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1.
K. D. Thomas 《Geoarchaeology》1987,2(3):231-240
Shackleton and van Andel have raised the question of past human selectivity in the collection of shellfish resources. They reconstruct, for the changing coastlines near Franchthi Cave during the post-glacial transgression, changes in availability of various species of shellfish. The model of availability is compared with the archaeological record of shellfish from the cave. Shackleton and van Andel conclude that selectivity is demonstrated and that this was, in part, “idiosyncratic”. A critical analysis of the model leads to the conclusion that, while the reconstructions of the likely positions of past coastlines may be acceptable, the reconstructions of mollusc availability at various times in the past are highly improbable. Sea-level change is not the only important determinant of past coastal ecology although it will, of course, have an impact on the ways in which coastal ecosystems developed. Other factors (including the physical and chemical properties of the substratum, levels of productivity, and biological interactions), operating at various spatial and chronological scales, cannot be ignored or even subordinated. The shellfish remains from the cave are the only objective evidence of man's exploitation of past coastal resources. Taphonomic analyses of the shells from the site would allow a number of important questions to be addressed, including the reasons for their collection and the possibility of over-exploitation of certain species in the past. 相似文献
2.
中国浅海贝藻养殖对海洋碳循环的贡献 总被引：32，自引：0，他引：32
中国是浅海贝藻养殖的第一大国,年产量超过1 000万t。根据贝藻养殖产量、贝藻体内碳元素的含量及其贝类能量收支,推算出2002年中国海水养殖的贝类和藻类使浅海生态系统的碳可达300多万t,并通过收获从海中移出至少120万t的碳。该结果不仅为探讨全球“遗漏的碳汇”问题提供了一个新的线索,同时也证明了浅海的贝类和藻类养殖活动直接或间接地使用了大量的海洋碳,提高了浅海生态系统吸收大气CO2的能力。另外,贝藻的养殖活动与浅海生态系统的碳循环之间关系复杂,相互作用明显,因此,它的生物地球化学过程是一个值得深入研究的科学问题。 相似文献
3.
Gary P. Richards 《Estuaries and Coasts》1987,10(1):84-85
The regulation of shellfish and their growing waters is based on total and fecal coliform standards. Application of these standards has reduced the incidence of shellfish-borne bacterial illnesses in humans, but outbreaks of viral diseases, such as hepatitis A, Norwalk illness, and viral gastroenteritis, prevail. Hepatitis A virus contributed to 1,395 cases of shellfish-associated illness since 1961. An additional 6,049 cases of shellfish-associated gastroenteritis were reported over the past 50 years, 75% of which (4,609 cases) occurred since 1980. The alarming rate of disease outbreaks during the past 5 years may further increase as better reporting practices are initiated by health professionals and state and federal agencies. Actions necessary to reduce the incidence of shellfish-associated viral illness include development of methods for detecting viral pathogens in shellfish and harvest waters, correlation of levels of viral pathogens with potential viral and bacterial indicators, and acceleration of field monitoring and enforcement efforts. 相似文献
4.
A two-year survey for diarrhetic shellfish poisoning (DSP) was conducted in Narragansett Bay using the mouse assay method. The suspected causative organisms,Dinophysis spp., were monitored at the same time. Only one shellfish sample, in September 1984, yielded an unequivocal positive result at a time when the dinoflagellate population was dominated byD. acuminata. False positive results were suspected in May, when the mussels appeared sexually matured, and in, the summer of 1985, at the time of an unusual massive picoplanktonic bloom. Evidence of toxin production byD. acuminata was obtained from an almost monospecific sample; we calculated that over 5.4×105 cells would be necessary to produce one mouse unit. The specificity and sensitivity of the assay method are questioned and improvements for DSP detection are suggested. 相似文献
5.
6.
