Natural Oyster Reefs Research Articles

Assessing the ecological functioning and biodiversity of remnant native flat oyster (Ostrea angasi) reefs in temperate southeast Australia

Oyster reefs are critically endangered coastal habitats which provide valuable ecosystems services. Despite their importance, there remains a significant knowledge gap in our understanding of how oyster and sediment characteristics influence the ecological functioning and biodiversity of remnant Australian flat oyster (Ostrea angasi) reefs. To inform restoration efforts, we assessed relationships between community respiration rates (CR), inorganic nitrogen fluxes, filtration rates, biodiversity, and oyster morphometrics as well as sediment conditions for three remanent flat oyster reefs (Oyster Cove, Ralphs Bay, and Quarantine Bay) in southeast Tasmania. Additionally, we explored relationships between net denitrification, and flat oyster morphometrics and sediment conditions at one of the sites (Ralphs Bay) in southeast Tasmania. We observed positive relationships between CR, inorganic nitrogen fluxes, filtration rates, and live flat oyster biomass, as well as between the richness and biomass of associated taxa and total flat oyster biomass (both tissue and shell including dead shell), across all three locations. We also found an increase in net denitrification associated with live oyster biomass at one of the oyster reefs (Ralphs Bay). The CR, inorganic nitrogen fluxes, filtration rates, diversity of taxa and biomass of bivalves and flat oyster biomass was higher at Ralphs Bay, which has the most intact reef, compared to the other two locations. In contrast to other studies, the organic and silt content of the sediment showed limited influence on CR, inorganic nitrogen fluxes, filtration rates and net denitrification. CR, and inorganic nitrogen fluxes in these flat oyster reefs were like other restored and natural oyster reefs globally, but net denitrification, filtration rate and taxonomic richness exceeded those previously observed globally. These results highlight the important role of oyster biomass in enhancing water quality and biodiversity. Burgeoning flat oyster reef restoration initiatives should prioritise the enhancement of both live oyster populations and dead shells to recover their associated ecological functions and biological diversity.

Restored oyster reefs and living shorelines can augment predator trophic dynamics

Coastal habitat loss has led to declines in many higher trophic level predators. These declines can be mitigated through habitat restoration, which putatively enhances predator populations and trophic dynamics by creating foraging opportunities in reestablished habitat, but this lacks empirical support. Here, we assess the prediction restored coastal habitat supports sportfish feeding relationships similar to natural habitat, at restored oyster reefs (Crassostrea virginica) and living shoreline habitats in Florida, U.S.A. Stable isotopes and gut contents were analyzed from young sportfish (i.e. predatory fish targeted by anglers) collected at control and restored sites for up to 3 years. The influence of habitat features, predator size, and prey availability on carbon and nitrogen isotope values were examined using a model species (mangrove/gray snapper [Lutjanus griseus]). In summary, sportfish species had distinct isotopic values, consuming similar prey but in different proportions between habitats. Prey abundance and richness, and reef height were influential predictors of L. griseus stable isotope values, with restored reefs contributing to their diet more than controls according to Bayesian mixing models. The trophic niche area of L. griseus and their predominant prey achieved trophic equivalence between restored and natural oyster reefs within 1 year following restoration. Stabilized living shorelines attained trophic equivalency to natural shorelines, but may take longer to accrue prey for some species. These findings generate fundamental ecological knowledge and actionable science, including targets, timelines, and indicator species, that natural resource managers and restoration practitioners can use to assess trophic structure and success of coastal habitat restoration.

Experimental laboratory tests of short-term habitat selection by hatchery-reared juvenile red drum (Sciaenops ocellatus)

Structured estuarine habitats enhance the survival and growth of wild juvenile fishes by mediating density-dependent processes. However, the habitat selection behavior of hatchery-reared fishes upon release to the wild is not well understood. The red drum (Sciaenops ocellatus) is a highly sought-after, estuarine-dependent sportfish and the subject of stock enhancement efforts along the southeastern US Atlantic and Gulf coasts. We investigated the habitat associations of hatchery-reared red drum using experimental mesocosms intended to mimic the habitat types available at or nearby typical release sites in South Carolina, USA. Specifically, we presented juvenile red drum (overall mean ∼ 60 mm standard length) with a choice between salt marsh vegetation (Spartina alterniflora) and oyster shell in the presence and absence of a common estuarine predator (blue crab, Callinectes sapidus). Red drum more commonly associated with oyster shell over Spartina in both the presence and absence of a blue crab predator. Oyster shell habitat tended to be favored even when the location of the free-ranging blue crab predator was taken into account. Our results provide evidence that oyster shells, representative of a healthy restored or natural oyster reef, may be preferentially utilized by hatchery-reared red drum during the period immediately following release. Further investigation of post-release behaviors, including field-based experimental studies focusing on hatchery-reared red drum, is necessary to determine if the patterns of habitat selection behavior documented here have implications for post-release survival or mortality.

Meta-analysis of ecosystem services associated with oyster restoration.

Restoration of foundation species promises to reverse environmental degradation and return lost ecosystem services, but a lack of standardized evaluation across projects limits understanding of recovery, especially in marine systems. Oyster reefs are restored to reverse massive global declines and reclaim valuable ecosystem services, but the success of these projects has not been systematically and comprehensively quantified. We synthesized data on ecosystem services associated with oyster restoration from 245 pairs of restored and degraded reefs and 136 pairs of restored and reference reefs across 3500km of U.S. Gulf of Mexico and Atlantic coastlines. On average, restoration was associated with a 21-fold increase in oyster production (mean log response ratio=3.08 [95% confidence interval: 2.58-3.58]), 34-97% enhancement of habitat provisioning (mean community abundance=0.51 [0.41-0.61], mean richness=0.29 [0.19-0.39], and mean biomass=0.69 [0.39-0.99]), 54% more nitrogen removal (mean=0.43 [0.13-0.73]), and 89-95% greater sediment nutrients (mean=0.67 [0.27-1.07]) and organic matter (mean=0.64 [0.44-0.84]) relative to degraded habitats. Moreover, restored reefs matched reference reefs for these ecosystem services. Our results support the continued and expanded use of oyster restoration to enhance ecosystem services of degraded coastal systems and match many functions provided by reference reefs.

Oyster and Barnacle Recruitment Dynamics on and Near a Natural Reef in China: Implications for Oyster Reef Restoration

Oysters and barnacles are dominant inhabitants of natural and restored oyster reefs around the world, and high areal coverage of barnacles at natural or restored reefs commonly decreases substrate accessibility for oyster settlement. The overall understanding of oyster and barnacle recruitment dynamics provides invaluable information on site selection and strategies employed for oyster reef restoration. This study documented the temporal and spatial patterns of oyster and barnacle recruitment on and near the largest natural intertidal oyster reef (Liyashan) in China during 2019–2020. The oyster Crassostrea sikamea recruitment appeared as a continuous process from June through late November or early December, with the peak in August. Greater recruits of oyster spat occurred on the sheltered inshore at the upstream of the natural oyster reef than on the reef and the nearby open coast (p < 0.05). The barnacle recruitment extended from spring to early winter, with mid-spring and mid-summer peaks. Conversely, higher barnacle recruitment appeared on the natural oyster reef and the nearby open coast than on the sheltered inshore. Across all the monitoring sites, the cumulative recruits of oysters in each of 2019 and 2020 was negatively correlated with those of barnacles (p < 0.05). The inshore sites (SH1 and SH2) with high oyster recruitment and low barnacle recruitment should be recognized as the natural spatfall sites for the natural oyster reef restoration. The separation in the recruitment peak between the oyster and the barnacle indicated that August was the most favorable window for capturing oyster spat through substratum addition to the water around the natural reef.

Fish and invertebrate use of restored vs. natural oyster reefs in a shallow temperate latitude estuary

AbstractCoastal marine habitats continue to be degraded, thereby compelling large‐scale restoration in many parts of the world. Whether restored habitats function similarly to natural habitats and fully recover lost ecosystem services is unclear. In estuaries, oyster reefs have been degraded by multiple anthropogenic activities including destructive fishing practices and reduced water quality, motivating restoration to maintain oyster fisheries and other ecosystem services, often at relatively high cost. We compared fish and invertebrate communities on recently restored (0–1 year post‐restoration), older restored (3–4 years post‐restoration), and natural oyster reefs to determine if and when restored reefs support functionally similar faunal communities. To test the influence of landscape setting on the faunal communities, the restored and natural reefs, as well as a control without reef present, were distributed among three landscapes (on the edge of salt marsh away from seagrass [salt marsh landscape], on mudflats [mudflat landscape], and near to seagrass and salt marsh [seagrass landscape]). Oyster density and biomass were greatest on restored reef habitat, as were those of non‐oyster bivalve species. Total abundance of invertebrates was much greater on oyster reefs than in control plots, regardless of reef or landscape type, yet were frequently highest on older restored reefs. Meanwhile, juvenile fish densities were greatest on natural reefs, at intermediate densities on older restored reefs, and least abundant on controls. When comparing the effects of reef age and landscape setting, juvenile fish densities were greatest on younger reefs within the mudflat landscape. Collectively, these results indicate that oyster reefs harbor higher densities of resident invertebrate prey, which may explain why reef habitat is also important for juvenile fish. Laboratory and field experiments supported the notion that gag grouper (a predatory demersal fish) forage more effectively on oyster reefs than on unstructured mud bottom, whereas our experiments suggest that flounders that utilize oyster reefs likely forage on adjacent mud bottom. Because landscape setting influenced fish and invertebrate communities on restored reefs, the ecological consequences of landscape setting should be incorporated into restoration decision making and site selection to enhance the recovery of ecosystem goods and services.

Oyster Habitat Restoration and Shoreline Protection

As the climate continues to change, coastal areas and the people that live there face increasing risks from erosion and wave damage. This is made worse by declines in natural oyster reefs, which would provide some natural protection. However, oysters can be restored for the specific purposes of protecting shorelines. The practicality and cost effectiveness of using oysters in this way is described in this publication, which is intended to be used by coastal property owners, as well as local governments that must make decisions about protecting shorelines in the face of a changing climate.

Differences in resident prey survival on newly created shell and established natural intertidal oyster reefs

Established natural oyster reefs historically provide a three‐dimensionally complex habitat utilized by a variety of resident and transient species, but newly created reefs designed to counter the loss of natural reefs initially may lack similar complexity. The loosely stacked shells of newly created reefs little resemble the vertically interconnected live and dead shell matrix typical of older reefs. Reduced complexity on created reefs may alter predator–prey dynamics and negatively affect ecological functions typically associated with natural reefs. We examined select physical characteristics (e.g. shell morphology) and short‐term survival of reef‐resident prey to determine if differences exist between newly created (<1‐year‐old shell bags) and established natural intertidal reefs in South Carolina. Shell physical characteristics differed consistently between reefs, with greater numbers of smaller and lighter shells found on natural reefs. However, short‐term survival of crabs (Panopeid sp.) and mussels (Geukensia demissa) generally was not dependent on reef type. The few instances of reef dependent prey survival were either inconsistent with expected results, assuming reduced complexity on created reefs, or not supported by effect size analyses. Evidence indicates that adding shell bags to create oyster reefs in intertidal environments almost immediately increases resident species survival similar to that on existing natural reefs and leads to the rapid return of a major ecosystem service associated with coastal oyster reefs.

Dynamics of Restored and Natural Oyster Reefs After a Hurricane

Restoration of shellfish reefs has increased exponentially over the past two decades, due in part to increased awareness of widespread oyster habitat loss. Large-scale, acute disturbances such as hurricanes have the potential to influence restoration outcomes, but because storm occurrence is unpredictable with respect to restoration timelines, the responses of restored habitats are not well understood. We quantified the ecological dynamics of a newly constructed Crassostrea virginica oyster reef and nearby reference reef in a Texas estuary immediately after Hurricane Harvey, a major category 4 storm. Biophysical structure (e.g., oyster density, shell height, sediment grain size), and community composition (abundance of reef-associated epifauna, and nearby infauna) were measured for 18 months. A sharp decrease in salinity and temporary deposition of fine sediments within the first 3 months corresponded with increases in oyster and epifaunal recruitment on the restored reef, although densities were generally below those measured on restored reefs without hurricanes. Criteria for oyster reef restoration success were met within 12–18 months post-storm. Infaunal densities decreased but returned to pre-storm densities within 2 months, but bivalves were delayed, returning to pre-storm levels after 9 months. A lack of historical baseline data on the newly restored reef limited our ability to assess the magnitude of reef recovery to pre-disturbance levels or separate the direct effects of the hurricane from the dynamics of early recruitment and growth. Results provide important information about restored and natural oyster reef dynamics after large-scale disturbance and can help inform effective management and conservation measures.

Effects of freshwater release on oyster reef density, reproduction, and disease in a highly modified estuary.

Few estuaries remain unaffected by water management and altered freshwater deliveries. The Caloosahatchee River Estuary is a perfect case study for assessing the impact of altered hydrology on natural oyster reef (Crassostrea virginica) populations. The watershed has been highly modified and greatly enlarged by an artificial connection to Lake Okeechobee. Accordingly, to generate data to support water management recommendations, this study monitored various oyster biometrics over 15years along the primary salinity gradient. Oyster reef densities were significantly affected by both prolonged high volume freshwater releases creating hyposaline conditions at upstream sites and by a lack of freshwater input creating hypersaline conditions at downstream sites. Low freshwater input led to an increase in disease caused by Perkinsus marinus and predation. Moderate (< 2000 cfs) and properly timed (winter/spring) freshets benefited oysters with increased gametogenesis, good larval mixing, and a reprieve from disease. If high volume freshets occurred in the late summer, extensive mortality occurred at the upstream site due to low salinity. These findings suggest freshwater releases in the late summer, when reproductive stress is at its peak and pelagic larvae are most vulnerable, should be limited to < 2000 cfs, but that longer freshets (1-3weeks) in the winter and early spring (e.g., December-April) benefit oysters by reducing salinity and lessening disease intensity. Similar strategies can be employed in other managed systems, and patterns regarding the timing of high volume flows are applicable to all estuaries where the management of healthy oyster reefs is a priority.

河北唐山曹妃甸-乐亭海域自然牡蛎礁分布及生态意义

牡蛎礁是生态系统服务价值最高的海洋生境之一，目前我国自然牡蛎礁分布和生态现状的基础信息仍然较缺乏。于2019年3月对河北唐山曹妃甸-乐亭海域自然牡蛎礁的空间分布、生态环境、牡蛎生物学和礁体动物群落开展了调查，并评估了该牡蛎礁的生态系统服务价值。该海域自然牡蛎礁分布于溯河（SR）、溯河口海域（SRE）和捞鱼尖海域（LYJ），总面积约15 km²，是目前我国面积最大的自然牡蛎礁。基于96个牡蛎样品的16S rDNA检测，共识别出92个长牡蛎Crassostrea gigas、3个侏儒牡蛎Nanostrea fluctigera和1个巨蛎属未知种Crassostrea sp.。自然牡蛎礁中牡蛎平均密度介于104-3912个/m²之间，不同礁区间牡蛎平均密度的大小排序为：SRE > SR > LYJ （P<0.05），平均生物量的大小排序为：SR > SRE > LYJ （P<0.05），平均壳高的大小排序为：SR > SRE=LYJ （P<0.05）。在该牡蛎礁内记录到49种礁体动物，其中软体动物16种、节肢动物16种、环节动物8种、棘皮动物5种、腔肠动物2种、星形动物和脊索动物各1种；礁体动物群落平均总密度介于28-552个/m²之间，不同礁区间大小排序为：SRE > SR > LYJ （P<0.05）。牡蛎密度与礁体动物群落总密度和总生物量之间呈显著正相关（P<0.05）。该自然牡蛎礁如未受破坏，则其生态系统服务价值高达6.90×10⁸元/年。该牡蛎礁是继海草场后在该海域发现的又一重要的温带海洋生境，是我国自然牡蛎礁地理分布的重大发现。建议加强该自然牡蛎礁的保护与修复，建设一个以牡蛎礁和海草场为核心的资源养护型国家级海洋牧场示范区。;Oyster reef is an important marine habitat that provides a variety of ecosystem services, including water filtration, nitrogen removal, carbon sink, habitat provision and erosion control. In the past decades, most of natural oyster reefs in the Chinese coasts were lost due to overfishing, pollution, sedimentation and habitat destruction. To date, little information was available on spatial distribution and ecological status of natural oyster reefs in China. This study investigated the spatial distribution, ecological environment, oysters and reef-associated resident benthic macroinvertebrate communities at the natural oyster reefs on the coast of Caofeidian-Leting, Tangshan, Hebei Province, and furthermore assessed the ecosystem service values of the natural oyster reefs on the coast. The natural oyster reefs, including three major distribution zones, namely Shouhe River (SR), Shouhe River estuary (SRE) and Laoyujian (LYJ), occupied the total area of about 15 km². To our knowledge it was recognized as the largest natural live oyster reefs in China. Ninety-two of 96 oyster specimens collected from the natural reefs were identified as pacific oyster Crassostrea gigas, 3 specimens for Nanostrea fluctigera and 1 specimen for unknown Crassostrea sp based on 16S rDNA gene sequence analysis. The mean live oyster densities ranged from 104 to 3912 ind./m² at the natural oyster reefs. The mean oyster metrics were ranked as follows (P<0.05):SRE > SR > LYJ for oyster densities, SR > SRE > LYJ for oyster biomass and SR > SRE=LYJ for oyster size (shell height). A total of 49 resident benthic macroinvertebrate species, belonging to 16 mollusks, 16 arthoropoda, 8 annelids, 5 echinodermata, 2 coelenterata, 1 sipuncula and 1 chordata, were recorded at the natural oyster reefs. The mean total densities of resident benthic macroinvertebrate communities varied between 28 and 552 ind./m² at the natural oyster reefs, with ranking as follows:SRE > SR > LYJ (P<0.05). The total densities and biomass of resident macroinvertebrate communities had significantly positive correlations with the oyster densities at the natural oyster reefs. The economic value of the full suite of ecosystem services derived from the natural oyster reefs was recently estimated to be as high as RMB 6.90×10⁸RMB/a. The discovery of the natural live oyster reefs contributed significantly to valuable information on the spatial distribution and ecological status of temperate coastal habitats in China. It was suggested that a national marine ranching demonstration zone should be built on the coast through the conservation and restoration of oyster reefs and seagrass beds.

