John W. Ewart

Maximum ration of four algal diets for the oyster Crassostrea virginica Gmelin

Abstract The rate of removal of four species of alga from suspension by the oyster Crassostrea virginica was determined. The number of cells removed per hour depended upon the size of algal cells, but the total dry weight of algal material removed over 24 h was independent of size. Filtration rate was dependent upon the density of the algal suspension, and large quantities of pseudofeces were produced by oysters filtering algae from suspensions denser than 10 μg/ml. Oysters showed periods of high filtering activity and periods of relative quiescence during experimental trials of 24 h duration. Based on the periodic filtering activity of the oysters, a discontinuous feeding regime is proposed along with an equation predicting the maximum daily ration of oysters of various sizes.

An exploratory study with the proton microprobe of the ontogenetic distribution of 16 elements in the shell of living oysters (Crassostrea virginica)

Study of the chemical composition of shell of exoskeletonous organisms in the past has required the sacrifice of the organism. Because the beam of the proton microprobe is relatively nondestructive and analyzes the surface layer of the shell, organisms do not have to be killed. The present paper presents results of a preliminary experiment in which distribution of elements (Na to Sr) in shell of living juvenile oysters, Crassostrea virginica (Gmelin), was studied in situ with a proton microprobe at monthly intervals for four months. The relative concentration of 16 elements was measured in the newly deposited prismatic edge of the right valve of three oysters reared in controlled laboratory conditions. Na, Mg, Al, Si, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Cu, Zn, Br, and Sr were detected in concentrations as low as a few parts per million relative to the concentration of standards added to pure CaCO3. Concentration of elements varied nominally among shells of the three individual oysters and in their successive ontogenetic stages. Fluctuations in concentration of Na, Mg, S, Cl, Ca, Mn, Fe, Cu, and Zn were generally similar in the two normally growing oysters, but differed from those in the oyster that stopped growing. Trends in concentration of Al, Si, and Sr were similar in the three oysters: those of Br were variable. Relative concentrations of Na, Cl, S, Mn, Fe, and Zn increased slightly with age of oysters, that of the other elements stayed relatively constant. Concentration of most elements was higher in shell than in seawater. Variable concentrations, especially of Na, Cl, and Si in valve edges, tend to support the hypothesis of earlier workers that separate mineral phases are present as impurities entrapped within the shell during calcification.

A tropical flagellate food for larval and juvenile oysters, Crassostrea virginica Gmelin

Abstract The relative values of Isochrysis galbana Parke and a high-temperature tolerant tropical flagellate Isochrysis aff. galbana (T-ISO) as foods for larval and juvenile oysters were compared. Two diets were utilized combining equal portions of either I. galbana or T-ISO and the centric diatom Thalassiosira pseudonana (3H). No significant differences in the growth of larval and juvenile oysters fed either diet were observed.

Ontogenetic trends of elements (Na to Sr) in prismatic shell of living Crassostrea virginica (Gmelin) grown in three ecologically dissimilar habitats for 28 weeks: a proton probe study