The natural aging process of Chesapeake Bay and its tributary estuaries has been accelerated by human activities around the shoreline and within the watershed, increasing sediment and nutrient loads delivered to the bay. Riverine nutrients cause algal growth in the bay leading to reductions in light penetration with consequent declines in sea grass growth, smothering of bottom-dwelling organisms, and decreases in bottom-water dissolved oxygen as algal blooms decay. Historically, bay waters were filtered by oysters, but declines in oyster populations from overfishing and disease have led to higher concentrations of fine-sediment particles and phytoplankton in the water column. Assessments of water and biological resource quality in Chesapeake Bay and tributaries, such as the Potomac River, show a continual degraded state. In this paper, we pay tribute to Owen Bricker’s comprehensive, holistic scientific perspective using an approach that examines the connection between watershed and estuary. We evaluated nitrogen inputs from Potomac River headwaters, nutrient-related conditions within the estuary, and considered the use of shellfish aquaculture as an in-the-water nutrient management measure. Data from headwaters, nontidal, and estuarine portions of the Potomac River watershed and estuary were analyzed to examine the contribution from different parts of the watershed to total nitrogen loads to the estuary. An eutrophication model was applied to these data to evaluate eutrophication status and changes since the early 1990s and for comparison to regional and national conditions. A farm-scale aquaculture model was applied and results scaled to the estuary to determine the potential for shellfish (oyster) aquaculture to mediate eutrophication impacts. Results showed that (1) the contribution to nitrogen loads from headwater streams is small (about 2 %) of total inputs to the Potomac River Estuary; (2) eutrophic conditions in the Potomac River Estuary have improved in the upper estuary since the early 1990s, but have worsened in the lower estuary. The overall system-wide eutrophication impact is high, despite a decrease in nitrogen loads from the upper basin and declining surface water nitrate nitrogen concentrations over that period; (3) eutrophic conditions in the Potomac River Estuary are representative of Chesapeake Bay region and other US estuaries; moderate to high levels of nutrient-related degradation occur in about 65 % of US estuaries, particularly river-dominated low-flow systems such as the Potomac River Estuary; and (4) shellfish (oyster) aquaculture could remove eutrophication impacts directly from the estuary through harvest but should be considered a complement—not a substitute—for land-based measures. The total nitrogen load could be removed if 40 % of the Potomac River Estuary bottom was in shellfish cultivation; a combination of aquaculture and restoration of oyster reefs may provide larger benefits. 相似文献
7.
Shellfish production areas are often located in shallow estuarine and coastal systems impacted by fluxes of faecal indicator organisms (FIOs) that exhibit extreme spatial and temporal variability. FIO abundance and distribution in the marine environment are determined by the combined effects of light intensity, water mixing, sewage content and suspended particulate matter. Favourable conditions for FIO survival are low solar radiation, low temperature, low salinity, low densities of micro-predators and high levels of organic matter. Rainfall is the parameter most commonly associated with peak levels of FIOs. Resuspension of contaminated sediments in the water column dominates FIO distribution in shallow and depositional estuaries during storm conditions. Water/flesh FIO ratios may differ between shellfish growing waters because salinities and water temperatures also influence filter-feeding activity. Data are lacking on the role of biological processes on FIOs uptake and clearance in shellfish, particularly during periods of good water quality. FIO accumulation is usually of higher magnitude in mussels and cockles than in oysters and surf clams. It is proposed that differences in FIO accumulation rates are associated with the biological activity and the position of shellfish in the water column in relation to the location of impacting pollution sources. Accurate information on catchment hydrology, land uses, FIO loads from sewerage-related sources and livestock production areas are required to adequately characterise the microbiological status of shellfisheries. 相似文献
8.
Rense Heath Kelsey Geoffrey I. Scott Dwayne E. Porter Thomas C. Siewicki Donald G. Edwards 《Estuaries and Coasts》2010,33(3):712-722
Currently, many states use precipitation information to regulate periodic closures of shellfish harvest areas based on a presumptive
relationship between rainfall and bacteria concentration. We evaluate this relationship in four South Carolina estuaries and
suggest new predictive models that integrate remote sensing precipitation data with additional environmental and climatic
data. Model comparisons using Akaike’s information criterion, tenfold cross-validation, and model r
2 values show substantial and consistent improvements using integrated precipitation, salinity, and water temperature data
as predictors. These models may be useful for shellfish area closure regulation support. The model development approaches
used here may also be useful in estimating bacteria concentration at beaches and can serve as the basis for developing near-real-time
estimates and forecast predictions of bacteria levels for closure decision-making tools. 相似文献
9.
