Isotopic variation of fishes in freshwater and estuarine zones of a large subtropical coastal lagoon     

A.M. Garcia  D.J. Hoeinghaus  J.P. Vieira  K.O. Winemiller 《Estuarine, Coastal and Shelf Science》2007,73(3-4):399-408

We used stable C and N isotope ratios of tissues from 29 fish species from a large subtropical lagoon in southern Brazil to examine spatial variability in isotopic composition and vertical trophic structure across freshwater and estuarine habitats. Nitrogen isotope ratios indicated a smooth gradation in trophic positions among species, with most fishes occupying the secondary and tertiary consumer level. Fish assemblages showed a significant shift in their carbon isotopic signatures between freshwater and estuarine sites. Depleted carbon signatures (from −24.7‰ to −17.8‰) were found in freshwater, whereas more enriched signatures (from −19.1‰ to −12.3‰) were obtained within the estuarine zone downstream. Based on our survey of the C₃ and C₄ plants and isotopic values for phytoplankton and benthic microalgae reported for ecosystems elsewhere, we hypothesized that the observed δ¹³C differences in the fish assemblage between freshwater and estuarine sites is due to a shift from assimilating organic matter ultimately derived from C₃ freshwater marsh vegetation and phytoplankton at the freshwater site (δ¹³C ranging from −25‰ to −19‰), to C₄ salt-marsh (e.g. Spartina) and widgeon grass (Ruppia maritima), benthic microalgae and marine phytoplankton at the estuarine sites (from −18‰ to −12‰). Our results suggested that fish assemblages are generally supported by autochthonous primary production. Freshwater fishes that likely were displaced downstream into the estuary during periods of high freshwater discharge had depleted δ¹³C values that were characteristic of the upper lagoon. These results suggest that spatial foodweb subsidies can occur within the lagoon.  相似文献   

Genetic history of the population of Atlantic salmon, Salmo salar L., under restoration in the Connecticut River, USA     

Ayllon  Fernando; Martinez  Jose L.; Juanes  Francis; Gephard  Stephen; Garcia-Vazquez  Eva 《ICES Journal of Marine Science》2006,63(7):1286-1289

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Numerical Experiment on Two-Dimensional Line Thermal     

J.H.W.LEE  G.Q.CHEN 《中国海洋工程》2002,16(4):453-467

The time evolution of a two-dimensional line thermal-a turbulent flow produced by an initial element with signifi-cant buoyancy released in a large water body, is numerically studied with the two-equation k - e model for turbulence closure. The numerical results show that the thermal is characterized by a vortex pair flow and a kidney shaped concentra-tion structure with double peak maxima; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless time around 10. There are two regions in the flow field of a line thermal: a mixing region where the concentration of tracer fluid is high and the flow is turbulent and rotational with a pair of vortex eyes, and an ambient region where the concentration is zero and the flow is potential and well-described by a model of doublet with strength very close to those given by early experimental and analytical studies. The added virtual mass coeffi-cient of the thermal motion is found to be approximat  相似文献   

Observations of a fast burst of the deep western boundary undercurrent and sediment transport in South Wilmington Canyon from DSRVAlvin     

Stephen J. Culver  Charlotte A. Brunner  Charles A. Nittrouer 《Geo-Marine Letters》1988,8(3):159-165

On October 3 and 4, 1986, DSRVAlvin dives encountered a strong current at 2,300 m in South Wilmington Canyon. The current, estimated at 1 knot, transported surficial sediment and constructed and modified bedforms. It appears to have been constant in its direction of flow from 30 to 40°. The observed current was probably a burst of fast flow in a region of slow average currents in the Deep Western Boundary Undercurrent. Such episodic events may have a greater influence on the stratigraphic record than the temporally longer more tranquil flow conditions.  相似文献   

Regulation of Tilapia metallothionein gene expression by heavy metal ions   总被引：4，自引：0，他引：4  

Cheung AP  Lam TH  Chan KM 《Marine environmental research》2004,58(2-5):389-394

Tilapia is a common fish species inhabiting inland waters and estuarine regions in Hong Kong and Southeast Asia, and useful for bio-monitoring of metal pollution. Metallothionein (MT) gene expression in fish tissues has been useful to sub-lethal risk assessment as biomarker of exposure to metal ions in fishes inhabiting metal contaminated area. To investigate metal inductions of Tilapia MT gene expression in vivo, Tilapias were injected with different concentrations of heavy metals and tissues were then removed for quantitative PCR assay using mimic PCR methods. All of the metal ions tested (Cu(2+), Cd(2+), Hg(2+), Ni(2+), Pb(2+) and Zn(2+)) were able to induce hepatic MT mRNA levels. Renal MT mRNA levels of Cd(2+) and Zn(2+) treated fish was not induced with significant fold induction, however MT mRNA levels in gills were sensitive to the administrations of these metal ions. These data indicated that Tilapia MT mRNA levels in gills and liver are sensitive biomarker of exposure to various metal ions.  相似文献   

The heave response of a spar buoy     

M.J. Tucker 《Ocean Engineering》1982,9(3):259-270

The vertical response of spar buoys to waves is examined. The response is the product of a rather complex wave forcing function and the resonant response of the buoy. With compound spar buoys (that is, consisting of more than one section of different diameters) the forcing function has a zero at a frequency which is usually close to the resonant frequency, but which can be arranged to be somewhat higher with beneficial effects on the response. Only the effects of pressure and inertia are considered, since this paper is mainly concerned to clarify some specific general principles and it is difficult to include the effects of drag, which are complex.  相似文献   

Lethal and sublethal effects of short term acute doses of Kuwait Crude Oil and a dispersant Corexit 9527 on bay scallops, Argopecten irradians (Lamarck) and two predators at different temperatures     

C.J. Ordzie  G.C. Garofalo 《Marine environmental research》1981,5(3):195-210

Investigations of short term acute exposure of bay scallops, Argopecten irradians and two scallop predators, the oyster drill Urosalpinx cinerea and the common starfish Asterias forbesi, to oil, dispersant, and oil-dispersant mixtures (Kuwait Crude Oil and Corexit 9527) suggested that predator and prey have different lethal susceptibilities. Scallops were most sensitive to dispersant and dispersant mixed with oil, starfish were only sensitive to dispersant while the oyster drill seemed unaffected even though all were exposed to dilutions of identically prepared stock solutions. Scallops were least susceptible during winter months and most susceptible at summer temperatures. Treatment had less effect on predators than on scallops at summer temperatures. Sublethal concentrations of dispersant and oil-dispersant mixtures diminished the behavioural ability of scallops to recognise drills and starfish. The degree of effect increased with temperature. Predator detection of prey at the same concentrations was more complex. The feeding response or posturing reflex of starfish was significantly slowed by all treatments. In contrast, drills were unaffected in their recognition of scallop effluent in a choice chamber after treatment.  相似文献   

Performance efficiency of swim fins     

J. Picken  C.T. Crowe 《Ocean Engineering》1974,2(6):251-258

Design improvements on swim fins are most difficult, if not impossible, to assess quantitatively by swimmers alone. In order to make reliable measurements of swim fin performance, an instrumented mechanical swimming device was developed and operated in a water tank. Using this facility, the performance of the more popular conventional fins and that of a new design concept were evaluated. The comparative performance of the various fins was correlated with their physical characteristics.  相似文献   

弧后盆地   总被引：5，自引：1，他引：5  

许靖华 《海洋学报》1979,1(2):243-251

有关岛弧的研究,在三十年代早已开始了.1930年时,荷兰一位地球物理学家在研究重力异常时发现,在印尼南部的诸岛形成了一个弧状的构造,称它为岛弧.而且发现了它以南弧形的爪哇海槽,这是个很深的海槽,在它北坡下有个很大的重力异常带.这个海槽发现后,许多地质学家普遍认为岛弧在海洋地质上是个很重要的现象,与造山运动有关.  相似文献   

The estimation of acid dissociation constants in seawater media from potentionmetric titrations with strong base. I. The ionic product of water — Kw     

A.G Dickson  J.P Riley 《Marine Chemistry》1979,7(2):89-99

The various assumptions implicit in the calculation of acid dissociation constants (based on ionic medium standard states) from potentiometric titrations using a cell with liquid junction (i.e. a pH measuring cell) have been examined. It was concluded that results can be obtained having an accuracy commensurate with the experimental precision. It has been shown that although the precise composition of the medium is a function of the hydrogen ion concentration (because of the protolytic nature of some of the ions in the media, e.g., sulphate and fluoride), the effect of such variations in the medium composition can be compensated for when defining the activity of hydrogen ion on an ionic medium standard state by defining the concentration of hydrogen ion as: where β_HSO4 and β_HF are the relevant association constants and S_T and F_T are the total concentrations of sulphate and fluoride, respectively.This approach was used to obtain values for the ionic product of water (K_W) in artificial seawater media at various temperatures and ionic strengths. These were fitted to give the equation (molal concentration units): where I is the formal ionic strength of the artificial seawater medium and T is the absolute temperature. The values obtained are in reasonable agreement with those found by previous workers.  相似文献