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1.
Abstract

Sediment traps were deployed at Fish River Reef (FRR), a relic oyster reef on the eastern side of Mobile Bay, and at Cedar Point Reef (CPR), a productive oyster reef on the western side of Mobile Bay, Alabama, from July through October 1999. Sediment accretion at FRR was two to three times greater than sediment accretion at CPR. The proportions of particulate organic matter and ash in the sediment at the two sites were similar. The proportion of coarse to fine sediment at CPR was greater than at FRR. Also, the sediment at FRR was black and had a sulfide odor suggesting anoxia, while the sediment at CPR was brown and odorless. Various fishes and invertebrates colonized the sediment traps at CPR, while those at FRR were devoid of live organisms. Oyster spat had settled on the shells in the traps at CPR but not on those at FRR. Results suggest that in order to restore oysters at FRR, cultch material should be dispersed during periods of peak larval settlement to prevent inhibitory levels of siltation on cultch before spat settle.  相似文献   

2.
The Sydney rock oyster Saccostrea glomerata (Gould, 1850) industry acquired hatchery-produced spat selected for faster growth for the first time in January 2004. Selectively bred and non-selected (Control) spat produced concurrently were used to compare performance when grown under commercial conditions. Spat were distributed to farmers in seven estuaries in New South Wales. Individual farmers cultivated these oysters using their own techniques and growth and mortality were recorded quarterly. At each site, the two oyster types were cultivated using the same culture method, location and density. Growth was compared when oysters were 27 months of age. At this time, selectively bred oysters were significantly larger and heavier than Control oysters. The same result was obtained when oysters were compared at the point in time when selectively bred oysters had reached 50 g at each site. No significant difference was found for cumulative mortality between the selectively bred oysters and Control oysters across all sites. However, the seven sites had significantly different levels of cumulative mortality. Overall, the performance of selectively bred oysters was superior to the Control oysters and selectively bred oysters reached the 50 g bench mark within 29.3 months when averaged across all sites.  相似文献   

3.
Pacific oysters (Crassostrea gigas) were first observed in the Dutch Wadden Sea near Texel in 1983. The population increased slowly in the beginning but grew exponentially from the mid-1990s onwards, although now some stabilisation seems to be occurring. They occur on a variety of substrates such as mussel beds (Mytilus edulis), shell banks, dikes and poles. After initial settlement spat may fall on older individuals and congregate to dense clumps and subsequently form reefs. Individual Pacific oysters grow 3–4 cm long in their first year and 2–3 cm in their second year. Many mussel beds (Mytilus edulis) are slowly taken over by Pacific oysters, but there are also several reports of mussel spat settling on Pacific oyster reefs. This might in the end result in combined reefs. Successful Pacific oyster spat fall seems to be related to high summer temperatures, but also after mild summers much spat can be found on old (Pacific oyster) shells. Predation is of limited importance. Mortality factors are unknown, but every now and then unexplained mass mortality occurs. The gradual spread of the Pacific oyster in the Dutch Wadden Sea is documented in the first instance based on historical and anecdotal information. At the start of the more in-depth investigation in 2002, Pacific oysters of all size classes were already present near Texel. Near Ameland the development could be followed from the first observed settlement. On dense reefs each square metre may contain more than 500 adult Pacific oysters, weighing more than 100 kg per m2 fresh weight.  相似文献   

