CLEARANCE PROBLEMS IN AFRICAN RESEARCH     

Frank E. Bernard  Bobbie J. Walter 《The Professional geographer》1968,20(1):28-32

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GEOGRAPHIC ACTIVITIES OF THE DIVISION OF EARTH SCIENCES,NATIONAL RESEARCH COUNCIL     

Walter H. Bailey 《The Professional geographer》1968,20(4):272-275

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The Bering Sea—A dynamic food web perspective     

Kerim Aydin  Franz Mueter   《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2501

The Bering Sea is a high-latitude, semi-enclosed sea that supports extensive fish, seabird, marine mammal, and invertebrate populations and some of the world's most productive fisheries. The region consists of several distinct biomes that have undergone wide-scale population variation, in part due to fisheries, but also in part due to the effects of interannual and decadal-scale climatic variation. While recent decades of ocean observation have highlighted possible links between climate and species fluctuations, mechanisms linking climate and population fluctuations are only beginning to be understood. Here, we examine the food webs of Bering Sea ecosystems with particular reference to some key shifts in widely distributed, abundant fish populations and their links with climate variation. Both climate variability and fisheries have substantially altered the Bering Sea ecosystem in the past, but their relative importance in shaping the current ecosystem state remains uncertain.  相似文献   

Mapping sediment acoustic impedance using remote sensing acoustic techniques in a shallow-water carbonate environment     

Donald J. Walter  Douglas N. Lambert  David C. Young  Kevin P. Stephens 《Geo-Marine Letters》1997,17(4):260-267

 Real-time trackline plots of surficial sediment acoustic impedance delineate several sedimentary facies off Garden Key in the Dry Tortugas. The sea floor within a 6×6 km surveyed area consists of carbonate muds (silts), sands and shell, rock, and live corals. The 4-kHz acoustic data supports this finding by providing a pictographic representation of the distribution and structure of several sediment facies types. Plotting the gridded acoustic data with commercial mapping software (Surfer) provides a three-dimensional (3D) perspective of the bottom topography with a color contour map of surficial sediment impedance (upper 0.4 m) draped over the 3D surface.  相似文献   

Sublethal effects of oiled sediment on the sand worm, Nereis (neanthes) virens: Induced changes in burrowing and emergence     

Bori L. Olla  Allen J. Bejda  Anne L. Studholme  Walter H. Pearson 《Marine environmental research》1984,13(2):121-139

The burrowing and emergence behavior of sand worms, Nereis (Neanthes) virens Sars, in sediment contaminated with sublethal concentrations of Prudhoe Bay crude oil ranging from 74 to 5222 ppm, was studied in the laboratory. Initial burrowing in oiled sediment did not differ from that observed in unoiled sediment. Emergence of exposed worms was related to the oil concentration and the extent of weathering of oiled sediment. Sand worms buried in unoiled sediment did not emerge. Worms dug from oiled sediment after 12 hours' exposure and placed on unoiled sediment were impaired, resulting in a significant increase in time to burrow. However, after 12h, they recovered and burrowed at normal rates. Worms held in oiled sediment for 96 h also recovered. Possible causes for recovery are discussed. Results suggest that oil-induced aberrations may increase vulnerability to predation.  相似文献   

Stimulation of Marine Productivity with Waste Heat and Mechanical Power     

Isaacs  John D.; Schmitt  Walter R. 《ICES Journal of Marine Science》1969,33(1):20-29

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Sediment mobility in the Pomeranian Bight (Baltic Sea): a case study based on sidescan-sonar images and hydrodynamic modelling     

Franz Tauber  Kay-Christian Emeis 《Geo-Marine Letters》2005,25(4):221-229

Sidescan-sonar surveys were performed on a 2×4 km area of seafloor in the southern Baltic Sea (Pomeranian Bight) in 1996 and 1998. Overlapping sub-areas of the individual surveys showing characteristic details were processed into geographically referenced mosaics. Sediment types were identified from echo characteristics and by comparison with granulometric data. The sea bottom covered by the mosaics consists predominantly of sand, with subordinate lag sediments with stones and small ripple fields consisting of coarse sand to fine gravel. A comparison of the two mosaics did not reveal any significant changes of the sea bottom over the 2-year period. Characteristic sedimentary features remained almost unchanged over this period on detailed sonar images of smaller sub-areas. Substantial transport of sandy sediments can thus be excluded in the course of the observation period. Grid files of advective velocity components and orbital velocity of wave motion of a three-dimensional hydrodynamical model for the period from September 1996 to October 1997 were used to estimate the current regime in the study area for the interval between the two sidescan surveys. Comparing critical velocities for the dominant sediment types with the results of the numerical bottom current simulations and the observations from sidescan images, it is apparent that strong current events during the modelled time interval were still too weak to resuspend and transport sand of any grain size, even though maximum current velocities of 30 cm/s at the seafloor were modelled. Only a few patches of newly accumulated (acoustically soft) material (mud, fluff and/or soft plant remnants), with a horizontal extension of about 10 m at a terrain step feature, were recognised in the 1998 mosaic. Our results imply that sand deposits in the southern Baltic Sea can remain stationary over time periods of several years, and that the transport of organic material, nutrients and associated pollutants to depositional areas in deeper water is predominantly accomplished by the movement of material finer than sand. A significant portion of this fine material is evidently transported in the bottom boundary layer under conditions of moderate hydrodynamical forcing.  相似文献   

Distribution of population-based indicators across multiple taxa to assess the status of Gulf of Alaska and Bering Sea groundfish communities     

Mueter  Franz J.; Megrey  Bernard A. 《ICES Journal of Marine Science》2005,62(3):344-352

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Detection of the water-soluble fraction of crude oil by the blue crab, Callinectes sapidus     

Walter H Pearson  Stephen E Miller  J.W Blaylock  Bori L Olla 《Marine environmental research》1981,5(1):3-11

The ability of the blue crab, Callinectes sapidus, to detect petroleum hydrocarbons was measured with behavioural techniques. When presented with a water-soluble fraction of Prudhoe Bay crude oil, blue crabs abruptly changed antennular orientation, began rhythmic beating of the maxillipedal flagellae, and increased antennular flicking rate. The threshold concentration at which 50% of the crabs detected the water-soluble fraction was 2 × 10^?6 mg/litre. The blue crab apparently can readily detect petroleum hydrocarbons at concentrations found in chronically polluted areas as well as oil spill situations.  相似文献   

Symbiotic Relations of Sediment-Agglutinating Nematodes and Bacteria in Detrital Habitats: The Enzyme-Sharing Concept   总被引：2，自引：0，他引：2  

Franz Riemann  & Elisabeth Helmke 《Marine Ecology》2002,23(2):93-113

Abstract. A new concept (‘enzyme sharing’) concerning the interaction of marine nematodes and microbes in the degradation of sedimentary detritus is presented. Elements of this concept are (1) the notorious tendency of many aquatic nematodes to agglutinate detrital particles by mucus secretions, (2) new observations on the stimulation of microbial growth by nematodes in agar plates, and (3) literature data on limited endogenous proteolytic capacities of aquatic nematodes.
Observations on nematode‐microbe associations in agar plates prompted the conceptual synthesis. In agar medium without the addition of any nutrients a spectacular growth of bacteria was visible on the sinusoidal crawling trails of nematodes only 2 – 3 days after introduction of the worms (species of Adoncholaimus, Anoplostoma and Sabatieria). Juveniles of Anoplostoma that hatched in the agar cultures left their minute trails in the medium and these were rapidly occupied by bacteria. The nematodes repeatedly visited their bacterial trails, which persisted as a peculiar biotic structure for more than one year and survived the nematodes.
In sterile agar preparations containing the fluorogenic methylumbelliferyl‐β‐glucoside in the presence of the nematode Adoncholaimus, an enhanced fluorescence of the medium was visible, indicating β‐glucosidase activity. We therefore assume that oncholaimid nematodes discharge enzymes that alone, or in concert with microbial activities, contribute to the hydrolytic cleavage of refractory polysaccharides containing β‐glucosidic bonds such as agar components and cellulose. The sugars thus produced may then be taken up by the nematodes and concomitantly support the conspicuous growth of microbes. Since we did not observe any feeding of the nematodes on the associated microbes in agar plates, we question the nutritive potential of intact microbial cells for a number of nematodes abounding in detrital habitats, and call attention to the significance of ambient dissolved or adsorbed organic monomeric nutrients.
Consequently, we perceive the puzzling perpetual accretion of detrital organic particles to sediment agglutinations by nematodes as an adaptation for operating an ‘enzymatic reactor’ for the production of dissolved nutrients. We hypothesise a relationship of mutual commensalism of nematodes and heterotrophic microbes in detrital habitats and propose the term ‘enzyme sharing’ for this relationship. Both parties invest in a common enzyme pool that decomposes organic detritus for their nutrition. We present here evidence that nematodes contribute β‐glucosidase, which is involved in the cellulase system. Data from the literature suggest that microbial enzymatic processing of detrital proteins yields amino acids available to nematodes, which apparently have no efficient proteolytic enzyme system in their intestines.  相似文献