Variability of a cyprinid lake ecosystem with special emphasis on the native fish fauna under intensive fisheries management including common carp (Cyprinus carpio) and silver carp (Hypophthalmichthys molitrix)     

Detlev BarthelmesUwe Brämick 《Limnologica》2003,33(1):10-28

The lake investigated (Lake Heiliger See near the town of Angermünde, North-East Germany) is small (10.2 ha) but deep (z_max = 12 m, ? = 6.5 m). During summer the thermocline is at a depth of 4-5 m, and the hypolimnion is filled with H₂S already by mid-June, making 60-75% of the bottom area inaccessible to fish. The native fish fauna is dominated by planktivorous roach (Rutilus rutilus). A test stocking of silver carp (Hypophthalmichthys molitrix) together with an unplanned and erroneous stocking of common carp (Cyprinus carpio), coupled with an incorrectly calculated strong stocking of eel (Anguilla anguilla), which assumed that the total lake area yielded fish food organisms, brought about a strong depression of the food biomass available to native fish. Both silver carp and common carp showed a pattern of behaviour which only partly agreed with results obtained in experimental ponds prior to lake stocking. At least for 10 years there was a very low zooplankton biomass (mostly below 1 mg/l fresh weight) caused by silver carp and a strongly reduced benthos biomass (frequently below 1 g/m² fresh weight) caused by common carp and eel on H₂S-free bottom areas. Despite this extreme situation, which lasted for 20 years and is rarely found in lakes elsewhere, it was not possible to demonstrate negative effects on the native fish fauna comprising 16 species. Also the dominance pattern seems uninfluenced in the long run. A strong decline of the catchable roach stock was observed for some years, but the stock reappeared soon in comparable quantity. During the time of roach stock depression the individual growth of roach (and common carp) was particularly low. Nevertheless, roach succeeded in reproduction during this time in spite of the reduced zooplankton and detritus concentrations. Fry numbers per year ranged from 500-15 000 individuals/ha. The pike perch (Stizostedion lucioperca) was perhaps the most endangered species of all those living at small population numbers in the lake, since its fry is confined to the limnion where competition from silver carp and adult roach and perhaps predation by roach is highest. However the pike perch stock remained unchanged at the low level of 1950, the time prior of carp and eel stocking. All other rare species of Lake Heiliger See spawn in the littoral zone where fry survival conditions were less impacted. In summary, we present more evidence that the fish fauna of cyprinid lakes is more robust than in salmonid lakes. The regulation capacity of fish communities of eutrophic lakes seems to be able to offset even severe direct and indirect influences of fisheries management.  相似文献   

贵州瓮安陡山沱组磷块岩的稀土元素地球化学特征与沉积古环境   总被引：7，自引：1，他引：7  

解启来  陈多福  漆亮  陈先沛 《矿物学报》2003,23(4):289-295

晚元古代末的陡山沱期(550-600Ma)是地球历史生物、化学和气候变化的剧烈时期。通过对贵州瓮安陡山沱组磷矿的稀土元素研究，确定上矿层磷块岩的北美页岩标准化稀土模式具负Ce异常、轻和重稀土亏损及中稀土富集特征。下矿层磷块岩稀土模式为轻微负Ce异常、轻微的轻和重稀土亏损及中稀土富集。下矿层磷块岩的Ceanom值为-0．065～-0．077，上矿层磷块岩的Ceanom为-0．26～-0．291，表明瓮安磷矿沉积古环境从下矿层的还原条件转变为上矿层的氧化条件。这种南沱冰期之后的环境变化可能为瓮安动物群的大爆发提供了必要的条件。  相似文献   

Tylotites petiolaris吻部构造的发现   总被引：1，自引：0，他引：1  

韩健  张志飞  舒德干 《西北地质》2003,36(1):87-93

早寒武世澄江动物群提供了探索早期翻吻动物辐射的一个绝佳的窗口。澄江动物群翻吻动物包括8科10属10种，其中罗惠麟等(1999)依据仅有的一块不完整的标本建立Tylotites petiolaris，并将其归入叶足动物。2002年西北大学早期生命研究所野外工作组在尖山剖面采集到两块完整的具有吻部的标本，本文籍此对该属进行了进一步完善和补充，特别是吻部和躯干表面的特征，从而说明T．petiolaris为翻吻动物。因为与澄江动物群中其他翻吻动物形态有较大差异，据此建立瘤节虫科，新科Tylotitidae fam.nov.。描述如下：虫体较长，呈圆管状，长可达100mm，宽2～4mm。身体基本可以分吻部和躯干部两部分。吻部与Cricocosmia特别相似，为典型的三段式构造，从下到上可依次分为Ⅰ、Ⅱ、Ⅲ段，Ⅰ段与躯干前端连接，直径同于躯干，表面有10列纵向的略为弯曲的小刺(图版Ⅰ，图1a，1b；插图1)。最前端吻刺最为粗壮，向后的吻刺逐渐变小。Ⅱ段位于Ⅰ段之前，向前略微收缩，光滑无刺。Ⅲ段位于吻部顶端，可进一步分为A、B两部分：A段直径后端大于Ⅱ段，表面密布斜列排列的小刺，从后向前，小刺变大；B段光滑无饰，直径小于A段。Ⅲ段可强烈自由弯曲(图版Ⅰ，图1a，1d)。颈部长约5mm，表面光滑无饰，直径略小于躯干。躯干表面具56～58个环脊，52排粗刺，最前面第4～6个环脊表面无刺，环脊之间为环沟。躯干由前向后直径逐渐增加，在中后部增至最大，然后虫体直径基本上一致。躯干刺成行成列排列。环状分布的躯干刺随着环脊与环沟落差的变化而改变，到躯干后部逐渐减小。每一个环脊之上有12个粗刺，腹刺长度小于背刺。有些躯干刺的轴部显示较强的黄铁矿化，表明其可能为中空结构(图版Ⅰ，图1c)，可能有体腔伸入，躯干末端具有一对尾刺，躯干整体弯曲成6字形(图版Ⅰ，图1a，1b)。肠管从吻部一直延伸到躯干末端。肠道位于一个空闻的体腔内，Ⅰ段表面宽约1mm的黑色区域可能为胃，肛门位于躯干末端的腹面(图版Ⅰ，图1b)。T．petiolaris很可能表栖生活于海底底面上。因为体表长刺具有很强的防御作用，腹刺在运动过程中可以抓牢沉积物，所以，很可能通过背腹波动在海底底面作蠕形运动，也不排除蜷曲一解蜷的运动方式。吻部的主要功能可能为捕食。几条T．petiolaris个体相互盘绕(图版Ⅰ，图2)，很可能与其两性交配有关。  相似文献   

兴蒙造山带中二叠世哲斯期腕足动物古生物地理归属   总被引：2，自引：0，他引：2  

张松梅  王成文 《地球科学进展》2004,(Z1)

两极分布的凉水型分子是古地理一级区划的重要标志之一。根据兴蒙遣山带中二叠世哲斯期的10个腕足动物属(族)的地理分布的特征分析,Yakovlevia等腕足动物的地理分布具有两极分布的特点。是典型的凉水型的腕足动物,并具有亲北极生物的特征,其古生物地理区划应该属于北方大区。  相似文献   

Characteristics of Albaillella （ Albaillellarian ,Radiolarian） Fauna from Guadalupian to Lopingian Series in Permian, South China     

SunDongying XiaWenchen 《中国地质大学学报(英文版)》2003,14(4):314-320

On the basis of establishment of radiolarian biostratigraphy and conodont biostratigraphy,a radiolarian Albaillella fauna in the transitional environment from Guadalupian to Lopingian Series in Permian was found at a pelagic chert section in southeast Guangxi, South China. Radiolarian Albaillella is one of the most sensitive biology to the transitional environment. The Albaillella fauna shows an ecological evolutionary process from Guadalupian to Lopingian: declined stage-recovery stage-flourishing stage. The study of characteristics of the Albaillella fauna in the transitional environment may provide more information, not only for the subdivision and correlation of a high-resolution biostratigraphy, but also for influence of radiolarian Albaillella fauna on the pre-Lopingian mass extinction.  相似文献   

内蒙古阿拉善地区的第三系     

王培玉  王伴月 《地层学杂志》1998,22(3):216-219

依据丰富翔实的地层古生物资料,首次在内蒙古西部建立了比较完整的第三纪地层层序：命名或厘订了中始新统乌兰乌珠尔组、上始新统查干布拉格组、下渐新统乌兰塔塔尔组、上渐新统、下中新统乌尔图组、上中新统呼和好来组和上新统昂冈浩特组等７个地层单元;区分出了中始新世乌兰乌珠尔、晚始新世查干布拉格、早渐新世早期克克阿木、早渐新世晚期乌兰塔塔尔、晚渐新世因德里沟、早中新世乌尔图、晚中新世呼和好来和上新世昂冈浩特等８个动物群（组合）。  相似文献   

断裂系统在油气成藏中的作用     

陈溥鹤 《海相油气地质》1998,(4)

断裂系统在油气地质及成藏规律研究中具有重要意义。对于勘探和研究程度较低或很低的地区,应拓宽思路,充分利用各个地区的有利条件,开展多样的勘探和研究工作。在充分依靠先进勘探技术的同时,还应重视地面地质调查,尤其是重视已发现的地表油苗价值的开发。江西弋阳盆地和浙江金衢盆地白垩系红色砂质岩层内广泛分布裂缝性含油、含沥青显示说明,其分布明显受区域性断裂系统的控制。断裂系统与孔渗性相对较好的砂质岩配置,可形成地表油苗相对富集。  相似文献   

The significance of the physical environment of the Macquarie Marshes     

Philippa M. Brock 《The Australian geographer》1998,29(1):71-90

This paper explores the significance of the Macquarie Marshes, in particular providing an overview of their physical attributes. Previous literature has generally been restricted to specific fields and much is unpublished ‘grey’ literature. This paper emphasises the importance of this internationally recognised wetland, both as a complete ecosystem, and for specific landscape, water‐quality filtering, vegetation and fauna attributes. It provides an extended summary of the area and of its 1997 status. By summarising previous research, it provides a base from which future research can be scoped.  相似文献   

藏南康马地区石炭系—二叠系研究新进展   总被引：3，自引：2，他引：3  

陈俊兵  徐兴永  李文庆  贡布 《现代地质》2002,16(3):237-242

根据西藏江孜幅和亚东幅 1:2 5万区域地质调查工作的成果 ,阐述了西藏康马地区石炭系—二叠系新的划分方案 ;并根据新采集的腕足类、单体珊瑚和菊石等化石组合 ,讨论了各组的地层时代 ,认为本区二叠纪沉积作用可延续到晚二叠世早期 (吴家坪期 ) ,在原二叠系白定浦组之上建立了一个新组———江浦组 (P3 j)。结合邻区的地层对比 ,分辨出 2个伸展不整合 ;2个Ⅰ类不整合和 3个Ⅱ类不整合。最后初步分析了康马地区杂砾岩的成因 ,认为其与冰期—间冰期冻融环境下的滨岸附近古水道重力流有关。  相似文献   

新疆阿图什温古尔地区二叠纪牙形石动物群   总被引：3，自引：1，他引：3  

姚建新  吴绍祖等 《地质论评》2002,48(5):505-508

新疆阿图什的温古尔－巴音库鲁提一带二叠系由于化石稀少而且保存不好，地层确切时代仍存在疑问，该区温古尔剖面二叠纪重要牙形石化石Neostreptognathodus pequopensis Behnken,Streptognathodus nashuiensis Zhong et Zhang等的发现为这套地层确切时代的确定提供了重要依据。通过牙形石生物相分析，推断温古尔地区中二叠世早期可能为盆地相较深水沉积环境。  相似文献