4.
1. Foveaux Strait, a narrow seaway that is exposed to heavy wave action and strong tidal currents, has been the subject of an oyster fishery for over 130 years. Before the oyster fishery commenced the seafloor was extensively covered by epifaunal reefs that were tidally‐oriented, linear aggregations of patch reefs. 2. Patch reefs are formed by the bryozoan Cinctipora elegans cemented by encrusting bryozoa, ascidians, sponges, and polychaetes. The molluscan epifauna is dominated by the oyster, Tiostrea chilensis and bysally attached bivalves. Mortality of oysters is probably lower and recruitment and growth may be higher within the reef habitat. 3. Fishers found commercial densities of oysters occurred only on epifaunal reefs. Fishers exploited local groups of reefs. These groups form the patchily distributed oyster beds characteristic of this fishery. 4. Dredging for oysters progressively modified reefs until oysters were the only epifauna remaining. Dredges caught oysters more efficiently after the catch bag no longer became saturated with other epifauna. This heightened efficiency allowed fishers to rapidly reduce oyster density to commercial extinction. Oyster density has not rebuilt on oyster beds abandoned by fishers. 5. The rate of modification of epifaunal reefs was slower during the early years of the fishery but has accelerated, especially over the last 37 years. Frequency of disturbance increased as the numbers of vessels fishing grew and fishers developed speedier dredging methods. Intensity of disturbance also increased as heavier dredges were introduced and allowed focused fishing of reefs. 6. Oysters became reduced to low densities in the eastern and central areas that fishers then abandoned. The commercially exploited area subsequently expanded to the limits of Foveaux Strait. 7. With accelerated modification of oyster habitat, disease mortality has become more important. 8. Attempting to rebuild the fishery by oyster enhancement may be more successful conjoined with habitat restoration. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

5.
To investigate the possibility of establishing oyster culture in Malta, growth trials with C. gigas and O. edulis were undertaken. The oysters were placed in floating cages at depths of 3 and 8 m at Marsaxlokk bay, Mistra bay and Rinella creek. These oysters were sampled at two-month intervals for their growth, meat-shell index and survival. The temperature, salinity, oxygen tension, chlorophyll-a levels and the levels of particulate matter in suspension in the water at the test sites were monitored concurrently. A programme of qualitative and quantitative analyses of the natural phytoplankton population was also carried out.O. edulis suffered catastrophic summer mortalities at all locations when the ambient temperature of the water reached about 25°C; this virtually rules out any possibility of starting any flat oyster industry using this system. As for C. gigas, Marsaxlokk bay 3 m appears to hold some promise for its culture. At this location, this species showed reasonable growth, relatively low mortality and normal shell growth. Although at Rinella overall growth of C. gigas was comparable to that at Marsaxlokk at 3 m, the Rinella oysters accumulated copper and exhibited abnormal and thickened shell growth with the result that the oysters were of a much inferior condition. Growth at Mistra (both depths) and Marsaxlokk 8 m was stunted.No clear correlation could be established between the performance of the oysters and the environmental parameters monitored. Several factors that may have been responsible for the observed differences in oyster performance are discussed. In particular, the nature of the water movements is thought to have played a key role in dictating the growth of the oysters.  相似文献   

6.
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7.
Growth, intensity of Perkinsus marinus (Levine) infection, and survival of synchronously spawned North Carolina (NC) and Chesapeake Bay‐heritage (CB) oysters, Crassostrea virginica (Gmelin) were evaluated under standard tray culture conditions at several sites in both regions (Wye River, Maryland; Mobjack Bay, Virginia; Pamlico River, NC and Bogue Banks, NC). Infection prevalence reached 100% in oysters held at all high‐ and moderate‐salinity sites, at which time the CB strain ceased to grow. Shortly after growth ceased, CB oysters exhibited mortality that rapidly progressed to 100%. Unlike the CB strain, growth continued in the NC strain despite high P. marinus prevalence. When mortality did occur in the NC strain, at a reduced rate of 37–40%, it was associated with higher intensity of P. marinus than the infection intensity correlated with death of CB oysters. At the low‐salinity site in NC, P. marinus infection persisted at low weighted prevalence throughout the latter portion of the culture period but was not associated with mortality of either strain. These trends in growth and disease resistance for the two strains demonstrate that aquaculture performance is related to the level of disease resistance in oyster strains, salinity of water in growing areas and virulence of P. marinus.  相似文献   

8.
通过2019年室内和野外附着实验,检验了牡蛎壳(新壳和旧壳)和生物膜(有生物膜和无生物膜)对牡蛎附着量的影响。室内附着实验表明,在生物膜处理下新壳上牡蛎附着量显著高于旧壳(P<0.05);而在无生物膜对照组中,新、旧壳上牡蛎附着量无显著差异(P>0.05)。野外附着实验发现,生物膜显著提升了旧壳上牡蛎附着量,但对新壳上牡蛎附着量无显著影响。通过2020年野外附着实验,检验了牡蛎壳(新壳和旧壳)和潮区(滩面以上0.6 m和1.1 m)对牡蛎和藤壶附着量的影响。牡蛎附着量在每个潮区中,15 d、45 d和70 d时新壳均显著高于旧壳(P<0.05)。藤壶附着量仅在0.6 m潮区中、15 d时新壳显著高于旧壳,而45 d和70 d时,各潮区中新、旧壳上藤壶附着量均无显著差异(P>0.05)。研究发现,总体来看新壳的附苗效果好于旧壳,这种差异涵盖了整个牡蛎繁殖、附着及补充的高峰期。因此,牡蛎礁修复中应优先选取新壳作为底物。  相似文献   

9.
The Damariscotta River estuary is a center of oyster culture in Maine, yet the comparative performance of flat oysters Ostrea edulis at different locations in this now Bonamia ostreae -enzootic estuary has not been assessed. Juvenile O. edulis were deployed in July 1997 among replicate floating trays at one estuarine (Little Point) and one marine site (Lowes Cove), and growth, mortality, and B. ostreae prevalence were compared through December 1999. Growth was faster at Little Point though oysters at both locations reached market size in less than three full growing seasons. Mortality was similar between locations except following a June 1998 rain event that decreased salinity more precipitously at Little Point. Cumulative mortality was greater at Little Point (45.8%) than Lowes Cove (26.7%). Surprisingly, B. ostreae was observed in only a single oyster from Little Point in May 1998. These data indicate that flat oysters in Maine may grow well across a wide range of environments, yet may demonstrate better survival at marine sites where salinity fluctuations are less extreme. While B. ostreae is likely still a threat, selection of sites where rapid growth to market size is possible may reduce its impact.  相似文献   

10.
When harvested, oysters represent a removal from the ecosystem of nutrients such as nitrogen (N) and carbon (C). A number of factors potentially affect nutrient content, but a quantitative understanding across the geographical range of the eastern oysters is lacking. This study was designed to quantify the relationships among various metrics of farmed eastern oysters near its northern geographical range focusing on nutrient content. Hatchery‐reared oysters were deployed in polyethylene bags at six sites, and were measured on multiple occasions from 2010 to 2012. A quadratic polynomial fit to the combined datasets for shell height indicated that on average a ‘cocktail’ size oyster (63 mm shell height) would be reached after 2 year, and ‘regular’ size (76 mm) would require 3 year. There were significant differences in growth rates and oyster nutrient content among the sites; means for %N in soft tissue ranged from 6.9 to 8.6, and 0.07 to 0.18 in shell. Per cent N in soft tissue and shell were highest at two sites at the mouths of rivers with elevated dissolved inorganic N concentrations in the water. Grand means (all sites, seasons and years combined) of soft tissue N and C for regular size oysters were 7.3% and 38.5%, respectively; and for shell N and C were 0.13% and 12.0% respectively. Our study extends the range of data on nutrient content of the eastern oyster to northern New England, and indicates that oyster size, seasonality, and nutrient concentration in ambient water potentially affect %N and %C content of oysters.  相似文献   

11.
A breeding program for Sydney rock oysters Saccostrea glomerata (Gould, 1850) has been selecting oysters for resistance to QX disease (Marteilia sydneyi) and winter mortality (Bonamia roughleyi) for three generations at three sites in Georges River, New South Wales, Australia. The experimental sites are located at the upper, middle and lower reaches of oyster growing areas in the estuary. QX disease mainly occurs in the middle and upper reaches and is most severe at the latter. Winter mortality on the other hand occurs mainly at the lower and middle reaches and is most severe at the former. Progeny of third‐generation Sydney rock oyster breeding lines were evaluated for resistance to both QX disease and winter mortality against a non‐selected control. Line 1, selected for QX disease resistance at the upper estuary site, had excellent resistance to one season of exposure to disease, but suffered high mortality during the second season of exposure. However, these oysters had already reached market size of 50 g whole weight, with low mortality at 2 years of age, before the second episode of QX disease. Line 2 showed good improvement in resistance to both diseases, whereas Line 3, was the most resistant to winter mortality. Selection for resistance to QX disease did not appear to confer resistance to winter mortality and the converse also applied.  相似文献   

12.
This study tested the effects of low salinity on phenoloxidase activity in Sydney rock oysters (Saccostrea glomerata). Phenoloxidase is a key component of the immune system in S. glomerata. Previously, we have shown that decreased phenoloxidase activity is associated with susceptibility to fatal QX disease. In the current study, laboratory-based experiments were used to identify factors that contribute to decreased phenoloxidase activity. We found that exposing oysters to water collected from a QX-prone oyster growing area after heavy rain significantly inhibited their phenoloxidase activities. Similar inhibition was evident when oysters were held in oceanic water with artificially lowered salinities. These results suggest that exposure to low salinity decreases phenoloxidase activity. Field trials that exploited a natural salinity gradient in the Georges River, Sydney, supported this conclusion. The phenoloxidase activities of oysters transplanted to up-river sites that had low salinities were significantly lower than those of oysters held at seaward sites with higher salinities. All of these data implicate low salinity as a key environmental stressor that is associated with inhibition of the S. glomerata immune system.  相似文献   

13.
  • 1. Marine protected areas (MPAs) are being used increasingly to manage and protect marine resources. Most studies of MPAs have focused on fish. In this study, the influence of MPA protection on coral reef benthic organisms on the Great Barrier Reef (GBR) was investigated. In addition, the interaction between protection and natural disturbance history was examined.
  • 2. Differences in benthic cover inside and outside MPAs were assessed at 15 pairs of Protected and General Use reefs on the GBR using annual monitoring data from the Australian Institute of Marine Science's Long‐Term Monitoring Programme (LTMP). At each reef, benthic cover was determined using a benthic video survey at three sites, with each site consisting of five 50 m transect lines separated by at least 250 m running parallel to the reef crest at 6–9 m depth.
  • 3. Benthic cover was related to both protection status and disturbance history, but natural perturbations exerted a stronger influence on benthic cover than did protection status. The influence of natural perturbation was most noticeable for hard coral.
  • 4. Most reefs where no natural disturbance events had occurred (‘undisturbed reefs’) had higher hard coral cover and lower soft coral cover than General Use reefs. While the high levels of hard coral on Protected reefs may be a result of protection status, it might also have resulted from selection bias that occurred during the initial zoning of the Great Barrier Reef Marine Park (i.e. managers may have given protection status to reefs with high coral cover).
  • 5. These results are likely influenced by the relatively low intensity of human use, both on the Great Barrier Reef in general and at the particular monitoring sites studied. Over time, as local populations and tourism increase, the effect of protection may become more evident at LTMP sites. Copyright © 2009 John Wiley & Sons, Ltd.
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14.
Selective breeding efforts have yielded oyster strains, Crassostrea virginica, with improved survival and resistance against Haplosporidium nelsoni (MSX); however, because of susceptibility to the oyster pathogen Perkinsus marinus (Dermo), their utility has been limited in areas where the two parasites co-occur. Dual resistance to H. nelsoni and P. marinus was achieved through four generations of artificial selection of wild Delaware Bay oyster progeny at a site in the lower York River, Virginia, USA where both diseases are enzootic. During 1993–1995, survival, growth, and disease susceptibility of third generation Delaware Bay (F3-DEBY) oysters were evaluated at the York River site in comparison to that of similarly selected third generation James River, Virginia oysters (F3-JR), and first generation Louisiana oysters (F1-LA), whose parents were naturally selected in the wild for resistance to P. marinus. During 1997–1999, the performance of F4-DEBY was evaluated at three sites in Virginia in comparison to two groups of first generation oysters whose parents originated from Mobjack Bay and Tangier Sound, Virginia where both P. marinus and H. nelsoni are enzootic. In the presence of high infection pressure from both H. nelsoni and P. marinus, the F3-DEBY stock showed significantly higher survival and growth than either the F3-JR or F1-LA strain. After 15 months of deployment, 79% of F3-DEBY, 11% of F3-JR and 17% of F1-LA oysters were market size (≥76.2 mm) and cumulative mortality was only 16% in F3-DEBY as compared to 42% in F3-JR and F1-LA. At the termination of the study, F3-DEBY oysters exhibited 22% lower mortality than the F1-LA stock, which outperformed the F3-JR stock. Relative performance in respect to disease varied considerably with sample date; however, average H. nelsoni weighted prevalence varied such that F3-DEBY1-LA=F3-JR and average P. marinus weighted prevalence varied such that F1-LA3-DEBY3-JR. In the 1997–1999 trial, F4-DEBY oysters experienced 34–61% lower mortality, greater growth rate, and consistently lower prevalence and intensity of P. marinus than either Mobjack Bay or Tangier Sound oysters. H. nelsoni prevalences were very low (<12%) in all three stocks. This is the first study to demonstrate that reduced susceptibility to both P. marinus and H. nelsoni can be achieved through selective breeding.  相似文献   

15.
The Australian edible oyster industry has been severely impacted by disease and declining yields since the 1970s. Selective breeding of Saccostrea glomerata is one measure addressing these problems by producing fast‐growing, disease‐resistant oysters. Farmers report that selected oysters have different growth characteristics than their wild counterparts using conventional grow‐out methods. This study investigated how different grow‐out methods influence commercially valuable oyster characteristics including shell length, shape, surface growth deformities and meat condition. In June 2015, selectively bred S. glomerata spat were deployed in two estuaries (Hawkesbury River and Georges River) in NSW, Australia, using three grow‐out methods (fixed trays, Stanway cylinders and floating baskets). In November 2015, oysters were transferred among grow‐out methods to test for the effects of changing grow‐out methods on oyster growth patterns. Oysters transferred from baskets to cylinders and from trays to cylinders had, on average, deeper and wider shells, a higher meat condition and fewer shell surface deformities than oysters in other grow‐out method combinations. However, these oysters were smaller than oysters not grown in cylinders. While there were some differences in growth patterns between the estuaries, overall it was the grow‐out methods that most influenced oyster characteristics. This was attributed to differences in the amount and magnitude of movement oysters experienced in the grow‐out methods, as recorded by motion sensors. This study demonstrates how grow‐out methods can be managed to achieve desired growth trajectories and therefore improve marketability among selective bred S. glomerata.  相似文献   

16.
Light spatfalls of the Pacific oyster, Crassostrea gigas, have occurred in the estuaries of the Rivers Exe, Teign and Dart (Devon) and in the Menai Strait (Gwynedd), near to sites of commercial cultivation of this species. Comparisons of the sizes of the naturally settled oysters with hatchery oysters suggests that the spat from the River Teign and Menai Strait settled in 1989 and 1990. The springs and summers of these years were exceptionally warm with mean monthly air temperatures 0.8°-1.3°C above the 1951–1980 average for the period April to August. Although sitings of Pacific oyster spat were made in Loch Sween and Emsworth Harbour over 20 years ago, there is no evidence that self-sustaining populations have developed. The spatfalls which occurred in some coastal waters of Devon and Gwynedd in 1989 and 1990 are unlikely to sustain natural fisheries and are likely to die out as did the Portuguese oysters which occasionally settled in the River Blackwater, Essex.  相似文献   

17.
为探究香港巨牡蛎(Crassostrea hongkongensis)的繁殖特性以及春季死亡原因,采用肉眼观察、活体镜检和组织切片方法研究了茅尾海沙井的香港巨牡蛎苗种吊养于大风江黄场的1龄牡蛎的性腺发育周年变化,并建立了快速判断香港巨牡蛎性腺发育程度的方法.对比分析了吊养在茅尾海沙井、大风江入海口内的黄场和入海口外的鑫丰场的2龄牡蛎性腺发育的启动和发展过程.结果显示,广西茅尾海的香港巨牡蛎每年只有1个繁殖周期,性腺发育过程可划分为未分化期(1-3月)、分化期(4月)、成熟排放期(5-10月)及休止期(11-12月)4个阶段;1龄和2龄牡蛎的性腺发育基本同步;大风江入海口外的牡蛎的性腺发育较入海口内的牡蛎提前约15d,而比茅尾海内海的牡蛎提前约30 d,入海口外的牡蛎的性腺4月即发育到成熟排放期,冬季饵料的丰富程度和温度、盐度等因素可能是造成这种差异的原因.研究还发现,高温少雨天气下,海水盐度高,抑制了牡蛎性细胞的排放,导致入海口外侧吊养牡蛎的大规模死亡,濒临死亡的牡蛎性腺处于退化和崩解状态.鉴于此,认为4月初即需密切监测吊养于入海口外的牡蛎性腺的发育状况和天气状况,及时收获性腺饱满的牡蛎,或将吊养牡蛎的蚝排放置在河流入海口内区域过冬.  相似文献   

