Showing papers on "Oyster published in 2001"

Cascading of habitat degradation: Oyster reefs invaded by refugee fishes escaping stress

Abstract: Mobile consumers have potential to cause a cascading of habitat degradation beyond the region that is directly stressed, by concentrating in refuges where they intensify biological interactions and can deplete prey resources. We tested this hypothesis on structurally complex, species-rich biogenic reefs created by the eastern oyster, Crassostrea virginica, in the Neuse River estuary, North Carolina, USA. We (1) sampled fishes and invertebrates on natural and restored reefs and on sand bottom to compare fish utilization of these different habitats and to characterize the trophic relations among large reef-associated fishes and benthic invertebrates, and (2) tested whether bottom-water hypoxia and fishery-caused degradation of reef habitat combine to induce mass emigration of fish that then modify community composition in refuges across an estuarine seascape. Experimentally restored oyster reefs of two heights (1 m tall “degraded” or 2 m tall “natural” reefs) were constructed at 3 and 6 m depths. We sampled...

A Vibrio splendidus strain is associated with summer mortality of juvenile oysters Crassostrea gigas in the Bay of Morlaix (North Brittany, France)

Abstract: Juvenile oysters Crassostrea gigas cultured in the Bay of Morlaix (France) have suffered unexplained summer mortalities for over a decade. In the present study, we tested the hypothesis that a bacterial pathogen could be responsible for this phenomenon. A first attempt failed to isolate a bac- terial pathogen from moribund or weak oysters. Only non-pathogenic, probably opportunistic, bac- teria were isolated. As an alternative approach, we focused on oysters presenting reduced stress- response capacities (determined by circulating noradrenaline measurements), a characteristic of juvenile oysters entering an early phase of the disease. Cultures of bacterial isolates on TCBS plates revealed that a Vibrio strain was present in diseased oysters and scarce or absent in healthy oysters. Experimental infections indicated that this Vibrio can cause mortalities of juvenile oysters when injected at concentrations ranging from 10 4 to 10 8 CFU oyster -1 . Similarly to the summer mortality dis- ease, the Vibrio isolate caused higher mortalities at higher temperatures; apparently, it could not be transmitted horizontally, it did not affect adult oysters and it induced stress-response dysfunctions in juvenile oysters. Phenotypic and genotypic characterizations identified the pathogen as Vibrio splen- didus. Taken together, the present results satisfy Koch's postulate and suggest that this bacterial strain is probably responsible for the juvenile oyster summer mortalities in the Bay of Morlaix.

Stress and stress-induced neuroendocrine changes increase the susceptibility of juvenile oysters (Crassostrea gigas) to Vibrio splendidus.

Abstract: Oysters are permanently exposed to various microbes, and their defense system is continuously solicited to prevent accumulation of invading and pathogenic organisms. Therefore, impairment of the animal's defense system usually results in mass mortalities in cultured oyster stocks or increased bacterial loads in food products intended for human consumption. In the present study, experiments were conducted to examine the effects of stress on the juvenile oyster's resistance to the oyster pathogen Vibrio splendidus. Oysters (Crassostrea gigas) were challenged with a low dose of a pathogenic V. splendidus strain and subjected to a mechanical stress 3 days later. Both mortality and V. splendidus loads increased in stressed oysters, whereas they remained low in unstressed animals. Injection of noradrenaline or adrenocorticotropic hormone, two key components of the oyster neuroendocrine stress response system, also caused higher mortality and increased accumulation of V. splendidus in challenged oysters. These results suggest that the physiological changes imposed by stress, or stress hormones, influenced host-pathogen interactions in oysters and increased juvenile C. gigas vulnerability to Vibrio splendidus.

Oyster reefs as fish habitat: Opportunistic use of restored reefs by transient fishes

Abstract: Under the Magnuson-Stevenson Fisheries Management Act of 1996, current fisheries management practice is focused on the conce_pt of Essential Fish Habitat (EFH). Application of the EFH concept to estuarine habitats relates directly to ongoing oyster reef restorat10n efforts. Oyster reef restoration typically creates complex habitat in regions where such habitat is limited or absent. While healthy oyster reefs provide structurally and ecologically complex habitat for many other species from all trophic levels including recreationally and commercially valuable transient finfishes, additional data is required to evaluate oyster reef habitats in the context of essential fish habitat. Patterns of transient fish species richness,. abundance, and size-specific habitat use were examined along an estuarine habitat gradient from complex reef habitat through simple sand bottom in the Piankatank River, Virginia. There was no clear delineation of habitat use by transient fishes along this cline of estuarine habitat types (oyster reef to sand bar). Atlantic croaker (Micropogonias undulatus), Atlantic menhaden (Brevoortia tyramws), bluefish (Pomatomus saltatrix), silver perch (Bairdiel/a chi)•soura), spot (Leiostomus xanthurus), spotted seatrout (Cynoscion regalis), striped bass (Marone saxatilis), and weakfish (Cynoscion nebulosus) were found in all habitat types examined. In general, the smallest fish were found on the sand bar, the site with the least habitat heterogeneity. As habitat complexity increased along the gradient from oyster shell bar through oyster reef, transient fish size and abundance increased. Opportunistic habitat use by this suite of generalists relates variations in habitat quality as related to habitat-specific productivity and suggests that oyster reefs may be important but not essential habitat for these fishes.

Evidence for interspecies transmission of oyster herpesvirus in marine bivalves

Abstract: Since 1991, numerous herpesvirus infections associated with high mortality have been reported around the world in various marine bivalve species. In order to determine whether these infections are due to ostreid herpesvirus-1 (OsHV1), a previously characterized pathogen of the Japanese oyster (Crassostrea gigas), PCR analysis was carried out on 30 samples of larvae collected from four bivalve species (C. gigas, Ostrea edulis, Ruditapes decussatus and Ruditapes philippinarum), most exhibiting mortality prior to collection. All samples were shown to be infected by OsHV1. Viral genomes in three samples of C. gigas and three of R. philippinarum that originated from the same hatchery were unusual in bearing a deletion of at least 2.8 kbp in an inverted repeat region. The results demonstrate that OsHV1 is capable of infecting several bivalve species, and this raises the possibility that interspecies transmission may be promoted by intensive rearing in modern hatcheries.

The History of Oyster Farming in Australia

Abstract: Aboriginal Australians consumed oysters before settlement by Europeans as shown by the large number of kitchen middens along Australia's coast. Flat oysters, Ostrea angasi, were consumed in southeastern Australia, whereas both flat and Sydney rock oysters, Saccostrea glomerata, are found in kitchen middens in southern New South Wales (NSW), but only Sydney rock oysters are found in northern NSW and southern Queensland. Oyster fisheries began with the exploitation of dredge beds, for the use of oyster shell for lime production and oyster meat for consumption. These natural oyster beds were nealy all exhausted by the late 1800's, and they have not recovered. Oyster farming, one of the oldest aquaculture industries in Australia, began as the oyster fisheries declined in the late 1800's. Early attempts at farming flat oysters in Tasmania, Victoria, and South Australia, which started in the 1880's, were abandoned in the 1890's. However, a thriving Sydney rock oyster industry developed from primitive beginnings in NSW in the 1870's. Sydney rock oysters are farmed in NSW, southern Queensland, and at Albany, Western Australia (WA). Pacific oysters, Crassostrea gigas, are produced in Tasmania, South Australia, and Port Stephens, NSW. FLant oysters currently are farmed only in NSW, and there is also some small-scale harvesting of tropical species, the coarl rock or milky oyster, S. cucullata, and th black-lip oyster, Striostrea mytiloides, in northern Queensland. Despite intra- and interstate rivalries, oyster farmers are gradually realizing that they are all part of one industry, and this is reflected by the establishment of the national Australian Shellfish Quality Assuarance Program and the transfer of farming technology between states. Australia's oyster harvests have remained relatively stable since Sydney rock oyster production peaked in the mid 1970's at 13 million dozen. By the end of the 1990's this had stabilized at around 8 million dozen, and Pacific oyster production reached a total of 6.5 million dozen from Tasmania, South Australia, and Port Stephens, a total of 14.5 million dozen oysters for the whole country. This small increase in production during a time of substantial human population growth shows a smaller per capita consumption and a declining use of oysters as a "side-dish."

Removal of Toxoplasma gondii oocysts from sea water by eastern oysters (Crassostrea virginica)

Abstract: Toxoplasma gondii infections have been reported in a number of marine mammals. Presently it is not known how these animals acquire T. gondii from their aquatic environment. The eastern oyster, Crassostrea virginica, has been shown to remove Cryptosporidiwn oocysts from seawater and a similar phenomenon may be occurring with T. gondii oocysts and marine invertebrates. The present study was done to determine if eastern oysters could remove and retain T. gondii oocysts from seawater. Oocysts of the VEG strain of T. gondii (1 x 10(6) oocysts) were placed in seawater (32 ppt NaCl) containing live eastern oysters. The infected seawater was removed one day postinoculation (PI) and replaced with fresh seawater. Selected oysters were removed at 1, 3 and 6 days PI. Hemolymph, gill washes, and oyster tissue were collected separately at each observation time. The oyster tissue was homogenized and all 3 samples fed separately to mice. Toxoplasma gondii positive mice were observed at each time period. The results indicate that T. gondii oocysts can be removed from seawater by eastern oysters and retain their infectivity. Contaminated raw oysters may serve as a source of T. gondii infection for marine mammals and humans.

Composition of biofouling communities on suspended oyster cultures: an in situ study of their interactions with the water column

Abstract: This study was based on in situ experiments conducted in a shellfish lagoon (Thau, France) to determine the interactions between suspended oyster Crassostrea gigas Thunberg cul- tures and their environment at a seasonal scale. Three groups of descriptors were considered simul- taneously during the course of the study: the taxonomic composition of an oyster culture unit (OCU), the nutrient and oxygen exchanges at the OCU-water interface (fluxes) and the water-column char- acteristics (water). We used a multiple factorial analysis (MFA) to assess in a single reference frame: (1) the seasonal organisation of the taxonomic groups which compose the OCU and (2) the interac- tions between this multispecific assemblage and the water column. We found strong seasonal vari- ability in the OCU composition and the OCU interactions with the water column. Taxonomic richness of the biofouling was at a maximum in spring and minimum in August after a bottom anoxia. Among biofouling species, ascidians always constituted the dominant group. The annual pattern of coexis- tence observed between ascidians and oysters might be explained by resource partitioning, and also by a beneficial trophic interaction between these 2 groups. The structure of the OCU was based on a complex system of interactions, particularly in spring. During this season, the development on the OCU of macrofauna of soft substratum such as polychaetes reflected the presence of a suspended sediment compartment. The influence of the OCU on the water column was maximum in summer and minimum in winter. In the shellfish zone, the OCU plays a central role in nutrient renewal, particu- larly in summer when benthic fluxes are insufficient to satisfy phytoplankton nitrogen requirements. We estimate that the multispecific assemblages occurring on the oyster ropes (oysters and biofouling) have a potential annual DIN production of 2 × 10 7 mol yr -1 , and thus oyster cultures could have a determining influence on nitrogen recycling in the water column in the Thau lagoon.

A herpes-like virus infects a non-ostreid bivalve species: virus replication in Ruditapes philippinarum larvae.

Abstract: Sporadic high mortalities were reported in June 1997 among hatchery-reared larval Manila clam Ruditapes philippinarum in a French commercial hatchery. Cellular abnormalities were observed in semi-thin sections in affected animals. Transmission electron microscopy revealed the presence of herpes-like virus particles in larvae. This is the first description of a herpes-like virus infection in larval R. philippinarum, a non-ostreid bivalve species. Virus particles were similar to other herpes-like viruses described from different oyster species with respect to ultrastructure and morphogenesis. Electron microscopic examination also demonstrated cells with condensed chromatin and extensive perinuclear fragmentation of chromatin. Like viruses infecting oysters, the herpes-like virus detected in clams may induce apoptosis in infected animals.

Geographic distribution of Perkinsus marinus genetic strains along the Atlantic and Gulf coasts of the USA

Abstract: Perkinsusmarinus (Mackin, Owen and Collier) is a major pathogen of the eastern oyster Crassostreavirginica (Gmelin). Elucidating the spatial distribution of genetic variation within the species is critical to an examination of potential virulence differences among strains and to understanding the implications of transferring infected oyster stocks. The genetic similarity of P. marinus in vitro cultures and their clonal composition was examined using isolates from individual oysters collected from 1991 through 1999 along the Atlantic and Gulf of Mexico coasts of the USA. P. marinus has been endemic to the Atlantic coast from the Virginia portion of Chesapeake Bay southward and into the Gulf of Mexico since its initial description in 1949, and over the last 10–15 years there has been a range expansion of this parasite into the Maryland portion of Chesapeake Bay and northward along the Atlantic coast from New Jersey to Maine. DNA purified from 76 primary (parental) cultures and 86 clonal cultures derived from the parental isolates was examined at eight polymorphic loci by restriction fragment length polymorphism analysis. Comparison of clonal and parental culture genotypes supported previous observations that isolate cultures initiated from a single oyster can be polyclonal, providing evidence that an individual oyster can be infected with multiple strains. Allelic and genotypic frequencies differed significantly among three regions of the USA; the Northeast Atlantic (Maine to Maryland), the Southeast Atlantic (Virginia to Florida's east coast), and the Gulf of Mexico (Florida's west coast to Texas). Overall, 12 different composite genotypes were detected in this study, with >88% of isolates possessing one of three predominant genotypes. One of the major composite genotypes was unique to Gulf coast isolates, while the genetic strain of P. marinus detected most frequently in oysters from the Northeast was not found in Gulf coast oysters. Perkinsusmarinus is ubiquitous along the Atlantic and Gulf coasts, but different regions possess unique assemblages of genetic strains. Apparently, the historically common practice of oyster transplantation between regions has not significantly altered the population genetic structure at the regional level. The data suggest a founder event in the Northeast region, corresponding to the recent range expansion. Previously documented differences in virulence are consistent with genotypic differences, indicating the potential to identify strain virulence with molecular genetic tools.

