Quantitative Validation of a Habitat Suitability Index for Oyster Restoration

Habitat suitability index (HSI) models provide spatially explicit information on the capacity of a given habitat to support a species of interest, and their prevalence has increased dramatically in recent years. Despite caution that the reliability of HSIs must be validated using independent, quantitative data, most HSIs intended to inform terrestrial and marine species management remain unvalidated. Furthermore, of the eight HSI models developed for eastern oyster (Crassostrea virginica) restoration and fishery production, none has been validated. Consequently, we developed, calibrated, and validated an HSI for the eastern oyster to identify optimal habitat for restoration in a tributary of Chesapeake Bay, the Great Wicomico River (GWR). The GWR harbors a high density, restored oyster population, and therefore serves as an excellent model system for assessing the validity of the HSI. The HSI was derived from GIS layers of bottom type, salinity, and water depth (surrogate for dissolved oxygen), and was tested using live adult oyster density data from a survey of high vertical relief reefs (HRR) and low vertical relief reefs (LRR) in the sanctuary network. Live adult oyster density was a statistically-significant sigmoid function of the HSI, which validates the HSI as a robust predictor of suitable oyster reef habitat for rehabilitation or restoration. In addition, HRR had on average 103–116 more adults m−2 than LRR at a given level of the HSI. For HRR, HSI ≥ 0.3 exceeded the accepted restoration target of 50 live adult oysters m−2. For LRR, the HSI was generally able to predict live adult oyster densities that meet or exceed the target at HSI ≥ 0.3. The HSI indicated that there remain large areas of suitable habitat for restoration in the GWR. This study provides a robust framework for HSI model development and validation, which can be refined and applied to other systems and previously developed HSIs to improve the efficacy of native oyster restoration

Settlement, Growth, And Survival Of Eastern Oysters On Alternative Reef Substrates

Restoration of the native eastern oyster (Crassostrea virginica) has been severely hindered by the dwindling supply and rising costs of fossil and new oyster shell (OS) for use in reef restoration. Consequently, emphasis has shifted to the use of alternative oyster reef materials, which need to be tested for their effectiveness as settlement substrate. Furthermore, low recruitment of wild larvae has also impeded restoration, indicating a need to assess the potential of field setting of cultured larvae. We experimentally examined oyster settlement, growth and survival on unconsolidated OS, vertically embedded oyster shell (ES) in concrete, and concrete Oyster Castles (OC) in field and mesocosm experiments. In addition, we examined settlement success of cultured larvae in the mesocosm experiment. In the field experiment, juvenile recruitment was 3 higher on castles and unconsolidated shell than on embedded shell. Castles retained 4Xthe number of oysters and hosted 5Xthe biomass than embedded shell, and retained 1.5Xthe oysters and hosted 3Xthe biomass than unconsolidated shell. The proportion of live oyster recruits on castles was 1.5Xthat on both embedded and unconsolidated shell. In the mesocosm experiment (90-d postlarval deployment), the castles recruited, retained, and hosted an oyster biomass 4Xhigher than that of unconsolidated and embedded shell. This study confirms that artificial reef materials, such as OC, are suitable alternative substrates for oyster restoration, and remote setting of larvae can be effective under controlled environmental conditions. Future restoration efforts should consider use of alternative reef substrates and field setting of larvae, where recruitment is limited, to maximize oyster recruitment, while simultaneously minimizing the cost of reef restoration

Workshop on the Norwegian Sea Aquaculture Overview

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Restoring shellfish reefs: Global guidelines for practitioners and scientists

Widespread global declines in shellfish reefs (ecosystem-forming bivalves such as oysters and mussels) have led to growing interest in their restoration and protection. With restoration projects now occurring on four continents and in at least seven countries, global restoration guidelines for these ecosystems have been developed based on experience over the past two decades. The following key elements of the guidelines are outlined: (a) the case for shellfish reef resto- ration and securing financial resources; (b) planning, feasibility, and goal set- ting; (c) biosecurity and permitting; (d) restoration in practice; (e) scaling up from pilot to larger scale restoration, (f) monitoring, (g) restoration beyond oyster reefs (specifically mussels), and (h) successful communication for shell- fish reef restoration projects

Development of a Habitat Suitability Index for the Eastern Oyster (Crassostrea virginica) in Great Wicomico River, Virginia