18.
The harvest of bay scallops (Argopecten irradians) from Buzzards Bay, Massachusetts, U.S.A. undergoes large interannual fluctuations, varying by more than an order of magnitude in successive years. To investigate the extent to which these fluctuations may be due to yearly variations in the transport of scallop larvae from spawning areas to suitable juvenile habitat (settlement zones), a high‐resolution hydrodynamic model was used to drive an individual‐based model of scallop larval transport. Model results revealed that scallop spawning in Buzzards Bay occurs during a time when nearshore bay currents were principally directed up‐bay in response to a persistent southwesterly sea breeze. This nearshore flow results in the substantial transport of larvae from lower‐bay spawning areas to settlement zones further up‐bay. Averaged over the entire bay, the spawning‐to‐settlement zone connectivity exhibits little interannual variation. However, connectivities between individual spawning and settlement zones vary by up to an order of magnitude. The model results identified spawning areas that have the greatest probability of transporting larvae to juvenile habitat. Because managers may aim to increase scallop populations either locally or broadly, the high‐connectivity spawning areas were divided into: (i) high larval retention and relatively little larval transport to adjoining settlement areas, (ii) both significant larval retention and transport to more distant settlement areas, and (iii) little larval retention but significant transport to distant settlement areas.  相似文献   

19.
The New Zealand dredge oyster Tiostrea lutaria Hutton is an incubatory ostreid species that produces fully developed pediveliger larvae, which typically settle shortly after release from the parent. Broods of larvae obtained by opening incubating oysters provide a potential method of spat production, but only a small proportion of the broods obtained in this way are the late‐stage, ready‐to‐settle pediveligers. The majority of the broods are gastrula‐, trochophore‐ and veliger‐stage larvae. Experiments were undertaken to determine whether these early stages, as well as the pediveliger stage, could be reared through to settlement, and so make spat production based on opening incubating oysters much more efficient. Experiments conducted at three temperatures (ambient, ambient + 3 °C and ambient + 6 °C) and under three food regimes (with and without cultured microalgae and without dissolved organics) were unsuccessful in ex‐parent rearing of early larvae (gastrulae and trochophores). Later stage larvae, both veligers and pediveligers, were successfully reared, and high (> 75%) but variable levels of settlement were achieved. Ex‐parent rearing did not benefit from elevated temperatures or the presence of food, and settlement of spat from these prematurely released larvae may be reduced in the presence of food. The ability to rear veliger larvae, as well as pediveligers, greatly increases the potential to use the opening of incubating adult oysters during the breeding season as a source of dredge oyster spat.  相似文献   

20.
The Sydney rock oyster breeding programme began in 1990 and initially focused on faster growth and resistance to winter mortality disease (WM, Bonamia roughleyi) before including QX disease (QX, Marteilia sydneyi) resistance in 1997. Four generations of oysters have now been exposed to these diseases at three sites in the Georges River, NSW, Australia (Lime Kiln Bar, LKB; Woolooware Bay, WB; and, Quibray Bay, QB). Non‐selected control oysters and lines developed at each site (Line 1 – LKB, Line 2 – WB, Line 3 – QB) were placed at the three sites alongside a new QX‐resistant line (Line 4) bred from QX survivors in other NSW estuaries. Line 1 oysters grew to a marketable size (>50 g) in two years with minimal losses following QX disease outbreaks: 28% mortality compared with 97% in controls. Losses in Line 3 oysters selected for WM resistance at QB were reduced by more than half (23% versus 52%). Line 2 performed best at WB, but this line showed excellent resistance to QX at LKB and WM at QB, indicating that breeding for resistance to both diseases is effective. However, selection of oysters for QX did not confer resistance to WM and vice versa.  相似文献   

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