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

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

Seawater carbonate chemistry and respiration of blue crab Callinectes sapidus

Quantifying the physiological impact of environmental stressors on living organisms is critical to predicting the response of any given species to future climate scenarios. Oxygen consumption rates (μmol/g/min) were measured to examine the physiological response of the juvenile blue crab Callinectes sapidus from the Chesapeake Bay (Patuxent River, Maryland) to elevated temperature and dissolved carbon dioxide in water (pCO2) reflective of projected future climate scenarios. Treatment levels were selected to represent current conditions in the Chesapeake Bay (26°C and 800 μatm) and conditions predicted to occur by the year 2100 (31°C and 8,000 μatm). Crabs were exposed in a factorial design to these conditions throughout two successive molts (approximately 30 days). At the end of the exposure, the oxygen consumption rates of individual crabs were determined over at least a 10-h period using a flow-through respiration chamber equipped with optical oxygen electrodes. No significant effect of temperature or pCO2 on oxygen consumption was observed, suggesting the absence of a respiratory impact of these two climate stressors on juvenile blue crabs. Oxygen consumption rates were also determined for crabs that experienced a rapid increase in temperature without prior acclimation. The oxygen consumption rate of crabs may have acclimated to increased temperature during the 30-day exposure period before respiratory measurement. This potential acclimation, combined with high individual variability, and a relatively small difference in temperature treatments are likely the cause for the lack of a statistically significant difference in mean oxygen consumption rates by temperature in the core experiment. The results of this study suggest that the blue crab may be quite resilient to future climate stressors and underscore the need for species-specific studies to quantify the effects of climate change on estuarine crustaceans

Acute osmotic tolerance of cultured cells of the oyster pathogen Perkinsus marinus (Apicomplexa : Perkinsida)

Cultured Perkinsus marinus cells were exposed for 24 hr to salinities of 0, 3, 6, 9, 12 and 22 ppt at temperatures of 1, 5, 10, 15 and 28°C in artificial seawater (ASW) and to the same salinities at 28°C in ASW with the osmotic concentration adjusted with sucrose to the equivalent of 22 ppt. At 28°C mortality increased as salinity decreased below 22 ppt. Mortality was greater than 99% at 0 ppt and greater than 90% at 3 ppt. Mortality was 70% at 6 ppt, 43% at 9 ppt and 20% at 12 ppt. Mortality was low (\u3c5%) and equal to that at 22 ppt in all treatments where osmotic concentration was maintained with sucrose. Mortality occurred rapidly, within 5 min of exposure to experimental conditions. In the region where mortality was most sensitive to salinity changes (6-12 ppt), lower temperature caused an increase in mortality, but the temperature effect was significant only at 9 ppt. © 1994

Composition, Shell Strength, and Metabolizable Energy of Mulinia lateralis and Ischadium recurvum as Food for Wintering Surf Scoters (Melanitta perspicillata).

Decline in surf scoter (Melanitta perspicillata) waterfowl populations wintering in the Chesapeake Bay has been associated with changes in the availability of benthic bivalves. The Bay has become more eutrophic, causing changes in the benthos available to surf scoters. The subsequent decline in oyster beds (Crassostrea virginica) has reduced the hard substrate needed by the hooked mussel (Ischadium recurvum), one of the primary prey items for surf scoters, causing the surf scoter to switch to a more opportune species, the dwarf surfclam (Mulinia lateralis). The composition (macronutrients, minerals, and amino acids), shell strength (N), and metabolizable energy (kJ) of these prey items were quantified to determine the relative foraging values for wintering scoters. Pooled samples of each prey item were analyzed to determine composition. Shell strength (N) was measured using a shell crack compression test. Total collection digestibility trials were conducted on eight captive surf scoters. For the prey size range commonly consumed by surf scoters (6-12 mm for M. lateralis and 18-24 mm for I. recurvum), I. recurvum contained higher ash, protein, lipid, and energy per individual organism than M. lateralis. I. recurvum required significantly greater force to crack the shell relative to M. lateralis. No difference in metabolized energy was observed for these prey items in wintering surf scoters, despite I. recurvum's higher ash content and harder shell than M. lateralis. Therefore, wintering surf scoters were able to obtain the same amount of energy from each prey item, implying that they can sustain themselves if forced to switch prey

Dry, ash, and organic matter masses of <i>Ischadium recurvum</i> collected in winter relative to shell length.

<p>Dry mass (DM; mg), ash mass (M_ash; mg), and organic matter (OM; mg) of <i>Ischadium recurvum</i> (including shell) as a function of length (mm) collected from the Chesapeake Bay in January, February, and March 2007. All regressions were significant at the 5% level (p<0.0001).</p

Dry, ash, and organic matter masses of <i>Ischadium recurvum</i> collected seasonally relative to shell length.

<p>Dry mass (DM; mg), ash mass (M_ash; mg), and organic matter (OM; mg) of <i>Ischadium recurvum</i> (including shell) as a function of length (mm) collected from the Chesapeake Bay in winter, spring, and summer. All regressions were significant at the 5% level (p<0.0001).</p

Amino acid amounts relative to lysine for six size classes of <i>Ischadium recurvum</i>.

<p>Amino acid amounts relative to Lysine for each size class (6–12, 12–18, 18–24, 24–30, 30–36, 36–42 mm) of <i>Ischadium recurvum</i> collected from the Chesapeake Bay in spring and winter 2007. Asp = Aspartic acid; Asn = Asparagine; Thr = Threonine; Ser = Serine; Glu = Glutamic acid; Gln = Glutamine; Gly = Glycine; Ala = Alanine; Val = Valine; Ile = Isoleucine; Leu = Leucine; Tyr = Tyrosine; Phe = Phenylalanine; Lys = Lysine; His = Histidine; and Arg = Arginine.</p