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81.
Joana F.M.F. Cardoso Denis Langlet Jos F. Loff Ana R. Martins Johannes IJ. Witte Paulo T. Santos Henk W. van der Veer 《Journal of Sea Research》2007,57(4):303-315
The Pacific oyster Crassostrea gigas was introduced in Europe for commercial purposes in the mid 1960s. It was initially thought that low winter temperatures would restrain this species' reproduction and settlement; however, its present distribution in areas where no introduction has taken place suggests that natural invasion and expansion has occurred. Along the European coast, wild populations of Pacific oysters are already found from northern Germany to southern Portugal. Whether C. gigas will continue to further expand through northern waters will depend on its physiological performance. In this study, the performance of wild oyster populations has been studied in terms of growth and reproduction at three stations: La Rochelle (France; 46°N), Yerseke (Oosterschelde estuary, The Netherlands, 51°N), and Texel (Wadden Sea estuary, The Netherlands, 53°N). The French population had the lowest somatic-shell mass ratio and an increase in maximum shell length, somatic and gonadal mass was observed from France to the Netherlands. In addition, mean oocyte diameter decreased significantly from south to north. The combination of increasing gonadal mass and decreasing oocyte volume suggests an increasing reproductive output in terms of egg numbers from France to The Netherlands. Differences in temperature between locations will at least be partly responsible for the observed patterns; however, other environmental factors (such as food availability, predation pressure, sediment type and/or seston concentration) cannot be excluded. Since smaller eggs (oocytes) are thought to have a longer development time, the environmental conditions along the Dutch coast may result in increased larval dispersal and possibly in further population expansion. 相似文献
82.
Joana F.M.F. Cardoso Johannes IJ. Witte Henk W. van der Veer 《Journal of Sea Research》2007,57(4):316-324
The bivalve Spisula subtruncata is usually abundant in shallow coastal waters along the Dutch coast. However, its biomass has been decreasing since 1995. In order to assess whether reproductive failure may be the cause of the observed decline over the last decades, the energy investment in reproduction of a population of S. subtruncata from central Dutch coastal waters was studied. The population studied consisted of individuals of up to four years old. Shell length reached maximum values of around 32 mm and individual total body, somatic and gonadal ash-free dry mass reached maximum values of about 278 mg AFDM, 252 mg AFDM and 76 mg AFDM, respectively. A clear seasonal cycle in somatic and gonadal mass was observed. Somatic and gonadal mass indices increased in early spring and reached maximum values during summer, followed by a decrease to minimum values at the beginning of the following year. Spawning was in June–July and settlement of spat seems to have occurred in July–August. Mean oocyte diameter was 57.43 ± 0.03 μm, corresponding to a volume of 98972 μm3. These results suggested that reproductive failure was not the cause of the current population decline. Most likely, unsuccessful settlement of spat and/or severe predation during the first months of life were responsible for the observed patterns. 相似文献
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85.
Accelerated relative sea-level rise and rapid coastal erosion:: testing a causal relationship for the Louisiana barrier islands 总被引:1,自引:0,他引:1
Jeffrey H. List Asbury H. Sallenger Jr. Mark E. Hansen Bruce E. Jaffe 《Marine Geology》1997,140(3-4):347-365
The role of relative sea-level rise as a cause for the rapid erosion of Louisiana's barrier island coast is investigated through a numerical implementation of a modified Bruun rule that accounts for the low percentage of sand-sized sediment in the eroding Louisiana shoreface. Shore-normal profiles from 150 km of coastline west of the Mississippi delta are derived from bathymetric surveys conducted during the 1880s, 1930s and 1980s. An RMS difference criterion is employed to test whether an equilibrium profile form is maintained between survey years. Only about half the studied profiles meet the equilibrium criterion; this represents a significant limitation on the potential applicability of the Bruun rule. The profiles meeting the equilibrium criterion, along with measured rates of relative sea-level rise, are used to hindcast shoreline retreat rates at 37 locations within the study area. Modeled and observed shoreline retreat rates show no significant correlation. Thus, in terms of the Bruun approach, relative sea-level rise has no power for hindcasting (and presumably forecasting) rates of coastal erosion for the Louisiana barrier islands. 相似文献
86.
In mammals, the induction of cytochrome P4501A forms by chlorinated dibenzo-p-dioxins, chlorinated dibenzofurans, and halogenated biphenyls is under control of a soluble protein known as the Ah (aromatic hydrocarbon) receptor. Little is known about the presence and properties of the Ah receptor in other vertebrate and invertebrate species. In these studies, we sought evidence for an Ah receptor in the liver or liver-equivalent of 20 species of marine and freshwater animals, using the photoaffinity ligand 2-azido-3-[125I] iodo-7,8-dibromodibenzo-p-dioxin (N3[125I]Br2DD). Specific labeling of cytosolic proteins by N3[125I]Br2DD was observed in seven species of teleost and elasmobranch fish, in PLHC-I fish hepatoma cells, and in beluga whales. No specifically labeled proteins were found in cytosol from two species of agnathan fish nor in any of nine invertebrate species representing eight classes of four phyla. The presence or absence of specifically labeled polypeptides corresponds with the inducibility of cytochrome P4501A and sensitivity to the toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related planar halogenated aromatic hydrocarbons in many of these groups. Thus, Ah receptor function may have arisen early invertebrate evolution and has been conserved from elasmobranch and teleost fish to mammals. 相似文献
87.
We describe industry funded contributions to the assessment of the SNA1 snapper (Pagrus auratus) fishery during the 1990s and discuss the advantages and disadvantages of industry funded research. We also provide background on the history of fisheries management in New Zealand, on the current assessment and management processes, and on the SNA1 snapper fishery. In the SNA1 fishery, the contributions of industry and the cooperation with Government scientists has resulted in high quality assessments. In our opinion, the advantages of industry funded research out weigh the disadvantages and suggest that industry funded assessments are highly desirable and should be an integral part of any management system. 相似文献
88.
89.
T.J. Hirst M. Perlow Jr. A.F. Richards B.S. Burton W.J. van Sciver 《Ocean Engineering》1975,3(1):17-27
The first-generation University of Illinois gamma-ray transmission densitometer, designed for the in situ measurement of sediment bulk density, was modified by incorporating in the detector probe (1) an Americium-241 alpha particle pulser and an anti-walk gain stabilization control to maintain better temperature stability and (2) a small power supply and a IC preamplifier to eliminate the need for a high-voltage coaxial cable between the detector and external signal conditioning electronics package. This second-generation Lehigh University system has been successfully deployed since 1971 in routine use from ships and submersibles in the Atlantic and Pacific Oceans and the Gulf of Mexico. Results are presented of system operations to (1) measure bulk density over the range of 1.2–1.8 Mg/m3 in the Hudson Canyon, (2) penetrate 1.9 m into the seafloor in the San Diego trough and, (3) be lowered to a water depth of 3.6 km in the Gulf of Mexico. 相似文献
90.
In 1984, on a transect covering the whole Baltic Sea and parts of the adjacent North Sea, 160 water samples were taken and analysed for their concentrations of particulate and dissolved metals. In addition, the suspended materials were investigated for their elemental bulk composition.The particulate fractions represented from about 5% (Cd, Cu and Ni) to 50% (Fe and Pb) of the total (particulate plus dissolved) concentrations. For some elements (Ba, Cd, Cu, Pb and Zn), the particulate matter from the surface microlayer was enriched with respect to those suspended materials taken from 0.2 m depth. This could reflect the atmospheric input of metal-rich aerosols. In anoxic deep waters, maximum contents of Zn (6400 μg g−1), Cu (1330 μg g−1) and Cd (12 μg g−1) were observed in the particulate matter, indicating sulphidic forms. On the other hand, under oxic conditions the distribution coefficients (Kd) decreased with the water depth (Cd, Fe and Pb).Relative to global background levels, the particulate matter contained metal “excesses” amounting to more than 90% of the total contents (Cd, Mn, Pb and Zn). Automated electron probe X-ray microanalysis (EPXMA) revealed that the elemental composition of sediments is mainly governed by post-depositional processes of early diagenesis and is only weakly related to the composition of suspended matter in the overlying water body. For instance, in relation to surface mud sediments of the central Baltic net-sedimentation basins, Zn, Cd, Cu and Mn had 30–100% higher levels in the suspended materials. The general pattern of metal contents of particulate matter taken from 10 m depth on a transect between the Bothnian Bay and the North Sea were—possibly as a result of anthropogenic inputs—rather similar for Pb, Zn and Cu. For Fe and Mn, the distribution patterns along the transect were probably governed by the natural loading characteristics and by the biogeochemistry of those elements. 相似文献