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
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? 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 Sustainability 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
Size Frequencies on 1 and 3 Year Old Reefs Fall 2004
Size/density comparable to natural populations What’s your benchmark? 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”
Reference reefs
70 Mean 50 30
66% of reefs were fair or better Overall Rating: Fair 27 Reefs were less than 3 years old at time of assessment.
Reefs sampled at 3 – 4 years
Alternative approach: Classify Natural Reefs
Strata E Excellent? Strata G Good Good Fair Strata C Fair Strata A Very Good Strata G Good Good Fair Strata C Fair
Very Good 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
Establishing Success Benchmarks 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
Trask 3 Years Population means: Good Percentiles: Good Strata G Good Strata A Very Good Population means: Good Percentiles: Good Strata convergence: Similar to G, may reach A
Palmetto 3 Years Population means: Good Percentiles: Good Strata G Good Strata A Very Good Population means: Good Percentiles: Good Strata Convergence: Similar to A or E Strata E Excellent? Or overcrowded
Dataw - 3 Years Population means: Fair Percentiles: Good Strata G Good Fair Strata C Population means: Fair Percentiles: Good Strata Convergence: Better than C, may reach G
72% of planted area remained at the end of the study 77% of sites were fair or better Overall Rating : Good
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.
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: