A study of the histozoic oyster parasite, Perkinsus marinus: I. Disease processes in American oysters (Crassostrea virginica). II. Biochemistry of Perkinsus marinus

Numerous studies have investigated the disease processes of Perkinsus marinus in the oyster, Crassostrea virginica. However, the transmission dynamics and factors affecting P. marinus infection are still unclear. The objectives of this study were to investigate: (1) the principal and most effective lifestage of P. marinus, (2) the synergistic effects of temperature, salinity and P. marinus dose on disease prevalence, (3) suppression of host reactive oxygen intermediates by P. marinus, (4) the localization of acid phosphatase in the parasite, (5) the effects of temperature and salinity on acid phosphatase secretion, and (6) the P. marinus lipid and fatty acid composition. Meronts were more infective than prezoosporangia, and infectivity was dose dependent (100 cells minimum). High temperatures, salinities and P. marinus doses increased infection prevalence and intensity. Temperature was the most important factor influencing disease susceptibility, followed by cell dosage and salinity. Both temperature and salinity significantly affected the host cellular and humoral factors in oysters. P. marinus suppression of hemocyte reactive oxygen intermediates production, as assessed by chemiluminescence was dose dependent. Zymosan stimulated hemocyte chemiluminescence was reduced, suggesting that live P. marinus cells or their extra-cellular products suppress host reactive oxygen intermediates production. Acid phosphatase activity in P. marinus cells increased with increasing temperature. Meronts had higher acid phosphatase activity than prezoosporangia. Extracellular acid phosphatase secretion by P. marinus was dose dependent, increasing with temperature and osmolality. Electron microscopy revealed that acid phosphatase activity was localized primarily in the nucleus, but was also present in the cell membrane. Lipid classes of meronts resembled those found in their media. Phospholipids were the major lipid class in meronts, while triacylglycerols were dominant in prezoosporangia isolated from infected oyster tissue. Results indicated that meronts may be capable of interconversion of lipid classes. Both meronts and prezoosporangia had much higher levels of arachidonic acid than the host

Comparison Of Infectivity And Pathogenicity Of Meront (Trophozoite) And Prezoosporangiae Stages Of The Oyster Pathogen Perkinsus-Marinus In Eastern Oysters, Crassostrea-Virginica (Gmelin, 1791)

Two experiments were conducted to compare the infectivity and pathogenicity of two life stages of the parasite Perkinsus marinus, meronts (trophozoites) and prezoosporangia (hypnospores), in eastern oysters, Crassostrea virginica. Oysters were inoculated with 5 X 10(4) meronts or prezoosporangia per oyster by injection into the shell cavity. Prevalence and intensity of P. marinus infections, condition index, serum protein concentrations, and lysozyme activities were measured in oysters after 15, 25, 40, and 65 days in experiment 1 and after 20, 40, 50, 65, and 75 days postchallenge by P. marinus cells in experiment 2. Controls were injected with filtered York River water. In the first experiment, P. marinus infections were initially detected in oysters exposed to prezoosporangia after 15 days postchallenge. In the second experiment, infection was not detected in oysters until 40 days postchallenge with either meronts or prezoosporangia. Intensity and prevalence of P. marinus infection were significantly higher (p \u3c 0.002) in oysters challenged by meronts compared with prezoosporangia-challenged oysters at the end of both experiments. In experiment 1, a significant decrease (p \u3c 0.05) was observed in serum protein in infected oysters challenged by prezoosporangia compared with uninfected oysters. Condition index was higher in uninfected oysters compared with infected oysters challenged by prezoosporangia. The differences in condition index and protein were insignificant between oysters infected by meronts or prezoosporangia. Lysozyme activities were significantly lower (p \u3c 0.05) in infected oysters than in uninfected oysters challenged with meronts. No significant differences were observed in condition index, protein concentrations, and lysozyme activities between oysters challenged by meronts and prezoosporangia in experiment 2. Lower condition index and protein concentrations in the groups of oysters infected with prezoosporangia compared with the groups infected by meronts and nonchallenged at the end of experiment 1 suggest a higher energetic demand on these oysters

A Comparison Of Crassostrea gigas And Crassostrea virginica: Effects Of Temperature And Salinity On Susceptibility To The Protozoan Parasite, Perkinsus marinus

The susceptibility of diploid and triploid (2N and 3N) Crassostrea gigas to Perkinsus marinus was compared, in the laboratory, with that of Crassostrea virginica al three test temperatures (10, 15, and 25 degrees C) at 20-22 ppt and at three test salinities (3, 10, and 20 ppt) at a temperature of 19-22 degrees C. Experimental oysters were challenged twice with freshly isolated P, marinus meronts, after acclimation to test temperatures and salinities. Although infection prevalence and intensity increased with temperature (p = 0.0001) and salinity in P. marinus-challenged oysters of both oyster species: they were highest in C. virginica groups. Infection intensity was significantly (p = 0.001) higher in P. marinus-challenged C. virginica than C. gigas (2N and 3N) at all temperatures; however, infection prevalence was not statistically different at any temperature treatment. In all salinity treatments, prevalence and infection intensity were significantly higher (p = 0.0001) in P. marinus-challenged C. virginica than 2N and 3N C. gigas. Because high infection prevalence and intensity were found in non-challenged C. virginica, part of the recorded prevalence and intensity in challenged C. virginica was probably attributed to latent infection carried over from the field. High mortality occurred in both 2N and 3N C. gigas during temperature and salinity adjustment, particularly at 25 degrees C and 3 psu