The eastern oyster, Crassostrea virginica, provides critical ecological functions to Chesapeake Bay. Unfortunately, as a result of overharvesting, disease, and poor water quality, the native oyster population of the Bay currently stands at less than 1% of its historic size. Within the Great Wicomico River, a tributary of the Bay, the United States Army Corps of Engineers (USACE) Norfolk District has successfully restored approximately 85 acres of “no take” sanctuary oyster reef. This study developed a habitat suitability index (HSI) for the eastern oyster in the Great Wicomico River in order to identify areas of suitable oyster habitat. The model was validated using live adult oyster density data derived from the 2011 VIMS monitoring survey of the USACE restored reefs. The results from this model can be used to inform the rehabilitation of the existing sanctuary oyster reef network and the construction of additional oyster reef in the Great Wicomico River

Theuerkauf_2017_CommunityStructure_LongTermExtendedStudy

Long-term community structure + extended study: Percent cover of each species on each replicate plate (n=3) at approximately >180 days after initial plate deployment. Specifically, long-term community structure (i.e., ≥ 180 days post initial plate deployment) was defined as the last sampling of the CD plates that could occur by December 2015 (following sampling every 90 days). The final sampling of CD plates occurred from October 2015 – December 2015. Extended study: plates deployed during Aug. 2014 were continually sampled every 90 days through Aug. 2016, including Feb. 2016, May 2016, and Aug. 2016, as reported in rows 31-39. Please see main text for additional information

Theuerkauf_2017_CommunityStructure_ShortTerm

Short-term community structure: Percent cover of each species on each replicate plate (n=3) at approximately 90 days after initial plate deployment. Plates were deployed during August 2014 - September 2015 and were sampled 90 days later (November 2014 - December 2015). Please see main text for additional information

Theuerkauf_2017_LarvalRecruitment_PresentStudy

Larval recruitment: Average monthly percent cover of larval species that settled on larval recruitment plates deployed from August 2014 – November 2015 and sampled four weeks later (September 2014 – December 2015). Recruitment patterns of Ascidia interrupta, Styela plicata, and Ostrea equestris were not observed during the course of this study. Please see main text for additional information

Density-dependent role of an invasive marsh grass, <i>Phragmites australis</i>, on ecosystem service provision

<div><p>Invasive species can positively, neutrally, or negatively affect the provision of ecosystem services. The direction and magnitude of this effect can be a function of the invaders’ density and the service(s) of interest. We assessed the density-dependent effect of an invasive marsh grass, <i>Phragmites australis</i>, on three ecosystem services (plant diversity and community structure, shoreline stabilization, and carbon storage) in two oligohaline marshes within the North Carolina Coastal Reserve and National Estuarine Research Reserve System (NCNERR), USA. Plant species richness was equivalent among low, medium and high <i>Phragmites</i> density plots, and overall plant community composition did not vary significantly by <i>Phragmites</i> density. Shoreline change was most negative (landward retreat) where <i>Phragmites</i> density was highest (-0.40 ± 0.19 m yr^-1 vs. -0.31 ± 0.10 for low density <i>Phragmites</i>) in the high energy marsh of Kitty Hawk Woods Reserve and most positive (soundward advance) where <i>Phragmites</i> density was highest (0.19 ± 0.05 m yr^-1 vs. 0.12 ± 0.07 for low density <i>Phragmites</i>) in the lower energy marsh of Currituck Banks Reserve, although there was no significant effect of <i>Phragmites</i> density on shoreline change. In Currituck Banks, mean soil carbon content was approximately equivalent in cores extracted from low and high <i>Phragmites</i> density plots (23.23 ± 2.0 kg C m^-3 vs. 22.81 ± 3.8). In Kitty Hawk Woods, mean soil carbon content was greater in low <i>Phragmites</i> density plots (36.63 ± 10.22 kg C m^-3) than those with medium (13.99 ± 1.23 kg C m^-3) or high density (21.61 ± 4.53 kg C m^-3), but differences were not significant. These findings suggest an overall neutral density-dependent effect of <i>Phragmites</i> on three ecosystem services within two oligohaline marshes in different environmental settings within a protected reserve system. Moreover, the conceptual framework of this study can broadly inform an ecosystem services-based approach to invasive species management.</p></div

Mean (±SE) normalized total below-ground carbon inventory (g C m^-3).

<p>Below-ground carbon inventory A) at Kitty Hawk Woods and Currituck Banks Reserves, B) between <i>Phragmites</i> Density treatments within Kitty Hawk Woods Reserve, and C) between <i>Phragmites</i> Density treatments within Currituck Banks Reserve. Note that the Medium <i>Phragmites</i> Density treatment was present only in Kitty Hawk Woods Reserve. See text for results of statistical analyses.</p