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排序方式: 共有268条查询结果,搜索用时 27 毫秒
91.
92.
M. M. Walker 《新西兰海洋与淡水研究杂志》2013,47(4):393-397
Development, settlement, and subsequent metamorphosis on several substrata were observed in cultures of Evechinus chloroticus larvae. The period from fertilisation to metamorphosis ranged between 30 and 63 days for larvae collected from spawnings induced at 3 different times. Newly settled sea urchins collected from the field grew about 1 mm per month in aquaria. Correlation of the larval life span with the growth rate of newly settled sea urchins suggested that the earliest spawning could occur was mid‐November. This finding corroborates the results of previous histo‐logical studies of the gonads of adult sea urchins in the Hauraki Gulf, New Zealand. 相似文献
93.
Alan N. Baker 《新西兰海洋与淡水研究杂志》2013,47(2):291-299
Analysis of 326 stomachs of the kahawai, Arripis trutta (Bloch and Schneider), from Wellington Harbour showed that the fish is a voracious carnivore which feeds mainly on fishes and to a lesser extent on planktonic crustaceans. The kahawai is principally a pelagic feeder, but occasionally takes food from the sea bottom; it appears to feed on those fishes which are locally most abundant, and follows shoals of small fish on which it preys. Small kahawai below 100 mm in length eat mainly copepods. 相似文献
94.
Framework of aftershock fragility assessment–case studies: older California reinforced concrete building frames 下载免费PDF全文
Current seismic design codes and damage estimation tools neglect the influence of successive events on structures. However, recent earthquakes have demonstrated that structures damaged during an initial event (mainshock) are more vulnerable to severe damage and collapse during a subsequent event (aftershock). This increased vulnerability to damage translates to increased likelihood of loss of use, property, and life. Thus, a reliable risk assessment tool is required that characterizes the risk of the undamaged structure subjected to an initial event and the risk of the damaged structure under subsequent events. In this paper, a framework for development of aftershock fragilities is presented; these aftershock fragilities define the likelihood that a building damaged during a mainshock will exhibit a given damage state following one or more aftershocks. Thus, the framework provides a method for characterizing the risk associated with damage accumulation in the structure. The framework includes the following: (i) creation of a numerical model of the structure; (ii) characterization of building damage states; (iii) generation of a suite of mainshock–aftershocks; (iv) mainshock–aftershock analyses; and (v) development of aftershock fragility curves using probabilistic aftershock demand models, defined as a linear regression of aftershock demand–intensity pairs in a logarithmic space, and damage‐state prediction models. The framework is not limited to a specific structure type but requires numerical models defining structural response and linking structural response with damage. In the current study, non‐ductile RC frames (low‐rise, mid‐rise, and high‐rise) are selected as case studies for the application of the framework. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
95.
古尔班通古特沙漠南缘心叶驼绒藜种群更新的空间格局 总被引:6,自引:3,他引:3
心叶驼绒藜(C. ewersmanniana)是干旱区优质牧草和防风固沙植被的主要物种。在古尔班通古特沙漠南缘选择两个200 m×200 m具代表性样地,采用Ripley’s K(d)函数分析了心叶驼绒藜种群更新空间特征以及与群落梭梭(Haloxylon ammodendron)、琵琶柴(Reaumuria soongorica)、新疆绢蒿(Seriphidium kaschgaricum)等三种主要灌木物种间作用关系。发现两个样点心叶驼绒藜大株(繁殖株)的空间分布对后代以及整个种群的空间分布影响极大,两个样点心叶驼绒藜大株、中株均与幼株间呈不同尺度的正关联,全部植株以及幼株都与新疆绢蒿呈正关联,与梭梭呈负关联,与琵琶柴关联性在两个样点结果相反。分析认,为心叶驼绒藜种群更新对成株依赖性极强,空间扩展能力很低。在0—35 m范围内种群更新的空间自相关性明显。四种灌木空间分布关系除受各自生态位决定外,主要受水等环境因素作用。最后对心叶驼绒藜等生态恢复方法提出建议。 相似文献
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Francisco Leitão Miguel N. Santos Karim Erzini Carlos C. Monteiro 《Marine Ecology》2008,29(4):435-448
Artificial reefs (ARs) have been deployed in Algarve (Southern Portugal) coastal waters to contribute to the sustainability of local nearshore fisheries. Herein, we describe the colonization process of the recently deployed Faro/Ancão AR, and assess the time until the fish assemblage reaches stability and their seasonal patterns. In addition, we compare the results from the present study with those previously reported for an older AR. The fish assemblages were monitored monthly over a 2‐year period by means of visual census. A rapid increase in fish colonization occurred within the first 4 months. After this initial period the assemblage structure showed high similarity (> 73%). The high rate of colonization of the AR was related to the maturity already achieved by the nearby 14‐year‐old AR and to the fish migration from the Ria Formosa lagoon, a nearby nursery habitat. The reef fish assemblage structure showed a seasonal pattern, mainly associated with recruitment episodes of occasional demersal species (Boops boops, Trachurus trachurus and Pagellus spp.) in spring and summer. A total of 66% of the species found in AR are of commercial and recreational importance. The overall mean density and biomass were 2.8 ind·m?3 and 207 g·m?3. The occasional demersal species accounted for 42% of the fish density. The most important species in terms of biomass belong to the Sparidae family along with Dicentrarchus labrax. The fish assemblage of the new ARs showed higher mean number of species, diversity, density and biomass values than those reported for the older AR. This result was associated with enlargement of the AR area and with the fishing exploitation of the isolated, small and patchy old AR. Moreover, the high biomass values recorded in the new ARs were mainly due to the increased density of D. labrax after AR enlargement. The results of the present study are used to define guidelines for suitable management strategies for the AR areas that are exploited by the local commercial and recreational fisheries. 相似文献
100.
Kangkuso Analuddin Sahadev Sharma Rempei Suwa Akio Hagihara 《Journal of Oceanography》2009,65(1):121-127
The crown foliage dynamics of Kandelia obovata (S., L.) Yong were investigated, including leaf recruitment, survival and leaf growth. Newly flushed leaves occurred successively
throughout the year, with a maximum in July and a minimum in January. The highest leaf death was in August, whereas it was
the lowest in January. The relative mortality rate of leaves seemed to depend on the season when new leaves flushed. The growth
pattern of leaves varied among seasons. The maximum leaf area was significantly larger in winter than in autumn, but showed
no significant difference between the winter and the other seasons. The half-expansion period and the intrinsic rate of increase
were respectively longer and lower in winter than in the other seasons. Therefore, leaves flushed in summer grew faster in
their initial stage and attained their maximum leaf area sooner than those flushed in winter. This most likely results from
the difference in temperature between summer and winter. The crown leaf area was almost stable throughout the year, as if
homeostatic control is likely to function. Stipule litterfall decreased significantly with increasing flower and propagule
litterfalls, indicating that a high production of flowers and propagules results in low leaf recruitment. This may be because
flower production and propagule growth impose a severe burden on K. obovata. 相似文献