Number Of Oysters Research Articles

Comparative analysis of anatomical structure of wood plant leaf under exposure to volatile organic compounds

Industrial enterprises of thermal power engineering, fuel, chemical and petrochemical industry, mechanical engineering, non-ferrous metallurgy are sources of volatile organic compounds, the emissions of which can now reach a significant amount due to changes in technological processes. Studying the effect of volatile organic compounds on changes in anatomical parameters of a plant sheet is a little-studied aspect compared to exposure to oxides of nitrogen, carbon, sulfur, ammonia, heavy metals. The aim of the work was therefore to study the anatomical features of the tree leaf as adaptive features under the influence of emissions from industrial plants containing selected volatile organic compounds. Time preparations of the cross section of the leaf were used for anatomical studies. The thickness of the epidermis, the mesophyll, the number of upper and lower epideric cells, the number of wellheads and their width, the size of the conductive beam, the palisadity coefficient (the ratio of the thickness of the columnar mesophyll to the sum of the thickness of the columnar and spongy mesophyll) and the oral index (the ratio of the number of wellheads to the total number of epidermal cells). Impressions of the upper and lower epidermis were made with colorless varnish. As objects for studying the features of the anatomy of the leaf were chosen the leaves of a number of species of wood plants, which are among the most common near the industrial enterprises of the city of Gomel: drooping birch Betula pendula Roth., maple holly Acer platanoides L. Leaf samples were taken in the zone of influence of emissions of industrial enterprises containing xylenes and butylacetate (JSC «Gomel plant leaves and normals»), as well as benz(a)pyrene (heat and power plant). As a result of the studies, the cells of the columnar mesophyll in the birch leaves were found to have the greatest sensitivity to organic toxicants (xylenes and butylacetate) at the end of the vegetation compared to the maple holly leaves and the parameters of the spongy mesophyll. Drooping birch was characterized as the species in which sclerenchyma in the region of the conducting bundle under technogenic conditions was the thinnest, especially at the beginning of the growing period. Also in birch, when growing around industrial plants, there was a decrease in the number of cells of the upper and lower epidermis compared to control in most variants, especially the upper epidermis in samples exposed to xylenes and butylacetate at the beginning of the growing period. Maple holly showed a more intense decrease in the number of oysters and the value of the oral index compared to control than birch. When exposed to the benz(a)pyrene of heat and power plant emissions, both wood plant species studied showed an increase in mesophyll palisadity coefficient during the most intensive sheet plate formation processes. The conducting bundles of the studied wood plants were characterized by a decrease in the largest diameter when growing under technogenic conditions, most intensively in may at the maple holly. In general, the study of anatomical features of leaf plates of wood plants when growing in the area of exposure to volatile organic compounds of industrial emissions is great interest in terms of understanding the adaptive mechanisms of plants to stress conditions. The seasonal dynamics of changes in anatomical parameters in the birch leaf was characterized by a decrease in their values in most cases in september compared to may in the territory of the industrial enterprises under consideration. In maple holly approximately in equal amounts there was both a decrease and an increase in anatomical parameters between may and september.

Incorporation of V. vulnificus into marine snow for oyster uptake and in vivo bacterial competition assays

Vibrio vulnificus is a significant human pathogen found in high numbers in oysters. Despite the environmental prevalence of V. vulnificus, clinical cases are uncommon. We hypothesised that in vivo competition between V. vulnificus and other strains/species resulted in the killing of hypervirulent strains, reducing clinical incidence. To assess this, we have developed an oyster model into which we can ensure ingestion of high quantities of V. vulnificus using a defined ‘marine snow’. Marine snow describes the aggregation of naturally occurring phytoplankton, bacteria, debris and other organic materials. Our marine snow substrate is comprised solely of the diatom, Thalassiosira pseudonana. Bottles containing artificial seawater, 109 T. pseudonana, V. vulnificus culture and hyaluronic acid were rotated at 16 r.p.m. for 24 h to generate aggregates. V. vulnificus-containing marine snow was added to beakers holding individual oysters. Following 24 h uptake, oyster stomachs were excised and homogenised in PBS. The resulting suspension was serially diluted for plate-counts and DNA extracted for downstream qPCR analysis. Diatom-based aggregates present a controllable and reproducible model for incorporating V. vulnificus into marine snow. Using this methodology, we demonstrate greater uptake of V. vulnificus by oysters than any current study. This has potential applications for future in vivo work studying a range of microorganisms in oysters, such as other human pathogens or those of interest to aquaculture. Future work will undertake in vivobacterial competition assays to determine the role that intra-/inter-species competition has on the ecology of V. vulnificus and whether this impacts the clinical incidence.

Assessment of bio-accumulation of bacteria in oysters from shellfish growing waters in Ashtamudi Lake (Kerala, India): A RAMSAR wetland

Oysters are commercially cultured from the Ashtamudi Lake in India, and support 12,000 tonnes of bivalve fisheries/year. Oysters and oyster growing waters were sampled from July 2012 to June 2013 for analysis of total coliforms (TC), faecal coliforms (FC), Escherichia coli, faecal Streptococci (FS) and total plate counts (TPC). E. coli MPN values in oyster growing waters were below the threshold limits set by the USFDA and EU during the months of December to April. Seasonally, the highest MPN values for E. coli were obtained during the monsoon season (June–September), and this trend gradually decreased during the post-monsoon (October–January) and pre-monsoon (February–May) periods. E. coli displayed a significant (p<0.01) variation in accumulation during different seasons. A strong negative correlation (R2=−0.70, p<0.05) between temperature and E. coli numbers in oysters was observed, while rainfall and E. coli were positively correlated (R2=0.695, p<0.05). Hence, we strongly recommend depuration and proper cooking of oysters before consumption during the monsoon season.

Settlement, Growth, and Survival of Eastern Oysters on Alternative Reef Substrates

ABSTRACT Restoration of the native eastern oyster (Crassostrea virginica) has been severely hindered by the dwindling supply and rising costs of fossil and new oyster shell (OS) for use in reef restoration. Consequently, emphasis has shifted to the use of alternative oyster reef materials, which need to be tested for their effectiveness as settlement substrate. Furthermore, low recruitment of wild larvae has also impeded restoration, indicating a need to assess the potential of field setting of cultured larvae. We experimentally examined oyster settlement, growth and survival on unconsolidated OS, vertically embedded oyster shell (ES) in concrete, and concrete Oyster Castles (OC) in field and mesocosm experiments. In addition, we examined settlement success of cultured larvae in the mesocosm experiment. In the field experiment, juvenile recruitment was 3× higher on castles and unconsolidated shell than on embedded shell. Castles retained 4× the number of oysters and hosted 5× the biomass than embedded she...

The Biology of Vibrio vulnificus.

Vibrio vulnificus, carrying a 50% fatality rate, is the most deadly of the foodborne pathogens. It occurs in estuarine and coastal waters and it is found in especially high numbers in oysters and other molluscan shellfish. The biology of V. vulnificus, including its ecology, pathogenesis, and molecular genetics, has been described in numerous reviews. This article provides a brief summary of some of the key aspects of this important human pathogen, including information on biotypes and genotypes, virulence factors, risk factor requirements and the role of iron in disease, association with oysters, geographic distribution, importance of salinity and water temperature, increasing incidence associated with global warming. This article includes some of our findings as presented at the "Vibrios in the Environment 2010" conference held in Biloxi, MS.

Analysis of Vibrio vulnificus Infection Risk When Consuming Depurated Raw Oysters

A beta Poisson dose-response model for Vibrio vulnificus food poisoning cases leading to septicemia was used to evaluate the effect of depuration at 15°C on the estimated health risk associated with raw oyster consumption. Statistical variability sources included V. vulnificus level at harvest, time and temperature during harvest and transportation to processing plants, decimal reductions (SV) observed during experimental circulation depuration treatments, refrigerated storage time before consumption, oyster size, and number of oysters per consumption event. Although reaching nondetectable V. vulnificus levels (<30 most probable number per gram) throughout the year and a 3.52 SV were estimated not possible at the 95% confidence level, depuration for 1, 2, 3, and 4 days would reduce the warm season (June through September) risk from 2,669 cases to 558, 93, 38, and 47 cases per 100 million consumption events, respectively. At the 95% confidence level, 47 and 16 h of depuration would reduce the warm and transition season (April through May and October through November) risk, respectively, to 100 cases per 100 million consumption events, which is assumed to be an acceptable risk; 1 case per 100 million events would be the risk when consuming untreated raw oysters in the cold season (December through March).

Snapshot of Vibrio parahaemolyticus densities in open and closed shellfish beds in Coastal South Carolina and Mississippi.

Vibrio parahaemolyticus is a Gram negative, halophilic bacterium that is ubiquitous in warm, tropical waters throughout the world. It is a major cause of seafood-associated gastroenteritis and is generally associated with consumption of raw or undercooked seafood, especially oysters. This study presents a snapshot of total V. parahaemolyticus densities in surface waters and shellstock American oysters (Crassostrea virginica) from open and closed shellfish harvesting areas, as well as "more rural areas" on two different US coasts, the Atlantic and the Gulf. Sampling was conducted from 2001 to 2003 at five sites near Charleston/Georgetown, SC and at four locations in the Gulfport/Pascagoula, MS area. V. parahaemolyticus numbers were determined by a direct plating method using an alkaline-phosphatase-labeled DNA probe targeting the species-specific thermolabile hemolysin gene (tlh) that was used for identification of bacterial isolates. The greatest difference between the two coasts was salinity; mean salinity in SC surface waters was 32.9ppt, whereas the mean salinity in MS waters was 19.2ppt, indicating more freshwater input into MS shellfish harvesting areas during the study period. The mean V. parahaemolyticus numbers in oysters were almost identical between the two states (567.4 vs. 560.1CFU/g). Bacterial numbers in the majority of surface water samples from both states were at or below the limit of detection (LOD = <10CFU/mL). The bacterial concentrations determined during this study predict a low public health risk from consumption of oysters in shellfish growing areas on either the Gulf or the Atlantic US coast.

Corrigendum: Bivalve-enhanced nitrogen removal from coastal estuaries

Data on N assimilation into oyster tissues were compared with N in phytoplankton (Ph N) to calculate the number of oysters required to completely remediate N loads and determine the percent N removed by oysters at different planting densities and areas. After publication, we discovered a conversion error that was made when calculating the Ph N load relative to estuary volume, and we accounted for the relatively high estimates of Ph N we reported compared with values reported elsewhere. Corrected estimated values for Ph N available to oysters based on estuary volume had a range of 44–281 kg N (Table 1), assuming a consistent chlorophyll a concentration without replacement for the 153-day estimated growing season (necessarily a conservative estimate). Under this reduced estimated Ph N load, a minimum of 250 000–770 000 oysters would be required to assimilate Ph N in the estuaries we studied (Table 1), assuming the entire estuary was available and suitable for planting. N removal capacity was estimated at 17%–100% of Ph N (consistent with or greater than the N removal capacity estimated for total land-derived N loads), with total Ph N removal possible in scenarios where oysters were planted at densities ≥550·m−2. Since estimates of Ph N depend heavily on estuary-specific physical and chemical attributes not accounted for in this study, as with our original estimates, we suggest these values be used with caution and estuary-specific empirical data be collected for application to other locations and growing conditions. This correction does not change our total land-derived N load comparisons or the conclusions of our originally published work, that a removal capacity of 1%–15% of land-derived N is most realistic given conditions typical to restoration and aquaculture activities in USA estuaries.

Distribution and survival of Vibrio vulnificus genotypes in postharvest Gulf Coast (USA) oysters under refrigeration

The effect of refrigeration on the seafood-borne pathogen Vibrio vulnificus was investigated in terms of genotype selection and persistence in refrigerated oysters. Naturally occurring numbers of V. vulnificus in oysters from two different locations were compared during a 2-week period under refrigeration conditions. At different time points, V. vulnificus isolates were recovered from oysters and ascribed to 16S rRNA gene type A, B or AB using restriction fragment length polymorphism. Initial V. vulnificus numbers were higher than 10(4) most probable number (MPN) g(-1) and remained unchanged throughout the duration of the study. 16S rRNA gene type B isolates accounted for 53% of the isolates recovered. Amplified fragment length polymorphism analysis confirmed the high genetic variability previously observed within this species but revealed the presence of two main genetic groups within the species that matched 16S rRNA gene ascription. Vibrio vulnificus numbers in oysters did not significantly declined over the shelf life of the product and refrigeration did not select for specific V. vulnificus types. The prevalence of V. vulnificus 16S rRNA gene type B in oysters was higher than previously reported from the same geographic area and was not significantly reduced during the storage period. Vibrio vulnificus is divided into two clear genotypes, regardless of the genetic marker used.

Gene Expression of Cold Shock and Other Stress-Related Genes in Vibrio vulniflcus Grown in Pure Culture under Shellstock Temperature Control Conditions

Shellstock refrigeration after harvesting is recommended to prevent further increases in Vibrio vulniflcus numbers in oysters, but it could potentially induce a cold shock response in this bacterium. V. vulniflcus was incubated at 35, 25, 20, and 15°C and then subjected to 7.2 and 4°C for 1 week. A cold-adaptation response that enhanced cell culturability was observed when cells were incubated at 15°C prior to cold shock at 7.2°C. In vitro cold shock gene expression was analyzed by reverse transcriptase PCR (RT-PCR). The expression of cold shock genes csp1 and csp5 (homologous genes to cspA and cspV) remained constant, despite cold shock. However, the transcript of csp3 was constitutively expressed before and after cold shock, with a few exceptions. The synthesis of csp3 mRNA in V. vulniflcus C7184Tr (an avirulent strain) was induced only after 15°C incubation and cold shock at 4°C. The expression of csp4 was repressed after cold shock. Our data showed that the csps tested in this study are not cold inducible. The transcripts of two oxidative stress-related genes, oxyR and katG, showed different induction patterns among strains after cold shock, suggesting that V. vulniflcus cells encountered oxidative stress during cold shock.

INTRAPOPULATIONAL VARIATION IN CRASSOSTREA VIRGINICA (GMELIN 1971) IS ASSOCIATED WITH THE HOST SIZE BUT NOT WITH DISEASE STATUS OR DEVELOPMENTAL STABILITY

Vibrio vulnificus is an important human pathogen, which occurs naturally in estuarine waters and in large numbers in oysters. The levels of V. vulnificus in shellfish vary greatly, and the causes of this variation are not well understood. A protozoan parasite, Perkinsus marinus, is a pathogen of oysters, which was earlier suggested to increase susceptibility of oysters to bacterial infections. A goal of our study is to determine whether the presence of P. marinus plays a role in determining the incidence or magnitude of V. vulnificus infection in oysters. We also used fluctuating asymmetry (FA) of shell weight as an indicator of developmental instability and thus of microbially-induced physiological stress in oysters. We harvested 155 adult oysters (Crassostrea virginica) from a small environmentally homogeneous site in North Carolina, and examined them for V. vulnificus and P. marinus infections. V. vulnificus and P. marinus were detected in 88% and 73% of the oysters, respectively. The incidence of the two pathogens in these oysters was independent, with no greater tendency to infection by V. vulnificus in oysters infected by P. marinus and vice versa. V. vulnificus loads per g tissue weight varied by over four orders of magnitude in oysters of the same size, weight and age, which were harvested from this single habitat. V. vulnificus loads were found to be unaffected by age of oysters (and thus by the length of exposure to this pathogen). On the contrary, there was a significant decrease in both incidence of V. vulnificus infection and tissue loads of this bacterium with the host weight, possibly indicating growth dilution. Infection with V. vulnificus or P. marinus did not affect FA of shell weight in oysters. Overall, our findings suggest that infection by P. marinus does not predict V. vulnificus loads in C. virginica, nor did oysters infected with either of these pathogens exhibit physiological stress that results in developmental instability.

Vertical structure and predator refuge mediate oyster reef development and community dynamics

In addition to their economic value, oysters supply a number of critical ecosystem services such as controlling eutrophication, recycling nutrients, and providing habitat for many invertebrates and fishes. Thus, the maintenance and restoration of oyster reefs is vital for properly functioning estuarine ecosystems. We hypothesized that spatially heterogeneous and refuge-rich reefs are superior habitats for oysters and associated invertebrates and fishes. If this is shown to be the case, then vertical structure and refuge should be included in the design of newly constructed oyster reefs and conserved in existing reefs. To test our hypothesis, models were built as concrete blocks into which shells were placed horizontally, vertically, and widely spaced, and vertically and closely spaced. Respectively, the units represent horizontal orientation with no refuge (HNR), vertical orientation with no refuge (VNR), and vertical orientation with refuge (VWR). Flume studies of velocity distributions over each model type showed distinctive differences that may contribute to differential settlement on the models in the absence of predators or sediment. A subsequent settlement study in the same flume showed significantly higher settlement densities to horizontal shells than to vertical shells regardless of refuge (HNR>VNR=VWR). This result indicates the primary importance of settlement surface orientation (horizontal vs. vertical) over predation refuge when predators are absent. In contrast, two field recruitment studies indicated that the importance of orientation relative to predation refuge might depend on sedimentation rates. When sedimentation was low, the number of oysters and barnacles (live, dead, and total) was significantly higher on no-refuge models than on refuge models (HNR=VNR>VWR). However, percent mortality was lower on the refuge models than on the no refuge models (HNR=VNR>VWR). This leads to a conclusion that although fewer oysters may settle on refuge shells, those that do have a higher rate of survival. In a year when sedimentation was high, recruitment and survival of oysters, barnacles, and bryozoans was higher on vertical models regardless of refuge. In aggregate, our results indicate that both vertical orientation and predation refuge are critical to the early development of the oyster reef community and should be included in restoration designs.

Oyster Crassostrea virginica Spat Settlement as it Relates to the Restoration of Fish River Reef in Mobile Bay, Alabama

Abstract.— Oyster spat settlement at four oyster reefs in Mobile Bay, Alabama, USA, was studied from August through October 1998 and May through mid November 1999. Spat collectors at the reefs were replaced every 2 wk and spat‐set estimated as number of oysters per meter square per day. Water quality data at Fish River Reef was monitored using remote sensors. Spat‐set data revealed significant variation between the four sites and between the 2 yr. Spat settlement was 5 to 10 times greater at the other three reefs than at Fish River Reef. Dates and intensity of oyster settlement at Fish River Reef were different from dates and intensity of oyster settlement at Shell Bank Reef, both on the eastern side of the bay. However, settlement was similar between Cedar Point Reef and White House Reef, both on the western side of the bay. Spat set appears to occur 3 wk after a rapid decline in water temperature, provided adequate oxygen concentrations are present at the time of settlement. Data collected suggest that intensity of settlement at Fish River Reef is considerably less than at other reefs in this study but could be adequate to reestablish the reef, if cultch and environmental conditions are suitable. The data also suggest that the source of larval oysters at Fish River Reef is different from the source of larval oysters at the other sites tested in the present study.

Predation by fish on intertidal oysters

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 187:203-211 (1999) - doi:10.3354/meps187203 Predation by fish on intertidal oysters M. J. Anderson*, S. D. Connell Centre for Research on Ecological Impacts of Coastal Cities, Marine Ecology Laboratories, A11, University of Sydney, New South Wales 2006, Australia *E-mail: mjanders@bio.usyd.edu.au ABSTRACT: Experiments in many parts of the world have indicated that sessile intertidal organisms are affected by fish predation. Farming of oysters Saccostrea commercialis (Iredale & Roughley) and Crassostrea gigas (Thunberg) in New South Wales, Australia, depends on their natural recruitment and growth on intertidal structures in estuaries. We investigated the effects of predation by fish on numbers of oysters recruiting to experimental panels of 3 different sizes. We tested effects of excluding fish of different sizes using different sizes of mesh (12.5 and 50 mm). Numbers of oysters were significantly reduced on panels open to predatory fish. Numbers of oysters per unit area and subsequent predation on them did not vary, however, across 3 different sizes of panels, indicating that predation was not dependent on patch size. Mortality on panels open to predation averaged 40.0% (±4.3% SE). Fish also significantly altered the distribution of sizes of oysters. The effect of predation was almost entirely attributable to toadfish Tetractenos spp. Previous knowledge of the life history of oysters and succession in these intertidal assemblages suggests that effects of predation may not, however, have important long-term consequences on natural populations. KEY WORDS: Oysters · Fish · Size-specific predation · Experimental cages · Recruitment · Post-settlement mortality Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 187. Publication date: October 14, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Distribution of heavy metals in soft bodies and shell cavity fluids of Crassostrea gigas.

A number of oysters were collected at the intertidal zone and kept in ice boxes, from which the specimens were serially picked up over 17 times at the interval of 6 hours for 96 hours. Copper, Zn Fe, Mn and Cd contents in soft bodies and shell cavity fluids were determined. At the same time, nitrogen contents in shell cavity fluids were also determined. Regression and correlation coefficients between the metal and nitrogen contents and the serial times were not significant. Namely, the contents fluctuated independently without regard to the elapsed time. This proved that the preserving method was adequate to confine the metabolic activity of the specimen oysters. Of the total absolute amounts of Cu and Zn in soft bodies and shell cavity fluids, more than 94% distributed in soft bodies, and consequently, less than 1% of the two metals existed in the fluids. Cadmium more than 98%, Mn more than 97% and Fe more than 96% distributed in soft bodies. Although the levels of metal contents in shell cavity fluid were clearly less than those in soft bodies, the levels in the fluids were surprisingly higher than those in normal sea waters. Taking into account the fluctuations of the heavy metal and the nitrogen contents in the shell cavity fluids mentioned above: it was suggested that the pre-concentration in shell cavity fluid through the uptake process of heavy metals is the main factor for the high heavy metal contents in the fluids. Since, for specimens frozen deeply with shell valves, heavy metal contents in shell cavity fluid have been determined for a long time together with those in soft bodies, heavy metal contents of lamellibranchs are estimated somewhat higher than those obtained from fresh specimens.

The potential food poisoning hazard ofVibrio parahaemolyticusin New Zealand Pacific oysters

Abstract The level of Vibrio parahaemolyticus was generally very low in Pacific oysters sampled from 4 New Zealand oyster farms between November 1982 and May 1983. Of the 149 samples collected, only one was found to contain greater than the 1000 organisms g‐1regarded as the maximum allowable by international standards (International Commission on Microbiological Specifications for Foods 1982: Micro‐organisms in Foods, Vol. 2. Academic Press, New York). V. parahaemolyticus was detected in 57% of the oyster samples, but 95% of these contained less than 10 organisms g‐1. Maximum levels appeared to coincide with high water temperatures at the farm sites. Chilling, freezing, and depuration reduced V. parahaemolyticus numbers in oysters after harvest. However, holding at ambient temperatures (19–25°C) resulted in up to a 35‐fold increase in organism numbers with a maximum after one day. The food poisoning hazard from V. parahaemolyticus in New Zealand‐grown Pacific oysters thus appears to be minimal. Recommenda...

AN INDUSTRY REVIEW OF THE OPERATIONS AND ECONOMICS OF MOLLUSCAN SHELLFISH HATCHERIES IN WASHINGTON STATE

ABSTRACTMolluscan shellfish hatcheries have been in operation since 1969 in Washington State. The progress and overall performance of these facilities since that time are reviewed. Hatchery operations are discussed from the viewpoint of biological methods and financial success.Biologically, a comparison of hatchery seed is made with the imported Japanese seed and the domestically cultched seed in Washington State. The oyster seed market is analyzed in relation to quality of seed, number of oysters per shell, competition from natural seed sources, failure to standardize a case of seed and the inability to supply promised markets.Economically, the discussion is of the advantages and disadvantages of a hatchery operation with reference to facility size, operational economics and market demand.

Gaping Oysters by Shock Wave Energy

A preliminary study showed that oysters (Crassostrea virginica) may be gaped for mechanical shucking by use of shock wave energy. Among the devices available for producing shock wave energy, the General Electric Electrohydraulic System and the PAR Air Gun were examined. Results indicate that as much as 87% of the total number of oysters subjected to treatment can be gaped at a rate of about one oyster per second.

Ecology of Fouling Organisms in a Polluted Area

LITTLE is known about the growth and development of fouling organisms in polluted areas. At times, large numbers of oysters and cockles have been killed by crude or fuel oil in certain beds along the French and English coasts1. On the other hand, it has been demonstrated2 that oysters are very tolerant of crude oil overlayering the water, emulsified in the water or periodically sprayed on the oysters. This subject has been reviewed quite recently3. The work reported here was carried out to study the attachment and growth of fouling organisms in a very polluted area of Pireus Port.

The Effects of the Orientation of Clutch Material on the Setting of the Sydney Rock Oyster

In 1945–46 in Port Hacking, N.S.W. there was some spawning over the entire year, but successful spat-falls occurred only over the summer, with the greatest number in November and again in March. On every 12-in. length of fibrocement slat approximately 24 oyster spat were present (on all faces) 12 months after the slats were set out. Thus on the average a four foot slat carried 96 oysters or approximately four oysters every five square inches of surface. A greater number of oysters settled when the slats were less than half an inch apart than when the slats were an inch apart. When the slats were one inch apart the central portion of the slats carried more oysters than the ends, but when the slats were within half an inch of each other the numbers at the ends and on the middle section were about the same. When the slats are within half an inch those oriented with the long axes parallel with the current show greater catches than those perpendicular to the current. However, when the slats are further apart the reverse is the case. The horizontal portion of the broad surface supplies the highest catches, but the catch is more evenly distributed when they are vertical, and this would permit better growth. The ratio of the catches on upper horizontal, lower horizontal, and vertical surfaces is similar to the ratio found by Schaeffer for O. gigas, which is a similar type oyster to O. commercialis. There is a horizontal gradient on the vertical surface across the batteries such that the number of oysters on the surface facing a particular direction increases on the columns more remote from that direction. There is a vertical gradient on the vertical and upper surfaces such that the number of oysters caught increases on the lower rows of vertical surfaces, but the evidence is anomalous for the horizontal surfaces. The discussion of the possible factors causing the pattern of set reveals that the reaction to light could be an explanation. But there are other explanations which are equally valid, and the experimental design was not such as to reveal the true causes. The practice in Australia of using closely bundled cultch material is a good one; but there is a possibility that better total catches would ensue if the cultch set out in spring were removed to growing areas in January and new cultch set out to catch the autumn spat fall.