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391.
392.
概述了北黄海盆地的区域地质背景和速度分析的原理,通过对北黄海盆地速度谱的解释和计算,得到了层速度、平均速度、砂岩百分含量等信息,利用这些速度资料识别多次波、辨别坳陷区和隆起区,进行时深转换、构造分析以及岩性分析,为北黄海盆地地震资料解释、沉积相分析以及资源量计算提供可靠的依据。 相似文献
393.
394.
The behaviour of a talitrid amphipod, Orchestoidea tuberculata Nicolet 1849, was investigated for populations inhabiting two exposed sandy beaches in south central Chile to evaluate orientation capabilities with respect to sun azimuthal changes and landscape. The study beaches (Calfuco and La Misión) were backed by high cliffs but differed in shoreline orientation. Under test conditions of dry substrate, both populations oriented seawards using celestial cues when landscape vision was screened off and showed a higher concentration seawards when they could see the landscape suggesting additive effects of these cues. The absence of a phototactic response to the sun implies the involvement of an inner circadian clock, as the experiments were conducted at different times of the day. The distribution of juveniles was more concentrated than adults in the trials, a result in accordance with their tendency to occupy a zone located closer to the water than adults. Our results suggest that the Calfuco population was oriented to its shoreline, while animals at La Misión tended to deviate from the expected direction and their distribution was more scattered. This observed difference between the populations may be related to the higher human impact on the latter beach, which was more intensively used for recreation and periodically cleaned, removing the wrack. The comparison of results on orientation of O. tuberculata with those of different sandhopper species contributes new phylogenetic insight concerning this important adaptation. This study not only represents an extension of contemporary knowledge of behavioural adaptations of beach amphipods to coasts differing geographically and ecologically, but also analyses orientation in a southern Pacific species of talitrid amphipod for the first time. 相似文献
395.
Juana Mireya Mendoza-Vera Samba K Corinne Cuoc Marc Bouvy Marc Pagano 《Estuarine, Coastal and Shelf Science》2008,79(4):740-750
Pseudodiaptomus hessei is a key species in many water bodies in the Senegal River hydrosystem but it became rare or completely disappeared from two ecosystems (Lake Guiers and Dakar Bango Reservoir; Senegal, West Africa) after major hydrological changes caused by human action, mainly impoundments on the river in 1985, and the opening of a new estuary mouth in 2003. Kâ et al. [Kâ, S., Pagano, M., Ba, N., Bouvy, M., Leboulanger, C., Arfi, R., Thiaw, O.T., Ndour, E.H.M., Corbin, D., Defaye, D., Cuoc, C., Kouassi, E., 2006. Zooplankton distribution related to environmental factors and phytoplankton in a shallow tropical lake (Lake Guiers, Senegal, West Africa). International Review of Hydrobiology 91(5), 389–405] put forward several hypotheses to explain the reasons for this decline: salinity and chemical changes in the water, predation by a cyclopid predator Mesocyclops ogunnus and/or the inhibiting effects of cyanobacteria and/or diatoms (allelopathy). This study assessed these hypotheses by studying the distribution of P. hessei in 13 stations (including the Dakar Bango reservoir and Lake Guiers) in relation to physical, chemical and biological (phyto- and zooplanktons) factors at each station. We produced a distribution pattern for this species in the Senegal River hydrosystem. Rank correlations and principal component analysis showed that P. hessei was not correlated with conductivity but was positively correlated with pH and alkalinity, suggesting chemical effects. The clear association with two filamentous cyanobacteria (Cylindrospermopsis raciborskii and Anabaena sp.) did not appear to support the hypothesis of cyanobacteria inhibition but blooming conditions were never encountered during the study. Negative correlation with diatoms (especially with Fragilaria sp.) suggested that aldehyde producing diatoms had a negative effect. Negative correlations with cyclopids such as Mesocyclops supported the hypothesis of cyclopid predation to explain the decline of P. hessei. This study proposes several lines of research for future studies to test these hypotheses. 相似文献
396.
Suzan S. Pool Richard D. Brodeur N. Lynn Goodman Elizabeth A. Daly 《Estuarine, Coastal and Shelf Science》2008
The Juan de Fuca Eddy is a seasonal, counter-clockwise gyre off the mouth of the Strait of Juan de Fuca between Washington, USA and British Columbia, Canada that may provide favorable feeding habitat for juvenile coho salmon (Oncorhynchus kisutch) during their early marine existence. In late September 2002, physical and biological sampling was conducted along two transects of the eddy region. Surface rope trawling was conducted to capture juvenile salmon and other nekton, along with bongo and neuston net tows to examine potential mesozooplanktonic salmon prey. Presence of the Juan de Fuca Eddy was confirmed with vertical water profiles. In addition, nutrient and chlorophyll a concentrations collected from 3-m depth were within the range observed in previous studies within the eddy region. In the mesozooplankton community, euphausiids, chaetognaths, and decapod megalopae were common. In the diet of juvenile coho salmon, euphausiids and decapod megalopae were dominant by percent number, and larval and juvenile fish were dominant by percent weight. Feeding intensity (percent body weight) based on stomach contents was variable, but not significantly different among stations. To compare the Juan de Fuca Eddy region with an upwelling area, we sampled along a transect off La Push (LP), Washington, USA which is south of the eddy. The eddy region was found to be less productive than the LP transect. Nutrients were lower, chlorophyll a concentrations were higher, and zooplankton abundance was generally higher along the LP transect than in the eddy region. In addition, more juvenile coho salmon were captured from the LP transect than the eddy region. Prey items in stomachs of salmon from the LP transect were heterogeneous compared to those from the eddy region. Feeding intensity along the LP transect was slightly lower and more variable than in the eddy region, and differences in feeding intensity among LP stations were significant. In addition, feeding intensities among stations nested within regions were significantly different. 相似文献
397.
Coral reefs are one of the most diverse ecosystems on Earth. They are currently exposed to increasing levels of anthropogenic perturbations. Several recent reviews point to the lack of good indicators for these perturbations especially to monitor their effects on fish populations or fish assemblages. The SW lagoon of New Caledonia is an ideal location to test indicator species in this context as contrasting sites are present within a small geographical range. This study analysed fish from four sites, one with heavy industrial pollution, another dominated by domestic waste, a third with historic mining activities, and the fourth as a control. The butterfly fish, Chaetodon speculum, was chosen to determine C. speculum's potential as an indicator species due to its link to coral, its sedentary behaviour and its wide geographical distribution. The size distribution, growth rate, age distribution and whole otolith composition were analysed at each site. Age and mean growth rate were analysed from daily increments of the otoliths. The concentrations of eight elements (Li, Mg, Co, Ni, Cu, Rb, Sr, and Ba) were measured by ICP-MS in the otoliths of a subset of individuals. The sites under anthropogenic impact were distinct from the control site by fish size frequencies, age distributions, and the chemical content of their otoliths. The chemical elements Mg, Co, Ni, Cu, and Rb showed differences amongst sites. Fish belonging to the sites furthest from Nouméa could be discriminated in nearly 80% of samples or 60% of the cases when otolith weight or fish age respectively were taken into account. Ni concentrations of the otoliths were also higher in the bays where water concentrations of this element were known to be higher, but these differences were no longer significant once corrected for otolith weight. These results should be mitigated by the fact that: (1) despite significant differences between sites in age distribution and size frequencies there were no differences in growth rates or body condition; (2) differences in age or size were not correlated to perturbation levels; and (3) discrimination between sites based on chemical levels in the otoliths, even though significant, was not sufficient to identify the origin of the fish at a level useful for screening tests. The hypothesis that environmental differences between sites would be reflected in the otolith chemical composition is therefore not fully supported by our results. 相似文献
398.
The EU's bilateral fishing policy towards developing third countries has evolved over the years to increasingly emphasise sustainability, culminating in 2002 with the release of a ‘fisheries partnership approach’. The Community has begun to operationalise the policy in various West African coastal states, where its new fisheries partnership agreements are intended to function as ‘development vectors’. This paper introduces the EU's new policy, examines its potential implications for the role of sustainability in future bilateral fishing relations and highlights the impetus for it with reference to analysis of the EU's most recent agreement with Senegal based on empirical research. 相似文献
399.
Kanchan Maiti Claudia R. Benitez-Nelson Yoshimi Rii Robert Bidigare 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1445
Mesoscale eddies may enhance primary production (PP) in the open ocean by bringing nutrient-rich deep waters into the euphotic zone, potentially leading to increased transport of particles to depth. This hypothesis remains controversial, however, due to a paucity of direct particle export measurements. In this study, we investigated particle dynamics using 234Th–238U disequilibria within a mesoscale cold-core eddy, Cyclone Opal, which formed in the lee of the Hawaiian Islands. 234Th samples were collected along two transects across Cyclone Opal as well as during a time-series within the eddy core during a decaying diatom bloom. Particulate carbon (PC), particulate nitrogen (PN) and biogenic silica (bSiO2) fluxes at 150 m varied spatially and temporally within the eddy and strongly depended on the 234Th model formulation used (e.g., steady state versus non-steady state, inclusion of upwelling, etc.). Particle fluxes estimated from a steady state model assuming an upwelling rate of 2 m day−1 yielded the best fit to sediment-trap data. These 234Th-derived particle fluxes ranged from 332±14 to 1719±53 μmol C m−2 day−1, 27±3 to 114±12 μmol N m−2 day−1, and 33±20 to 309±73 μmol Si m−2 day−1. Although PP rates within Cyclone Opal were elevated by a factor of 2–3, PC and PN fluxes were the same, within error, inside and outside of Cyclone Opal. The ratio of PC export to PP remained surprisingly low at <0.03 and similar to those measured in surrounding waters. In contrast, bSiO2 fluxes within the eddy core were three times higher. Detailed analyses of 234Th depth profiles consistently showed excess 234Th at 100–175 m, associated with the remineralization and possible accumulation of suspended and dissolved organic matter from the surface. We suggest that strong microzooplankton grazing facilitated particulate organic matter recycling and resulted in the export of empty diatom frustules. Thus, while eddies may increase PP, they do not necessarily increase PC and PN export to deep waters. This may be a general characteristic of wind-driven cyclonic eddies of the North Pacific Subtropical Gyre and suggests that eddies may preferentially act as a silica pump, thereby playing an important role in promoting silicic-acid limitation in the region. 相似文献
400.
Sachiko Oguma Tsuneo Ono Akira Kusaka Hiromi Kasai Yasuhiro Kawasaki Tomonori Azumaya 《Journal of Oceanography》2008,64(4):525-539
In this study we used two stable isotopes, δ13C and δ18O, for water mass classification in the coastal region off eastern Hokkaido. δ13C* values, which were corrected for the biological effect, and δ
18O values up to 300 m depth suggested that the isotopic character of the onshore and offshore water in the southern Okhotsk
Sea, the Nemuro Strait and the western North Pacific could be explained by the mixing of three source waters: the Oyashio
water (OYW), Soya Warm Current water (SWCW) and East Sakhalin Current water (ESCW). In summer, δ
13C*-δ
18O plots indicated mixing between SWCW from the southern Okhotsk Sea and OYW in the Pacific coast of southeastern Hokkaido,
while temperature-salinity plots of the onshore water showed minimal difference from the offshore OYW. In winter, on the other
hand, the mixed water of ESCW and OYW (or SWCW) appeared in the Pacific coastal region, distributed as cold, low salinity
onshore water. Finally, we estimated mixing ratios of OYW, SWCW and ESCW in the coastal region of western North Pacific using
their mean values of δ
13C* and δ
18O as endmembers. These results suggest seasonal and yearly changes of water mass combination en route from the southern Okhotsk
Sea to the western North Pacific. 相似文献