Fish community structure of the St Lucia Estuarine System under prolonged drought conditions and its potential for recovery after mouth breaching     

Leon Vivier  Digby P. CyrusHendrik L. Jerling 《Estuarine, Coastal and Shelf Science》2010

The St Lucia Estuarine System, South Africa, has been under pressure due to recent drought conditions, which have led to closure of the mouth, extremely low lake levels and hypersaline conditions. The estuary mouth closed in June 2002 and remained so for almost 5 years before being breached by Cyclone Gamede in May 2007. After mouth closure in August 2007, salinities in South and North Lake gradually increased to reach highs of 68 at the end of 2008, while salinities in the Narrows gradually declined during the study. Fish were sampled biannually during 2006–2008 with seine and gill-nets at six sites throughout the system. A total of 20,422 fish from 72 species were recorded, with the number of species and CPUE gradually decreasing from the Narrows throughout the system to Hells Gate in the upper parts of the system. The fish community was dominated by the freshwater species Oreochromis mossambicus, and two estuarine species, Ambassis ambassis and Hyporamphus capensis. The fish community was dominated in terms of species numbers by marine spawning species, but in terms of fish abundance by freshwater and estuarine breeding species. Recruitment of post-larvae of 20 marine species into the system occurred following opening of the mouth in March 2007, highlighting the importance of the system as a nursery area for marine species. The fish community was structured by spatial differences between sampling areas and between the three main compartments of the system, and not by temporal changes during the study period.  相似文献   

Wave propagation in an inhomogeneous cross‐anisotropic medium     

Cheng‐Der Wang  Ya‐Ting Lin  Yu‐Shiuh Jeng  Zheng‐Wei Ruan 《国际地质力学数值与分析法杂志》2010,34(7):711-732

Analytical solutions for wave velocities and wave vectors are yielded for a continuously inhomogeneous cross‐anisotropic medium, in which Young's moduli (E, E′) and shear modulus (G′) varied exponentially as depth increased. However, for the rest moduli in cross‐anisotropic materials, ν and ν′ remained constant regardless of depth. We assume that cross‐anisotropy planes are parallel to the horizontal surface. The generalized Hooke's law, strain–displacement relationships, and equilibrium equations are integrated to constitute governing equations. In these equations, displacement components are fundamental variables and, hence, the solutions of three quasi‐wave velocities, V_P, V_SV, and V_SH, and the wave vectors, $\mathop{\mathop{l}\limits^{\rightharpoonup}}\nolimits_{P}$ $\mathop{\mathop{l}\limits^{\rightharpoonup}}\nolimits_{\mathit{SV}}$, and $\mathop{\mathop{l}\limits^{\rightharpoonup}}\nolimits_{{\mathit{SH}}}$, can be generated for the inhomogeneous cross‐anisotropic media. The proposed solutions and those obtained by Daley and Hron, and Levin correlate well with each other when the inhomogeneity parameter, k, is 0. Additionally, parametric study results indicate that the magnitudes and directions of wave velocity are markedly affected by (1) the inhomogeneous parameter, k; (2) the type and degree of geomaterial anisotropy (E/E′, G′/E′, and ν/ν′); and (3) the phase angle, θ. Consequently, one must consider the influence of inhomogeneous characteristic when investigating the behaviors of wave propagation in a cross‐anisotropic medium. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

大气科学类专业毕业生就业意向对气象部门人才招聘工作的启示     

蔡金玲  林巧  乐青 《气象科学进展》2020,10(2):83-86,122

大气科学类专业毕业生是全国气象部门补充人才资源、建设气象人才梯队的主要来源。然而,随着气象事业发展的需求以及外部竞争的加剧,气象部门招聘大气科学类专业毕业生面临的压力持续增长。调查研究大气科学类专业毕业生的就业意向,对气象部门提高招聘工作效率和招聘质量有重要意义。  相似文献   

