Native Oyster Research Articles

Natural Analogues in pH Variability and Predictability across the Coastal Pacific Estuaries: Extrapolation of the Increased Oyster Dissolution under Increased pH Amplitude and Low Predictability Related to Ocean Acidification.

Coastal-estuarine habitats are rapidly changing due to global climate change, with impacts influenced by the variability of carbonate chemistry conditions. However, our understanding of the responses of ecologically and economically important calcifiers to pH variability and temporal variation is limited, particularly with respect to shell-building processes. We investigated the mechanisms driving biomineralogical and physiological responses in juveniles of introduced (Pacific; Crassostrea gigas) and native (Olympia; Ostrea lurida) oysters under flow-through experimental conditions over a six-week period that simulate current and future conditions: static control and low pH (8.0 and 7.7); low pH with fluctuating (24-h) amplitude (7.7 ± 0.2 and 7.7 ± 0.5); and high-frequency (12-h) fluctuating (8.0 ± 0.2) treatment. The oysters showed physiological tolerance in vital processes, including calcification, respiration, clearance, and survival. However, shell dissolution significantly increased with larger amplitudes of pH variability compared to static pH conditions, attributable to the longer cumulative exposure to lower pH conditions, with the dissolution threshold of pH 7.7 with 0.2 amplitude. Moreover, the high-frequency treatment triggered significantly greater dissolution, likely because of the oyster’s inability to respond to the unpredictable frequency of variations. The experimental findings were extrapolated to provide context for conditions existing in several Pacific coastal estuaries, with time series analyses demonstrating unique signatures of pH predictability and variability in these habitats, indicating potentially benefiting effects on fitness in these habitats. These implications are crucial for evaluating the suitability of coastal habitats for aquaculture, adaptation, and carbon dioxide removal strategies.

Variation in Survival and Gut Microbiome Composition of Hatchery-Grown Native Oysters at Various Locations within the Puget Sound.

ABSTRACTThe Olympia oyster (Ostrea lurida) of the Puget Sound suffered a dramatic population crash, but restoration efforts hope to revive this native species. One overlooked variable in the process of assessing ecosystem health is association of bacteria with marine organisms and the environments they occupy. Oyster microbiomes are known to differ significantly between species, tissue type, and the habitat in which they are found. The goals of this study were to determine the impact of field site and habitat on the oyster microbiome and to identify core oyster-associated bacteria in the Puget Sound. Olympia oysters from one parental family were deployed at four sites in the Puget Sound both inside and outside of eelgrass (Zostera marina) beds. Using 16S rRNA gene amplicon sequencing of the oyster gut, shell, and surrounding seawater and sediment, we demonstrate that gut-associated bacteria are distinct from the surrounding environment and vary by field site. Furthermore, regional differences in the gut microbiota are associated with the survival rates of oysters at each site after 2 months of field exposure. However, habitat type had no influence on microbiome diversity. Further work is needed to identify the specific bacterial dynamics that are associated with oyster physiology and survival rates.IMPORTANCE This is the first exploration of the microbial colonizers of the Olympia oyster, a native oyster species to the West Coast, which is a focus of restoration efforts. The patterns of differential microbial colonization by location reveal microscale characteristics of potential restoration sites which are not typically considered. These microbial dynamics can provide a more holistic perspective on the factors that may influence oyster performance.

Recent change in spatial distribution of the European flat oyster (Ostrea edulis) inferred from field data and empirical models of living oysters and empty shells.

Marine coastal areas are increasingly affected by human activities resulting in changes in species and habitat distributions. Understanding these patterns and its causes and consequences is important for conservation and restoration of such changing habitats. One habitat that has been heavily affected by human use are the North Sea oyster beds which once were abundant but have lost large parts of its coastal distribution due to overexploitation. Based on data of living and dead assemblages of Ostrea edulis collected using video transects, we used an ensemble modeling technique to model and predict current and recent distribution of O. edulis along the Swedish west coast where its distribution is, in relative terms, still rather unaffected. We could detect a recent change in the distribution of O. edulis along the coast which to a large extent could be attributed to a change in depth distribution, suggesting that the population of O. edulis have a slightly shallower distribution today than in the past. Although a potential mismatch between living and dead assemblages, caused by a complex combination of biological and environmental conditions, needs to be considered in the interpretations drawn, it may be a way around the lack of suitable background data in management decisions. This provides important information for management and conservation of the native oyster beds. Furthermore, this study illustrates a method for identifying recent changes in species distribution using dead assemblages of bivalves.

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.

Production of biomaterials from seafood waste for application as vegetable wash disinfectant

The production of seafood waste was studied by analyzing calcium oxide from the shells of tropical oyster and chitosan from the shells of white shrimp to use as a vegetable wash disinfectant. The preparations used were: natural oyster shell powder (NOSP), calcined tropical oyster shell powder in a programmable furnace for 2 h at 700 °C (OSP700), 800 °C (OSP800) and 900 °C (OSP900) including white shrimp shell chitosan (CS). The physical properties of all biomaterials were analyzed using Thermogravimetric analysis, X–ray diffraction and Fourier–transformed infrared spectrometry. The results showed that NOSP and OSP700 were calcite calcium carbonate crystal, but OSP800 and OSP900 were transformed to calcium oxide and calcium hydroxide. The amino group found in the chitin from white shrimp shell was deacetylated to chitosan. By investigating the qualitative antibacterial activity of OSP900 and CS, the inhibition zone of OSP900 against E. coli was higher than that of CS (p < 0.05); however, the inhibition zone of CS against S. aureus was higher than that of OSP900 (p < 0.05). In addition, OSP900 had significantly higher quantitative antibacterial activity against E. coli than S. aureus. The MIC of OSP900 against E. coli and S. aureus for 15 min were 2.5 and 5 mg/mL, respectively; furthermore, the MBC of OSP900 against E. coli and S. aureus were 5 and 10 mg/mL, respectively. However, the inhibitory activity of CS against S. aureus was higher than against E. coli with MIC and MBC values of 5 and 10 mg/mL, respectively, for 15 min. When testing the biomaterials, OSP900 and CS, to inhibit the bacteria on kale and lettuce, 2.5 mg/mL of OSP900 for a vegetable–washing time of 15 min had the highest E. coli inhibition for both vegetables, while 2.5 mg/mL of CS for the same washing time had the highest S. aureus inhibition for both vegetables. Therefore, this research indicated that biomaterials prepared from tropical oyster shell and white shrimp shell wastes could be used as effective wash disinfectants to eliminate contaminated bacteria on vegetables.

Settlement of oyster Magallana bilineata (Röding, 1798) spat in the natural environment: seasonality and substrate texture preference

ABSTRACT This study determined the seasonality of Magallana bilineata spat settlement in a natural oyster bed and established surface texture preference of competent larvae by comparing the numbers of spat settling on the smooth and rough surfaces of ceramic tiles over a period of 31 months. This will guide farmers when to deploy cultches to maximise spat harvest. Regardless of tile orientation, spat numbers were significantly higher on the rough side (129.07 ± 9.3 m−2) than on the smooth side (66.95 ± 7.0 m−2). Spat collection was highest in March, June and July in each of 2015, 2016 and 2017. There was no significant correlation between the number of spat settling in each month with temperature, salinity, pH, dissolved oxygen (DO), sulphide, phosphate, nitrate, nitrite and ammonia concentrations, plankton density measured at deployment and retrieval of tiles, except for DO during deployment. The only significant correlations with mean shell length (SL) were with DO and ammonia during tile retrieval. Mean SL did not significantly differ between tile orientations and surfaces but differed between months, being highest in August 2015 and August 2016. From these results, it is best to deploy roughened cultches in this particular area in March, June and July.

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.

Mapping oysters on the Pacific coast of North America: A coast-wide collaboration to inform enhanced conservation.

To conserve coastal foundation species, it is essential to understand patterns of distribution and abundance and how they change over time. We synthesized oyster distribution data across the west coast of North America to develop conservation strategies for the native Olympia oyster (Ostrea lurida), and to characterize populations of the non-native Pacific oyster (Magallana gigas). We designed a user-friendly portal for data entry into ArcGIS Online and collected oyster records from unpublished data submitted by oyster experts and from the published literature. We used the resulting 2,000+ records to examine spatial and temporal patterns and made an interactive web-based map publicly available. Comparing records from pre-2000 vs. post-2000, we found that O. lurida significantly decreased in abundance and distribution, while M. gigas increased significantly. Currently the distribution and abundance of the two species are fairly similar, despite one species being endemic to this region since the Pleistocene, and the other a new introduction. We mapped the networks of sites occupied by oysters based on estimates of larval dispersal distance, and found that these networks were larger in Canada, Washington, and southern California than in other regions. We recommend restoration to enhance O. lurida, particularly within small networks, and to increase abundance where it declined. We also recommend restoring natural biogenic beds on mudflats and sandflats especially in the southern range, where native oysters are currently found most often on riprap and other anthropogenic structures. This project can serve as a model for collaborative mapping projects that inform conservation strategies for imperiled species or habitats.

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 (&lt;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.

The Curriculum and Community Enterprise for Restoration Science Making STEM Accessible, Equitable and Environmentally Relevant

Underrepresented and marginalized students have challenges when connecting their personal identities to STEM identities. This has a direct impact on the post-secondary educational and career choices of these students. Some factors which contribute to the disenfranchisement of marginalized students include inequity in academic preparation, students’ lack of self-efficacy and self-identity in STEM, students’ lack of connection to the STEM curriculum and students’ lack of role models and mentors. Although the opportunities in the STEM workforce are abundant and lucrative, students who identify as students of color, female and/or English language learners are poorly represented in the STEM professions. Through the CCERS STEM + C Program, students are asked to expand their STEM identity through near-peer mentoring, encounters with STEM experts and individual STEM Research projects that are focused on the environmental restoration of New York Harbor, its watershed and the native oyster population.

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

Beyond Residence Time: Quantifying Factors that Drive the Spatially Explicit Filtration Services of an Abundant Native Oyster Population

Beyond Residence Time: Quantifying Factors that Drive the Spatially Explicit Filtration Services of an Abundant Native Oyster Population

Shotgun analysis to identify differences in protein expression between granulocytes and hyalinocytes of the European flat oyster Ostrea edulis

Recovery of wild populations of the European flat oyster Ostrea edulis is important for ecosystem health and conservation of this species, because native oyster populations have dramatically declined or disappeared in most European waters. Diseases have contributed to oyster decline and are important constrains for oyster recovery. Understanding oyster immune system should contribute to design effective strategies to fight oyster diseases. Haemocytes play a pivotal role in mollusc immune responses protecting from infection. Two main types of haemocytes, granulocytes and hyalinocytes, are distinguished in O. edulis. A study aiming to explore differential functions between both haemocyte types and, thus, to enrich the knowledge of Ostrea edulis immune system, was performed by comparing the proteome of the two haemolymph cell types, using a shotgun approach through liquid chromatography (LC) coupled to mass spectrometry (MS). Cells from oyster haemolymph were differentially separated by Percoll density gradient centrifugation. Shotgun LC-MS/MS performance allowed the identification of 145 proteins in hyalinocytes and 138 in the proteome of granulocytes. After a comparative analysis, 55 proteins with main roles in defence were identified, from which 28 were representative of granulocytes and 27 of hyalinocytes, plus 11 proteins shared by both cell types. Different proteins involved in signal transduction, apoptosis, oxidative response, processes related with the cytoskeleton and structure, recognition and wound healing were identified as representatives of each haemocyte type. Important signalling pathways in the immune response such as MAPK, Ras and NF-κβ seemed to be more relevant for granulocytes, while the Wnt signalling pathway, particularly relevant for wound healing, more relevant in hyalinocytes. The differences in proteins involved in recognition and in cytoskeleton and structure suggest differential specialisation in processes of phagocytosis and internalisation of pathogens between haemocyte types. Apoptosis seemed more active in granulocytes. The differences in proteins involved in oxidative response also suggest different redox processes in each cell type.

One in a Million: Genetic Diversity and Conservation of the Reference Crassostrea angulata Population in Europe from the Sado Estuary (Portugal).

The production of cupped oysters is an important component of European aquaculture. Most of the production relies on the cultivation of the Pacific oyster Crassostrea gigas, although the Portuguese oyster Crassostrea angulata represents a valuable product with both cultural and economic relevance, especially in Portugal. The authors of the present study investigated the genetic diversity of Portuguese oyster populations of the Sado estuary, both from natural oyster beds and aquaculture facilities, through cox1 gene fragment sequencing. Then, a comparison with a wide dataset of cupped oyster sequences obtained from GenBank (up to now the widest available dataset in literature for the Portuguese oyster) was performed. Genetic data obtained from this work confirmed that the Pacific oyster does not occur in the natural oyster beds of the Sado estuary but showed that the species occasionally occurs in the oyster hatcheries. Moreover, the results showed that despite the founder effect and the bottleneck events that the Sado populations have experienced, they still exhibit high haplotype diversity. Risks are arising for the conservation of the Portuguese oyster reference populations of the Sado estuary due to the occurrence of the Pacific oyster in the local hatcheries. Therefore, researchers, local authorities, and oyster producers should work together to avoid the loss of this valuable resource.

Marine heat waves differentially affect functioning of native (Ostrea edulis) and invasive (Crassostrea [Magallana] gigas) oysters in tidal pools

The frequency and duration of short-term extreme climatic events, such as marine heat waves (MHWs), are increasing worldwide. The rapid onset of MHWs can lead to short-term stress responses in organisms that may have lethal or sub-lethal effects. In addition, increased temperature variability and extremes are predicted to favour and facilitate the spread of non-native species, altering rates of key ecosystem processes and functions. It is possible, however, that compensatory mechanisms, such as increased feeding rates, may enable the maintenance of metabolic functioning and prevent detrimental temperature effects. Using a mesocosm-based approach, we experimentally tested for the effects of MHWs in tidal pools on the mortality, individual length, width and biomass, and respiration rates for both a native oyster, Ostrea edulis, and invasive oyster, Magallana gigas, with or without food supply. No mortality was recorded for either O. edulis or M. gigas for the duration of the four week experiment. Increases in length were greater in O. edulis compared to M. gigas but were not affected by temperature or food supply. Increases in width, however, did not differ between species but were reduced overall in heat wave treatments regardless of food supply. O. edulis gained more biomass than M. gigas in ambient treatments regardless of food supply but, in heat wave treatments, only gained greater biomass than M. gigas at additional levels of food supply. Respiration rates did not reflect changes in temperature or food supply in either species but differed through time, with greater rates post-heat wave in all treatments. Thermal responses of O. edulis and M. gigas to MHWs thus appear to be context dependent and, if food supply is sufficient, O. edulis may be able to maintain its presence in the intertidal. The ability of M. gigas to remain unaffected by fluctuating environmental conditions, however, suggests future resilience of invasive populations to climatic extremes that may result in competitive exclusion and a further decline in native oyster populations. This information is critical for developing effective management plans to ensure the sustainability of natural oyster populations whilst maintaining key ecosystem functioning.

Response of eelgrass (Zostera marina) to an adjacent Olympia oyster restoration project.

Recent restoration efforts for the native Olympia oyster, Ostrea lurida, are commonly motivated by potential return of oyster-associated ecosystem services, including increased water filtration. The potential impact of such restoration on another species of ecological concern, eelgrass, Zostera marina, is unclear, but has been hypothesized to be positive if oyster filter feeding increases light penetration to eelgrass. For two years after construction of an oyster restoration project, we assessed the response of adjacent eelgrass (impact) compared to control and reference eelgrass beds by monitoring changes in light intensity, eelgrass shoot density, biomass, leaf morphometrics, and epiphyte load. We observed lower light intensity consistently over time, including prior to restoration, near the constructed oyster bed relative to the control and one of the reference locations. We also observed minor variations between control and impact eelgrass morphology and density. However, the changes observed were not outside the range of natural variation expected in this system, based upon comparisons to reference eelgrass beds, nor were they detrimental. This limited impact to eelgrass may be due in part to the incorporation of a buffer distance between the restored oyster bed and the existing eelgrass bed, which may have dampened both positive and negative impacts. These findings provide evidence that Olympia oyster restoration and eelgrass conservation goals can be compatible and occur simultaneously.

Modeling Oyster Reef Restoration: Larval Supply and Reef Geometry Jointly Determine Population Resilience and Performance

Restoration of native oyster (Crassostrea virginica) populations in Chesapeake Bay shows great promise after three decades of failed attempts. Population models used to inform oyster restoration had integrated reef habitat quality, demonstrating that reef height determines oyster population persistence and resilience. Larval recruitment drives population dynamics of marine species, yet its impact with reef height and sediment deposition upon reef restoration is unknown. To assess the influence of reef height, sediment deposition and larval supply, we adapted a single-stage population model to incorporate stage structure using a system of four differential equations modeling change in juvenile density (J), and changes in volume of adults (A), oyster shell reef (R), and sediment (S) on an oyster reef. The JARS model was parameterized with empirical data from field experiments. Larval supply included larvae from the natal population and from outside populations. The stage-structured model possessed multiple non-negative equilibria (i.e., alternative stable states). Different initial conditions (e.g., oyster shell reef height) resulted in different final states. The main novel findings were that the critical reef height for population persistence and resilience was jointly dependent on sediment input and larval supply. A critical minimum larval supply was necessary for a reef to persist, even when initial sediment deposition was zero. As larval supply increased, the initial reef height needed for reef persistence was lowered, and oyster reef resilience was enhanced. A restoration oyster reef with higher larval influx could recover from more severe disturbances than a reef with lower larval influx. To prevent local extinction and assure a positive population state, higher levels of larval supply were required at greater sediment concentrations to overcome the negative effects of sediment accumulation on the reef. In addition, reef persistence was negatively related to sediment deposited on a reef prior to larval settlement and recruitment, implying that restoration reefs should be constructed immediately before settlement and recruitment to minimize sediment accumulation on a reef before settlement. These findings are valuable in oyster reef restoration because they can guide reef construction relative to larval supply and sediment deposition on a reef to yield effective and cost-efficient restoration strategies.