Oyster Populations Research Articles

Genome-wide analysis of natural and restored eastern oyster populations reveals local adaptation and positive impacts of planting frequency and broodstock number.

The release of captive‐bred plants and animals has increased worldwide to augment declining species. However, insufficient attention has been given to understanding how neutral and adaptive genetic variation are partitioned within and among proximal natural populations, and the patterns and drivers of gene flow over small spatial scales, which can be important for restoration success. A seascape genomics approach was used to investigate population structure, local adaptation, and the extent to which environmental gradients influence genetic variation among natural and restored populations of Chesapeake Bay eastern oysters Crassostrea virginica. We also investigated the impact of hatchery practices on neutral genetic diversity of restored reefs and quantified the broader genetic impacts of large‐scale hatchery‐based bivalve restoration. Restored reefs showed similar levels of diversity as natural reefs, and striking relationships were found between planting frequency and broodstock numbers and genetic diversity metrics (effective population size and relatedness), suggesting that hatchery practices can have a major impact on diversity. Despite long‐term restoration activities, haphazard historical translocations, and high dispersal potential of larvae that could homogenize allele frequencies among populations, moderate neutral population genetic structure was uncovered. Moreover, environmental factors, namely salinity, pH, and temperature, play a major role in the distribution of neutral and adaptive genetic variation. For marine invertebrates in heterogeneous seascapes, collecting broodstock from large populations experiencing similar environments to candidate sites may provide the most appropriate sources for restoration and ensure population resilience in the face of rapid environmental change. This is one of a few studies to demonstrate empirically that hatchery practices have a major impact on the retention of genetic diversity. Overall, these results contribute to the growing body of evidence for fine‐scale genetic structure and local adaptation in broadcast‐spawning marine species and provide novel information for the management of an important fisheries resource.

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.

The density and distribution of Pacific Oyster (Crassostrea gigas) in Krueng Cut, Aceh Besar

Crassostrea gigas is a Pacific oyster that has the largest size among the other oysters. This oyster is most often found because of its ability to adapt to a variety of environments. Krueng Cut is an estuary area that gets a lot of nutrient input from sea water because it is directly adjacent to the ocean. This condition makes this area has a high abundance of oysters with high fishing and antropogenic activities as well. The purpose of this study was to determine the density and distribution of the oyster population from 3 representative stations along the estuary area of Krueng Cut. The method used in this study is random sampling using a quadratic transect. The results show that the highest density is indicated by station 3 with 55.67 ind/m2 and the lowest density is indicated by station 1 is 40.33 ind/m2. These results indicate that the activities of residents, the entry of contaminants from antropogenic affect the density of oysters. The distribution of oysters from the three stations showed similarities, namely they tended to grouping. The aquatic environment at the three research stations still supports the growth of oysters. This study confirms that there has been a decline in the population, which is characterized by a decrease in the number of catches and a smaller size of oysters.

Historical abundance and distribution of the native flat oyster (

Reefs of the flat oyster (Ostrea angasi) were once common along the southern coasts of Australia. Historical and current literature relating to O. angasi was used to identify bays and estuaries where this species once existed. In many estuaries of Western Australia, current populations are significantly lower than historical levels, including in Princess Royal Harbour and Oyster Harbour, near Albany. The main causes of the declines included overfishing, combined with the use of destructive fishing methods, such as dredging. Other factors, such as sedimentation, increased nutrient input and loss of seagrass, may have contributed to the loss of oyster reefs, and may have inhibited effective recovery. The possible impact of the protozoan pathogen Bonamia exitiosa is uncertain, although it is known to have severely affected flat oyster populations in other parts of the world. The fact that O. angasi reefs in Oyster Harbour did not recover after the fishery ceased suggests that restoration activities, aimed at restarting the ecosystem services that the oyster reefs once provided, should be undertaken. This paper suggests that the historical presence of O. angasi could be an effective starting point for prioritising potential restoration sites and details the prioritisation protocol that was used in recent restoration activities.

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.

Negligible Greenhouse Gas Release from Sediments in Oyster Habitats.

After centuries of decline, oyster populations are now on the rise in coastal systems globally following aquaculture development and restoration efforts. Oysters regulate the biogeochemistry of coastal systems in part by promoting sediment nutrient recycling and removing excess nitrogen via denitrification. Less clear is how oysters alter sediment greenhouse gas (GHG) fluxes-an important consideration as oyster populations grow. Here, we show that sediments in oyster habitats produce carbon dioxide (CO2), with highest rates in spring (2396.91 ± 381.98 μmol CO2 m-2 h-1) following deposition of seasonal diatom blooms and in summer (2795.20 ± 307.55 μmol CO2 m-2 h-1) when temperatures are high. Sediments in oyster habitats also consistently released methane to the water column (725.94 ± 150.34 nmol CH4 m-2 h-1) with no seasonal pattern. Generally, oyster habitat sediments were a sink for nitrous oxide (N2O; -36.11 ± 7.24 nmol N2O m-2 h-1), only occasionally releasing N2O in spring. N2O release corresponded to high organic matter and dissolved nitrogen availability, suggesting denitrification as the production pathway. Despite potential CO2 production increases under aquaculture in some locations, we conclude that in temperate regions oysters have an overall negligible impact on sediment GHG cycling.

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.

Examining stakeholder perceptions of oyster ecosystem services using fuzzy cognitive mapping

AbstractNature provides numerous ecosystem services to people, yet the prioritization of these services often depends on the goals of various stakeholder groups. The eastern oyster (Crassostrea virginica) is an ecologically important species along the Gulf and Atlantic coasts of the United States, where it provides essential fish habitat and may mitigate against climatic variations in urban areas. The eastern oyster also supports a multimillion dollar aquaculture industry in coastal communities. Recent declines in eastern oyster populations, however, have spurred widespread restoration activities. Here, we look at three expert stakeholder groups (academics, nongovernmental organizations, and governmental agencies) in Rhode Island (United States) to understand how stakeholder perceptions of oyster ecosystem services differ. Stakeholders' mental models showed differences among the groups' topologies and components, although the terms “Water Quality” and “Habitat/Structural Complexity” were prioritized in all the groups. Our results suggest that there is substantial intergroup variation, but that there are common threads around which future oyster restoration and management programs can be designed. By making these mental models of ecosystem services explicit, we illuminate tacit assumptions held by different stakeholders of the oyster stakeholder community in Rhode Island. In doing so, we highlight opportunities for more efficient collaboration around commonly shared goals for sustainable social and ecological management.

Genomic signatures of artificial selection in the Pacific oyster, Crassostrea gigas.

The Pacific oyster, Crassostrea gigas, is an important aquaculture shellfish around the world with great economic and ecological value. Selective breeding programs have been carried out globally to improve production and performance traits, while genomic signatures of artificial selection remain largely unexplored. In China, we performed selective breeding of C. gigas for over a decade, leading to production of several fast‐growing strains. In the present study, we conducted whole‐genome resequencing of 20 oysters from two fast‐growing strains that have been successively selected for 10 generations, and 20 oysters from the two corresponding wild populations. Sequencing depth of >10× was achieved for each sample, leading to identification of over 12.20 million SNPs. The population structures investigated with three independent methods (principal component analysis, phylogenetic tree, and structure) suggested distinct patterns among selected and wild oyster populations. Assessment of the linkage disequilibrium (LD) decay clearly indicated the changes in genetic diversity during selection. Fixation index (F st) combined with cross‐population composite likelihood ratio (XP‐CLR) allowed for identification of 768 and 664 selective sweeps (encompassing 1042 and 872 genes) tightly linked to selection in the two fast‐growing strains. KEGG enrichment and functional analyses revealed that 33 genes are important for growth regulation, which act as key components of various signaling pathways with close connection and further take part in regulating the process of cell cycle. This work provides valuable information for the understanding of genomic signatures for long‐term selective breeding and will also be important for growth study and genome‐assisted breeding of the Pacific oyster in the future.

Temporally balanced selection during development of larval Pacific oysters (Crassostrea gigas) inherently preserves genetic diversity within offspring.

Balancing selection is one of the mechanisms which has been proposed to explain the maintenance of genetic diversity in species across generations. For species with large populations and complex life histories, however, heterogeneous selection pressures may create a scenario in which the net effects of selection are balanced across developmental stages. With replicated cultures and a pooled sequencing approach, we show that genotype-dependent mortality in larvae of the Pacific oyster (Crassostrea gigas) is largely temporally dynamic and inconsistently in favour of a single genotype or allelic variant at each locus. Overall, the patterns of genetic change we observe to be taking place are more complex than what would be expected under classical examples of additive or dominant genetic interactions. They are also not easily explained by our current understanding of the effects of genetic load. Collectively, temporally heterogeneous selection pressures across different larval developmental stages may act to maintain genetic diversity, while also inherently sheltering genetic load within oyster populations.

Larval development in the Pacific oyster and the impacts of ocean acidification: Differential genetic effects in wild and domesticated stocks.

The adaptive capacity of marine calcifiers to ocean acidification (OA) is a topic of great interest to evolutionary biologists and ecologists. Previous studies have provided evidence to suggest that larval resilience to high pCO2 seawater for these species is a trait with a genetic basis and variability in natural populations. To date, however, it remains unclear how the selective effects of OA occur within the context of complex genetic interactions underpinning larval development in many of the most vulnerable taxa. Here we evaluated phenotypic and genetic changes during larval development of Pacific oysters (Crassostrea gigas) reared in ambient (~400 µatm) and high (~1600 µatm) pCO2 conditions, both in domesticated and naturalized “wild” oysters from the Pacific Northwest, USA. Using pooled DNA samples, we determined changes in allele frequencies across larval development, from early “D‐stage” larvae to metamorphosed juveniles (spat), in both groups and environments. Domesticated larvae had ~26% fewer loci with changing allele frequencies across developmental stages and <50% as many loci affected by acidified culture conditions, compared to larvae from wild broodstock. Functional enrichment analyses of genetic markers with significant changes in allele frequency revealed that the structure and function of cellular membranes were disproportionately affected by high pCO2 conditions in both groups. These results indicate the potential for a rapid adaptive response of oyster populations to OA conditions; however, underlying genetic changes associated with larval development differ between these wild and domesticated oyster stocks and influence their adaptive responses to OA conditions.

Medium-term monitoring reveals effects of El Niño Southern Oscillation climate variability on local salinity and faunal dynamics on a restored oyster reef.

Human activities and regional-scale climate variability drive changes in the ecology of coastal and marine ecosystems. Ecological restoration has emerged as a best-management practice to combat habitat degradation and restore lost ecological functions. However, relatively short project monitoring timeframes have limited our understanding of the effects of interannual climate cycles on water quality and restoration dynamics. We collected measurements on a 23-ha oyster reef constructed in the Gulf of Mexico to determine the relationship between El Niño Southern Oscillation (ENSO)-driven climate variability and local salinity patterns, and to evaluate the effects of this climate variability and salinity on oyster population dynamics and faunal community composition over a medium-term (five-year) timeframe. The role of ENSO-driven climate variability on local salinity patterns (primarily from changes in precipitation and evaporation) and faunal dynamics was investigated using the Oceanic Niño Index (ONI). Salinity was negatively correlated with ONI with an approximately 4-month lag. Higher ONI values (El Niño periods) were followed by reductions in salinity, increases in oyster recruitment and density, and reductions in resident motile fauna density and species richness. Lower ONI values (La Niña periods) had higher and less variable salinities, and higher areal coverage of restoration substrates by large oysters. ENSO-driven salinity reductions in the second year after reef construction coincided with a shift in resident motile faunal community composition that was maintained despite a second strong salinity reduction in year 5. Our results indicate that it is important to expand the typical monitoring timeframes to at least five years so that resource managers and restoration practitioners can better understand how both short-term environmental variability and longer-term climate cycles can affect the outcomes of restoration actions.

Effects of flood-associated stressors on growth and survival of early life stage oysters (Crassostrea virginica)