Fish and invertebrate use of restored vs. natural oyster reefs in a shallow temperate latitude estuary

Fish and invertebrate use of restored vs. natural oyster reefs in a shallow temperate latitude estuary

Saved by the shell: Oyster reefs can shield juvenile blue crabs Callinectes sapidus

Juvenile blue crabs Callinectes sapidus use seagrass and other structured habitats as refuges from predation. Oyster reef habitats provide structural complexity that may offer refuge, but the value of these habitats for juvenile blue crabs has not been examined. We quantified survival of juvenile C. sapidus in structured oyster reef habitat versus unstructured soft-bottom habitat. In a field tethering experiment in the York River, lower Chesapeake Bay (USA), juvenile C. sapidus (10-50 mm carapace width [CW]) were tethered in sand (n = 40) or oyster reef (n = 39) habitats at subtidal sites 1-2 m deep. An underwater camera system was used to record predation activity during 24 h trials. Juvenile crab survival was significantly higher on the oyster reef habitat (53.8%) than on bare sand (15.0%), and tended to increase with crab CW in both habitats. The main successful predators on juvenile blue crabs were northern pufferfish Sphoeroides maculatus in the oyster reef habitat and adult blue crabs in the sand habitat. The high survival rate of juvenile C. sapidus in oyster reef habitats suggests that oyster reefs include physical habitat complexity that may offer refuge from predators. Restored and natural oyster reefs could provide an alternative nursery habitat for juvenile blue crabs, expanding the ecosystem services provided by restored oyster reefs.

Oyster growth across a salinity gradient in a shallow, subtropical Gulf of Mexico estuary

Abstract An increase in oyster aquaculture as a sustainable method of shellfish production is one response to overharvest and degradation of natural oyster reefs over the past century. Successful aquaculture production requires determining the environmental conditions optimal for oyster growth. In this study, the salinity, temperature, chlorophyll a concentration and the growth of Crassostrea virginica were monitored at four locations within the Mission-Aransas Estuary, Texas (USA), a shallow subtropical estuary influenced by relatively low freshwater inflow. Mean growth of the oyster shell (0.205 mm d–1 and 0.203 g d–1) and soft tissues (3.447 mg d–1) was highest when salinity was low (mean = 15.5) and chlorophyll a concentration was high (8.4 μg l–1). Oyster growth also varied temporally with periods of spawning. In low-inflow estuaries such as the Mission-Aransas Estuary, oyster farms should be sited close to river mouths so that oysters can benefit from freshwater inflows and lower salinities.