基于个体模型的东海鲐鱼渔场形成机制研究   总被引：4，自引：2，他引：2  

李曰嵩  潘灵芝  严利平  陈新军 《海洋学报》2014,36(6):67-74

鲐鱼Scomber japonicus资源丰富,在我国近海渔业中占有重要地位。其渔场的形成受海洋环境的制约,本文确定鲐鱼运动和物理环境之间的响应关系,建立起了基于个体的东海鲐鱼生长洄游模型。结果显示,鲐鱼集群分布与捕捞生产渔场基本吻合,鲐鱼聚集主要受台湾暖流、大陆沿岸水、黑潮影响,往往集群在一定温度范围内并在冷暖交汇区温盐梯度大偏暖水一侧。在台湾暖流和沿岸水交汇的锋面附近、台湾暖流暖水舌前端、黑潮与中国大陆沿岸水形成的潮境区域均有大量的鲐鱼聚集,并形成渔场。产卵位置的变动使偏西产卵位置的鲐鱼由于受台湾暖流影响较大,鲐鱼会呈长带状大量聚集在台湾暖流和沿岸水的锋面附近,并使在台湾暖流暖水舌前端的聚集数量增多,而偏东的产卵的鲐鱼受黑潮影响较大,聚集分布范围较大,会使黑潮形成的锋面附近聚集数量增多,而使台湾暖水舌的前端的聚集量减少。正常产卵位置在生存率方面是最佳产卵位置。研究表明鲐鱼所处空间位置不同,会影响其集群的位置,用数值模型验证了物理环境会对鲐鱼的洄游和渔场的形成产生影响。  相似文献   

Climatic Controls of Saguaro (Carnegiea Gigantea) Regeneration: A Potential Link With El Niño     

《自然地理学》2013,34(6):465-475

Saguaro cacti establish periodically in cohorts during years that are climatically favorable. Determining the establishment year is complicated by age-height relationships that vary considerably from site to site and require extensive data collection. Estimations of age-height relationships for only a few locales have thus limited the ability of researchers to estimate age in other populations, and consequently to relate periods of regeneration to climate. We collected data for 254 saguaros in the arid western portion of the species' range and employed a recently developed site-specific technique for estimating saguaro age to reconstruct the population structure at this locale. Second, we used discriminant analysis to determine which climate variables best predict regeneration years. We found that above-average temperatures in November coupled with concurrent high soil moisture levels, conditions typically associated with El Niño years, are associated with years characterized by high regeneration. Accordingly, these results suggest that El Niño events may be related to years of favorable regeneration for saguaros.  相似文献   

A Meta-analysis of the Effects of Warming and Elevated CO2 on Soil Microbes     

FU Gang  ZHANG Haorui  LI Shaowei  SUN Wei 《资源与生态学报(英文版)》2019,10(1):69-76

Soil microbes play important roles in terrestrial ecosystem carbon and nitrogen cycling. Climatic warming and elevated CO₂ are two aspects of climatic change. In this study, we used a meta-analysis approach to synthesise observations related to the effects of warming and elevated CO₂ on soil microbial biomass and community structure. Ecosystem types were mainly grouped into forests and grasslands. Warming methods included open top chambers and infrared radiators. Experimental settings included all-day warming, daytime warming and nighttime warming. Warming increased soil actinomycetes and saprotrophic fungi, while elevated CO₂ decreased soil gram-positive bacteria (G⁺). Mean annual temperature and mean annual precipitation were negatively correlated with warming effects on gram-negative bacteria (G^-) and total phospholipid fatty acid (PLFA), respectively. Elevation was positively correlated with the warming effect on total PLFA, bacteria, G⁺ and G^-. Grassland exhibited a positive response of total PLFA and actinomycetes to warming, while forest exhibited a positive response in the ratio of soil fungi to bacteria (F/B ratio) to warming. The open top chamber method increased G^-, while the infrared radiator method decreased the F/B ratio. Daytime warming rather than all-day warming increased G^-. Our findings indicated that the effects of warming on soil microbes differed with ecosystem types, warming methods, warming times, elevation and local climate conditions.  相似文献   

