Matthew W. Johnson S. Powers, J. Senne, K. Park ICSR 2008 Charleston, SC 21 November 2008

Oyster Reefs  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. Oyster “tonging” Hydraulic dredges

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

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

Settlement & Growth Physical and Biological Challenges Healthy Oyster Reef

After Katrina Before Katrina August 2007

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

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

Relic Reef Mud Bottom ADCNR “Reef Donut”

 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

 A priori designation of 3 different oxygen regimes  Similar larvae supply  Similar Depth, m  Control predation Extreme Hypoxia Moderate Hypoxia No Hypoxia

0.5 X 0.5 m 5 X 5 or 4 X 6 79 ± 19 (SD) spat 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 m 1.25 m Mesh size 1 cm 2

 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 Dissolved Oxygen

Bottom 1.3 M Off Whitehouse Reef

AnoxiaHypoxiaNormoxia June 29July 5July 19 August 14August 27

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

Theodore Industrial Canal Whitehouse Reef Dauphin Island

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

0.5 m 1.25 m > 1.0 m Practical Applications……

 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

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

 Decreased long-term production  Stabilized production in recent past

Population in trouble?