Evaluating Success of Oyster Restoration

Deriving Benchmarks

From Natural Populations

Hadley, N. H., L.D. Coen, V. Shervette, and M. Hodges

Success depends on your goals– Harvestable product– Ecosystem services– Public awareness

Sustainability may be an over-riding goal which applies to all

• When can/should success be determined?

• What constitutes success?

• Multiple year classes

• Size/density comparable to natural populations

• How do you establish the targets?

• Habitat functioning

Evaluating Success Based on Goals

• Harvestable oysters

• Large percentage of market size oysters

• This does not reflect natural populations patterns and may never be achievable

• Ecosystem services

•Many are difficult to measure

•Develop at different rates

•Habitat functioning may be inferred from presence of other species but does not necessarily depend on having oysters present

• When can/should success be determined?

• Multiple year classes

• Recruitment

• Survival/growth

• Size/density comparable to natural populations (convergence)

• Retention of hard substrate for continued recruitment

Evaluating Success Based on Goals

Sustainability

Size Frequencies on 1 and 3 Year Old Reefs Fall 2004

Dataw

0

100

200

300

400

500

600

700

800

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 >95

Oyste

rs/m

2 +

1 S

E

2001 - 3 Years

2003 - 1 Year

•Reference reefs

• Do they exist?

• Are they “good”?

• Long-term datasets

•Mean values

•Percentiles

•What proportion of natural reefs are in “good” condition?

• Classifying natural reefs along a continuum of “goodness”

Size/density comparable to natural populations

What’s your benchmark?

2006 - 12 yearsSite Experimental Natural Experimental NaturalInlet 29.2 128.1 414.2 395.6Tolers 15.2 88.7 307.7 322.6

Oyster Density on Paired Experimental and Natural Reefs in 1998 and 2006

1998 - 4 years

p<0.05 ns

Reference reefs

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

Oyste

rs/m

2 +

1SE

Sample Year

Natual Oyster Density in South Carolina

Series1 mean 30th 50th 70th

Mean= 2,348

70Mean50

30

Mean HeightMax

Height Total DensityDensity of

small oysters

Density of large

oysters % Recruits % Largemm mm #/m2 #/m2 #/m2 % %

Good 32 102 2,350 1,100 240 42-58 12Fair 23-32 84-102 850-2,350 140-1,100 100-240 25-42,>58 3-12

Poor <23 <84 <850 <140 <100 <25 <3

Mean HeightMax

Height Total DensityDensity of

small oysters

Density of large

oysters % recruits % largemm mm #/m2 #/m2 #/m2 % %

Good >35 >110 >2800 >1400 >300 50 15Fair 28-35 93-110 1400-2800 450-1400 145-300 30-50 6-15

Poor <28 <93 <1400 <450 <145 <30 <6

Target Values Based on Natural Population Percentiles

Target Values Based on Population Means

Good22%

Fair42%

Poor36%

Success Evaluation Based on Oyster Population Parameters for Large Scale Restored Sites in SC

20 Sites 45 Reefs

10

19

16

27 Reefs were less than 3 years old at time of assessment.

66% of reefs were fair or better

Overall Rating: Fair

Success of 19 Small-scale Reefs based on oyster population parameters

48%

26%

26%Good

Fair

Poor

Reefs sampled at 3 – 4 years

Alternative approach: Classify Natural Reefs

Fair

Good

FairStrata C

Strata E Excellent?

Strata A Very Good

Strata G Good

0

5

10

15

20

25

30

35

40

0

500

1000

1500

2000

2500

3000

3500

4000

4500

E strata A strata Gstrata Fstrata F1 strata C strata D strata

Shell H

eig

ht

(mm

)

Oy

ste

rs/m

2

Abundance/ Size Characteristicsof SC Oyster Strata

Total abundance

Abundance less YoY

Abundance YoY

Abundance Large

Mean Size

Good

Very Good

Fair

Poor

Characteristics of Natural Intertidal Oyster Populations in South Carolina

• Few large oysters – usually less than 20% • High recruitment – usually 50% of populations• Mean size for all strata ranges from 25 – 35 mm • High variability within and among sites • High variability among years

• A “good” reef one year may seem like a “poor” reef in another year

What proportion of natural reefs are in “good” condition?

Very Good – 5% - Stratas A and E

Good – 37% - Stratas F and G

Fair – 38% - Stratas F1 and C

Poor -19% - Stratas D and W

Establishing Success Benchmarks

Trask 3 YearsPopulation means: Good

Percentiles: Good

Strata convergence: Similar to G, may reach A

Strata G Good Strata A Very Good

Palmetto 3 YearsPopulation means: GoodPercentiles: Good

Strata Convergence: Similar to A or E

Strata G Good Strata A Very Good

Strata E Excellent? Or overcrowded

Dataw - 3 YearsPopulation means: Fair

Percentiles: Good

Strata Convergence: Better than C, may reach G

FairStrata CStrata G Good

72% of planted area remained at the end of the study77% of sites were fair or better

Overall Rating : Good

Good48%

Fair38%

Poor14%

Success Evaluation based on Footprint for Large-scale Restoration in SC

Total number of sites=21Total number footprints=52

7

25

20

CONCLUSIONS• Size frequency of restored populations is useful for evaluating

rate of development and sustainability.

• Using natural population means or percentiles as targets may be striving for mediocrity.

• Stratifying natural populations may provide more meaningful targets and allows us to examine development trajectories.

• Success ratings for large and small-scale restored sites ranging in age from 3 to 6 years are similar regardless of which of these targets are used

• Approximately 25% of restoration sites examined, both large and small scale, appear to be failures with little potential for development of sustainable populations of oysters.

AcknowledgementsShellfish Research Section personnel who have measured thousands of oysters each year to generate this dataset.

All the volunteers who helped build and sample the reefs!

Funded by: