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1. 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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2. Characterizing canopy complexity of natural and restored intertidal oyster reefs ( Crassostrea virginica ) with a novel laser‐scanning method

   https://doi.org/10.1111/rec.13973  

   Cannon, David_J; Kibler, Kelly_M; Taye, Jyotismita; Medeiros, Stephen_C (July 2023, Restoration Ecology)

   The structural complexity of oyster reef canopy plays a major role in promoting biodiversity, balancing the sediment budget, and modulating hydrodynamics in estuarine systems. Although oyster canopy structure is both spatially and temporally heterogeneous, oyster canopies are generally characterized using simple first‐order quantities, like oyster density, which may lack the ability to sufficiently parameterize reef roughness. In this study, a novel laser‐scan approach was used to map the surface of intact reference and restored reefs (restoration age: 1–4 years) during low tide, when the oyster canopy was fully exposed. Measurements were used to estimate hydrodynamically relevant roughness characteristics over the entire reef surface (>140 m²; 0.50 m resolution), providing estimates of the canopy height (h_c), standard deviation (), rugosity index (R), and fractal dimension (D). Average canopy heights ranged from 3.6 to 4.9 cm, with canopy height standard deviations between 1.4 and 2.0 cm. Mean rugosity indices and fractal dimensions were relatively low on the youngest (1 year) restored reef (R = 1.28;D = 2.67), with substantial increases observed for more mature reef canopies (4 years:R = 1.56;D = 2.71). Structural complexity was consistently greater on reef margins than in reef interiors. Increases in complexity were linked to restoration age, with older reefs exhibiting more complex oyster canopies. The highest fractal dimension was observed on the intact reference reef, highlighting the importance of sustained reef growth for maintaining higher‐order structural complexity. Results provide spatially explicit surface roughness characterizations for healthy, intertidal oyster reefs, with applications in both restoration science and natural and nature‐based feature design. 

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3. Oyster Reef Restoration May Influence Local Sediment Geochemistry Prior to Introduction of Live Oysters

   https://doi.org/10.18785/gcr.3401.23  

   Sniff, Ilya; Smee, Lee; Steinmuller, Havalend (January 2023, Gulf and Caribbean Research)

   Oyster reefs provide crucial ecosystem services, but their populations are declining worldwide. Oyster reef restoration efforts are underway in many regions, including the Gulf Coast of the United States, where the intertidal oyster populations of the eastern oyster, Crassostrea virginica, have experienced significant declines. A novel method of restoration aimed at decreasing oyster mortality from predators through induction of predatory defenses has been implemented in coastal Alabama. The first step in this novel oyster reef restoration method is the deployment of a base layer of uninhabited oyster shells directly on the sediment prior to the introduction of live oysters. This study evaluated the impacts of the first step of this novel method of restoration, construction of the reef structure, on local sediment physicochemical characteristics. Results indicate that the vertical structure of the oyster reef affects sediment grain size and physicochemical properties. After 47 days, sediment pH increased from 8.29 ± 0.04 to 8.86 ± 0.03 with a concomitant increase in calcium carbonate from 0.509 ± 0.021 % to 0.818 ± 0.112 %. Despite many positive geochemical effects of oyster reef restoration being mediated by the presence of live oysters, the increased pH and calcium carbonate demonstrated herein represent more ideal conditions for oyster growth and survivability, potentially increasing the long-term efficacy of oyster reef restoration via this method. 

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4. Effects of landscape setting on oyster reef structure and function largely persist more than a decade post‐restoration

   https://doi.org/10.1111/rec.12651  

   Ziegler, Shelby L.; Grabowski, Jonathan H.; Baillie, Christopher J.; Fodrie, F. J. (December 2017, Restoration Ecology)

   Long‐term monitoring is vital to understanding the efficacy of restoration approaches and how restoration may enhance ecosystem functions. We revisited restored oyster reefs 13 years post‐restoration and quantified the resident and transient fauna that utilize restored reefs in three differing landscape contexts: on mudflats isolated from vegetated habitat, along the edge of salt marsh, and in between seagrass and salt marsh habitat. Differences observed 1–2 years post‐restoration in reef development and associated fauna within reefs restored on mudflats versus adjacent to seagrass/salt marsh and salt marsh‐only habitats persisted more than 10 years post‐restoration. Reefs constructed on open mudflat habitats had the highest densities of oysters and resident invertebrates compared to those in other landscape contexts, although all restored reefs continued to enhance local densities of invertebrate taxa (e.g. bivalves, gastropods, decapods, polychaetes, etc.). Catch rates of juvenile fishes were enhanced on restored reefs relative to controls, but to a lesser extent than directly post‐restoration, potentially because the reefs have grown vertically within the intertidal and out of the preferred inundation regime of small juvenile fishes. Reef presence and landscape setting did not augment the catch rates of piscivorous fishes in passive gill nets, similar to initial findings; however, hook‐and‐line catch rates were greater on restored reefs than non‐reef controls. We conclude that ecosystem functions and associated services provided by restored habitats can vary both spatially and temporally; therefore, a better understanding of how service delivery varies among landscape setting and over time should enhance efforts to model these processes and restoration decision‐making. 

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5. Success of concrete and crab traps in facilitating Eastern oyster recruitment and reef development

   https://doi.org/10.7717/peerj.6488  

   Johnson, Emma E.; Medina, Miles D.; Bersoza Hernandez, Ada C.; Kusel, Gregory A.; Batzer, Audrey N.; Angelini, Christine (January 2019, PeerJ)

   Background Abundance of the commercially and ecologically important Eastern oyster, Crassostrea virginica , has declined across the US Eastern and Gulf coasts in recent decades, spurring substantial efforts to restore oyster reefs. These efforts are widely constrained by the availability, cost, and suitability of substrates to support oyster settlement and reef establishment. In particular, oyster shell is often the preferred substrate but is relatively scarce and increasingly expensive. Thus, there is a need for alternative oyster restoration materials that are cost-effective, abundant, and durable. Methods We tested the viability of two low-cost substrates—concrete and recycled blue crab ( Callinectes sapidus ) traps—in facilitating oyster recovery in a replicated 22-month field experiment at historically productive but now degraded intertidal oyster grounds on northwestern Florida’s Nature Coast. Throughout the trial, we monitored areal oyster cover on each substrate; at the end of the trial, we measured the densities of oysters by size class (spat, juvenile, and market-size) and the biomass and volume of each reef. Results Oysters colonized the concrete structures more quickly than the crab traps, as evidenced by significantly higher oyster cover during the first year of the experiment. By the end of the experiment, the concrete structures hosted higher densities of spat and juveniles, while the density of market-size oysters was relatively low and similar between treatments. The open structure of the crab traps led to the development of larger-volume reefs, while oyster biomass per unit area was similar between treatments. In addition, substrates positioned at lower elevations (relative to mean sea level) supported higher oyster abundance, size, and biomass than those less frequently inundated at higher elevations. Discussion Together, these findings indicate that both concrete and crab traps are viable substrates for oyster reef restoration, especially when placed at lower intertidal elevations conducive to oyster settlement and reef development. 

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