Studies on the oyster pathogen Perkinsus marinus (Apicomplexa): Interactions with host defenses of Crassostrea virginica and Crassostrea gigas, and in vitro propagation

The disease caused by the protozoan Perkinsus marinus has been a major source of mortality in the eastern oyster, Crassostrea virginica. Variations in susceptibility to P. marinus infection among eastern oysters collected from the Chesapeake Bay and Gulf of Mexico, as well as between eastern and Pacific (Crassostrea gigas) oysters were determined. Since oyster host defense may play a role in determining susceptibility to pathogen infection, cellular and humoral defense activities of the oyster and their interactions with P. marinus were investigated. Procedures also had to be established to isolate, purify, and propagate in vitro, P. marinus. Eastern oysters from all sites were found to be highly susceptible to the pathogen. Cellular and humoral activities were significantly affected by heavy intensity of P. marinus infection. Prevalence and intensity of P. marinus infection were lower in Pacific oysters than in eastern oysters. Pacific oysters may offer a less favorable environment for the development of P. marinus compared to eastern oysters for at least two possible reasons: the elevated cellular and humoral activities may degrade the parasite more effectively, and lower plasma protein levels may limit parasite growth. Incubation of merozoites with hemocytes of eastern and Pacific oysters in vitro suggested that limited intracellular killing of P. marinus occurred but that killing was not mediated by oxygen metabolites. Perkinsus marinus was successfully propagated in vitro in a culture medium containing most of the known constituents of cell-free oyster hemolymph. Cultures of the parasite were initiated from heart fragments of infected oysters. The cultured protozoan was similar in morphology to P. marinus, enlarged in fluid thioglycollate medium, reacted with polyclonal antibodies raised against hypnospores and was infective. Continuous cultures of P. marinus could also be initiated from hypnospores. Two types of division, progressive cleavage and successive bipartition of the mother cell protoplast, were observed

Predicting the impacts of Mississippi River diversions and sea-level rise on spatial patterns of eastern oyster growth rate and production

© 2017 There remains much debate regarding the perceived tradeoffs of using freshwater and sediment diversions for coastal restoration in terms of balancing the need for wetland restoration versus preserving eastern oyster (Crassostrea virginica) production. Further complicating the issue, climate change-induced sea-level rise (SLR) and land subsidence are also expected to affect estuarine water quality. In this study, we developed a process-based numerical modeling system that couples hydrodynamic, water quality, and oyster population dynamics. We selected Breton Sound Estuary (BSE) (∼2740 km2) in the eastern Mississippi River Deltaic Plain since it is home to several of the largest public oyster seed grounds and private leases for the Gulf coast. The coupled oyster population model was calibrated and validated against field observed oyster growth data. We predicted the responses of oyster population in BSE to small- (142 m3 s−1) and large-scale (7080 m3 s−1) river diversions at the Caernarvon Freshwater Diversion structure planned in the 2012 Coastal Master Plan (Louisiana) under low (0.38 m) and high (1.44 m) relative sea-level rise (RSLR = eustatic SLR + subsidence) compared to a baseline condition (Year 2009). Model results showed that the large-scale diversion had a stronger negative impact on oyster population dynamics via freshening of the entire estuary, resulting in reduced oyster growth rate and production than RSLR. Under the large-scale diversion, areas with optimal oyster growth rates (\u3e15 mg ash-free dry weight (AFDW) oyster−1 wk−1) and production (\u3e500 g AFDW m−2 yr−1) would shift seaward to the southeastern edge of the estuary, turning the estuary into a very low oyster production system. RSLR however played a greater role than the small-scale diversion on the magnitude and spatial pattern of oyster growth rate and production. RSLR would result in an overall estuary-wide decrease in oyster growth rate and production as a consequence of decreased salinities in the middle and lower estuary because rising sea level likely causes increased stage and overbank flow downstream along the lower Mississippi River

Factors Influencing State and Nation Wetland Management: Building Effective Management Models.