Progression Of Diseases Caused By The Oyster Parasites, Perkinsus Marinus And Haplosporidium Nelsoni, In Crassostrea Virginica On Constructed Intertidal Reefs

The progression of diseases caused by the oyster parasites Perkinsus marinus and Haplosporidium nelsoni were evaluated by periodic sampling (May 1994-December 1995) of eastern oysters Crassostrea virginica on an artificial reef located in the Piankatank River, Virginia. The infections observed were recorded as a function of: (1) prevalence and intensity; (2) oyster size and age; and (3) depth below mean low water at which the host oyster was found on the reef. Only a very small number of oysters were infected with the two species of pathogens on the oyster reef during the first 11 months of Life. In the second year of oyster life. epizootiological patterns of disease development followed temperature and salinity trends. Oysters at residence depths less than or equal to 45 cm below mean low water exhibited significantly (P \u3c 0.0001) lower prevalence and intensity of infections than oysters at depths greater than or equal to 90 cm. In contrast, oysters at residence depths greater than or equal to 90 cm had significantly higher growth rates (P \u3c 0.05) than those at less than or equal to 45 cm. However, size differences were not significant (P \u3e 0.05) at the end of the study. Results from this study may be used in managing oyster fisheries on natural or artificial reefs

Mercury Accumulation in Sharks From the Coastal Waters of Southwest Florida

As large long-lived predators, sharks are particularly vulnerable to exposure to methylmercury biomagnified through the marine food web. Accordingly, nonlethal means were used to collect tissues for determining mercury (Hg) concentrations and stable isotopes of carbon (δ13C) and nitrogen (δ15N) from a total of 69 sharks, comprising 7 species, caught off Southwest Florida from May 2010 through June 2013. Species included blacknose (Carcharhinus acronotus), blacktip (C. limbatus), bull (C. leucas), great hammerhead (Sphyrna mokarran), lemon (Negaprion brevirostris), sharpnose (Rhizoprionodon terraenovae), and tiger sharks (Galeocerdo cuvier). The sharks contained Hg concentrations in their muscle tissues ranging from 0.19 mg/kg (wet-weight basis) in a tiger shark to 4.52 mg/kg in a blacktip shark. Individual differences in total length and δ13C explained much of the intraspecific variation in Hg concentrations in blacknose, blacktip, and sharpnose sharks, but similar patterns were not evident for Hg and δ15N. Interspecific differences in Hg concentration were evident with greater concentrations in slower-growing, mature blacktip sharks and lower concentrations in faster-growing, young tiger sharks than other species. These results are consistent with previous studies reporting age-dependent growth rate can be an important determinant of intraspecific and interspecific patterns in Hg accumulation. The Hg concentrations observed in these sharks, in particular the blacktip shark, also suggested that Hg may pose a threat to shark health and fitness

Reproductive strategy of the invasive green mussel may result in increased competition with native fauna in the southeastern United States

International audienceUnderstanding the population dynamics of invasive species, such as the green mussel Perna viridis (Linnaeus, 1758), can aid in explaining the success of newly introduced populations and help predict the potential for spread. During a two-year field study of established populations in the invaded region of southwest Florida, year round gametogenesis and continuous spawning capabilities were observed through histological analysis of mussels collected monthly. This was supported by overall stable energetic reserves as measured through proximal biochemical composition (protein, glycogen and lipid content). However, egg outputs in the summer (6.4 × 10 6 ± 2.6 × 10 6 eggs / female) were significantly higher than egg outputs of winter-spawned mussels (7.7 × 10 4 ± 1.4 × 10 4 eggs / female). Stability in biochemical composition, suggests temperature and food availability were sufficient year round, allowing for the maintenance of reserves and active gametogenesis. Protein ranged from 409.0–628.0 mg g −1 , glycogen from 44.3–158.5 mg g −1 and total lipids from 7.4–13.5 mg g −1. Year-round reproductive capabilities supported by sufficient energy reserves may help explain the rapid colonization and high densities of green mussels along the southeastern United States and suggests the potential for competition with native species, particularly the eastern oyster Crassostrea virginica (Gmelin, 1791)

Host-parasite interactions: Marine bivalve molluscs and protozoan parasites, Perkinsus species.

International audienceThis review assesses and examines the work conducted to date concerning host and parasite interactions between marine bivalve molluscs and protozoan parasites, belonging to Perkinsus species. The review focuses on two well-studied host-parasite interaction models: the two clam species, Ruditapes philippinarum and R. decussatus, and the parasite Perkinsus olseni, and the eastern oyster, Crassostrea virginica, and the parasite Perkinsus marinus. Cellular and humoral defense responses of the host in combating parasitic infection, the mechanisms (e.g., antioxidant enzymes, extracellular products) employed by the parasite in evading host defenses as well as the role of environmental factors in modulating the host-parasite interactions are described