People who exploit marine resources choose among them according to technological, economic, and social considerations. Prehistoric selectivity in their exploitation has often been postulated, but can be established only by comparing the archaeological record with an estimate of the kinds and quantities available in the environments of the time. Only then can those factors be considered that might have influenced their choice, a subject which is the domain of the archaeologist. In Franchthi Cave, a thick Upper Paleolithic through Neolithic sequence (ca. 23,000–5000 yrs B.P.) of occupational deposits has been excavated. As might be expected at a site now only a few meters from the sea, this sequence has yielded ample evidence for the use of marine resources, though only from ca. 11,000 B.P. onward. Moreover, the marine molluscan record exhibits drastic changes in composition over time, implying either major variation in availability or selective collecting. A marine geophysical study supplemented by an examination of present shore environments in the area has permitted the reconstruction of the changing coastal environments since ca. 20,000 B.P., thus providing an estimate of the probably available shellfish resources. Comparison with the molluscan assemblages found in the cave demonstrates that only during the latest Paleolithic and most of the Neolithic were the collected shellfish reasonably representative of what should have been available in the area. At other times the inhabitants made highly specialized, seemingly idiosyncratic choices from the spectrum of available species. 相似文献
10.
A buried archaeological site at Tecolote Canyon provides an ideal case study for relating past human land use patterns to changes in coastal paleogeography. Postglacial sea level transgression, erosion, and other marine and fluvial processes form the context for examining two deeply buried archaeological components excavated at CA‐SBA‐72. Archaeological shellfish assemblages provide proxy data for evaluating the evolution of local marine environments. Pismo clams dominate shellfish assemblages dated to 5800 cal yr B.P., suggesting the presence of a broad and sandy, high‐energy beach environment. At 5500 cal yr B.P., the almost exclusive use of California mussels by humans signals the development of rocky intertidal habitats. During the late Holocene, estuarine species dominate the marine mollusk assemblages at CA‐SBA‐72, reflecting the development of local estuarine conditions or trade with nearby Goleta Slough villages. The buried components at Tecolote Canyon appear to have served as temporary camps for shellfish harvesting and processing. While general changes in coastal paleogeography and human subsistence have been reconstructed for the Santa Barbara Coast, high resolution ecological data from Tecolote Canyon suggest that Native peoples also adapted to localized and shorter‐term shifts in intertidal habitats, changes not evident in most larger or more disturbed surface sites in the region. Linking these changes with shifts in human land use patterns highlights the interaction between humans and a dynamic coastal system. These data demonstrate the importance of small, buried sites in understanding the full spectrum of human subsistence and settlement choices and local environmental change. © 2004 Wiley Periodicals, Inc. 相似文献
11.
Records of massive fish kills and paralytic shellfish poisoning (PSP) in Europe and North America go back to the 17th century. But, it was not until the 1940s when the relationship between PSP, red tide and toxic dinoflagellateGonyaulax was established. Recent records show that PSP and related poisons caused by toxic dinoflagellates in coastal waters and estuaries, are a world-wide problem. Diarrhetic shellfish poisoning (DSP) and neurotoxic poisoning (NSP), believed earlier as bacterial or viral infections are now shown to be caused by other toxic dinoflagellates such asDinophysis. The shellfish most often involved in the poisoning are mussels and clams. Other dinoflagellates,Gyrodinium, occasionally cause massive fish kills in vast coastal areas, resulting in fishery and economic losses. Factors promoting toxic dinoflagellate bloom development and PSP/DSP outbreaks are not fully understood. In previous studies, temperature was considered as the principal factor influencing dinoflagellate blooming. Recent studies showed that other factors such as salinity, sunlight, freshwater runoff and water stability are also important. Pollution from land drainage and sewage discharge in inshore waters were also implicated. Current knowledge indicates that although chemical and biotic factors are important forin-situ growth of dinoflagellate cells, convergence by thermal and tidal fronts is essential for cell accumulation and bloom development. Advances in physical oceanographic research, modelling and remote sensing enabled the detection of fronts and bordering eddies with high precision. There is a potential for an increased use of these technological advances in predicting and monitoring the bloom development. The present paper overviews the history and distribution of toxic dinoflagellates, and the physical factors influencing bloom development and PSP/DSP outbreaks. Future research needs to improve the predictability and control of this world-wide hazard are also discussed. 相似文献
12.
Records of massive fish kills and paralytic shellfish poisoning (PSP) in Europe and North America go back to the 17th century. But, it was not until the 1940s when the relationship between PSP, red tide and toxic dinoflagellateGonyaulax was established. Recent records show that PSP and related poisons caused by toxic dinoflagellates in coastal waters and estuaries, are a world-wide problem. Diarrhetic shellfish poisoning (DSP) and neurotoxic poisoning (NSP), believed earlier as bacterial or viral infections are now shown to be caused by other toxic dinoflagellates such asDinophysis. The shellfish most often involved in the poisoning are mussels and clams. Other dinoflagellates,Gyrodinium, occasionally cause massive fish kills in vast coastal areas, resulting in fishery and economic losses.Factors promoting toxic dinoflagellate bloom development and PSP/DSP outbreaks are not fully understood. In previous studies, temperature was considered as the principal factor influencing dinoflagellate blooming. Recent studies showed that other factors such as salinity, sunlight, freshwater runoff and water stability are also important. Pollution from land drainage and sewage discharge in inshore waters were also implicated.Current knowledge indicates that although chemical and biotic factors are important forin-situ growth of dinoflagellate cells, convergence by thermal and tidal fronts is essential for cell accumulation and bloom development. Advances in physical oceanographic research, modelling and remote sensing enabled the detection of fronts and bordering eddies with high precision. There is a potential for an increased use of these technological advances in predicting and monitoring the bloom development.The present paper overviews the history and distribution of toxic dinoflagellates, and the physical factors influencing bloom development and PSP/DSP outbreaks. Future research needs to improve the predictability and control of this world-wide hazard are also discussed. 相似文献
13.
Pamela J. Ford 《Geoarchaeology》1989,4(2):157-173
Research about the impact of prehistoric human subsistence strategies upon prey populations of shellfish is based on the assumption that trends in shell size are directly related to collection strategies. A shell midden on San Juan Island, Washington, where archaeological research is sponsored by the University of Washington and hosted by the National Park Service, provides large samples of shells from separate archaeological deposits. the shells from each deposit produce size-frequency distributions that vary in shape (modality). Because several factors (the original prey population, the method of collection and transport, the environment of deposition, and post-depositional processes) affect the size-frequency distribution differentially, the shell measurements do not provide the direct archaeological information expected. 相似文献
14.
Sara L. Webb 《Quaternary Research》1986,26(3)
Rapid rates of species range extension during the Holocene represent seed dispersal distances of at least 6 to 8 km per generation for North American species of Fagus, Quercus, and Carya, taxa whose fruits are heavy nuts. Occasional seed dispersal by biotic seed predators is necessary for these dispersal distances. One likely agent for dispersal across long distances and habitat discontinuities was the extinct (since 1914 A.D.) passenger pigeon (Ectopistes migratorius). This bird's abundance, capacity for delayed digestion, and nomadic habits strongly suggest an occasional seed dispersal role, although a coevolutionary seed dispersal relationship cannot be inferred from available evidence. The capacity of some heavy seeds for dispersal distances greater than those of most light, wind-dispersed seeds has biogeographic and genetic implications. 相似文献
15.
微型计算机是国际上近年来迅速发展起来的一个重要分支,它具有价廉、方便、体积小、多效能等优点,正在向各个领域普及。在岩石学、矿物学研究领域中,随着科学技术的发展和研究工作的深入,能获得的数据越来越多,数据处理量也越来越大。有的数据处理特别繁琐,要花费大量时间,比如标准矿物分子计算法,有的是手算无法进行的,如三斜晶系的晶胞参数修正。1983年,作者利用美国Cromemco Ⅱ微型计算机,研制成功岩石矿物数据处理微型计算机软件系统(PM-C2系统),这个系统包括岩石化学、矿物分子式、温度压力、晶胞参数修正等程序。 相似文献
16.
Heavy metals in the Derwent Estuary 总被引：2，自引：0，他引：2
Analyses of the concentrations of Cd, Cr, Co, Cu, Fe, Pb, Mn, Hg, Ni, and Zn in filtered waters, suspended particulates, sediments,
shellfish, fish, airborne particulates, and sewage have confirmed work of other investigators showing that the Derwent Estuary
is heavily contaminated, particularly withmercury, cadmium, lead, andzinc, and have added further information regarding the distribution of each metal. Apparently most of the contamination originated
from the earlier operation of a zinc refining plant. A study of shellfish growing in variously contaminated regions found
that more than 20 species could be listed in order of their respective abilities to accumulate each heavy metal. For example,
the mussel (Mytilus edulis) was found to be a good indicator of cadmium and mercury contamination, but less valuable as an indicator of zinc. The surf
barnacle, (Catophragmus polymerus) was found to be one of the most sensitive biological indicators of cadmium contamination. An indication of the steps by
which a waste metal is eventually accumulated at high and even toxic concentrations in seafoods, may be seen from a comparison
of the relative concentrations of cadmium, lead, mercury, and zinc found in mussels, sediments, suspended particulates, and
filtered waters. The high concentrations recorded for metals include: 1,100 μg/g Hg, 10,000 μg/g Zn, and 862 μg/g Cd in dried
sediments; 1,500 μg/g Cd in airborne dust fallout; 200 μg/g Cd and 100,000 μg/g Zn in dried oysters; and 16 μg/l Hg, 15 μg/l
Cd and 1,500 μg/l Zn in filtered waters. 相似文献
17.
Michael S. Riley 《Mathematical Geology》2004,36(6):683-702
A statistical, rule-based algorithm for generating fracture patterns similar to those observed in Limestone is presented. For each fracture set, initial seed points are randomly positioned within the modelled domain with the same density as the fractures observed in the field. An orientation is associated with each point by sampling from the distribution of orientations for the corresponding fracture set. Fractures are then allowed to grow from the seed points in both directions with this orientation until they meet other fractures whereupon they continue or terminate according to a fixed probability. A mathematical analysis of this method is presented for the case in which fractures within a set are assumed to be parallel. Approximations to the distribution of semi-trace lengths are derived which are shown to be in good agreement with simulation results. Fracture spacing distributions are also derived for this case. 相似文献
18.
Germination and growth responses ofScirpus robustus Pursh were determined for a variety of environmental conditions. A period of after-repening was required for seed germination; the most effective pretreatment was chilling at 2 C. Alternate freezing and thawing, freezing, and warm dry storage resulted in lower germination. Scarification was effective in increasing seed germination. Low concentrations of salt depressed germination and growth. A definite light requirement was found, but photoperiod length had no effect on germination responses. Alternating temperatures promoted germination; the best overall response occurred with 35 C day/25 C night. Presence ofS. robustus within the marsh community is discussed in relation to germination and seedling establishment characteristics of the species. 相似文献
19.
以蒙古扁桃（Amygdalus mongolica Maxim）种群和种子为研究材料,通过物理特性、休眠特性、萌发特性的研究,探讨种群致濒因素。结果表明,蒙古扁桃种子比重、体积和千粒重大,散布时间较集中,散布格局是聚集型散布,散布主要依靠自身重力,靠动物散布和水力作用的散布,使种子能传播较远的距离。制约种子萌发的主要因素是种皮障碍和生理休眠（10%）,采用35 ℃条件下处理72 h后机械破除果皮可破除种子休眠,种子低温（2~5 ℃）层积处理能极显著（P <0.01）提高活力,种子变温（5~10 ℃）层积能极显著（P <0.01）提高发芽率和活力,种子萌发对光照不敏感。蒙古扁桃种子休眠较浅,种子萌发所需温度较低,冬前进入土壤库的种子迅速萌发,因不能度过严冬而死亡,是致濒的主要原因。封冻时进入土壤库的种子,在种皮保护下越冬,仍有很高成苗率,开展人工繁育是拯救蒙古扁桃资源的直接措施。 相似文献
20.
基于Surfer的有限元后处理等值线图批处理程序开发 总被引：1，自引：4，他引：1
利用Surfer8.0的二次开发平台Scripter以及其与VisualBasic良好的兼容性,编制了等值线图批处理程序,实现了一次性大批等值线图的自动绘制。该程序可依据用户需要,进行指定样式的等值线图形自动拼合。为了操作方便还建立了友好的操作界面,有效地提高了有限元后处理的效率。 相似文献