).


  • Growth for freshwater crayfish is limited by the exoskeleton.

  • To increase in size the crayfish must molt.

  • Ionic calcium in the water aids in the hardening of the new exoskeleton (Hammond et al. 2005).


  • The calcium concentration in surrounding water may be a limiting factor for the survival of crayfish during postmolt (Cairns and Yan 2009).

Crayfish collected from Sinking Creek

Introduction a recent study
Introduction- A Recent Study

  • Comparisons of crayfish number and weight were done in the in the Lake Michigan drainage basin.

  • Ford River (hard water)

  • Baraga Creek (soft water)

  • Densities of crayfish were higher in the Ford River (Stelzerand Burton 2011).

  • Introduction a recent study1
    Introduction- A Recent Study

    • Water hardness linked to number and growth of the two populations of crayfish

    • The researchers could not establish causality(Stelzerand Burton 2011).

    Introduction another study
    Introduction- Another Study

    • Juvenile crayfish were placed in aquariums treated with varying levels of Ca2+

    • The survival rate of crayfish (70-80%) was significantly greater in high calcium environments than low (Hammond et al. 2005).

    Based on previous studies
    Based on Previous Studies…

    • Hypothesis: we will find a greater density of crayfish in waterways with higher levels of Calcium concentrations.

    • The specific size and weight is difficult to predict


    • We predict the average length of crayfish to be over 7.5cm in sinking creek, while crayfish in the softer streams will be less than that, as well as less numerous.

    Introduction sampling sites
    Introduction- Sampling Sites

    • 3 chosen sites:

    • Sinking Creek: high hardness

      • dolostone and limestone (U.S. Geological).

    Introduction sampling sites1
    Introduction- Sampling Sites

    • Both dolostone and limestone leech metals cations

      • limestone leeches calcium

      • dolostoneleeches both magnesium and calcium.



    Image from: http://core.ecu.edu/geology/harper/Sedimentary/display_new.cfm?ID=7

    Image from: http://geology.com/rocks/limestone.shtml

    Introduction sampling sites2
    Introduction- Sampling Sites

    2) Little Stony Creek for its low level of hardness.

    • sandstone and granite (U.S. Geological).

    Introduction sampling sites3
    Introduction- Sampling Sites

    3) Tom’s Creek: very high hardness

    • elbrookformations: dolostoneand limestone (U.S. Geological).

    • Runoff/ pollution


    • Water hardness

    • In this experiment, water hardness was tested using the LaMott’s water chemistry kit.

    Sarah using the lamott kit to test water hardness
    Sarah Using the LaMott Kit to Test Water Hardness


    • USGS Water-Quality Information

    • General guidelines for classification of waters are:

    • 0 to 60 mg/L as calcium carbonate is classified as soft

    • 61 to 120 mg/L as moderately hard

    • 121 to 180 mg/L as hard

    • more than 180 mg/L as very hard.


    • We visited each stream varying times between 15 October and 26 November.

    • Hardness kit used to evaluate water hardness and see if there was any variation during the time span of this experiment.

      • Hardness was measured 3 times on two occasions and the average was used in the results


    • A 25 meter transect was the designated sample area for each stream.

    • Crayfish were collected by hand

    • In each stream zone we systematically collected crayfish in 30 minute intervals.

    • Crayfish abundance in that zone was recorded.


    • Each crayfish we caught was put into an ethanol bucket for storage.

    • Length and weight was measured and recorded in the lab

    • ANOVA tests used for comparison

    • Regression and r2 used for signifigance


    • Several buckets

    • Ethanol

    • Ruler

    • Scale

    • LaMott hardness kit


    Observed Means For Each Variable:

    • Largest Measured Growth Indicators: Sinking Creek

    • Smallest Measured Growth Indicators: Little Stony Creek

    • Highest Measured Hardness: Tom’s Creek

      • Unanticipated

  • Lowest Measured Hardness: Little Stony Creek

  • Between population variance for each variable
    Between Population Variance for each Variable

    • Almost all measured variables show significant variance between each population

    • Abundance shows no significant variance

    • Where is significant variance coming from?

    T tests

    • Compared each variable between each population using t-tests (post-hoc not available)

    • Hardness differences are unilaterally significant

    • Sinking Creek vs. Tom’s Creek

    Comparisons to hardness across populations
    Comparisons to Hardness Across Populations


    Hypothetically, this trend should hold. Right?

    Why is r 2 so low
    Why is R^2 So Low?

    • Strange Observation

      • Shouldn’t growth be correlated to [CaCO3]?

      • Why that not observed?

      • Most likely confounding variable in populations somewhere.

    Tom s creek omitted1
    Tom’s Creek Omitted


    What does this mean?

    Discussion conclusion
    Discussion/ Conclusion

    • Finding more Crayfish at Sinking Creek than Little Stony does support our hypothesis.

    • The low numbers of crayfish found in Tom’s Creek contradicts our hypothesis.

    Discussion conclusion1
    Discussion/ Conclusion

    • Calcium important to crayfish growth causality not known

    Discussion conclusion2
    Discussion/ Conclusion

    • This contradiction may be due to varying habitats.

    • More Sediments at Tom’s Creek

    • More Rocks at Sinking Creek

    • Little Stony had boulders

    • Sinking Creek had more cobble in the sampling area

    Results conclusion
    Results/ Conclusion

    • Future Experiments:

      • Send the same person to each stream near the same time of day on the same day

      • Different capturing strategies, weather patterns, seasons and amount of sunlight may affect the numbers of crayfish caught

    Literature cited
    Literature Cited

    • Cairns, Allegra, Yan Norman. 2009. A Review of the Influence of Low Amvient Calcium Concentrations on Freshwater Daphniids, Gammarids, and Crayfish. NRC Research Press website at er.nrc.ca.

    • Edwards, Brie A., Jackson, Donald A., Somers, Keith M. 2009. Multispecies Crayfish Declines in Lakes: Implications for Species Distributions and Richness. J. N. Am. Benthol. Soc 2009, 28(3): 719-732.

    • Hammond, Kent S., Hallows, John W., Townsend, Colin R., Lokman Mark P. 2005. Effects of Temperature and Water Calcium Concentration on Growth, Survival and Moulting of Freshwater crayfish, Paranephropszealandicus. Aquaculture 251(2006): 271-279.

    Literature cited1
    Literature Cited

    • Reynolds, Julian, Souty-Grosset, Catherine. 2012. Manage of Freshwater Biodiversity Crayfish as Bioindicatiors. Cambridge University Press, New York.

    • Stelzer, Robert S. and Burton, Thomas M. 2011. Growth and Abundance of the Crayfish Orconectespropinouus in a Hard Water and a Soft Water Stream. Journal of Freshwater Ecology, 8:4, 329-340.

    • U.S. Geological Survey. "Virginia Geologic Map Data." Virginia Geologic Map Data. U.S. Department of the Interior, 2005. Web. 24 Oct. 2012. <http://tin.er.usgs.gov/geology/state/state.php?state=VA>.

    • "Northern Virginia Ecology." Northern Virginia Ecology. Fairfax County Public Schools, n.d. Web. 07 Nov. 2012. <http://www.fcps.edu/islandcreekes/ecology.htm>.

    • "Water Hardness and Alkalinity." USGS Water-Quality Information:. U.S. Department of the Interior, n.d. Web. 28 Nov. 2012. <http://water.usgs.gov/owq/hardness-alkalinity.html>.