Evaluation of the impact that moderate hypoxia can have on oyster growth at potential reef restorati

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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
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Oyster Reefs

• Exploitable fishery and an essential habitat for
  many other species.

Oyster tonging

• Destructive fishing practices remove not only
  harvestable oysters, but the complicated reef
  matrix future generation of oysters require.

Hydraulic dredges
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Point Clear Reefs
Whitehouse Reef
Fish River/Shell Bank
Cedar Point/Dauphin Island 1407 hectares
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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
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Healthy Oyster Reef
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(No Transcript)
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After Katrina
Before Katrina
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(No Transcript)
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Hypoxia and Restoration
2.5 m
1. Stop the reason for hypoxia
Normoxic
Hypoxic
Anoxic
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Whitehouse Reef
ADCNR Reef Donut
Relic Reef
Mud Bottom
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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

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Design

• A priori designation of 3 different oxygen
  regimes
• Similar larvae supply
• Similar Depth, 2.75-3 m
• Control predation

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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
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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

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Bottom Dissolved Oxygen
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Dissolved Oxygen 0-1m (mg l-1)
August 14
August 27
June 29
July 5
July 19
Anoxia
Hypoxia
Normoxia
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Depth and Growth
Repeated Measures ANOVA
Location- plt0.001 Depth- NS Time- plt0.001 Time x
Location plt0.001
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Theodore Industrial Canal
Whitehouse Reef
Dauphin Island
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When the hypoxia ends
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Height and Length
2-way ANOVA Location x Depth- plt0.001 K-W ANOVA
on Ranks Location- plt0.001 Depth- plt0.001
2-way ANOVA Location x Depth- plt0.001 K-W
ANOVA on Ranks Location- plt0.001 Depth- plt0.001
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Practical Applications
1.25 m
0.5 m
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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

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Acknoweldgements

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

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Oyster Reefs in Alabama

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

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2005-2008
Population in trouble?