Restoration potential of Asian oysters on heavily developed coastlines

Reef‐building oysters historically provided the main structural and ecological component of temperate and subtropical coastal waters globally. While the loss of oyster reefs is documented in most regions globally, assessments of the status of Asian oyster reefs are limited. The feasibility of restoration within the regional biological and societal contexts needs to be assessed before implementation. Here, we quantified the current distribution of natural oyster reefs (Crassostrea spp.) in the shallow coastal waters of Hong Kong, assessed the biological feasibility of reestablishing reefs using natural recruitment, and examined their current and potential water filtration capacity as a key ecosystem service provided by restoration. We found natural low‐relief oyster beds in the low intertidal coastal areas at a subset of the locations surveyed. These areas are, however, degraded and have sparse densities of oysters generally &lt;2 years old. Recruitment was high in some areas (&gt;500,000 indiv./m2) and while survival to maturity varied across sites there was adequate larval supply and survival for restoration. Filtration rates for a 1‐year‐old recruit (90 mm length, approximately 30 L/hour per individual) at summer temperatures (30°C) meant that even the small remnant populations are able to provide some filtration services (up to 31.7 ML/hour). High natural recruitment means that oyster reef restoration can be achieved with the addition of hard substrate for recruitment, increased protection of restoration sites, and would not only increase the ecological value of reefs regionally but also serve as a model for future restoration in Asia.

Eastern Oyster Recruitment Patterns on and Near Natural Reefs: Implications for the Design of Oyster Reef Restoration Projects

The spatial relationship between adult eastern oyster Crassostrea virginica populations and recruitment to the benthos of their offspring is not well understood. It is well established that larvae can be widely dispersed, but the relationship between dispersal potential and actual recruitment patterns across the full range of spatial scales involved remains unknown. To explore this relationship, spat collectors were deployed on and near (up to 1 km distance) three natural oyster reefs in New Hampshire in 2014 and 2015. Spat densities on the reefs and within 400 m of the reefs were nearly 10-fold higher than densities more distant. These data do not negate the potential importance of widespread dispersal and recruitment, but they do indicate a surprising level of recruitment very near their likely source. Additional research is needed in other areas to test the generality of the findings and to assess potential causal factors for the observed patterns. The overall implication for choosing sites for oyster reef restoration projects, particularly in recruitment-limited areas, is that they may need to be located much closer to spawning adults than previously thought to maximize the likelihood of adequate natural recruitment and reef development.

Habitat assessment of a restored oyster reef in South Texas

Oyster reefs are important foundational habitats and provide many ecosystem services. A century of habitat degradation has resulted in substantial reductions in the extent and quality of oyster reefs in many estuaries, thus spurring restoration efforts. In this study, a 1.5 ha oyster reef complex was constructed in Copano Bay, Texas to restore habitat for oysters and associated fauna. Oysters and resident and transient fishes and crustaceans were monitored at the restored reef as well as at nearby natural oyster reef and unrestored bottom (i.e., dense mud with shell hash) habitats for two years following reef construction. The restored reef had substantial oyster recruitment and growth, with oyster abundance and size comparable to nearby habitats within the first year. Resident and transient fauna communities recruited to the restored reef within six months post-construction, and abundance and diversity were comparable to nearby habitats. Significant changes observed in oyster densities between the first and second year post-restoration demonstrate the importance of monitoring over multiple years to capture multiple recruitment cycles and growth to market size. Nekton densities did not change significantly after the first year, but changes in community assemblages were observed through the end of the study. The high densities of oysters and resident nekton relative to other studies indicate that this restoration project was successful in restoring suitable habitat. The design of the reef complex, consisting of relatively high-relief reef mounds and deeper corridors, likely contributed to the relatively high oyster and nekton densities observed in this study. Overall, the restored reef in this study showed tremendous near-term success in providing important ecological functions associated with habitat provision and oyster production.

