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

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

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

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

Healthy Oyster Reef Physical and Biological Challenges Settlement & Growth

August 2007 After Katrina Before Katrina

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

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

Whitehouse Reef ADCNR “Reef Donut” Relic Reef Mud Bottom

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

Design Extreme Hypoxia Moderate Hypoxia No Hypoxia 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 200 100 10 5 2 1

3 replicates per location 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

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

Bottom Dissolved Oxygen 1.3 M Off Bottom @ Whitehouse Reef

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

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

Theodore Industrial Canal Whitehouse Reef Dauphin Island

When the hypoxia ends…

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

Practical Applications…… > 1.0 m 1.25 m 0.5 m

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

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

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

2005-2008 Population in trouble?