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951.
952.
The photosynthetic responses of the south Pacific kelp Lessonia nigrescens of the coast of Valdivia, Chile (40°S), were investigated by exposing its different thallus parts, fronds, stipes and holdfasts, to UV radiation in the laboratory. Biologically effective doses (BEDphotoinhibition300) between 400 and 800 kJ m−2 were required for a 40% inhibition in photosynthesis under UVA+UVB radiation. At BEDphotoinhibition300 close to 250 kJ m−2 (in treatments without UVB), the inhibition of photosynthesis did not exceed 20%. These UV doses were in the range of current daily doses measured in Valdivia on cloudless summer days. In general, exposure to UVB for periods longer than 12 h reduced photosynthesis, measured as maximal quantum yield (F v/F m) and electron transport. The fronds were the most UV-sensitive section of this alga, coinciding with the highest pigments contents and carbon fixation. Evidence of a photodamage was also seen. After a 48 h exposure to PAR+UVA+UVB, a decrease of F v/F m in the fronds was close to 41%, while in the stipes and holdfasts it was 12 and 18%, respectively. Although the thalli from the different size classes showed marked differences in their morphology and morphometry, no obvious differences in the UV tolerance of the fronds were detected. The results indicated that the UV-related responses are integrated in the suite of morpho-functional adaptations of the alga. Although the fronds are spatially more exposed to solar radiation than basal structures (stipes and holdfast), due their high turnover rate they may compensate better detrimental effects of UV. In contrast, stipes and the holdfast are key support structures characterized by low replacement rates and designed to confer hydrodynamic resistance to drag forces.  相似文献   
953.
Loss of two pesticides with different mobility characteristics, bentazone (Koc approximately 34) and propiconazole (Koc approximately 1800), were studied at three agricultural fields (Askim, Bj?rnebekk and Syverud) in SE Norway. A conservative tracer (Br) was used to follow the flow of water. The loss of pesticides varied among the fields, depending on hydrological characteristics and soil properties. The loss of pesticides was higher from two artificially levelled silty clay loam soils with poor aggregate stability (Askim and Bj?rnebekk) compared to a loam/silt loam soil with increased content of organic carbon and better aggregate stability (Syverud). The total accumulated loss was <0.5% from all fields. The highest pesticide concentrations were measured at the first runoff episode after application for both the mobile (bentazone) and less mobile pesticide (propiconazole) in the surface runoff. In the drainage water, the peak for the less mobile pesticide coincided with the Br tracer, while the peak for mobile pesticide appeared earlier than the Br tracer. Rapid movement of water, particles and pesticides through soils indicate flow through macropores. Larger proportions (in percent of total applied) of both the mobile and the strongly sorbed pesticides were lost through the drainage as compared to the loss through surface runoff at Askim. Here, it is suggested that macropore flow contribute to the increased loss of pesticides through the drainage. At Syverud, high infiltration capacity reduces the amount of water available for surface runoff, and somewhat higher loss of the mobile pesticide was registered in the drainage compared to the surface runoff. For the strongly sorbed pesticide, however, propiconazole was neither detected in surface nor in drainage water at Syverud. Generally, there was a higher percentage loss of the mobile compared to the strongly sorbed pesticide in both surface and drainage water, which is in agreement with the pesticides mobility characteristics in soil. An exception was, however, the erodible soil Bj?rnebekk, where a higher fraction of propiconazole was lost in the surface runoff compared to bentazone. Large amounts of sediment transport from the Bj?rnebekk field probably contributed to enhanced transport of the strongly sorbed pesticide.  相似文献   
954.
The coastline of South Africa is characterized by extensive dune fields which are threatened by development, and thus the demand of stabilization of drift sand will increase. The non-invasive alien grass speciesAmmophila arenaria is at present the dominant sand stabilizer. Due to its foreign origin and invasiveness in North America its use was criticized and indigenous sand-binding species would be preferred. The germination requirements of the nativeArctotheca populifolia, Ipomoea pes-caprae. Myrica cordifolia andScaevola plumieri were investigated. The results showed that for all four species the total germination time and germination phase could be shortened and germination success (number of germinated seeds) improved. The different scarification and stratification treatments broke the dormancy ofI. pes-caprae, M. cordifolia andS. plumieri, whereas the seeds ofA. populifolia were not dormant. Seeds ofI. pes-caprae andM. cordifolia had induced an innate dormancy, respectively, whereas the type of dormancy in seeds ofS. plumieri dormancy processes remained unknown.  相似文献   
955.
Diel changes in the composition of crustacean zooplankton and the diets of fish predators from an intertidal eelgrass flat were monitored concurrently. The zooplankton is characterized by two major components. The obligate zooplankters (holoplanktonic calanoid copepods and meroplanktonic decapod larvae) appear to exhibit vertical migration, being present in higher densities near the surface of the water column at night. The facultative zooplankton (amphipods and ostracods) are benthic during the day, but move up into the water column at night. Planktivorous midwaterdwelling fish consume calanoid copepods and decapod larvae during the day and cease feeding or switch their diet to amphipods at night. Benthic-dwelling fish consume some amphipods during both day and night. The factors important in prey selection by fish and the functional significance of vertical migration in both components of the zooplankton are discussed in the light of the changing patterns of fish predation.This paper is Publication No. 183 in the Ministry for Conservation of Victoria, Environmental Studies Series.  相似文献   
956.
