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Coral reefs are generally considered to be the most biologically productive of all marine ecosystems, but in recent times these vulnerable aquatic resources have been subject to unusual degradation. The general decline in reefs has been greatly accelerated by mass bleaching in which corals whiten en masse and often fail to recover. Empirical evidence indicates a coral reef bleaching cycle in which major bleaching episodes are synchronized with El Niño events that occur every 3–4 years on average. By heating vast areas of the Pacific Ocean, and affecting the Indian and Atlantic Oceans as well, El Niño causes widespread damage to reefs largely because corals are very sensitive to temperature changes. However, mass bleaching events were rarely observed before the 1970s and their abrupt appearance two decades ago remains an enigma. Here we propose a new explanation for the sudden occurrence of mass bleaching and show that it may be a response to the relative increase in El Niño experienced over the last two decades. 相似文献
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The morphological life-forms, that is to say, physiognomic-structural attributes, of two coral reef communities were used in a numerical analysis to determine the power of these attributes in recovering the underlying community structure. We used 17 attributes from the benthic communities at 6 reef slope sites on each of a midshelf and off-shore reef of the central Great Barrier Reef. These reefs had been previously well studied by traditional species-level means for several major taxonomic groups such as corals, fish and soft corals. Our multivariate analyses were able to recover broad patterns of between-reef affinity and discrete within-reef zonation patterns similar to those found in earlier studies, and in broad accord with the prevailing model of reef community structure, but with far greater efficacy. But perhaps more importantly, by placing all the benthos within the same context for the first time, our analyses were able to recover new patterns of community structure independent of the ones described earlier. This suggests that single-model explantations for the complex phenomena of coral reefs are likely to be inadequate. 相似文献
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Compartmentation of glutamate metabolism in brain. Evidence for the existence of two different tricarboxylic acid cycles in brain 总被引:18,自引:9,他引:9
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1. (14)C from [1-(14)C]glucose injected intraperitoneally into mice is incorporated into glutamate, aspartate and glutamine in the brain to a much greater extent than (14)C from [2-(14)C]glucose. This difference for [1-(14)C]glucose and [2-(14)C]glucose increases with time. The amount of (14)C in C-1 of glutamate increases steadily with time with both precursors. It is suggested that a large part of the glutamate and aspartate pools in brain are in close contact with intermediates of a fast-turning tricarboxylic acid cycle. 2. (14)C from [1-(14)C]acetate and [2-(14)C]acetate is incorporated to a much larger extent into glutamine than into glutamate. An examination of the time-course of (14)C incorporated into glutamine and glutamate reveals that glutamine is not formed from the glutamate pool, labelled extensively by glucose, but from a small glutamate pool. This small glutamate pool is not derived from an intermediate of a fast-turning tricarboxylic acid cycle. 3. It is proposed that two different tricarboxylic acid cycles exist in brain. 相似文献
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Physical illness or disability inevitably has a damaging effect on sexual relationships. Physicians are usually unaware of the sexual consequences of illness on their patients, and lack experience in treating sexual dysfunctions.The report of treatment of a couple with serious cardiovascular disease illustrates the potential efficacy of brief sex therapy for improving the quality of a patient''s life. If a primary physician lacks the skills to conduct sex therapy, he may collaborate with nonphysician therapists. The physician''s knowledge of the physiological and psychological effects of a specific illness on his patient is essential to successful therapy. Often, simple education, encouragement or reassurance by the physician is enough to overcome the damaging effects of illness on a patient''s sex life. 相似文献
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Nithyanand Paramasivam Eitan Ben-Dov Luba Arotsker Esti Kramarsky-Winter Assaf Zvuloni Yossi Loya Ariel Kushmaro 《Microbial ecology》2013,65(1):50-59
Colonies of the hydrocoral Millepora dichotoma along the Gulf of Eilat are exhibiting unusual tissue lesions in the form of white spots. The emergence and rapid establishment of these multifocal tissue lesions was the first of its kind reported in this region. A characterization of this morphological anomaly revealed bleached tissues with a significant presence of bacteria in the tissue lesion area. To ascertain possible differences in microbial biota between the lesion area and non-affected tissues, we characterized the bacterial diversity in the two areas of these hydrocorals. Both culture-independent (molecular) and culture-dependent assays showed a shift in bacterial community structure between the healthy and affected tissues. Several 16S rRNA gene sequences retrieved from the affected tissues matched sequences of bacterial clones belonging to Alphaproteobacteria and Bacteroidetes members previously associated with various diseases in scleractinian corals. 相似文献
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This study investigates the effect of water depth on stable isotope composition and density-band formation in the skeletal material of the zooxanthellate coral Porites lutea. In February 1991, several colonies were stained with Alizarin red-S and then transferred from 6 to 40 m. Ten years later, in February 2001, one colony was retrieved and analyzed. This provided us with the unique opportunity to maintain the corals genetic integrity and hence to isolate environmental factors affecting skeletal isotopic composition and density patterns. Despite extreme environmental changes experienced by the corals, the downward transplants showed no mortality after 10 years. Acclimatization of the coral to the deep-water environment involved changes in mean annual extension rates and colony morphology. The growth rate at 6 m was 5.66±0.47 mm/year, almost twice the growth rate following transplantation to 40 m, which was 3.00±0.37 mm/year. A significant difference in mean annual 18O between the shallow and deep growth phases (–3.10±0.10 and –2.80±0.14, respectively) and amplitude (1.14±0.15 and 1.49±0.20, respectively) was detected. Mean annual 13C in the shallow growth phase was –1.58±0.12, significantly heavier than that of the deep growth phase which was –1.92±0.14. The phase relation between 18O and 13C was also depth dependent. These results suggest that the role of the kinetic effect in determining skeletal isotopic composition of deep-water hermatypic corals in the study site is greater than in that of shallow-water colonies. The timing of density-band formation was found to be depth independent. At both depths, low-density skeleton is produced during summer, and high-density skeleton is produced during winter, implying that it is intrinsically controlled rather than environmentally governed. The implications of these results on paleoclimate and sea level reconstruction are discussed. 相似文献
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