Subtidal and intertidal restored reefs in North Carolina Jonathan H. Grabowski 1, Sean P. Powers 2, Pete Peterson 3, and Hunter S. Lenihan 4 1 Gulf of Maine Research Institute/U. Maine-Darling Marine Center 2 Dauphin Island Sea Lab/University of South Alabama 3 University of North Carolina, Institute of Marine Sciences 4 University of California at Santa Barbara
Summary Outline I. Brief synopsis of previous restoration research Metrics quantified & major conclusions/lessons learned II. Ongoing Investigations Metrics quantified, preliminary data, & success status (initial assessment)
I. Historical Overview: Decline of the Eastern Oyster 6 5 19 194 198 1912 1916 192 1924 1928 1932 1936 194 1944 1948 1952 1956 196 1964 1968 1972 1976 198 1984 1988 1992 1996 2 4 3 2 1 Oyster Meat ( Million lbs)
1. Elevation of subtidal reef habitat above anoxic bottom waters A 3 m Station 4 m Station 3 m surface 1.5 km 6 m Station (2-m tall reef) (1-m tall) 4 m oxygenated surface layer 6 m 1.5 m Water Depth 2.1 m 2.4 m 2.4 m 2.9 m 2.9 m 3.3 m 3.3 m 2 4 6 2 4 hypoxic bottom layer Short reefs 3.3 m 3.9 m Tall reefs Short reefs 4.3 m 2 4 B Live Oysters Dead Oysters No. oysters per.1 m 2 Short reefs 5.2 m 5.7 m 6.1 m 2 4 6 Tall reefs 4.2 m 4.9 m 5.2 m 5.7 m 6.1 m 2 4 6 Lenihan 1999
2. Oyster reef as essential fish habitat 2 16 12 8 4 A 3 m - tall reefs 18 15 12 9 6 3 B 3 m - short reefs fish/trap 2 16 12 8 4 crustaceans/trap 18 15 12 9 6 3 2 16 12 8 4 2 16 12 8 4 31 May 6 July 13 June 18 July 2 July Hypoxia/anoxia 5 Aug 6 m - tall reefs 6 m - short reefs 3 Sept. 18 15 12 9 6 3 18 15 12 9 6 3 15 May 1 June 7 July 21 July 6 Aug Hypoxia/anoxia mud crabs grass shrimp amphipods Lenihan et al. 21
3. Restoring oyster reefs within the estuarine landscape Grabowski et al. 24 (in review)
Landscape study Design Landscape effects Restored (1997 vs. 2) vs. natural reefs Metrics Resident and transient fauna (cores, quadrats, gill nets, traps, popup nets) Oyster settlement & adult densities (cores and quadrats) Oyster reef complexity (quadrats)
II. Ongoing Research: Restoration Strategy Restoration efforts have targeted both the oyster fishery and reef ecosystem services No harvest or sanctuary reefs are central to proposed restoration efforts along the east coast Concern about disease dynamics has led to a movement to bring in exotic species
Reefs monitored Each area has 1-24 sanctuary reefs, age ranges from 2 to 12 yrs old. Harvestable areas created by NCDMF Natural (harvested) reef areas. Sanctuary included in this study Sanctuary not included in this study Reef & oyster condition and disease monitored late spring and late summer
Success criteria Density of living oysters benchmark set relative to natural reefs (non-harvested when available) Spat recruitment Size-distribution (multiple age classes should be represented)
Status of Sanctuaries Highly successful Neuse River < 4 m West Bay (Shell) Middle Marsh I & II Successful West Bay (Marl) Deep Bay Wanchese
Status of Sanctuaries Failing Bogue Sound (burial) Cape Hatteras (poor recruitment) Neuse River > 5 m (post-settlement loss due to poor water quality) Neuse River 4 m (burial?)
Alternative Substrates Small marl experimental reefs (1996 in West Bay) Less successful settlement than adjacent shell reefs Large marl sanctuaries Four built in 1996 throughout coastal NC Difficult to harvest Expensive and difficult to build Limited success
Oyster - P. marinus relationships Disease prevalence and severity vs: harvest status age of non-harvested area density of oysters Disease dynamics and variability in environmental setting of oyster reefs
Metrics Density of live & Dead Oysters Size-distribution Disease prevalence & severity (Dermo only) Physical/chemical parameters (Temp, Sal., D.O., velocity)
Current & Pending Funding Current funding Sea Grant Oyster Disease Program 24-25 Importance experimental approaches i.e., reef design & replicate reefs provide opportunities for longterm empirical studies
Disease severity 22 Relative Frequency.6.4.2 May/June 22 September 22. 1 3 5 Increasing severity
Disease vs. age of oyster reef Disease prevalence Disease severity Proportion infected.8.7.6.5.4.3.2.1 F = 17.28; p <.1 1.6 F = 12.42; p <.1 1.4 1.2 1.8.6.4.2 2 1999 1998 1996 1993 Year created Infection Level (1-5) 2 1999 1998 1996 1993 Year created
Sanctuary vs. harvested areas Disease prevalence Disease intensity Proportion infected.5.4.3.2.1 Harvest p <.1 Sanctuary Infection Level (1-5).8.7.6.5.4.3.2.1 Harvest p =.4 Sanctuary
Disease prevalence vs. oyster density # Oysters m -2 7 6 5 4 3 2 1 r = -.49; p <.1.1.2.3.4.5.6.7.8.9 1 Prevalence
Oyster condition, sanctuary status, and reef age Sanctuary Harvest Reef Status 2 1999 1998 1996 1993 Year created Condition Index = Weight/volume for oysters collected in early summer before disease level increases 4 3 2 1 4 3 2 1 Condition Index
Landscape setting vs. disease prevalence Proportion of oyster with dermo.4.2 Mudflat Saltmarsh Seagrass
Within reef factors: reef height Proportion of oyster with dermo.4.2 p =.11 Crest Base u (cm s -1 ) See also Lenihan et al. 1999, L&O Vol. 44
Feasibility of monitoring other variables Resident and transient fauna Filtering capacity Reproductive output Habitat dimensional complexity Shoreline/reef stability Indicator species
Summary & Conclusions Design, structure, and physical setting (e.g., landscape) of oyster reefs are critical in the success of restoration efforts. Restoration and management plans must consider and (when possible) test how actions may influence disease dynamics. Experimental investigations of the processes that structure oyster reef communities and determine successful provision of ecosystem goods and services should be investigated at large spatial scales (i.e., geographic variation).
Acknowledgements Hunter Lenihan (UCSB) Craig Hardy & Mike Marshall (NCDMF) FerryMON & MODMON Projects (H. Paerl & R. Luettich) Funding was provided by Sea Grant s Oyster Disease Research Program and by the State of North Carolina