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

Sarah DeelChris Brassell

Ben WadeJeff Rosemond

Crayfish Collected during the experiment

Introduction

• Freshwater Crayfish naturally inhabit most all the continents.

• The US is home to two families (Reynolds and Souty-Grosset 2012).– Astacidae– Camvaridae

Introduction

• 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).

Introduction

• 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).

Introduction

• 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

• 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 (Stelzer and Burton 2011).

Introduction- A Recent Study

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

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

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…

• 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

Introduction

• 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

• 3 chosen sites:

1) Sinking Creek: high hardness

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

Introduction- Sampling Sites

• Both dolostone and limestone leech metals cations– limestone leeches calcium– dolostone leeches both magnesium and

calcium.Limestone

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

Dolostone

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

Introduction- Sampling Sites

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

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

Introduction- Sampling Sites

3) Tom’s Creek: very high hardness

– elbrook formations: dolostone and limestone (U.S. Geological).

– Runoff/ pollution

Methods

• 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

Methods

• 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.

Methods

• 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

Methods

• 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.

Methods

• 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

Equipment

• Several buckets• Ethanol• Ruler • Scale• LaMott hardness kit

Chris and Jeff Measuring Crayfish

Weighing the Crayfish

Chris measuring length

Ben working out the statistics

Results

Mean Length (cm) Mean Mass (g) Abundance

Mean Hardness

(ppm)

Sinking Creek 11.03182 14.79409091 18 121.2727

Little Stony Creek 9.236364 9.848181818 11 28.54545

Tom's Creek 8.388235 4.770588235 17 232.9167

• 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

Observed Means For Each Variable:

Between Population Variance for each Variable

VariableBetween Population Variance

(P-value)

Hardness 7.74843E-26

Mass 5.17261E-05

Length 0.000658702

Abundance 0.059667724

• Almost all measured variables show significant variance between each population

• Abundance shows no significant variance

• Where is significant variance coming from?

T-TestsStreams Comparison Hardness Mass

Length

Sinking vs. Tom’s 2.62164E-05 0.0067290.0023184

52

Little Stony vs. Tom’s 1.0486E-07 0.2055810.8138352

62

Little Stony vs. Sinking 1.36484E-05 0.1072140.0859850

66

• 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

Abundance:

Hypothetically, this trend should hold. Right?

0 50 100 150 200 250 3000

1

2

3

4

5

6

R² = 0.488450801065093

Abundance vs Mean Hardness

Mean Hardness (ppm)

Abun

danc

e

Comparisons to Hardness Across Populations

Wrong.• Mass:

0 50 100 150 200 250 3000

5

10

15

20

25

R² = 0.0682925825879584

Mean Mass vs Mean Hardness

Mean Hardness (ppm)

Mea

n M

ass (

g)

Comparisons to Hardness Across Populations

• Length

0 50 100 150 200 250 3000

2

4

6

8

10

12

R² = 0

Mean Length vs Mean Hardness

Mean Hardness (ppm)

Mea

n Le

ngth

(cm

)

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 Omitted

• Mass:

0 20 40 60 80 100 120 140 1600

5

10

15

20

25

R² = 0.507538825418463

Mean Mass vs Mean Hardness (Tom's Creek Ommitted)

Mean Hardness (ppm)

Mea

n M

ass (

g)

Tom’s Creek Omitted

0 20 40 60 80 100 120 140 1600

2

4

6

8

10

12

14

R² = 0.479611244719436

Mean Length vs Mean Hardness (Tom's Creek Ommit -ted)

Mean Hardness (ppm)

Mea

n Le

ngth

(cm

)Length:

What does this mean?

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/ Conclusion

• Calcium important to crayfish growth causality not known

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

• 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• 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, Paranephrops zealandicus. Aquaculture 251(2006): 271-279.

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 Orconectes propinouus 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>.

Questions?