Recognition that the interaction of people and nature is implicit in every environmental problem has increased over the last century. Yet, solutions to environmental problems are impeded by uncertainty concerning the importance of socioeconomic and political conditions in dealing with environmental issues. The development of interdisciplinary management models is necessary in order to address both the biological and social causes of environmental degradation. Protection of wetland systems varies among both nations and US. states. This variation provides a unique opportunity to explore the hypothesis that socioeconomic, political and environmental variables are critical influences on wetland protection. Structural equation modeling and logistic regression were used to identify the effects of social, economic, political and environmental variables on the level of wetland protection. Wetland management outcome data were used to evaluate the success of wetland programs in the U.S. State and nation data supported the hypothesis that local conditions influence wetland management. At the national level, 57 percent of the variation in wetland protection could be explained by five predictor variables: social and economic capital, environmental and political characteristics and land use pressure. Social capital (i.e. education) was found to have the greatest influence on wetland protection overall. At the state level, environmental groups (p \u3c 0.005) and the importance of fisheries and industry (p \u3c 0.005) increased the likelihood of a strong wetland program, while increased population density (p \u3c 0.15) had the opposite effect. The collection of outcome data for wetland programs suggests that monitoring and evaluation is spotty at best, and a set of indicators are suggested that would allow comparisons between states. These find argue for management approaches that are both responsive to local condition, and are adaptive by integrating socioeconomic trends into decision-making processes. Overall, a multi-disciplinary approach to environmental management leads to the recognition of a range of factors influencing management actions and outcomes suggesting an expanded range and flexibility of opportunities for intervention. The results of this research argue that the issue of wetland protection is a compelling example of how a combination of social, political, economic and environmental factors can serve as important elements in environmental management and conservation

Development Of Disease Caused By The Parasite, Perkinsus-Marinus And Defense-Related Hemolymph Factors In 3 Populations Of Oysters From The Chesapeake Bay, Usa

The development of infection caused by the protozoan parasite, Perkinsus marinus (Dermo) and some specific potential defense-related cellular and humoral components in oysters collected from three geographic areas, Deepwater Shoal of James River (DW), Wachapreague (WP), and Mobjack Bay (MJ) were examined over time. Oysters were maintained in estuarine water (salinity = 20 ppt) or in water at a salinity similar to the ambient salinity of the collection sites. Oysters were sampled at the initiation of the experiment (day 0), day 35, and day 100 to determine defense-related parameters and disease prevalence and intensity. All populations experienced a significant increase in P. marinus infection prevalence and intensity from the initiation of the experiment to the termination of the study. Oyster mortality differed between oyster populations. None of the DW oysters perished while cumulative mortalities for WP at 32 ppt and 20 ppt and MJ oysters were respectively, 23, 25, and 35%. The experimental oyster populations demonstrated significant differences with respect to cellular and humoral defense-related variables. As the study progressed, the mean number of total hemocytes declined in the WP and MJ populations and increased in the DW population. The percentage of granulocytes in DW oysters was consistently higher than other populations. DW oysters also had the highest concentrations of protein and lysozyme. This pattern persisted throughout the experimental period. Oyster condition index significantly decreased during the course of the study in all populations except the DW oysters at 10 ppt. Results suggest that the increase of hemocyte number and higher percentage of granulocytes, and lysozyme concentration in DW oysters may have contributed to the high (100%) survival rate of this population. Salinity may have affected disease development. Disease prevalence and intensity tended to be lower in the WP oysters maintained at low salinity than those maintained at high salinity. In the DW population, unexpectedly, oysters maintained at 20 ppt had lower infection prevalence and intensity than oysters maintained at 10 ppt. Salinity induced, to some extent, changes in certain hemolymph components: lysozyme concentration tended to be higher in oysters maintained at low salinity than those maintained at high salinity. Increase in percentage of granulocytes was also observed in WP oysters after transferring to a salinity lower than ambient salinity