Metabolic rates of the ctenophore Beroe ovata within the length range from 0.4 mm (newly hatched larvae) to 60 mm were investigated. At 20° the respiration rates (Q, µg O2 ind.–1 h–1) of individuals with wet weights (W, mg) less than or greater than 100 mg changed according to the equations Q=0.093W0.62 and Q=0.016W0.99, respectively. The weight-specific respiration rate of the juvenile ctenophores with wet body weights of 0.021–100 mg diminished approximately 20-fold (from 0.35 to 0.017 µg O2 mg–1 h–1, respectively), but did not change within the range from 100 to 30,000 mg. The difference in the slope of the regression lines seems to be attributable to the ontogenetic changes in B. ovata metabolism. For the tested temperature range of 10–28°, the mean Q10 coefficient was equal to 2.17±0.5. The basal metabolism of B. ovata narcotised by chloral hydrate was 4.5±0.9 times lower than total metabolism. Such a metabolic range is considered to be characteristic of aquatic invertebrates with high levels of locomotory activity.Communicated by O. Kinne, Oldendorf/Luhe  相似文献   
957.
The hypothesis that the behaviour of deep-sea scavenging fishes is influenced by seasonal input of organic matter from the ocean surface was investigated by observing responses to baits placed on the sea floor at 4800 m depth in the NE Atlantic (48°50′N; 16°30′W) during spring (April 1994). Data from the present study are compared with those from previous studies of the same location made in summer 1989. The first fishes to arrive at baits were the grenadier Coryphaenoides (Nematonurus) armatus and the eel Histiobranchus bathybius, after delays of 28 and 29 min, respectively; these results are not significantly different from those of summer 1989. Similarly, other indices of activity (staying time and swimming speed) showed no evidence of differences between years/seasons. However, the rate of radial dispersal of bait (0.009 m s−1) by C. (N.) armatus was much slower than in all previous studies. A change in the size distribution of C. (N.) armatus to smaller individuals in spring 1994 was also evident. It is suggested that the fish on the abyssal plain may not comprise a steady-state population and that major episodic or seasonal migrations may occur. Received: 18 October 1996 / Accepted: 20 December 1996  相似文献   
958.
A study of gonadal state in 39 small specimens of Arctica islandica Linné collected in April 1976 from the Middle Atlantic shelf of North America suggests that sexual maturity is reached at a later age than has been reported for other shelf bivalves. Eight of the specimens had gonads in the undifferentiated state. On the basis of annual internal growth banding in the shells of these immature specimens, age ranged between 4 and 14 years. Average age was 9.38 years (standard deviation, s,= 3.54). Shell length ranged from 24 to 47 mm (average 38.85 mm, s=9.25). Differentiated gonads were found in specimens as young as 6 years. Age of maturity shows a wide range and may be dependent upon growth rate and locality.  相似文献   
959.
The production of bacterioplankton in tropical waters is shown to be a major food source for filter feeders. Since this production greatly exceeds autotrophic production by phytoplankton, the external energy source is believed to be soluble organic material transported from temperate latitudes. In the latter environment this material is produced as part of excessive autotrophic production, but its destruction by bacteria is inhibited at low temperature. The organic material is transported by global circulation to warm tropical waters, where it is utilized to form particulate organic aggregates which serve as food for filter feeders.  相似文献   
960.
Escape-swimming speeds (U max) were studied in settled turbot (Scophthalmus maximus L.) reared at 18°C. Metamorphosis was complete at 4.0 cm total length (TL). U max scaled in proportion to TL0.74 in fish of 0.88 5o 8.00 cm TL at 18C. The scaling relationship for U max was similar for temperatures between 13 and 23°C and could be fitted by the model: . U max temperature-dependent, with a Q10 of 1.77 over the temperature range studied. Analysis of covariance showed that U max for farmed turbot was 14% lower than for wild fish filmed within 2 wk of capture; 3 mo after capture the average differences in escape performance were no longer significant, which suggests that the lower escape speeds of farmed fish are due to acclimation effects and not genetic stock differences. In order to assess the individual variability of U max, 18 wild juvenile turbot [TL=6.2±0.4 cm (Week 1) to 7.5±0.5 cm (Week 17); means±SD] were maintained in individual containers at 18°C. U max was determined weekly for 6 wk, standardised for fish length using the scaling relationship U max=1.46 TL 0.74, and individuals were ranked in order of performance. Temperature was reduced after 6 wk to 13°C, resulting in a significant decline in U max from 104.0±14.4 to 87.8±12.5 cm s-1 (means±SD). After 3 wk at 13°C U max had increased to a level not significantly different from that at 18°C. Kendall's coefficient of concordance showed that repeatability of ranking of the experimental U max of individuals was maintained over a 13 wk period and through temperature change. The results demonstrate that escape-swimming speeds in juvenile turbot are repeatable, individually variable, and can be modified in response to temperature acclination.  相似文献   
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