民勤白刺枝条形态对人工增雨的响应   总被引：1，自引：0，他引：1  

张金鑫  吴波  朱雅娟  卢琦  李永华 《中国沙漠》2012,32(3):709-716

为研究全球变化情景下降雨格局变化对干旱区植被的影响,以甘肃民勤的典型荒漠植被白刺灌丛为研究对象,在生长季内人工模拟不同增雨梯度（+0%、+25%、+50%、+75%和+100%多年平均降水量）,分析白刺枝条形态特征的变化规律。结果表明,白刺枝条各形态指标间存在很好的相关性。7-9月,75%和100%增雨的枝条长度显著大于0%增雨,枝条新生叶片数只在8月表现为100%增雨显著大于0%增雨。8-9月,100%增雨的营养枝基部直径显著大于0%增雨,成熟叶片数和干物质重量在增雨梯度下各月均不显著。花枝的基部直径在7-9月均表现为100%增雨显著大于0%增雨,7月100%增雨的花枝成熟叶片数显著大于0%增雨,而花枝干物质重量在6-8月表现为100%增雨显著大于0%增雨。针对降雨格局变化,白刺不同枝条形态特征的调节适应机制之间存在着一定的内在协调性。  相似文献   

Puerulus and juvenile abundance in the rock lobster Jasus edwardsii at Stewart Island,New Zealand (Note)     

Paul A. Breen  John D. Booth 《新西兰海洋与淡水研究杂志》2013,47(4):519-523

Settlement of puerulus‐stage New Zealand red rock lobsters (Jasus edwardsii) and abundance of the first three juvenile cohorts were measured from 1981 to 1989 near Halfmoon Bay, Stewart Island. Puerulus settlement on subtidal collectors shows great annual variation. Juvenile abundance, estimated from the number caught in annual diver collections, shows less variation. One‐year‐olds appear less vulnerable to diver sampling than older juveniles. Abundance of 2‐ and 3‐year‐olds is highly correlated with puerulus settlement 2 and 3 years previously. Survival between puerulus and 1+ stages appears to be density‐dependent, but survival of older juveniles does not. Size is inversely related to abundance in 3+ females but not in the other cohorts, suggesting density‐dependent growth between ages 2 and 3. Puerulus settlement rates and processes on shallow inshore reefs appear to be important in determining recruitment strength in this species.  相似文献   

东海鲐鱼(Scomber japonicus)仔幼鱼游泳行为对输运和补充量的影响     

李曰嵩  潘灵芝  陈新军  费岳军 《海洋与湖沼》2013,44(2):318-325

采用物理环境因子,确定鲐鱼仔幼鱼运动和物理环境之间的响应关系,建立起了基于个体具有游泳行为的鲐鱼早期生长史模型。结果表明,具有游泳行为仔幼鱼前期对输运分布的影响不大,后期随着游泳能力的增强,逐渐在温盐梯度较大锋面,靠近暖水的一侧进行集群和滞留,并使向东北输运速度降低,输运到太平洋和日本海的幼鱼数量下降,所处水深降低,适应生长发育,死亡率降低。产卵场位置的变动使偏西产卵的集群受台湾暖流影响较大,导致集群偏西,主要聚集在偏北的台湾暖流水和长江冲淡水交汇区高温、高盐一侧。偏东产卵受黑潮影响较大,集群偏东,不形成大量聚集和滞留;在生存率方面正常产卵位置是最佳产卵位置。研究认为,物理环境和生物因素同样会对具有游泳行为仔幼鱼的输运和补充产生影响。  相似文献   

A limit reference point to prevent recruitment overfishing of Pacific bluefin tuna     

《Marine Policy》2017

Pacific bluefin tuna (PBF) (Thunnus orientalis) is commercially important in the North Pacific Ocean. Although its stock has been relatively low for decades, international discussions on a long-term management framework, including the definition of a limit reference point (LRP), have only recently started. This paper argues that an LRP for PBF could be developed by determining a biomass level that would prevent recruitment overfishing. First, it reviews the development of LRPs for various tuna species and demonstrates that most of these limits are not necessarily based on biological information on the respective species. Then, the current management of PBF is also reviewed as background information for considering an LRP for PBF. Finally, a variety of simple analyses of the stock–recruitment relationship of PBF are conducted to find a biomass level that would prevent recruitment overfishing—i.e. an LRP below which stocks should not fall. It is concluded that, for the first time to our knowledge, defining such an LRP for a tuna species is possible (about 30 thousand tonnes or 5% of estimated unfished spawning stock biomass in our calculation). Not only is the LRP based on actual experience, but also the logic behind it would be easier for stakeholders to understand than the theoretical LRPs used elsewhere. This LRP should be useful in future in more comprehensive management framework, such as one through management strategy evaluations, in which stakeholder involvement in decision-making is crucial.  相似文献