Abstract Distribution of 16 trace and minor chemical elements was examined ontogenetically with PIXE in the calcitic-prismatic margin of the shell of genetically close individuals of Crassostrea virginica (Gmelin) growing in three different marine habitats. Concentration of elements was also related to that in ostreid soft tissues and in suspended sedimentary particles in the ambient seawater. Distribution of the elements (Na, Mg, Al, Si, S, Cl, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, Br and Sr) was analyzed every 4 weeks (from May to November) with a non-destructive probe (PIXE) in newly deposited shell of the left valve, and in pigmented, non-pigmented and the right valve of 30 living C. virginica grown for 28 weeks in three dissimilar environments (10 oysters in each habitat): closed laboratory mariculture (HI), closed laboratory mariculture plus suspended sediment (HII) and natural flowing estuary (HIII). The same elements were analyzed weekly in suspended particles (on 0.4 μm Millipore filters) in the culture seawater in HI and HII and in ambient seawater in HIII; and at the end of the study in gills, adductor muscles, gonads and tissues of whole oysters. Elements in suspended sediment were concentrated primarily on the particles; not in the seawater filtrate. Barite crystals were present in some of the plankton samples. Growth rate was slowest in HI oysters, that of HII and HIII was similar and greater than that of HI. Seasonal trends in concentration of elements in valves in the different habitats varied. Ti remained relatively constant in HI valves during culture, but tended to decrease in HII, and increased in HIII. Other elements in HI tended to remain constant (Cu), or to increase (Fe); in HII some elements decreased conspicuously; in HIII some increases were prominent (Mg, Zn). A temporal change in level of many elements in shell paralleled that of the same element in suspended particles (Fe in HI, Mg, Cu, Zn in HIII); levels decreased in HII (Al, Ti, Fe). Parallelism of elemental concentration in shell and suspended particles was expressed as major peaks in both, mostly in HIII, the natural estuarine setting. For Ni, Cu, Zn and Br, especially in HII, peaks were out of phase. Comparison of concentration of elements in old (4th week of culture) and new (28th week) shell showed some trends among the three habitats; consistent association was evident in 10 elements in HIII. Maximal concentration of most elements occurred in the right valve. Pigmented shell contained slightly higher levels of most elements, but differences were only suggestive. After 28 weeks of culture, soft tissues contained several times the concentration of elements, and greater variability, than shell. Maximal concentration (biomagnification) of 13 elements took place in gills, gonads and adductor muscles, but not in whole oysters. There were clear differences in concentration of many of the elements among gills, gonads and adductor muscles in HI, HII and HIII, decreasing or increasing incrementally from HI to HII. Concentration of a few elements was associated in shell and tissues: in shell in HI, Fe, and in HIII, Zn increased during the 28 weeks and was also maximal in the three organs at the end of the study. All other elements (less Ca, Mn and Sr) were more concentrated in tissues than in shell, Zn, Cl and Br to a high degree. The relationship between biomagnification in different organs and the different microstructures of the shell is still unclear. The investigation focused on ecological aspects of biomineralization in living bivalves, an aspect little studied in the past. It was made possible by the use of the non-destructive PIXE probe and suggests a model from which to initiate further comparative studies.

Significance of environment and chronology on distribution of 16 elements (Na to Sr) in the shells of living oysters

Abstract Although use of the shells of bivalves has been suggested for monitoring metals in natural waters, little is known of the relationship of environmental conditions and age of molluscs with the concentration and distribution of elements in the shells. This report covers technical aspects as well as some preliminary results for an experiment designed to provide information of the effects of these parameters. Using in-air and -helium PIXE, monthly analyses, covering a 7 month period, have been made on new shells of 10 young American oysters growing in each of three habitats: (I) filtered Atlantic seawater, fed cultured algae; (II) as for I with addition of silt from the Broadkill estuary; and (III) Broadkill estuary. Weekly analyses were also performed on particulates collected on 0.45 μm pore filters. After the 7 month period oysters were sacrificed, and soft tissues dried to constant weight and analyzed. Although definitive conclusions cannot be drawn until the study is completed, results demonstrate certain effects which suggest further experimentation.

Consumer Analysis in Ethnic Live Seafood Markets in the Northeast Region of the United States

During September through November of 2006, in-store intercept surveys of consumers who buy live seafood in retail markets in New Jersey, New York, and Pennsylvania revealed that the average live seafood consumer makes 6.2 visits per month, spends

Prevalence of Perkinsus marinus (Dermo), Haplosporidium nelsoni (MSX), and QPX in Bivalves of Delaware's Inland Bays and Quantitative, High‐Throughput Diagnosis of Dermo by QPCR

14.80 per visit on live seafood, travels 7.8 miles mainly by car, and is purchasing for 3.7 people in his or her household. Consumers value physical appearance of the product over price, generally have no preference for either “Product of the USA” or imported, and generally have no preference for either wild-caught or farm-raised. Many had no preference whether their fish was alive or dead before leaving the store, but if the fish is to be slaughtered in-store, preferred to have their fish gutted or filleted. Consumers generally prefer to purchase live seafood during the winter months and on either a Friday or Saturday.

