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.
This content will become publicly available on June 21, 2024
Coastal and estuarine habitats that provide crucial nursery areas for many economically and ecologically important fish species are in decline. Restoration of benthic habitats can improve fish populations, biomass, and feeding opportunities, but there is limited research on how restoration impacts growth and survival with ontogeny. To address this knowledge gap, here we examine the biometrics (size, biomass, and body condition), recruitment, size structure, and trophic shifts of a sportfish (mangrove snapper,
- NSF-PAR ID:
- 10441410
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Restoration Ecology
- Volume:
- 31
- Issue:
- 7
- ISSN:
- 1061-2971
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Restoration aims to reverse the global declines of foundation species, but it is unclear how project attributes, the physical setting, and antecedent conditions affect restoration success. In coastal seas worldwide, oyster reef restoration is increasing to counter historical habitat destruction and associated declines in fisheries production and biodiversity. Yet, restoration outcomes are highly variable and the factors that enhance oyster production and nekton abundance and diversity on restored reefs are unresolved. To quantify the drivers of oyster restoration success, we used meta‐analysis to synthesize data from 158 restored reefs paired with unstructured habitats along the United States Gulf and Atlantic coasts. The average recovery of oyster production was 65% greater in subtidal (vs. intertidal) zones, 173% greater in polyhaline (vs. mesohaline) environments and increased with tidal range, demonstrating that physical conditions can strongly influence the restoration success of foundation species. Additionally, restoration increased the relative abundance and richness of nektonic fishes and invertebrates over time as reefs aged (at least 8 years post‐construction). Thus, the restoration benefits for provisioning habitat and enhancing biodiversity accrue over time, highlighting that restoration projects need multiple years to maximize ecosystem functions. Furthermore, long‐term monitoring of restored and control sites is needed to assess restoration outcomes and associated drivers. Last, our work reveals data constraints for several potential drivers of restoration outcomes, including reef construction material, reef dimensions, harvest pressure and disease prevalence. More experimental and observational studies are needed to target these factors and measure them with consistent methods across studies. Our findings indicate that the assisted recovery of foundation species yields several enhancements to ecosystem services, but such benefits are mediated by time and environmental conditions.
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Abstract Metapopulation and source–sink dynamics are increasingly considered within spatially explicit management of wildlife populations, yet the application of these concepts has generally been limited to comparisons of the performance (e.g., demographic rates or dispersal) inside vs. outside protected areas, and at spatial scales that do not encompass an entire metapopulation. In the present study, a spatially explicit, size‐structured matrix model was applied to simulate the dynamics of an Eastern oyster (
Crassostrea virginica ) metapopulation in the second largest estuary in the United States—the Albemarle‐Pamlico Estuarine System in North Carolina. The model integrated larval dispersal simulations with empirical measures of oyster demographic rates to simulate the dynamics of the entire oyster metapopulation consisting of 646 reefs and five reef types: (1) restored subtidal reefs closed to harvest (i.e., sanctuaries or protected areas;n = 14), (2) restored subtidal reefs open to harvest (n = 53), (3) natural subtidal reefs open to harvest (n = 301), (4) natural intertidal reefs open to harvest (n = 129), and (5) oyster reefs on manmade, hard structures such as seawalls (n = 149). Key findings included (1) an overall stable, yet slightly declining oyster metapopulation, (2) variable reef type‐specific population trajectories, largely dependent on spatiotemporal variation in larval recruitment, (3) a greater relative importance of inter‐reef larval connectivity on metapopulation dynamics than local larval retention processes, and (4) spatiotemporal variation in the source–sink status of reef subpopulations wherein subtidal sanctuaries and reefs located in the northeastern portion of the estuary were frequent sources. From a management perspective, continued protection of oyster sanctuaries is warranted. Sanctuaries represented only 6.2% of the total reef area, however, they harbored 19% (± 2%) of all oysters and produced 25% (± 6%) of all larvae settling within the metapopulation. Additional management priorities should focus on restoration or conservation of subpopulations that serve as frequent source subpopulations (including those with poor demographic rates, but high connectivity potential), and management of harvest from sink subpopulations. The application of a source–sink framework and similar integrated modeling approach could inform management of oysters in other systems, as well as other species that exhibit similar metapopulation characteristics. -
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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.
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Restoration of degraded estuarine oyster reefs typically involves deploying recycled oyster shell. In low‐salinity, low‐predation areas of estuaries, high‐volume shell deployments are known to improve flow conditions and thus oyster survival and growth. It is also hypothesized that the physical structure of restored reefs could suppress foraging by oyster predators in high‐salinity, high‐predation zones. That hypothesis is untested. Given limited resources, it is important to determine how much shell is needed for successful restoration and whether there are diminishing returns in shell addition. In Apalachicola Bay, Florida, we manipulated shell volume on an oyster reef to create three 0.4 ha areas of low (no shell addition), moderate (153 m3shell), and high (306 m3shell) habitat structure. We repeated experiments and surveys over 2 years to determine if restoration success increased with habitat structure. Predation on oysters was greater on the non‐shelled area than on the reshelled reefs, but similar between the two reshelled reefs. Oyster larval supply did not differ among the reef areas, but by the end of the experiment, oyster density (per unit area) increased quadratically with habitat structure, plateauing at high levels of structure. Model selection indicated that the most parsimonious explanation for these patterns was that increased habitat structure reduced predation and increased overall recruitment, but that the higher reshelling treatment did not have better outcomes than moderate reshelling. Thus, restoration could be optimized by deploying a moderate amount of shell per unit area.
