Evaluation of the impact that moderate hypoxia can have on oyster growth at potential reef restoration sites in Mobile B

1. Evaluation of the impact that moderate hypoxia can have on oyster growth at potential reef restoration sites in Mobile Bay, AL. Matthew W. Johnson S. Powers, J. Senne, K. Park ICSR 2008 Charleston, SC 21 November 2008

2. Oyster Reefs Oyster “tonging” • Exploitable fishery and an essential habitat for many other species. • Destructive fishing practices remove not only harvestable oysters, but the complicated reef matrix future generation of oysters require. Hydraulic dredges

3. Point Clear Reefs Whitehouse Reef Fish River/Shell Bank Cedar Point/Dauphin Island 1407 hectares

4. Oyster Reefs in Alabama • Sub-tidal Reefs • Unconsolidated • Thin veneer • Put and Take Fishery • Low relief • Good for tonging Photos Courtesy of Mississippi Department of Marine Resources

5. Physical and Biological Challenges Healthy Oyster Reef Settlement & Growth

7. After Katrina August 2007 Before Katrina

8. 1 2 5 200 100 10 Larval supply Predation Dissolved Oxygen # spat m-2 d-1 (Hoese et al. 1972)

9. 2 m 2. Build out of the hypoxia 1 m Hypoxia and Restoration 2.5 m 1. Stop the reason for hypoxia Normoxic Hypoxic Anoxic

10. Whitehouse Reef ADCNR “Reef Donut” Relic Reef Mud Bottom

11. Objectives • Determine extent of hypoxia in this area. • Ensure that adequate larval settlement to area. • Measure oyster spat survival and growth to see how this related to depth • Short-cut to reef design

12. 1 5 200 100 10 2 Design • A priori designation of 3 different oxygen regimes • Similar larvae supply • Similar Depth, 2.75-3 m • Control predation Extreme Hypoxia Moderate Hypoxia No Hypoxia

13. Mesh size 1 cm2 • 3 replicates per location • Oysters deployed on 7/11/2007 and checked biweekly until 9/6/2007, 10/9/2007 • Oyster were cleaned of epibionts and counted • Measured at final date 0.5 X 0.5 m 5 X 5 or 4 X 6 79 ± 19 (SD) spat 1.25 m 0.5 m

14. Dissolved Oxygen • YSI deployed at each depth at each location • June 29- Aug 27 (5X), Sept 24, Oct 17 Measured DO at 19 stations near Whitehouse Reef

15. Bottom Dissolved Oxygen Bottom 1.3 M Off Bottom @ Whitehouse Reef

16. Dissolved Oxygen 0-1m (mg l-1) August 14 August 27 June 29 July 5 July 19 Anoxia Hypoxia Normoxia

17. Depth and Growth Repeated Measures ANOVA Location- p<0.001 Depth- NS Time- p<0.001 Time x Location p<0.001

18. Theodore Industrial Canal Whitehouse Reef Dauphin Island

19. When the hypoxia ends…

20. Height and Length 2-way ANOVA Location x Depth- p<0.001 K-W ANOVA on Ranks Location- p<0.001 Depth- p<0.001 A A A A 2-way ANOVA Location x Depth- p<0.001 K-W ANOVA on Ranks Location- p<0.001 Depth- p<0.001 B B B B C A A C B B C C C C A A B B C C

21. Practical Applications…… 1.25 m > 1.0 m 0.5 m

22. Conclusions • Settlement at all depths and all locations • Dissolved oxygen did influence population growth, individual growth • Response under moderate hypoxia similar to that of severe hypoxia

23. Acknoweldgements • Funding • University of South Alabama Oyster Restoration Project • NOAA/NMFS • Personnel • Crystal Hightower • Matt Kenworthy • Jason Herrmann • Stan Bosarge • Multiple Interns

24. Oyster Reefs in Alabama • Decreased long-term production • Stabilized production in recent past

25. 2005-2008 Population in trouble?