Oyster Reef Restoration Supports Increased Nekton Biomass and Potential Commercial Fishery Value

Across the globe, discussions centered on the value of nature drive many conservation and restoration decisions. As a result, justification for management activities increasingly asks for two lines of evidence: (1) biological proof of augmented ecosystem function or service, and (2) monetary valuation of these services. For oyster reefs, which have seen significant global declines and increasing restoration work, the need to provide both biological and monetary evidence of reef services on a local-level has become more critical in a time of declining resources. Here, we quantified species biomass and potential commercial value of nekton collected from restored oyster (Crassostrea virginica) reefs in coastal Louisiana over a 3-year period, providing multiple snapshots of biomass support over time. Overall, and with little change over time, fish and invertebrate biomass is 212% greater at restored oyster reefs than mud-bottom, or 0.12 kg m−2. The additional biomass of commercial species is equivalent to an increase of local fisheries value by 226%, or $0.09 m−2. Understanding the ecosystem value of restoration projects, and how they interact with regional management priorities, is critical to inform local decision-making and provide testable predictions. Quantitative estimates of potential commercial fisheries enhancement by oyster reef restoration such as this one can be used directly by local managers to determine the expected return on investment

Perkinsus marinus susceptibility and defense-related activities in eastern oysters Crassostrea virginica: temperature effects

he relationship of potential defense-related cellular and humoral activities and the sus- ceptibility of eastern oysters Crassostrea virginica to the parasite Perkinsus marinus were examined at 10, 15, 20 and 25 C. Oysters were acclimated at experimental temperatures for 20 d and then chal- lenged with R marinus. Total hemocyte counts (TC) and percentage of granulocytes (PG) 20 d after temperature acclimation were higher in oysters at high than at low acclimation temperature. Higher protein (P) and lysozyme (L) concentrations were found in oysters at 10 and 15 C. No significant differ- ences in hemagglutination (H) titers due to temperature acclimation were observed. Infection preva- lence 46 d after challenge by R marinus was 100, 91, 46 and 23 % respectively, for oysters at 25, 20, 15 and 10 C. Disease intensity increased with temperature. Oysters at higher temperatures had greater PG and TC and hemocyte phagocytic activity. No difference was found in TC and PG between control and challenged oysters within each temperature treatment. Bleeding may to some extent reduce TC and PG in oysters. P did not vary much among temperatures. No reduction of P in oysters was found due to P. marinuschallenge and infection. L tended to be higher in oysters at lower than at higher treat- ment temperatures. The oysters at 10 C had the highest L concentration and lowest P marinus infec- tion. But, it is not known whether the high extracellular L in oysters at 10 DC is attributable to the low R marinus susceptibility in these oysters. There was no significant difference in condition index (Cl) between control and challenged oysters and between infected and uninfected oysters. However, C1 de- creased with increasing temperatures. The H titers were not associated with any measured variables. The greater TC, PG, and phagocytic capability in oysters at higher temperatures did not result in fewer or less intense P marinus infections

Perkinsus marinus extracellular protease modulates survival of Vibrio vulnificus in eastern oyster (Crassostrea virginica) hemocytes

The in vitro effects of the Perkinsus marinus serine protease on the intracellular survival of Vibrio vulnificus in oyster hemocytes were examined by using a time-course gentamicin internalization assay. Results showed that protease-treated hemocytes were initially slower to internalize V. vulnificus than untreated hemocytes. After 1 h, the elimination of V. vulnificus by treated hemocytes was significantly suppressed compared with hemocytes infected with invasive and noninvasive controls. Our data suggest that the serine protease produced by P. marinas suppresses the vibriocidal activity of oyster hemocytes to effectively eliminate V. vulnificus, potentially leading to conditions favoring higher numbers of vibrios in oyster tissues