Oxygen metabolism of intertidal oyster reefs measured by aquatic eddy covariance

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 599:75-91 (2018) - DOI: https://doi.org/10.3354/meps12627 Oxygen metabolism of intertidal oyster reefs measured by aquatic eddy covariance Martin P. Volaric*, Peter Berg, Matthew A. Reidenbach Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia 22904, USA *Corresponding author: mpv3a@virginia.edu ABSTRACT: Oyster reef restoration is pursued at numerous places worldwide, yet little is known about how ecosystem function changes as these reefs develop. In this study, we used the non-invasive aquatic eddy covariance technique to measure the in situ oxygen flux of 4 intertidal sites on the Virginia (USA) coast: a natural oyster reef, 2 restoration reefs, and a mudflat. Oyster densities of the 3 reefs were 350, 295, and 186 oysters m-2. Mean summer values of nighttime oxygen flux (FluxDARK) were -488, -428, -300, and -56 mmol m-2 d-1 over the natural reef, 2 restoration reefs, and mudflat, respectively. All 4 sites had smaller daytime vs. nighttime oxygen uptake, with mean summer differences between FluxDARK and FluxLIGHT of 360, 250, 239, and 27 mmol m-2 d-1. Light was an important short-term driver of daytime reef oxygen flux due to its effect on microalgal photosynthesis. All 3 oyster reefs were significantly heterotrophic, with summer net ecosystem metabolism values ranging from -157 to -298 mmol m-2 d-1. FluxDARK values were similar across the 3 reefs when normalized by density, with values between -1.8 and -2.3 mmol m-2 d-1 oyster-1. This study represents the most detailed measurements to date of in situ oyster reef oxygen flux, and shows that benthic microalgae can significantly impact reef oxygen dynamics. FluxDARK values scale with oyster density, and consequently can be used as a metric for reef restoration success. KEY WORDS: Crassostrea virginica · Oxygen flux · Net ecosystem metabolism · Production · Hydrodynamics · Benthic microalgae Full text in pdf format PreviousNextCite this article as: Volaric MP, Berg P, Reidenbach MA (2018) Oxygen metabolism of intertidal oyster reefs measured by aquatic eddy covariance. Mar Ecol Prog Ser 599:75-91. https://doi.org/10.3354/meps12627 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 599. Online publication date: July 12, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Fish Utilization of Created vs. Natural Oyster Reefs (Crassostrea virginica)

Once viewed as an inexhaustible fishery resource, eastern oyster reefs (Crassostrea virginica) have been dramatically depleted. In North Carolina alone, eastern oyster harvests have declined by 90% since the early 1900s. However, eastern oyster restoration and management efforts have substantially increased since the 1970s. Oyster reefs provide habitat and refuge for organisms, improve water quality, and decrease erosion. Oyster restoration projects aim to construct reefs that function similarly to their natural counterparts. Therefore, post-creation monitoring of these reefs is crucial in determining restoration success. However, monitoring is often lacking or focused only on oyster density and size rather than ecosystem functions such as nekton utilization. This study examines nekton utilization among created reefs compared to natural reefs in an estuary in Wilmington, North Carolina. The objective was to determine whether the created reefs function similarly to the natural reefs in abundance, species richness, and fish size. Using seine nets and Breder traps, reefs were sampled over a 5-month period. No significant difference was detected among reefs for nekton abundance, species richness, and standard length. This is a promising result for future management, indicating that created and natural reefs can support similar communities of fishes and shrimp.

Restoring Angasi oyster reefs: What is the endpoint ecosystem we are aiming for and how do we get there?

SummaryThree‐dimensional reefs and beds created predominately by the native Angasi Oyster or Flat Oyster (Ostrea angasi) were once common across its range in Australia's southern coastal waters but were lost during the mid‐late1800s and early 1900s due to a combination of destructive fishing practices, overfishing and changes to estuarine conditions. Despite the continued presence of low densities of individuals and cessation of commercial fishing, reefs structures and their associated communities have shown little signs of natural recovery. Since 2014, a range of oyster reef restoration projects have commenced in Australia, guided by international restoration protocols that prioritise the re‐establishment of the keystone species on artificial stable substrates placed in locations where natural oyster reefs have previously existed. These projects invariably need clear and realistic goals and objectives for restoration, which are aided by the use of a reference ecosystem as a model or target, for the local oyster reef ecosystem being restored, yet few reference sites exist. Reefs, established by Angasi, are absent from much or all of its geographical distribution, and the ecosystem has been poorly studied to date; hence, the application of restoration target ecosystems will largely depend on deriving a model based on historical descriptions and observation of what remains. Here, we develop an interim reference model to help set restoration objectives and recommended procedural framework for Angasi reef restoration based on available knowledge of the ecology, biology and aquaculture of the keystone species. We use the Port Phillip Bay oyster reef restoration project as a case study for using the reference model to guide interventions and evaluate the progress of recovery.