Presentation on theme: "Eastern oyster settlement and early survival on alternative reef substrates adjacent to intertidal marsh, rip rap, and manmade oyster reef habitats in."— Presentation transcript:
Eastern oyster settlement and early survival on alternative reef substrates adjacent to intertidal marsh, rip rap, and manmade oyster reef habitats in Lynnhaven Bay, Virginia R. Burke*, R. Lipcius, M. Luckenbach, P.G. Ross, J. Woodward, and D. Schulte ICSR Charleston ICSR Charleston11/17/06
Acknowledgements US Army Corp of Engineers - Norfolk District: for providing funding and field support VIMS Eastern Shore Field Crew: for transport and assistance in deployment of >100 cages in the midst of a hectic schedule Homeowners on Long Creek and First Landing State Park: for permission to place cages and have land access to them. Special thanks to the entire Marine Conservation Biology group at VIMS for their field support.
Native Oyster Restoration – Lynnhaven River US ACoE’s Investment: An estimated $6.59 million “...restore up to 111.3 acres of oyster habitat (which could be constructed out of shells and/or alternative materials) and by Year 5 are predicted to have an associated oyster biomass of approximately 130,000 kilograms (kg) on the restored habitat alone.” –Final Decision Document Amendment, Section 704B as Amended, Chesapeake Bay Oyster Recovery Phase IV, Lynnhaven River, Virginia (November 2005)
VIMS’ Role Pre-Deployment: Plan Development Estimating oyster density across the variety of habitats/substrates Reef: –Site Selection –Composition (Shell and/or some alternative) Oyster Disease Prevalence and Burden Oyster Genetic Make- up/Diversity Post-Deployment: Monitoring of Oyster: –Survival –Settlement –Recruitment –Growth –Disease Prevalence and Burden –Genetic Make- up/Diversity VIMS serves an advisory role to the ACoE in:
Relevance of Research Production of experimental oyster recruitment, and survival on loose shells and different size classes of granite, limestone marl, and concrete at different depths in the intertidal zone provides the ACoE with system-specific information regarding which substrates are suitable amongst the suite of available options.
Alternative Oyster Reefs: Rip-Rap Average Broad Bay Oyster Density 770 oysters per m 2 95 % CI: 729-811 oysters per m 2 Shell Height (mm)
Experimental Design Fixed Factors –Intertidal Zone Lower: Natural Marsh Middle: Rip Rap (Granite and Concrete) and Concrete) Upper: Restored Oyster Reef Reef –Caged/Uncaged –Substrate Type 36 Treatments x 3 replicates = 108 Trays Substrates –OSU - Oyster Shell Unconsolidated (from Long Creek Restored Oyster Reef) –CVS - Demolished Concrete (very small) –GL - Granite (Large) –GS - Granite (Small) –LML - Limestone Marl (Large) –LMS - Limestone Marl (Small) *Materials and Cages Provided by Dr. Mark Luckenbach and PG Ross
Sampling Regime Deployed: –Late August 2005 Sampling Regime –Late Fall 2005 Post-Recruitment –Late Spring 2006 Pre-Recruitment –Late Fall 2006 Post-Recruitment (Ongoing) Non-Destructive Sampling –On-site sampling of ¼ (1 quadrant) of each 0.25 sq m replicate and return it to its original depth/location Monitor –Spat settlement –Growth Shell Height measured for a subset of samples (36) –Survival –Fouling –Presence/Absence of: Mud crabs Blue Crabs Reef fishes Bryozoans, Sponges, Algae, etc.
Hypothesis #1 H o :Spat survival will not significantly differ across different substrates –H A1 : Spat survival will be higher on substrates with higher fractal dimension –H A2 : Spat survival will be higher on larger substrates as larger interstitial spaces will not provide ample protection for mud crabs – one of the major predators of small oyster spat
245 mm 140 mm ConcreteLimestone Marl Small Medium Large IV=47.9%; FD=1.073 IV=52.5%; FD=1.051 IV=52.2%; FD=1.039 IV=53.4%; FD=1.126 IV=57.0%; FD=1.171 IV=64.5%; FD=1.159
Oyster Population Parameters Alternative Substrate Experiment Interstital Space Surface Complexity 245 mm 140 mm
Hypothesis #2 H o :Spat survival in Caged treatments will not significantly differ from uncaged treatments –Due to the size of mud crabs, their tendency to find refuge in the crevices created by small substrates, and their territorial nature, the 1-inch mesh of the cages should not hinder their recruitment or migration into the cages. –H A : Spat survival in cages may be significantly less than in uncaged treatments due to exclusion of larger mud crab predators (i.e. large blue crabs, predatory fish)
Hypothesis #3 H o :Spat recruitment and survival will not significantly differ between the Lower, Mid, and Upper Intertidal Zones. –H A : Oyster spat recruitment and survival may be highest in the lower intertidal and lowest in the upper intertidal (Bartol and Mann, 2001).
Statistical Analysis Two-way ANOVA (substrate & cage control) for the following response variables: –Count of Live Spat per sample (1/16 th m 2 ) –Proportion of Live Spat per sample (1/16 th m 2 ) –Exterior Live Spat per sample (1/16 th m 2 ) –Interior Live Spat per sample (1/16 th m 2 ) Three-Way ANOVA (including Intertidal Zone) for the same response variables as the Two-ANOVAs. Student’s t-test to distinguish any handling effects
Conclusions “Substrate Matters” –Granite (Lg or Sm) may be a favorable oyster reef construction material, since it had significantly higher recruitment and, on average, the highest proportion of live oysters amongst the different substrate types Caging negatively impacted oyster survival especially on the granite treatments: –The large difference of means for caged v. uncaged trays of granite indicates a higher susceptibility of oyster spat on this substrate upon an apparent relaxation of predation on small predators, such as mud crabs, provided by the caged controls.
Conclusions Intertidal Zone significantly influenced recruitment: Lower > Mid > Upper Exterior Live Spat Count > Interior Live Spat Count (Edge effects) Interiors of trays were not negatively impacted by caging. Although there was significant mortality from the Fall to the Spring in quadrant #1 (Paired t-test), 2-sample t-tests for each substrate type revealed no significant handling effect.
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