Oyster Reefs in Northern Gulf of Mexico Estuaries Harbor Diverse Fish and Decapod Crustacean Assemblages: A Meta-Synthesis

Oyster reefs provide habitat for numerous fish and decapod crustacean species that mediate ecosystem functioning and support vibrant fisheries. Recent focus on the restoration of eastern oyster (Crassostrea virginica) reefs stems from this role as a critical ecosystem engineer. Within the shallow estuaries of the northern Gulf of Mexico (nGoM), the eastern oyster is the dominant reef building organism. This study synthesizes data on fish and decapod crustacean occupancy of oyster reefs across nGoM with the goal of providing management and restoration benchmarks, something that is currently lacking for the region. Relevant data from 23 studies were identified, representing data from all five U.S. nGoM states over the last 28 years. Cumulatively, these studies documented over 120,000 individuals from 115 fish and 41 decapod crustacean species. Densities as high as 2,800 ind m(-2) were reported, with individual reef assemblages composed of as many as 52 species. Small, cryptic organisms that occupy interstitial spaces within the reefs, and sampled using trays, were found at an average density of 647 and 20 ind m(-2) for decapod crustaceans and fishes, respectively. Both groups of organisms were comprised, on average, of 8 species. Larger-bodied fishes captured adjacent to the reef using gill nets were found at an average density of 6 ind m(-2), which came from 23 species. Decapod crustaceans sampled with gill nets had a much lower average density, \u3c1 ind m(-2), and only contained 2 species. On average, seines captured the greatest number of fish species (n = 33), which were made up of both facultative residents and transients. These data provide general gear-specific benchmarks, based on values currently found in the region, to assist managers in assessing nekton occupancy of oyster reefs, and assessing trends or changes in status of oyster reef associated nekton support. More explicit reef descriptions (e.g., rugosity, height, area, adjacent habitat) would allow for more precise benchmarks as these factors are important in determining nekton assemblages, and sampling efficiency

Osmotic Tolerance And Volume Regulation In In Vitro Cultures Of The Oyster Pathogen Perkinsus Marinus

Growth rate. cell size, osmotic tolerance, and volume regulation were examined in cells of Perkinsus marinus cultured in media of osmolalities ranging from 168 to 737 mOsm (6.5-27.0 ppt). Cells cultured at the low osmolalities of 168 and 256 mOsm (6.5 and 9.7 ppt) began log phase growth 4 days postsubculture, whereas cells cultured at the higher osmolalities 341, 433, and 737 mOsm (12.7. 16.0, and 27.0 ppt) began log phase growth 2 days postsubculture. During log phase growth, cells from the higher osmolalities 341, 433, and 737 mOsm had shorter doubling times than cells from the lower osmolalities 168 and 256 mOsm. During both log and stationary phase growth, the mean cell diameter of cells cultured at 168 mOsm was significantly greater than cells cultured at 341 and 737 mOsm; the mean diameters of cells cultured at 341 and 737 mOsm did not differ significantly from each other. P. marinus cells cultured in various osmolalities were exposed to artificial seawater treatments of 56-672 mOsm (2.5-24.7 ppt). After the hypoosmotic treatment of 56 mOsm, cells that had been cultured in medium of low osmolality, 168 mOsm, showed only 41% mortality whereas the cells from the 341-, 433-, and 737-mOsm culture groups experienced 100% mortality. During the hyperosmotic shock, all of the groups exhibited mortalities of less than 10%. In P. marinus cells cultured in medium of 737 mOsm and then placed in a 50% dilution, cell diameter increased 13% which was a volume increase of 44.5%, but cells returned to baseline size (size before osmotic shock) within 5 minutes. P. marinus cells cultured at low osmolalities can withstand both hypo- and hyperosmotic stress and use volume-regulatory mechanisms during hypoosmotic stress. Results suggest that transferring infected oysters to low salinity will result in strains of P. marinus acclimated to low salinity that will be able to withstand periodic events of extremely low salinity