Oyster reefs provide essential ecosystem services but are severely degraded worldwide. Extreme flooding events, which can be intensified by water management decisions, reduce water quality in estuaries and further threaten oyster populations. Restoration and conservation of oysters is dependent on the success of early oyster life stages. This study examined the effect of water quality stressors associated with flooding events on the growth and survival of larval and juvenile oysters (Crassostrea virginica). In 96-h assays, we exposed D-stage larvae to a range of dissolved oxygen, microcystin-LR, pH, and salinity concentrations. These conditions were selected based on water quality data from the Mississippi Sound during a 2019 freshwater flooding event caused by the Bonnet Carré Spillway opening. There was no negative effect of microcystin-LR or pH on early veligers at the concentrations tested, but low salinity significantly reduced shell growth, and hypoxia (< 2 mg L−1 O2) decreased both larval growth and survival. Post-metamorphosis juvenile oysters were exposed to the same water quality stressors for 24 days in the lab. Low DO, pH, and salinity treatments reduced juvenile change in wet weight and shell growth rates, but had no effects on survival. These laboratory-exposed juveniles were subsequently deployed into the field to assess the ability of juveniles to recover from short-term exposure to simulated flooding-associated stressors. After deployment to natural conditions in the Mississippi Sound, juvenile oysters were able to compensate for reduced growth during the lab exposure, even though survival was reduced for juveniles previously exposed to low pH during the first two weeks in the field. In general, early oyster life stages were relatively tolerant of the duration and stressor concentrations tested, but negative sublethal impacts of flood-associated stressors must be considered in the face of increasing frequency and duration of flooding events due to climate change.

Aquaculture potential of two Kumamoto oyster (Crassostrea sikamea) populations and their reciprocal hybrids in southern China

The Kumamoto oyster, Crassostrea sikamea, is a potential aquaculture species with a unique shape and delicious taste. It is naturally distributed along the coasts of East Asia, but it was inadvertently introduced into America from Japan, and has formed several geographic populations. In order to evaluate the aquaculture potential of C. sikamea hybrids, a complete diallel cross between two geographical populations (China and America) was conducted by using mixing gametes at an experimental station in Zhanjiang, Guangdong Province in southern China. Two intra-population mating groups (CC and AA) and two reciprocal inter-population crosses (CA and AC) were produced in triplicates. High fertilization rate and hatching rate were observed in all experimental groups, suggesting that there was no sperm-egg recognition barrier between these two geographic populations. Throughout the life cycle, the survival rate of reciprocal hybrids was higher than that of pure breeds. The heterosis in growth of whole weight of reciprocal hybrids in adulthood was significant, which was mainly influenced by mating strategy. In view of the performance difference between the progenies of the two pure populations, the aquaculture potential of the progenies of the American C. sikamea population was higher than that of the progenies of the Chinese indigenous population. The results demonstrated that the crossbreeding between Chinese and American C. sikamea populations can produce considerable heterosis, which can improve the C. sikamea aquaculture industry in southern China.

Molecular characterization and antibiotic resistance of Vibrio parahaemolyticus from Indian oyster and their probable implication in food chain.

Vibrio parahaemolyticus is one of the leading causes of diarrhoea and gastroenteritis in human on consumption of raw or insufficiently cooked seafood. This study was aimed at isolating and characterizing the pathogenic and pandemic V. parahaemolyticus from oysters (n = 90) in coastal parts of West Bengal, India; their antibiotic resistance and potential for involvement in the food chain. During bacteriological culture, typical V. parahaemolyticus colony was recovered in 88.9% samples followed by presumptive identification in 71 (78.9%) samples by characteristic biochemical (K/A) test. All the presumptive isolates (n = 71) were confirmed by species specific Vp-toxR PCR assay. Of these, 10 (14.08%) were tdh+ and none for the trh. Further, 5 (50%) of these tdh+ isolates were found to carry the pandemic potential gene in PGS-PCR assay; however, none in GS-PCR. Majority (80%) of these pathogenic (tdh+) isolates belonged to pandemic serovars (OUT: KUT; OUT: K24; O1: KUT; O1:K25; O10: KUT) and only 20% to non-pandemic serovars (OUT: K15; O9:K17). All the isolates (100%) exhibited resistance to cefpodoxime followed by ampicillin and cefotaxime (90%), ceftizoxime (60%), tetracycline (50%), ceftriaxone (40%), ciprofloxacin and nalidixic acid (10% each). Overall, the study findings suggested that 11.1% (10/90) of commonly marketed oysters in this area were harbouring pathogenic V. parahaemolyticus. Moreover, 5.5% (5/90) of the oyster population were harbouring pandemic strains of this pathogen. Besides, the pathogenic isolates from oysters were exhibiting a considerable genetic relatedness (53 to 70%) to human clinical isolates in PFGE analysis that relates to a substantial public health risk. Further, their multidrug resistance added gravity to the antimicrobial resistance (AMR), a globally growing public health threat and this is a critical area of concern especially during the treatment of foodborne gastroenteritis.

