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1. Utilizing airborne LiDAR data to quantify marsh edge morphology and the role of oyster reefs in mitigating marsh erosion

   https://doi.org/10.3354/meps13728  

   Hogan, S; Wiberg, PL; Reidenbach, MA (July 2021, Marine Ecology Progress Series)

   null (Ed.)

   Marsh habitats, experiencing accelerated change, require accurate monitoring techniques. We developed methods to quantify marsh edge morphology using airborne LiDAR data. We then applied these methods within the context of oyster reef restoration within the shallow coastal bays of Virginia, USA, by comparing retreat and morphology quantified at paired reef-lined and control marsh edges at 10 different marsh sites. Retreat metrics were analyzed between 2002 and 2015, utilizing a LiDAR derived edge for the year 2015 from points of maximum slope and aerial imagery pre-2015. Retreat was also compared before and after oyster reef restoration to determine if reefs slow erosion. We found that slope statistics from airborne LiDAR elevation data can accurately capture marsh edge morphology. Retreat rate, measured at edges typically found near the vegetation line, was not significantly different between reef-lined and control marshes and ranged from 0.14 to 0.79 m yr -1 . Both retreat rate (ρ = -0.90) and net movement (ρ = -0.88) were strongly correlated to marsh edge elevation. Exposed control marshes had significantly greater mean and maximum slope values compared to reef-lined marshes. The mean edge slope was 11.4° for exposed marshes and 6.0° for reef-lined marshes. We hypothesize that oyster reefs are causing an elongation of the marsh edge by reducing retreat at lower elevations of the marsh edge. Therefore, changes in marsh edge morphology may be a precursor to changes in marsh retreat rates over longer timescales and emphasizes the need for repeated LiDAR measurements to capture processes driving marsh edge dynamics. 

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2. Salt marsh shoreline geomorphology influences the success of restored oyster reefs and use by associated fauna

   https://doi.org/10.1111/rec.12992  

   Keller, Danielle A.; Gittman, Rachel K.; Brodeur, Michelle C.; Kenworthy, Matthew D.; Ridge, Justin T.; Yeager, Lauren A.; Rodriguez, Antonio B.; Fodrie, F. Joel (July 2019, Restoration Ecology)

   Restoration is increasingly implemented as a strategy to mitigate global declines in biogenic habitats, such as salt marshes and oyster reefs. Restoration efforts could be improved if we knew how site characteristics at landscape scales affect the ecological success of these foundation species. In this study, we determined how salt marsh shoreline geomorphologies (e.g. with variable hydrodynamic energy, fetch, erosion rates, and slopes) affect the success of restored intertidal oyster reefs, as well as how fauna utilize restored reefs and forage along marsh habitats. We constructed oyster reefs along three marsh shoreline geomorphologies in May 2012: 1) “creek” (small‐fetch, gradual‐sloped shoreline), “ramp” (large‐fetch, gradual‐sloped shoreline), and “scarp” (large‐fetch, steep‐sloped shoreline). Following recruitment, oyster spat density was greatest on ramp reefs; however, 2 years later, the highest adult oyster densities were found on creek reefs. Total nekton and blue crab catch rates in trawl nets were highest in the creek, while piscivore catch rates in gill nets were highest along the scarp shoreline. We found no difference in predation on snails in the salt marsh behind constructed reef and nonconstructed reference sites, but there were more snails consumed in the creek shoreline, which corresponded with the distribution of their major predator—blue crabs. We conclude that oyster reef construction was most successful for oysters in small‐fetch, gradual‐sloped, creek environments. However, nekton abundance did not always follow the same trends as oyster density, which could suggest constructed reefs may offer similar habitat‐related functions (prey availability and refuge) already present along existing salt marsh borders. 

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3. Quantifying Tradeoffs in Ecosystem Services Under Various Oyster Reef Restoration Designs

   https://doi.org/10.1007/s12237-021-01010-4  

   Hogan, S.; Reidenbach, M.A. (January 2021, Estuaries and Coasts)

   null (Ed.)