Noradrenaline modulates hemocyte reactive oxygen species production via β-adrenergic receptors in the oyster Crassostrea gigas

Abstract: Catecholamines (CA) are known to be present in the microenvironment of molluscan immunocytes. In the present study, experiments were conducted to determine the effects of noradrenaline (NA), the principal CA circulating in bivalve hemolymph, on the luminol-dependent chemiluminescence (CL) of oyster Crassostrea gigas hemocytes. Results show that NA had a dose-dependent inhibitory effect on the CL-response at the physiological concentration of 0.1 microM and above. The alpha-adrenoceptor agonist phenylephrine had no significant effect on the CL-response whereas the beta-adrenoceptor agonist isoproterenol mimicked the inhibitory effects of NA on the CL-response. The beta-adrenoceptor antagonist propanolol, but not the alpha-adrenoceptor antagonist prazosin, prevented the negative effects of NA on the CL-response. Taken together, these results show that beta-adrenergic receptors are present at the surface of oyster hemocytes and allow NA to down-regulate the CL-response.

Diet and habitat use by bluefish, Pomatomus saltatrix, in a Chesapeake Bay estuary

Abstract: Bluefish, Pomatomus saltatrix, are recreationally valuable finfish along the Atlantic seaboard and in the Chesapeake Bay. Diet and habitat use patterns for bluefish life history intervals in Chesapeake Bay estuaries are poorly described although it is widely acknowledged that this apex piscivorous species relies on estuarine habitat for feeding and nursery grounds after oceanic spawning and inshore migration of larvae. Bluefish diet, distribution, and abundance patterns were examined in relation to oyster reef, oyster bar, and sand bottom habitat in the Piankatank River, Virginia. Bluefish from all sites were predominantly piscivorous and were more abundant at reef sites than non-reef sites. Bluefish caught in association with the oyster reef consumed a wider diversity of prey items than fish from other sites; diet diversity may contribute to bluefish success during periods when small pelagic food fish abundance is reduced. Bluefish estuarine habitat use is positively correlated with the presence of oyster shell habitat and the complex trophic communities centering on oyster reefs.

A herpes-like virus infecting Crassostrea gigas and Ruditapes philippinarum larvae in France.

Abstract: Concomitant sporadic high mortalities were reported in June 1997 among batches of larval Pacific oyster, Crassostrea gigas, and Manila clam, Ruditapes philippinarum, in a French commercial hatchery. Histological observation showed the presence of cellular abnormalities in affected animals. Electron transmission microscopy revealed the presence of herpes-like virus particles in infected larvae of both bivalve species. Viruses observed in C. gigas and R. philippinarum are closely related with respect to ultrastructure and morphogenesis. They were detected simultaneously in both bivalve species larvae indicating possible interspecific transmission. Moreover, PCR analysis using oyster herpes-like virus specific primers allowed amplification of fragments of expected sizes for both bivalve species and demonstrated the presence of viral DNA. The PCR products obtained for both bivalve species and digested by restriction enzymes displayed the same patterns. These data suggest that the same herpes-like virus may infect larval oysters and clams.

Utilization of Gracilaria chilensis (Rhodophyta: Gracilariaceae) as a Biofilter in the Depuration of Effluents from Tank Cultures of Fish, Oysters, and Sea Urchins

Abstract: An evaluation was made on a seasonal basis of the effect of the marine macroalga culture Gracilaria chilensis on concentrations of some soluble and particulate wastes emitted during tank cultures of a fish Isacia conteptionis, an oyster Crassostrea gigas, and a sea urchin Loxechinus albus species. The animals were each cultured in separate tanks, and effluent from each was directed through separate tanks, which contained dense cultures of the Gracilaria chilensis. Inflow-outflow monitoring was conducted for the presence of nitrate, nitrite, ammonium, and phosphate. Also evaluated were particulate nitrogen and phosphate. The most significant wastes were ammonium from the fish culture and nitrate from the oyster culture. These were completely removed from the water, with minor exceptions, by the alga during all seasons of the year. Lesser amounts of soluble phosphate and nitrite, arising from the fish cultures, were also removed. Of the particulate matter, only nitrogen was in evidence from the fish cultures in the summer. It was concluded that Gracilaria chilensis culture was highly efficient at biofiltration of the soluble nutrients tested but had little effect on particulate emissions. The best growth of Gracilaria chilensis occurred in the ammonium-rich effluent from the fish culture.