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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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Quantifying Tradeoffs in Ecosystem Services Under Various Oyster Reef Restoration Designs
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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- Award ID(s):
- 1832221
- PAR ID:
- 10301729
- Date Published:
- Journal Name:
- Estuaries and Coasts
- ISSN:
- 1559-2723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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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.more » « less
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Oysters are described as estuarine ecosystem engineers because their reef structures provide habitat for a variety of flora and fauna, alter hydrodynamics, and affect sediment composition. To what spatial extent oyster reefs influence surrounding infauna and sediment composition remains uncertain. We sampled sediment and infauna across 8 intertidal mudflats at distances up to 100 m from oyster reefs within coastal bays of Virginia, USA, to determine if distance from reefs and physical site characteristics (reef elevation, local hydrodynamics, and oyster cover) explain the spatial distributions of infauna and sediment. Total infauna density increased with distance away from reefs; however, the opposite was observed for predatory crustaceans (primarily crabs). Our results indicate a halo surrounding the reefs of approximately 40 m (using an increase in ~25% of observance as the halo criterion). At 90 m from reefs, bivalves and gastropods were 70% more likely to be found (probability of observance), while there was an approximate 4-fold decrease for large crustaceans compared to locations adjacent to reefs. Increases in percent oyster reef cover and/or mean reef area did not statistically alter infauna densities but showed a statistical correlation with smaller sediment grain size, increased organic matter, and reduced flow rates. Weaker flow conditions within the surrounding mudflats were also associated with smaller grain sizes and higher organic matter content, suggesting multiple drivers on the spatial distribution of sediment composition. This study emphasizes the complexity of bio-physical couplings and the considerable spatial extent over which oyster reefs engineer intertidal communities.more » « less
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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.more » « less
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IntroductionCoastal infrastructure and property, as well as intertidal wetlands, are increasingly being threatened by shoreline erosion; a consequence of human activities and climate change. Nature-based solutions, such as intertidal engineered oyster reefs, can reduce erosion and promote sediment accretion, thereby promoting the restoration and persistence of salt marshes and preventing the loss of coastal lands. Engineered oyster reef substrate and design options have rapidly expanded in the last decade, yet our understanding of how these approaches influence ecosystems and intertidal morphology is limited. Drones (or small uncrewed aerial systems [sUAS]) coupled with structure-from-motion (SfM) photogrammetry have recently been suggested as a low-cost method that offers optimal spatial coverage, fine-scale resolution, and high vertical accuracy for monitoring changes around living shorelines. MethodsWe evaluated how using different vertical and horizontal uncertainty thresholds for detection of drone-based shoreline change can influence interpretation of performance of engineered oyster reefs on coastal morphology and vegetation. We monitored three sites with engineered oyster reefs installed in 2020 and one reference site located on Carrot Island along Taylor Creek in Beaufort, NC, USA. ResultsComparisons of the Digital Elevation Models (DEMs) and orthomosaics derived from the drone imagery revealed all sites saw marsh edge retreat from 2022 to 2023 (2-3 years post-restoration), and all sites except one low-relief oyster reef site saw elevation loss. Elevation loss was highest at the control site, but marsh edge retreat was highest at one of the engineered oyster reefs. DiscussionWhile horizontal thresholds did not yield statistically different results, vertical thresholds did. Our results support using a 95% confidence interval for conservative volumetric estimates and recommend that future studies consider aligning uncertainty thresholds with monitoring goals and timelines.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s12237-021-01010-4
