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

Size Frequencies on 2 and 3 Year Old Reefs Fall 2004

Size Frequency of Oysters on 2 and 3 Year Old Reefs Fall 2005

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?

Reference reefs

70 Mean 50 30

Targets based on population means

27 Reefs were less than 3 years old at time of assessment. 66% of reefs were fair or better Overall Rating: Fair

Reefs sampled at 3 – 4 years

Alternative approach: Classify Natural Reefs

Fair Good Fair Strata C Strata E Excellent? Strata A Very Good Strata G Good

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

Relative frequency of occurrence of different strata in SC Ben Dyar 12 June 2006 Total beds classified: 2519 >50%

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

Pinckney 3 Years Population mean: Fair Strata Mean: Fair Fair Not yet converging

Edisto 3 Years Fair Population means: Poor Strata Means: Fair Different from all defined strata

Trask 3 Years Population means: Good Percentiles: Good Strata convergence: Similar to G, may reach A Strata G Good Strata A Very Good

Palmetto 3 Years Population means: Good Percentiles: Good Strata Convergence: Similar to A or E Strata G Good Strata A Very Good Strata E Excellent? Or overcrowded

Dataw - 3 Years Population means: Fair Percentiles: Good Strata Convergence: Better than C, may reach G Fair Strata C Strata G Good

72% of planted area remained at the end of the study 77% of sites were fair or better Overall Rating : Good

47 % of sites were above average 76% of sites were average or better Overall Rating: Good

Shortcomings of Using Population Means or Percentiles Targetting mediocrity? Site rankings all similar Even one year old sites rank fair No definition for “Excellent”

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.

Future Directions % vertical coverage Confidence limits Validation at natural sites Test targets in other geographic areas Habitat functioning –Diversity indices –Transient fauna Weighting of metrics Relate success to site characteristics

Evaluation of Reef Success Footprint: how much of the shell area remained? Resemblance to natural populations –Quantity of oysters –Size of oysters –Percentage of recruits –Percentage of large oysters Average of footprint and population scores = composite score

Conclusions A total of 76 reefs were constructed at 32 sites, totally ~9 acres Overall 72% of reef area remains (Good) 77% of sites had average or better shell retention (Good) 64% of reefs fair or good compared to natural populations after 1-4 years (Fair) Composite success rating: Good

Acknowledgements Shellfish 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: