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751.
The mutualism between the Hawaiian bobtail squid Euprymna scolopes and the luminescent symbiont Vibrio fischeri has been used extensively as a model system for studies ranging from co-speciation and biogeography to gene regulation and the evolution of pathogenesis. In this association, the luminescent bacterium V. fischeri is housed in a complex light organ within the mantle cavity of E. scolopes. Prior hypotheses have assumed that sepiolid squids in general utilize the bioluminescence produced by their V. fischeri symbionts for counterillumination, a behavior that helps squid camouflage themselves by matching down-welling moonlight via silhouette reduction. This assumption, based solely on the morphology of the squid light organ, has never been empirically tested for Euprymna in the laboratory. Here, we present data demonstrating that E. scolopes can modify the intensity of light produced by V. fischeri in the light organ as down-welling light intensity changes. Bacterial bioluminescence from the light organ is directly correlated with down-welling light intensity, suggesting that E. scolopes individuals utilize and control V. fischeri luminescence for counterillumination.Communicated by P.W. Sammarco, Chauvin  相似文献   
752.
Annual internal growth increments in shells of hard clams (Mercenaria mercenaria) provide an accurate record of both growth history and some types of environmental change. These increments were used to determine age and growth rate of hard clams collected in 1984–1985 from ten sites in Narragansett Bay, Rhode Island, USA, and to assess geographic variation in growth within the bay. The regional comparisons were facilitated by modeling the clam growth using the von Bertalanffy equation and the parameter of Gallucci and Quinn. The optimum region for hard clam growth was near the head of the bay, with areas further north (Providence River) and south (lower bay) not as productive. The relationship between size and age was similar to that reported for hard clams from northern New Jersey. Using dendrochronological techniques, variations in growth were analyzed on a temporal (year-to-year) basis. The comparative longevity of the hard clams (individuals with 40 annual bands were encountered) demonstrated that sclerochronologies of several decades were possible. A 26 yr growth record based upon 100 individuals was established, covering the years 1959–1984. Significant temporal variations occurred in bivalve growth, and a broad trend of increasing growth indices over the last two decades of the record was noted. The yearly standardized growth index values were highly and positively correlated with mean annual water temperatures in Narragansett Bay for the same time interval. The incremental shell records of these bivalves provide a quantitative indication of marine climatic (temperature) variability and growth which can be used in hindcasting the effects of natural or anthropogenic environmental perturbations.  相似文献   
753.
The Mediterranean endemic seagrass Posidonia oceanica forms beds characterised by a dense leaf canopy and a thick root-rhizome ‘matte’. Death of P. oceanica shoots leads to exposure of the underlying matte, which can persist for many years, and is termed ‘dead’ matte. Traditionally, dead matte has been regarded as a degraded habitat. To test whether this assumption was true, the motile macroinvertebrates of adjacent living (with shoots) and dead (without shoots) matte of P. oceanica were sampled in four different plots located at the same depth (5–6 m) in Mellieha Bay, Malta (central Mediterranean). The total number of species and abundance were significantly higher (ANOVA; P<0.05 and P<0.01, respectively) in the dead matte than in living P. oceanica matte, despite the presence of the foliar canopy in the latter. Multivariate analysis (MDS) clearly showed two main groups of assemblages, corresponding to the two matte types. The amphipods Leptocheirus guttatus and Maera grossimana, and the polychaete Nereis rava contributed most to the dissimilarity between the two different matte types. Several unique properties of the dead matte contributing to the unexpected higher number of species and abundance of motile macroinvertebrates associated with this habitat are discussed. The findings have important implications for the conservation of bare P. oceanica matte, which has been generally viewed as a habitat of low ecological value.  相似文献   
754.
Interaction between peat, humic acid and aqueous metal ions   总被引:2,自引:0,他引:2  
Analysis of peat samples from four regions of the British Isles indicates that the concentrations of Al, Pb and common transition metals tend, as expected, to be higher in regions subject to industrial pollution, but that the concentrations of the nontransition metals Na, K, Mg, Ca and Zn tend to be higher in regions remote from industrial pollution. Humic acids were extracted from the most polluted and least polluted of the peat samples and some characteristics of these acids were compared with those of two commercial acids. Values for stability constants of complexes formed between humic acids extracted from peat and Cu2+, Zn2+ or Pb2+ have been obtained by an ionexchange equilibrium method. Of the three metal ions examined, Pb2+ was found to form the most stable humic acid complexes, followed by Cu2+: this order agrees with the findings of Irving and Williams and of Bunzl. Implications to the binding of actinide and other heavy metal ions in aqueous humic acid are discussed.  相似文献   
755.
Distribution of the ring-necked pheasant (Phasianus colchicus) is nearly co-extensive with the boundary of Wisconsinan glaciation; this is an area of base-rich soils that are mostly developed in calcareous tills. Anderson and Stewart (1973) speculated that barium in the diet might be a factor limiting the pheasant establishment in habitats adjacent to areas of long-term sustaining populations in Illinois. Total Ba was calculated for soils of 74 conterminous counties for which there were pheasant population data. Barium over the range of about 480 to 700 mg kg–1 soil was unrelated to pheasant occurrence or to population indeces. The selective eating of iron-manganese concretions that are enriched in Ba might present a unique pathway for Ba loading.  相似文献   
756.
Laboratory measurements of oxygen consumption were made on Penaeus monodon (Fabricius) from protozoea to adult stage at temperatures between 15° and 35°C. The logarithmic relationship between weight-specific respiration rate (WRt) and temperature (T) for two size groups, Protozoea 1 (PZ1) to Postlarva 1 (PL1) and PL to adult, are given as; WRt=100.431+0.0146 (T) (ml O2 g-1 h-1) and WRt=10-0.948+0.0338 (T) (ml O2 g-1 h-1), respectively. Additionally, equations relating metabolic rate, temperature and size for the two size groups are; PZ1-PL1: log M=0.431+0.0146T+(1.25 (log TL)+0.579), and PL1-adult: log M=-0.948+0.0338T+(2.60(log CL)-0.683), where M=oxygen consumption in ml O2 individual -1h-1, T=temperature in °C, TL=total length in cm, and CL=carapace length in cm. Activation energies of 6 186.75 J for PZ1-PL1 and 14 066.62 J for PL-adults point to different metabolic pathways or to differences in the ratio between the metabolic pathways used.  相似文献   
757.
Some aspects of mining subsidence and its control in the US coalfields   总被引:1,自引:0,他引:1  
The problem of surface subsidence is rapidly becoming an important environmental consideration of active as well as abandoned mining operations in the USA. The damages attributed to this phenomenon range from simple land settlement to severe structural damage and have been experienced in both rural and urban areas spreading across thirty states.This paper presents a discussion on mining subsidence and its characteristics above US longwall and room-and-pillar mines. The influence of the geological controls on subsidence is discussed in detail and the effects of subsidence on man and his environment are presented and exemplified. In addition, a historical review of rules and regulations governing subsidence-related problems is given, leading to Public Law 95-87, the Surface Mining Control and Reclamation Act of 1977, and finally, the new regulations being developed under the regulatory reform program are discussed.  相似文献   
758.
759.
A monitoring scheme for blood lead was based on cord blood samples and maternal blood samples taken in Swansea, South Wales. A fall of around 20% during 1984–85 is described. During this period there was virtually no change in petrol sales in the area and no overall change in air lead levels. Air lead showed large seasonal changes but these were not reflected in blood lead. Water lead levels gave no evidence of changes of any importance during the period of monitoring. These results suggest that petrol lead was at most a minor contributor to blood lead.  相似文献   
760.
The functions of the third maxilliped of Penaeus merguiensis de Man are described. It has a 6-segmented endopodite which is used in feeding, grooming and possible pheromone reception. In feeding, large pieces of food are gripped by the stout spines on inner borders of the ischia which hold them to the mouth so that particles can be torn off and ingested. All the distal segments have long setae used in grooming chelate pereiopods and the antennules. In mature males there is a tuft of about 300 slender setae at the end of the propus, but its function remains obscure.  相似文献   
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