Amino acid metabolism in ribbed mussel gill tisue during hypersmotic stress: role of transaminases and pyruvate dehydrogenase

The cytosolic (cAAT) and mitochondrial (mAAT) aspartate aminotransferases were partially purified from gill tissue of the ribbed mussel, Modiolus demissus, and individually characterized with respect to heat stability, electrophoretic mobility, pH optimum, K(,m) for substrates, and reactivity with aminooxyacetic acid (AOA). The mAAT was a single isozymic form with a broad pH optimum and relatively low K(,m)s for aspartate, oxaloacetate, and (alpha)-ketoglutarate and high K(,m) for glutamate. The cAAT used for the kinetic studies was a single (homozygous) isozymic form, showed great variation in K(,m) and V(,max) with pH, and high K(,m)s for the amino acid substrates and low K(,m)s for the keto acid substrates. Both enzymes were inhibited to the same degree by AOA (I(,50) = 3 x 10(\u27-6)M). In a physiological sense, it is hypothesized that the cAAT is involved more with aspartate synthesis and the mAAT with aspartate catabolism;Differential centrifugation of ribbed mussel gill tissue homogenates and extraction of the mitochondrial fraction demonstrated that most (72%) alanine aminotransferase (AlAT) activity was mitochondrial. Subsequent characterization of the cytosolic activity indicated that it had properties identical to those demonstrated by the mitochondrial enzyme. Both enzyme fractions showed little variation in V(,max) with pH, had low K(,m)s for keto acid substrates, and were inhibited by aminooxyacetic acid (AOA), L-cycloserine, and (beta)-chloro-L-alanine. It appeared that the AlAT in ribbed mussel gill tissue was strictly mitochondrial and that alanine production and synthesis during hypoxia or during hypo- or hyperosmotic stress must be mitochondrial;The pyruvate dehydrogenase complex has been demonstrated in high speed (150,000 g) pellet preparations from sonicated ribbed mussel gill mitochondria. The complex is inhibited by low (\u3c100 mM) chloride concentrations, succinate and ATP. ATP inhibition was enhanced by NaF and reversed by high Mg(\u27++) concentrations in the absence of NaF. Pyruvate and thiamine pyrophosphate inhibited the inactivation by ATP. Factors involved in the ATP inhibition and Mg(\u27++) reversal are lost with freezing or cold storage. The activity of the complex may be regulated by a phosphorylation/dephosphorylation mechanism

Effects Of Perkinsus marinus Infection In The Eastern Oyster, Crassostrea virginica: II. Disease Development And Impact On Growth Rate At Different Salinities

In order to assess the impact of Perkinsus marinus infection on oyster growth and mortality, oysters were raised in floating rafts at six sites around Chesapeake Bay. The sites were comprised of two low salinity sites (8-10%0), two moderate salinity (12-15%0) sites and two high salinity sites (16-20%0). Oyster growth was monitored biweekly along with various water qualities including temperature and salinity. Condition index was measured monthly and disease diagnosis was perfonned bimonthly. Oyster growth was initially greatest at the high salinity sites but was subsequently retarded by Perkinsus infection at both the moderate and high salinity sites (where the parasite was more prevalent). Comparison of pre-infection and post-infection growth rates between sites showed that the reduction in growth rate was mitigated by lower salinity. Condition index was not related to salinity or site but was significantly reduced by P. marinus infection. Reduction in condition, however, was not associated with increased mortality. Mortality was also less related to salinity or temperature than it was to infection history (previous infection). Groups which incurred high infection prevalences and intensities exhibited low mortality during their first year, but suffered high mortality during the following year. The results are discussed in relation to management and aquacultural practices and their relation to genetics and selective breeding of disease resistant oysters

Oyster reef ecosystem services: Macrofauna utilization of restored oyster reefs - Harris Creek, Maryland, USA

Oyster reefs provide habitat for a variety of macrofauna species. Our studies focused on the relationship between oyster tissue biomass density and reef-associated macrofauna biomass density. Studies were conducted in 2015-2017 and sites encompassed the majority of the area in which restoration activities were conducted with the Harris Creek Oyster Sanctuary in Maryland. Results presented in this report focus on: 1) interactions between oyster biomass density and season in determining macrofauna biomass, 2) responses of macrofauna to oyster biomass densities below “threshold” levels (0-14.9 g DW m-2) and between threshold and “target” levels (15-49.9 g DW m-2) defined in the success metrics for the Harris Creek restoration effort, 3) the role of tray-scale (0.1 m2), plot-scale (10 m2), and reef-scale oyster biomass density in determining associated macrofauna biomass, and 4) larger scale patterns in macrofauna biomass density within the creek

Lessons Learned From Efforts To Restore Oyster Populations In Maryland And Virginia, 1990 To 2007

A century-long decline of the fishery for the Eastern oyster Crassostrea virginica (Gmelin, 1791) in Maryland and Virginia stimulated numerous efforts by federal, state, and nongovernmental agencies to restore oyster populations, with limited success. To learn from recent efforts, we analyzed records of restoration and monitoring activities undertaken between 1990 and 2007 by 12 such agencies. Of the 1,037 oyster bars (reefs, beds, or grounds) for which we obtained data, 43% experienced both restoration and monitoring, with the remaining experiencing either restoration or monitoring only. Restoration activities involved adding substrate (shell), transplanting hatchery or wild seed (juvenile oysters), bar cleaning, and bagless dredging. Of these, substrate addition and transplanting seed were common actions, with bar cleaning and bagless dredging relatively uncommon. Limited monitoring efforts, a lack of replicated postrestoration sampling, and the effects of harvest on some restored bars hinders evaluations of the effectiveness of restoration activities. Future restoration activities should have clearly articulated objectives and be coordinated among agencies and across bars, which should also be off limits to fishing. To evaluate restoration efforts, experimental designs should include replication, quantitative sampling, and robust sample sizes, supplemented by pre- and postrestoration monitoring

A Comparison Of Crassostrea Virginica And C. Ariakensis In Chesapeake Bay: Does Oyster Species Affect Habitat Function?

We examined the possibility that a nonnative oyster species would provide an ecologically functional equivalent of the native oyster species if introduced into the Chesapeake Bay. Habitat complexity and associated benthic communities of experimental triploid Crassostrea virginica and Crassostrea ariakensis reefs were investigated at 4 sites of varying salinity, tidal regime, water depth, predation intensity, and disease pressure in the Chesapeake Bay region (Maryland and Virginia). Four experimental treatments were established at each site: C. virginica, C. ariakensis, 50:50 of C. virginica and C. ariakensis, and shell only. Abundance, biomass, species richness, evenness, dominance, and diversity of reef-associated fauna were evaluated in relation to habitat location and oyster species. Although habitat complexity varied with location, no differences among complexity were associated with oyster species. Similarly, differences in faunal assemblages were more pronounced between sites than within sites. Our results show functional equivalency between oyster species with respect to habitat at the intertidal site and the low-salinity subtidal location. At subtidal sites of higher salinity, however, the numbers of organisms associated with C. virginica reefs per unit of oyster biomass were significantly greater than the numbers of organisms associated with C. ariakensis reefs. Multivariate analyses of data from subtidal high-salinity sites revealed unique communities associated with C. virginica treatments, whereas mixed-oyster species assemblages were functionally equivalent to monospecific C. ariakensis experimental treatments. Our study represents the first effort to quantify the potential habitat function of C. ariakensis, which has been proposed for an intentional introduction into Chesapeake Bay, and provides evidence of species-specific similarities and differences in reef-associated communities

Survival And Growth Of Triploid Crassostrea Virginica (Gmelin, 1791) And C-Ariakensis (Fujita, 1913) In Bottom Environments Of Chesapeake Bay: Implications For An Introduction

Survival and growth of triploid Crassostrea virginica and triploid C. ariakensis were investigated at four sites Surrounding Chesapeake Bay, United States, that varied tried in salinity, tidal regime, water depth, predation intensity and disease pressure. Four experimental treatments were established at each site: C. virginica; C. ariakensis; 50:50 of C. virginica: C. ariakensis: and shell only. Oysters were deployed at mean shell heights of 12.80 min and 13.85 mm (C. virginica and C. ariakensis, respectively), at an overall density of 347.5 oysters m(-2). Oyster survival and growth varied significantly, with site and species. Survival was significantly higher in C. virginica than C. ariakensis at the intertidal site, and significantly higher in C. ariakensis than C. virginica at the highest salinity, subtidal site. Survival did not differ significantly between species at the mid and low salinity, subticial sites. For both Species. survival differed significantly between sites, with lowest survival in both species Occurring Lit the intertidal site. Among the subtidal sites. C. virginica survival varied inversely with salinity, whereas C. ariakensis had the lowest Survival at the mid salinity site. Eight months after deployment C. ariakensis were significantly, larger than C. virginica at all sites. This difference generally persisted throughout the experiment, though the size differences between oyster species at the lowest salinity site were small (\u3c 10%). Shell heights within single-species treatments differed significantly between sites; highest growth rates were observed at the high salinity, subtidal site, whereas lowest growth rates were observed at the high salinity, intertidal site. At low and mid salinity subtidal sites, C. ariakensis shell heights were significantly greater in the single-species treatment compared with the mixed-species treatment. Perkinsus marinus infections occurred in both species at all sites, with prevalences varying between sites. In C. virginica, moderate and high intensity infections were only common at the two higher salinity sites, whereas infections in C. ariakensis were generally low, to rare. Haplosporidium nelsoni infections in C. virginica were only observed at the two higher salinity sites and prevalences were generally low. Two out of 53 C. ariakensis tested at the high salinity, subtidal site had rare H. nelsoni infections. Bonamia spp. infections were never observed. Our study supports previous laboratory findings and observations from its native range that C. ariakensis Survives poorly in intertidal habitats. In subtidal habitats, however, C. ariakensis displayed broad environmental tolerances, often exceeding native oyster Survival and growth rates. Post-introduction C. ariakensis Populations would be shaped by the survival and growth patterns described here, but also by their reproductive success, larval Survival, predator-prey interactions and prevailing disease dynamics

Integrated assessment of oyster reef ecosystem services: Macrofauna utilization of restored oyster reefs

Within the Harris Creek Oyster Sanctuary in the Maryland portion of Chesapeake Bay, we evaluated relationships between basic oyster reef characteristics and the abundance and biomass of macrofauna. The eight sites selected for these studies included five restored oyster reef sites and three sites suitable for restoration that had not been restored. These sites encompassed a range of oyster biomass density and were spread throughout the sanctuary area. At each site one month prior to each of four sampling periods, divers filled four wire mesh baskets (0.1m2 surface area x 15 cm depth) with material from the site and embedded them so that the surface was flush with the surrounding substratum. In spring, early summer, late summer and fall of 2015, divers collected baskets and returned them to the laboratory where all macrofauna ≥1 mm were collected from each sample and their identity, abundance and biomass were determined. In addition to the abundance and biomass of oysters, we also assessed the amount of surface as the volume of live oysters along with that of any oyster shells whose surface was at least 50% oxic based on coloration (i.e. black shell was presumed to have been buried below the surface in anoxic conditions). Positive relationships were identified for all three reef characteristics and the three major macrofaunal groups examined. In the majority of seasons, the relationship between both biomass and abundance of the hooked mussel, Ischadium recurvum, as a power function of oyster tissue biomass density, oyster abundance per square meter and surface shell volume. The relationship between oyster reef characteristics and the biomass and abundance of the mud crab, Eurypanopeus depressus, and of the naked goby, Gobiosoma bosc, were always positive but were more variable than that for I. recurvum. These data demonstrate that relationships can be found between oyster reef characteristics and macrofauna abundance and biomass. They further demonstrate that, in many cases, simple measures of reef characteristics such as oyster abundance and shell volume can provide predictions of macrofauna abundance and biomass that are comparable to more labor intensive measures such as oyster tissue biomass

Integrated assessment of oyster reef ecosystem services: Fish and crustacean utilization and trophic linkages

Using a regression design that encompassed the continuum of oyster reef biomass density in Harris Creek, MD, from unrestored reefs to those restored reefs with the greatest oyster biomass, we examined finfish and crustacean utilization of these habitats. Of the eight sites studied, three had not been subject to any restoration activities and five had been planted in 2012 with juvenile oysters set on oyster shell. All sites were sampled in April, June, August, and October 2015. During each sampling period, we assessed abundance, total length and biomass of finfish and examined gut contents to assess the diets of selected finfish species. Of the species collected that were likely to use reefs as habitat or a foraging ground, only striped bass and white perch were sufficiently abundant to support robust statistical analyses. Regression analyses found no clear relationship between oyster biomass density and catch per unit effort, total length or biomass for striped bass or white perch. Analyses of the effects of sampling period and restoration status (restored versus non-restored sites) on fish utilization frequently found an effect of sampling period but rarely found an effect of restoration status. In all cases where differences were detected, they suggested greater utilization of non-restored sites. Overall, data were sparse and the power of statistical analyses was low. Analyses of striped bass and white perch diets suggest that they are using oyster reefs as a foraging ground. Although comparisons of the proportion of striped bass and white perch that contained prey in their stomachs found no difference between those caught on restored sites versus non-restored sites, gut contents of both species contained prey taxa that are likely more abundant on restored oyster reefs than nonrestored sites. As a percentage of total prey wet weight, polychaete worms were the most important component of striped bass diets in both April (50%) and August (47%). Of the polychaete worms identifiable to species, 100% were Alitta succinea, a species found in much greater abundance and biomass on restored oyster reefs than on comparable non-restored sites (Kellogg et al. 2013, Rodney and Paynter 2006). White perch diets were dominated by the ascidian Molgula manhattensis (52%), a species generally found in greater abundance on hard substrates including oyster reefs. Of the identifiable species of fish found in the stomachs of striped bass, 93% by weight were naked gobies (Gobiosoma bosc) or striped blennies (Chasmodes bosquianus), two species found in greater abundance and biomass on restored oyster reefs than nonrestored sites in Chesapeake Bay (Kellogg et al. 2013, Rodney and Paynter 2006). For white perch, naked gobies accounted for 95% of the identifiable fish species by weight. Direct comparisons of white perch and striped bass diets to the prey fields at each sampling site will be conducted as part of a companion project also funded by NOAA Chesapeake Bay Office (Award #: NA13NMF4570209: Integrated assessment of oyster reef ecosystem services: Macrofaunal utilization, secondary production and nutrient sequestration). This companion project will also provide data on abundance, biomass and distribution of small, reef-associated species including naked gobies, striped blennies, and oyster toadfish (Opsanus tau)

Amino acid metabolism in ribbed mussel gill tisue during hypersmotic stress: role of transaminases and pyruvate dehydrogenase

The cytosolic (cAAT) and mitochondrial (mAAT) aspartate aminotransferases were partially purified from gill tissue of the ribbed mussel, Modiolus demissus, and individually characterized with respect to heat stability, electrophoretic mobility, pH optimum, K(,m) for substrates, and reactivity with aminooxyacetic acid (AOA). The mAAT was a single isozymic form with a broad pH optimum and relatively low K(,m)s for aspartate, oxaloacetate, and (alpha)-ketoglutarate and high K(,m) for glutamate. The cAAT used for the kinetic studies was a single (homozygous) isozymic form, showed great variation in K(,m) and V(,max) with pH, and high K(,m)s for the amino acid substrates and low K(,m)s for the keto acid substrates. Both enzymes were inhibited to the same degree by AOA (I(,50) = 3 x 10('-6)M). In a physiological sense, it is hypothesized that the cAAT is involved more with aspartate synthesis and the mAAT with aspartate catabolism;Differential centrifugation of ribbed mussel gill tissue homogenates and extraction of the mitochondrial fraction demonstrated that most (72%) alanine aminotransferase (AlAT) activity was mitochondrial. Subsequent characterization of the cytosolic activity indicated that it had properties identical to those demonstrated by the mitochondrial enzyme. Both enzyme fractions showed little variation in V(,max) with pH, had low K(,m)s for keto acid substrates, and were inhibited by aminooxyacetic acid (AOA), L-cycloserine, and (beta)-chloro-L-alanine. It appeared that the AlAT in ribbed mussel gill tissue was strictly mitochondrial and that alanine production and synthesis during hypoxia or during hypo- or hyperosmotic stress must be mitochondrial;The pyruvate dehydrogenase complex has been demonstrated in high speed (150,000 g) pellet preparations from sonicated ribbed mussel gill mitochondria. The complex is inhibited by low (<100 mM) chloride concentrations, succinate and ATP. ATP inhibition was enhanced by NaF and reversed by high Mg('++) concentrations in the absence of NaF. Pyruvate and thiamine pyrophosphate inhibited the inactivation by ATP. Factors involved in the ATP inhibition and Mg('++) reversal are lost with freezing or cold storage. The activity of the complex may be regulated by a phosphorylation/dephosphorylation mechanism.</p