   Oyster populations within the coastal bays of Virginia have greatly declined, mainly due to overharvesting and disease, and past restoration efforts have largely focused on increasing their populations. Current restoration goals have now expanded to simultaneously procure the wider ecosystem services oysters can offer, including shoreline protection and ecosystem diversification. However, tradeoffs exist in designing artificial reefs because it is unlikely one design will optimize all services. This study compares the services provided by reef designs varying in elevation and width located adjacent to an intertidal marsh within a coastal bay of VA, USA. We quantified wave attenuation to determine potential coastal protection of the adjacent marsh, and changes to sediment composition and infaunal communities before and after reef construction for 3 years. After construction, we also quantified oyster size and population density to compare high and low elevation reef designs. High elevation reefs were more effective at attenuating waves and fostering oyster growth compared to low elevation reefs. Oysters atop high elevation reefs were on average approximately twice as dense and 20% larger than those on low elevation designs. Reef width had a minimal effect on oyster population density; densities on high and low reefs were similar for designs with one or three rows. The presence of oyster reefs also increased infaunal diversity and sediment organic matter. Our results indicate that artificial reef design can differentially affect the services provided through restoration, and elevation is especially important to consider when designing for oyster population enhancement and coastal protection. 

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4. Oyster and associated fauna counts and lengths from restored and reference reefs in the coastal bays of Virginia, 2005-2019

   https://doi.org/10.6073/pasta/18231a2eecfce87cdbbbda3a678689ca  

   Lusk, Bo; Smith, Rachel; Castorani, Max_C N (January 2024, Environmental Data Initiative)

   This dataset has been superceded by Lusk, B., R. Smith, and M.C.N. Castorani. 2024. Oyster fauna lengths, counts, and biomass from restored and reference reefs in Virginia coastal bays, 2005-2023 ver 1. Environmental Data Initiative. https://doi.org/10.6073/pasta/d68de69f29cee5f737313a07f813f245 (Accessed 2024-02-22). which includes additional years and parameters. Oyster and associated reef fauna counts and lengths were sampled at 16 natural reference reefs and 61 restored shell plant reefs located at 18 sites in the Virginia Coast Reserve. Overfishing and disease decimated oyster reefs in the Virginia Coast Reserve in the 1900s. Reference reefs were defined as remnant reefs that naturally recovered in the early 2000s to develop the pronounced vertical structure and multiple oyster size classes that represent the desired endpoint of restoration efforts. Nearly every year since 2003, The Nature Conservancy and Virginia Marine Resource Commission have constructed oyster reefs in intertidal areas in the VCR. To construct the restored reefs, practitioners applied dredged, fossilized oyster shell to intertidal locations chosen for their bottom stability and accessibility (locations lacked oysters prior to construction). Whelk shell supplemented the oyster shell at 9 of the restored reefs. 

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5. Long-term data reveal greater intertidal oyster biomass in predicted suitable habitat

   https://doi.org/10.3354/meps13949  

   Smith, RS; Hogan, S; Tedford, KN; Lusk, B; Reidenbach, MA; Castorani, MCN (February 2022, Marine Ecology Progress Series)

   Habitat suitability models have been used for decades to develop spatially explicit predictions of landscape capacity to support populations of target species. As high-resolution remote sensing data are increasingly included in habitat suitability models that inform spatial conservation and restoration decisions, it is essential to validate model predictions with independent, quantitative data collected over sustained time frames. Here, we used data collected from 12 reefs over a 14 yr sampling period to validate a recently developed physical habitat suitability model for intertidal oyster reefs in coastal Virginia, USA. The model used intertidal elevation, water residence time, and fetch to predict the likelihood of suitable conditions for eastern oysters Crassostrea virginica across a coastal landscape, and remotely sensed elevation was the most restrictive parameter in the model. Model validation revealed that adult oyster biomass was on average 1.5 times greater on oyster reefs located in predicted ‘suitable’ habitat relative to reefs located in predicted ‘less suitable’ habitat over the 14 yr sampling period. By validating this model with long-term population data, we highlight the importance of elevation as a driver of sustained intertidal oyster success. These findings extend the validation of habitat suitability models by quantitatively supporting the inclusion of remotely sensed data in habitat suitability models for intertidal species. Our results suggest that future oyster restoration and aquaculture projects could enhance oyster biomass by using habitat suitability models to select optimal site locations. 

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