SURVEY OF ETHNIC LIVE SEAFOOD MARKET OPERATORS IN THE NORTHEASTERN USA

ABSTRACT. Restoration of oyster reef habitat in the Inland Bays of Delaware was accompanied by an effort to detect and determine relative abundance of the bivalve pathogens Perkinsus marinus, Haplosporidium nelsoni, and QPX. Both the oyster Crassostrea virginica and the clam Mercenaria mercenaria were sampled from the bays. In addition, oysters were deployed at eight sites around the bays as sentinels for the three parasites. Perkinsus marinus prevalence was measured with a real‐time, quantitative polymerase chain reaction (PCR) methodology that enabled high‐throughput detection of as few as 31 copies of the ribosomal non‐transcribed spacer region in 500 ng oyster DNA. The other pathogens were assayed using PCR with species‐specific primers. Perkinsus marinus was identified in Indian River Bay at moderate prevalence (∼40%) in both an artificial reef and a wild oyster population whereas sentinel oysters were PCR‐negative after 3‐months exposure during summer and early fall. Haplosporidium nelsoni was restricted to one oyster deployed in Little Assawoman Bay. QPX and P. marinus were not detected among wild clams. While oysters in these bays have historically been under the greatest threat by MSX, it is apparent that P. marinus currently poses a greater threat to recovery of oyster aquaculture in Delawares Inland Bays.

Low Incidence and Limited Effect of the Oyster Pathogen Dermo (Perkinsus marinus) on an Artificial Reef in Delaware's Inland Bays

From February through August of 2006, a team of two researchers visited 130 ethnic live seafood markets in the northeastern USA that sell live seafood. Operators of 27% of these locations completed a survey asking basic information about their businesses with respect to live seafood. This study provides interesting baseline information on these markets directly from market managers and operators. The markets surveyed have been in business for median of nine years. Sixty-three percent receive more than one live fish shipment per week. Fifty-five percent of markets sell over 227 kg of live seafood per month. Asians are the predominant clientele in most of these locations. Most market operators stated they prefer freshness and quality over price and availability. About the same number of markets identified strong sales during the winter months as those that indicated constant live seafood sales. Live tilapia and hybrid striped bass are the two most common products. Sixty-two percent of market operators view the live seafood section as very important to overall sales in their store and roughly one-quarter of those surveyed are considering expansion.

COMPARATIVE GROWTH OF Isochrysis galbana PARKE AND Isochrysis aff. galbana, CLONE T-ISO AT POUR TEMPERATURES AND THREE LIGHT INTENSITIES

Delawares Inland Bays comprise a large estuarine system with a restricted access to the Atlantic Ocean (Indian River Inlet). As part of a local oyster stock enhancement and restoration effort, we conducted a survey for the protozoan pathogenPerkinsus marinus (Dermo) in oysters from a newly established reef. Using standardized methods for the polymerase chain reaction (PCR) amplification of the non-transcribed spacer (NTS) region, we were surprised to find no detectable titers of this pathogen in the 30 oysters sampled in the first year of the project. The detection threshold of the PCR coupled with chemiluminescent detection was 30 fgP. marinus NTS DNA. We were able to detect a trace presence of this pathogen in a few hard clams (Mercenaria mercenaria) from the same locale, indicating that aPerkinsus sp. was present in the Inland Bay system. Subsequent monitoring of the reef system using a fluid thioglycollate assay over 3 yr revealed no epizootic outbreaks of this pathogen within the planted oyster population. Two large mortality episodes that did appear in the oyster population were attributable to abiotic conditions and not pathogen exposure. This study emphasizes that all potential sources of mortality in the environment are important to consider when designing oyster seeding projects. In the Delaware Inland Bays,P. marinus does not appear to have a large enough oyster host population to become a significant disease threat at present. Because of the low parasite incidence levels in the Inland Bay system in 2000, the James Farm oyster reef restoration project presents an ideal model system to follow the population dynamics between an oyster-host population and a latent or reservoir pathogen population.