An assessment of “fishing down marine food webs” in coastal states during 1950–2010     

丁琪  陈新军  余为  陈勇 《海洋学报(英文版)》2017,36(2):43-50

渔获物平均营养级（Mean trophic level of fishery landings,MTL）是目前评估人类捕捞活动影响的研究中使用最广泛的生物多样性指标之一。根据联合国粮农组织FAO提供的渔获生产统计数据,结合Fishbase提供的相关鱼种营养级数据,本文评估了1950-2010年太平洋、大西洋和印度洋各沿海国海洋渔业开发状态。研究发现,在全球三大洋75个主要捕捞国中,43个国家MTL呈显著下降趋势,发生了Pauly于1998年提出的“捕捞降低海洋食物网”现象;但是,仅16个国家MTL的下降是由于高营养级种类的衰退,而27个国家属于“捕捞沿着海洋食物网”的下降机制。此外,20个国家MTL呈恢复上升趋势,但是,该恢复上升趋势通常伴随着传统低营养级种类产量的大幅下降;在上述20个国家中,11个国家的低营养级鱼类产量呈显著下降趋势。需谨慎分析“捕捞降低海洋食物网”现象,掌握MTL的潜在变化机制。  相似文献   

Reconstructing past eutrophication trends from diatoms and biogenic silica in the sediment and the pelagic zone of Lake Constance, Germany     

Martin Wessels  Kirsten Mohaupt  Reiner Kümmerlin  Angela Lenhard 《Journal of Paleolimnology》1999,21(2):171-192

In Lake Constance, phosphorus concentrations and the seasonal development of phytoplankton communities in water samples from the pelagic zone were regularly recorded since the 1950's. Before the 1950's, there were occasional investigations of plankton communities since 1896. We compared these data with the sedimentary record in two sediment cores. Then, the eutrophication history of Lake Constance was inferred from diatoms. The record of biogenic silica in the cores is discussed with respect to diatom biomass increase.Diatom assemblages in the sediment cores precisely reflected the pelagic diatom development for the period 1971--1992. Both sediment cores and the water samples have a high interannual variability of diatom assemblages. Below a sediment depth of 27 cm (AD 1920), more than 50% of the diatoms were partly corroded, and we limited the reconstruction of trophic state changes to the interval of 1920--1993. Oligotrophic conditions of Lake Constance were indicated by the dominance of various Cyclotella taxa from 1920 to 1940. Since 1939/1940, increasing abundance of it Tabellaria fenestrata showed oligotrophic to mesotrophic conditions. Between 1953 and 1956, increasing Stephanodiscus hantzschii and disappearing Cyclotella indicated advanced eutrophication and total phosphorus values ranged between 8--10 mg m-3 during turnover in late winter. Further eutrophication was shown by disappearing T. fenestrata and increasing S. minutulus in 1963. Maximum TP concentrations of 87 mg m-3 occurred in 1979/80 and was accompanied by increasing abundances of Aulacoseira granulata. From 1986 to 1992, reoccurrence of Tabellaria fenestrata and Cyclotella indicate some recovery of Lake Constance.Biogenic silica and diatom abundances were similar among cores but indicate a 3--4 fold increase of diatom biomass only. This was far below the estimate of biomass increase from sedimentary pigment data (25 fold) and the estimate of phytoplankton data from the literature (70 fold).  相似文献   

论“重力归一化总梯度法”中的问题     

蔡越虹  蔡宗熹 《物探与化探》1999,23(1):46-50

重力归一化总梯度G^H(z)的没有明确的物理意义,归一化总梯度方法本身无完整的数学理论作为基础,二维和三维情况都只能探索其实验性的规律.弄清楚G^H(z)有无物理、数学的理论依据很有益处,这使人们在使用G^H(z)方法时不得不采取谨慎的探索态度  相似文献   

Basic limnological characteristics of the shallow eutrophic lake Grimnitzsee (Brandenburg, Germany)     

Frank Gervais  Sven Berger  Ilka Schnfelder  Renate Rusche 《Limnologica》1999,29(2):105

The medium shallow lake Grimnitzsee (maximum depth: 9.9 m; mean depth: 4.6 m; area: 7.7 · 10⁶ m²) which is situated in the biosphere reserve “Schorfheide-Chorin” in northern Brandenburg (Germany) was studied in 1994 and 1995. A bathymetric map of Grimnitzsee is given for the first time. The lake is usually polymictic although in 1994 and 1995 relatively long summer stratification was observed due to very high global radiation input. Nutrient concentration, light climate, oxygen status, phytoplankton biomass and the species composition of littoral diatoms characterize the lake as eutrophic. Special features deducible from the lake's polymictic character were the multiple development of aerobic or anaerobic strata above the sediment, the fast recovery of silicon concentration in the water column after diatom sedimentation, the importance of resuspension for the success of planktonic diatom populations, and an only moderate correlation between chlorophyll a concentration and light attenuation as well as seston dry weight probably due to the influence of suspended particles.  相似文献   

A Preliminary Trophic Model of the Continental Shelf, South-western Gulf of Mexico     

S. Manickchand-Heileman  L.A. Soto  E. Escobar 《Estuarine, Coastal and Shelf Science》1998,46(6):885-899

A preliminary mass-balance trophic model was constructed to determine the flow of energy in a community of fish and invertebrates on the continental shelf of the south-western Gulf of Mexico. Input parameters were taken from the literature, except for the biomass of fish groups which was obtained from trawl surveys in the study area. The model consists of 12 fish groups, five invertebrate groups, phytoplankton and detritus. Results indicate an imbalance between primary production and consumption, with only about 10% of primary production being consumed in the water column. Most of the primary production is exported to detritus which forms the basis of the food-web, with a detritivory/herbivory ratio of 2·5. Benthic invertebrates play a significant role in transferring energy from detritus to higher trophic levels. Eight discrete trophic levels were found, with very reduced flow at levels higher than the fifth. The highest fractional trophic level is 4·3, and consists of sharks. Analysis of mixed trophic impacts showed that detritus and lower trophic levels have a significant positive impact on other groups in the system. Mean transfer efficiency is 9·2%. Some whole system properties are also given. Of net primary production, 6·7% is required to sustain current catch levels, suggesting that the resources in this area are fully exploited.  相似文献   

Annual production of fish larvae and their prey in relation to size-fractionated primary production (Scotian Shelf, NW Atlantic)   总被引：4，自引：0，他引：4  

Mousseau  Laure; Fortier  Louis; Legendre  Louis 《ICES Journal of Marine Science》1998,55(1):44-57

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Basis functions for shallow-water temperature profiles based on the internal-wave eigenmodes     

Qianqian Li  Shoulian Cao  Yu Luo  Kai Zhang  Fanlin Yang 《海洋学报(英文版)》2023,42(2):56-64

The shallow-water temperature profile is typically parameterized using a few empirical orthogonal function(EOF)coefficients. However, when the experimental area is poorly known or highly variable, the adaptability of the EOFs will be significantly reduced. In this study, a new set of basis functions, generated by combining the internal-wave eigenmodes with the average temperature gradient, is developed for characterizing the temperature perturbations. Temperature profiles recorded by a thermisto...  相似文献   

黄淮海平原封丘试区水体营养状态的综合评价   总被引：8，自引：2，他引：6  

蔡庆华  刘瑞秋  黎道丰  倪乐意  伍焯田  梁彦龄 《湖泊科学》1992,4(2):46-51

选择封丘试区内有代表性的7类水体,对其营养状态进行综合评价和聚类分析,初步提出了用于水体营养状态评价的方法和标准。结果表明:各水体营养状态可依其植物组成而明显分成挺水植物、沉水植物和浮游植物型等,而且草型水体的营养指数均高于藻型水体。总的看来,该试区各类水体营养状态较为相似,营养指数均很高,属富营养—重富营养型,渔业发展潜力较大。  相似文献   

互花米草入侵东滩盐沼对大型底栖无脊椎动物群落的影响   总被引：29，自引：5，他引：24  

陈中义  付萃长  王海毅  李博  吴纪华  陈家宽 《湿地科学》2005,3(1):1-7

外来种互花米草 (Spartina alterniflora)已经成功入侵崇明东滩 ,正在大量取代潮间带的优势种海三棱草 (Scirpus mariqueter)。采用圆筒取样比较了大型底栖无脊椎动物 (不包含蟹类 )的密度、多样性和群落结构在这两种植物群落的变化差异。大型底栖无脊椎动物的密度在互花米草群落和海三棱草群落中分别为 3119个 /m2 和 345 9个 /m2 ,两者之间没有显著差异 ,但一些常见种的密度在两种植物群落中存在显著差异。从物种的相对多度看 ,两种植物群落中 ,大型底栖无脊椎动物的优势种都是堇拟沼螺 (Assimineaviolacea)和丝异须虫(Heteromastusfiliforms)。物种多样性分析表明 ,互花米草群落中 ,平均每一个圆筒取样中大型底栖无脊椎动物的物种丰富度、香农 -威纳指数、均匀度都显著低于海三棱草群落中 ,而优势度则相反。互花米草群落中 ,食碎屑者的数量百分比显著大于海三棱草群落中 ,食悬浮物者和食植者的数量百分比显著小于海三棱草群落中。这表明互花米草入侵东滩海三棱草群落 ,竞争取代土著植物后 ,显著降低了大型底栖无脊椎动物的物种多样性 ,同时显著改变了营养类群的结构。互花米草入侵所引起的植物群落高度、密度、盖度、生物量的变化可能是造成大型底栖无脊椎动物群落结构改变的主要原因。  相似文献   

氮稳定同位素基准的可变性及对营养级评价的影响   总被引：10，自引：2，他引：8  

徐军  张敏  谢平 《湖泊科学》2010,22(1):8-20

稳定同位素技术已经成为生态学家研究生态系统特征与过程的重要手段之一。在利用稳定同位素研究植物-动物和动物之间的营养关系或者进行多生态系统的比较研究过程中,通常需要选择某种生物的稳定同位素作为"基准(baseline)"。同位素基准的目的是反映食物网生物最初物质来源的同位素特征。同位素基准的选择取决于具体研究问题与系统。本文综述了水域生态系统研究中初级生产者和初级消费者氮稳定同位素作为基准的应用。不同的研究都根据自身所关注的生态学问题对基准进行选择和校正。然而,找到适当的同位素基准取决于同位素基准种内、种间和时空上的同位素变化特征,同时还取决于所关注的生态学问题的时间、空间尺度。本文评估了季节性和种内的同位素变异性对消费者营养级位置的影响。质量平衡模型的计算结果说明同位素基准可变性可以显著影响对消费者营养级位置的评估。  相似文献