Submarine groundwater discharge as a potential driver of eastern oyster, Crassostrea virginica, populations in Georgia

Reef-building eastern oysters, Crassostrea virginica, provide many ecosystem services, including production of valuable commercial products, formation of complex habitats, improved water quality and shoreline protection. Despite this, oyster populations have experienced dramatic declines throughout their range, spawning massive investment in management and restoration. Restoration efforts typically consider several well-studied metrics that normally influence oyster success; however, one potential factor that has not received much prior attention is submarine groundwater discharge (SGD). We conducted a series of field surveys and field experiments to explore the relationship between SGD and oysters in a marsh-lined tidal creek in Georgia, USA. SGD was mapped across multiple time points using a natural radon tracer (radon-222), and fluxes were paired with discrete measurements of oyster density, condition, size, recruitment and growth at multiple locations along the creek. Variation in oyster metrics was best explained by a combination of SGD, pH, and DO, which displayed a high degree of multicollinearity. We found an overall negative, nonlinear relationship between oyster density and groundwater flux. Interestingly, juvenile and adult condition and growth were not negatively impacted by groundwater. Rather, our results suggest that the likely mechanism for the density-flux relationship was interruption of the larval recruitment, which was also negatively related to flux. We hypothesize that larval interruption is due to the low dissolved oxygen and pH conditions of the groundwater at high flux sites. Overall, the interaction between SGD and oysters appears complex, and may be affected by other variables. This study provides evidence of a potential negative effect of a previously understudied natural phenomena on oyster demographics, and we suggest that SGD be considered in future management efforts.

Defining Success for A Declining Resource: Mental Models of Oyster Management in Apalachicola, Florida

Wild oyster populations are in decline globally, affecting communities of generational fishers and changing the cultural dynamics of coastal communities. Managers have employed a range of approaches to conserve and restore oyster populations and sustainable fisheries; yet there is little agreement among managers, scientists, and resource users regarding what constitutes success. This study uses a qualitative, mental models approach to compare understandings of management, perceptions of management success, and barriers to achieving successful management outcomes among three critical stakeholder groups: natural resource managers, oyster harvesters, and aquaculture farmers. We found similarities among the mental models of all three groups in the causes and consequences of the oyster fishery decline, but major differences in definitions of management, factors needed for successful management, and barriers to success. This study takes a more comprehensive look at the understandings of stakeholders than previous research by mapping the causes and effects, from the decline of the oyster fishery to expectations of future success. Managers can improve stakeholder investment in management projects by gaining a better understanding of the differing definitions of project success, stakeholder participation, and stakeholder understanding of the role of management.

Optimizing surveillance for early disease detection: Expert guidance for Ostreid herpesvirus surveillance design and system sensitivity calculation

To keep pace with rising opportunities for disease emergence and spread, surveillance in aquaculture must enable the early detection of both known and new pathogens. Conventional surveillance systems (designed to provide proof of disease freedom) may not support detection outside of periodic sampling windows, leaving substantial blind spots to pathogens that emerge in other times and places. To address this problem, we organized an expert panel to envision optimal systems for early disease detection, focusing on Ostreid herpesvirus 1 (OsHV-1), a pathogen of panzootic consequence to oyster industries. The panel followed an integrative group process to identify and weight surveillance system traits perceived as critical to the early detection of OsHV-1. Results offer a road map with fourteen factors to consider when building surveillance systems geared to early detection; factor weights can be used by planners and analysts to compare the relative value of different designs or enhancements. The results were also used to build a simple, but replicable, model estimating the system sensitivity (SSe) of observational surveillance and, in turn, the confidence in disease freedom that negative reporting can provide. Findings suggest that optimally designed observational systems can contribute substantially to both early detection and disease freedom confidence. In contrast, active surveillance as a singular system is likely insufficient for early detection. The strongest systems combined active with observational surveillance and engaged joint industry and government involvement: results suggest that effective partnerships can generate highly sensitive systems, whereas ineffective partnerships may seriously erode early detection capability. Given the costs of routine testing, and the value (via averted losses) of early detection, we conclude that observational surveillance is an important and potentially very effective tool for health management and disease prevention on oyster farms, but one that demands careful planning and participation. This evaluation centered on OsHV-1 detection in farmed oyster populations. However, many of the features likely generalize to other pathogens and settings, with the important caveat that the pathogens need to manifest via morbidity or mortality events in the species, life stages and environments under observation.